Core Internals — SQLAlchemy 1.2 Documentation

Release: 1.2.19 | Release Date: April 15, 2019

# SQLAlchemy 1.2 Documentation

# Core Internals

Some key internal constructs are listed here.

class `sqlalchemy.engine.interfaces.` `Compiled`(dialect, statement, bind=None, schema_translate_map=None, compile_kwargs={})

  Represent a compiled SQL or DDL expression.

  The `__str__` method of the `Compiled` object should produce the actual text of the statement. `Compiled` objects are specific to their underlying database dialect, and also may or may not be specific to the columns referenced within a particular set of bind parameters. In no case should the `Compiled` object be dependent on the actual values of those bind parameters, even though it may reference those values as defaults.

  `__init__`(dialect, statement, bind=None, schema_translate_map=None, compile_kwargs={})

    Construct a new `Compiled` object.

    Parameters

      - dialect – `Dialect` to compile against.

      - statement – `ClauseElement` to be compiled.

      - bind – Optional Engine or Connection to compile this statement against.

      - schema_translate_map –

        dictionary of schema names to be translated when forming the resultant SQL

        New in version 1.1.

        See also

        Translation of Schema Names

      - compile_kwargs – additional kwargs that will be passed to the initial call to `Compiled.process()`.

  `compile`()

    Produce the internal string representation of this element.

    Deprecated since version 0.7: The `Compiled.compile()` method is deprecated and will be removed in a future release. The `Compiled` object now runs its compilation within the constructor, and this method does nothing.

  `construct_params`(params=None)

    Return the bind params for this compiled object.

    Parameters

      params – a dict of string/object pairs whose values will override bind values compiled in to the statement.

  `execute`(*multiparams, **params)

    Execute this compiled object.

  `execution_options` = {}

    Execution options propagated from the statement. In some cases, sub-elements of the statement can modify these.

  `params`

    Return the bind params for this compiled object.

  `scalar`(*multiparams, **params)

    Execute this compiled object and return the result’s scalar value.

  `sql_compiler`

    Return a Compiled that is capable of processing SQL expressions.

    If this compiler is one, it would likely just return ‘self’.

class `sqlalchemy.sql.compiler.` `DDLCompiler`(dialect, statement, bind=None, schema_translate_map=None, compile_kwargs={})

  Bases: `sqlalchemy.sql.compiler.Compiled`

  `__eq__`

    inherited from the `__eq__` attribute of `object`

    Return self==value.

  `__init__`(dialect, statement, bind=None, schema_translate_map=None, compile_kwargs={})

    inherited from the `__init__()` method of `Compiled`

    Construct a new `Compiled` object.

    Parameters

      - dialect – `Dialect` to compile against.

      - statement – `ClauseElement` to be compiled.

      - bind – Optional Engine or Connection to compile this statement against.

      - schema_translate_map –

        dictionary of schema names to be translated when forming the resultant SQL

        New in version 1.1.

        See also

        Translation of Schema Names

      - compile_kwargs – additional kwargs that will be passed to the initial call to `Compiled.process()`.

  `__le__`

    inherited from the `__le__` attribute of `object`

    Return self<=value.

  `__lt__`

    inherited from the `__lt__` attribute of `object`

    Return self<value.

  `__ne__`

    inherited from the `__ne__` attribute of `object`

    Return self!=value.

  `compile`()

    inherited from the `compile()` method of `Compiled`

    Produce the internal string representation of this element.

    Deprecated since version 0.7: The `Compiled.compile()` method is deprecated and will be removed in a future release. The `Compiled` object now runs its compilation within the constructor, and this method does nothing.

  `construct_params`(params=None)

    Return the bind params for this compiled object.

    Parameters

      params – a dict of string/object pairs whose values will override bind values compiled in to the statement.

  `define_constraint_remote_table`(constraint, table, preparer)

    Format the remote table clause of a CREATE CONSTRAINT clause.

  `execute`(*multiparams, **params)

    inherited from the `execute()` method of `Compiled`

    Execute this compiled object.

  `params`

    inherited from the `params` attribute of `Compiled`

    Return the bind params for this compiled object.

  `scalar`(*multiparams, **params)

    inherited from the `scalar()` method of `Compiled`

    Execute this compiled object and return the result’s scalar value.

class `sqlalchemy.engine.default.` `DefaultDialect`(convert_unicode=False, encoding='utf-8', paramstyle=None, dbapi=None, implicit_returning=None, supports_right_nested_joins=None, case_sensitive=True, supports_native_boolean=None, empty_in_strategy='static', label_length=None, **kwargs)

  Bases: `sqlalchemy.engine.interfaces.Dialect`

  Default implementation of Dialect

  `__eq__`

    inherited from the `__eq__` attribute of `object`

    Return self==value.

  `__le__`

    inherited from the `__le__` attribute of `object`

    Return self<=value.

  `__lt__`

    inherited from the `__lt__` attribute of `object`

    Return self<value.

  `__ne__`

    inherited from the `__ne__` attribute of `object`

    Return self!=value.

  `connect`(*cargs, **cparams)

    return a callable which sets up a newly created DBAPI connection.

    The callable accepts a single argument “conn” which is the DBAPI connection itself. It has no return value.

    This is used to set dialect-wide per-connection options such as isolation modes, unicode modes, etc.

    If a callable is returned, it will be assembled into a pool listener that receives the direct DBAPI connection, with all wrappers removed.

    If None is returned, no listener will be generated.

  `construct_arguments` = None

    Optional set of argument specifiers for various SQLAlchemy constructs, typically schema items.

    To implement, establish as a series of tuples, as in:

        construct_arguments = [
            (schema.Index, {
                "using": False,
                "where": None,
                "ops": None
            })
        ]

    If the above construct is established on the PostgreSQL dialect, the `Index` construct will now accept the keyword arguments `postgresql_using`, `postgresql_where`, nad `postgresql_ops`. Any other argument specified to the constructor of `Index` which is prefixed with `postgresql_` will raise `ArgumentError`.

    A dialect which does not include a `construct_arguments` member will not participate in the argument validation system. For such a dialect, any argument name is accepted by all participating constructs, within the namespace of arguments prefixed with that dialect name. The rationale here is so that third-party dialects that haven’t yet implemented this feature continue to function in the old way.

    New in version 0.9.2.

    See also

    `DialectKWArgs` - implementing base class which consumes `DefaultDialect.construct_arguments`

  `create_connect_args`(url)

    Build DB-API compatible connection arguments.

    Given a `URL` object, returns a tuple consisting of a *args/**kwargs suitable to send directly to the dbapi’s connect function.

  `create_xid`()

    Create a random two-phase transaction ID.

    This id will be passed to do_begin_twophase(), do_rollback_twophase(), do_commit_twophase(). Its format is unspecified.

  `dbapi_exception_translation_map` = {}

    mapping used in the extremely unusual case that a DBAPI’s published exceptions don’t actually have the __name__ that they are linked towards.

    New in version 1.0.5.

  `ddl_compiler`

    alias of `sqlalchemy.sql.compiler.DDLCompiler`

  `denormalize_name`(name)

    inherited from the `denormalize_name()` method of `Dialect`

    convert the given name to a case insensitive identifier for the backend if it is an all-lowercase name.

    this method is only used if the dialect defines requires_name_normalize=True.

  `do_begin`(dbapi_connection)

    Provide an implementation of `connection.begin()`, given a DB-API connection.

    The DBAPI has no dedicated “begin” method and it is expected that transactions are implicit. This hook is provided for those DBAPIs that might need additional help in this area.

    Note that `Dialect.do_begin()` is not called unless a `Transaction` object is in use. The `Dialect.do_autocommit()` hook is provided for DBAPIs that need some extra commands emitted after a commit in order to enter the next transaction, when the SQLAlchemy `Connection` is used in its default “autocommit” mode.

    Parameters

      dbapi_connection – a DBAPI connection, typically proxied within a `ConnectionFairy`.

  `do_begin_twophase`(connection, xid)

    inherited from the `do_begin_twophase()` method of `Dialect`

    Begin a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

  `do_close`(dbapi_connection)

    Provide an implementation of `connection.close()`, given a DBAPI connection.

    This hook is called by the `Pool` when a connection has been detached from the pool, or is being returned beyond the normal capacity of the pool.

  `do_commit`(dbapi_connection)

    Provide an implementation of `connection.commit()`, given a DB-API connection.

    Parameters

      dbapi_connection – a DBAPI connection, typically proxied within a `ConnectionFairy`.

  `do_commit_twophase`(connection, xid, is_prepared=True, recover=False)

    inherited from the `do_commit_twophase()` method of `Dialect`

    Commit a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

      - is_prepared – whether or not `TwoPhaseTransaction.prepare()` was called.

      - recover – if the recover flag was passed.

  `do_execute`(cursor, statement, parameters, context=None)

    Provide an implementation of `cursor.execute(statement, parameters)`.

  `do_execute_no_params`(cursor, statement, context=None)

    Provide an implementation of `cursor.execute(statement)`.

    The parameter collection should not be sent.

  `do_executemany`(cursor, statement, parameters, context=None)

    Provide an implementation of `cursor.executemany(statement, parameters)`.

  `do_prepare_twophase`(connection, xid)

    inherited from the `do_prepare_twophase()` method of `Dialect`

    Prepare a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

  `do_recover_twophase`(connection)

    inherited from the `do_recover_twophase()` method of `Dialect`

    Recover list of uncommitted prepared two phase transaction identifiers on the given connection.

    Parameters

      connection – a `Connection`.

  `do_release_savepoint`(connection, name)

    Release the named savepoint on a connection.

    Parameters

      - connection – a `Connection`.

      - name – savepoint name.

  `do_rollback`(dbapi_connection)

    Provide an implementation of `connection.rollback()`, given a DB-API connection.

    Parameters

      dbapi_connection – a DBAPI connection, typically proxied within a `ConnectionFairy`.

  `do_rollback_to_savepoint`(connection, name)

    Rollback a connection to the named savepoint.

    Parameters

      - connection – a `Connection`.

      - name – savepoint name.

  `do_rollback_twophase`(connection, xid, is_prepared=True, recover=False)

    inherited from the `do_rollback_twophase()` method of `Dialect`

    Rollback a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

      - is_prepared – whether or not `TwoPhaseTransaction.prepare()` was called.

      - recover – if the recover flag was passed.

  `do_savepoint`(connection, name)

    Create a savepoint with the given name.

    Parameters

      - connection – a `Connection`.

      - name – savepoint name.

  classmethod `engine_created`(engine)

    inherited from the `engine_created()` method of `Dialect`

    A convenience hook called before returning the final `Engine`.

    If the dialect returned a different class from the `get_dialect_cls()` method, then the hook is called on both classes, first on the dialect class returned by the `get_dialect_cls()` method and then on the class on which the method was called.

    The hook should be used by dialects and/or wrappers to apply special events to the engine or its components. In particular, it allows a dialect-wrapping class to apply dialect-level events.

    New in version 1.0.3.

  `execute_sequence_format`

    alias of `builtins.tuple`

  `execution_ctx_cls`

    alias of `DefaultExecutionContext`

  `get_check_constraints`(connection, table_name, schema=None, **kw)

    inherited from the `get_check_constraints()` method of `Dialect`

    Return information about check constraints in table_name.

    Given a string table_name and an optional string schema, return check constraint information as a list of dicts with these keys:

    name

      the check constraint’s name

    sqltext

      the check constraint’s SQL expression

    **kw

      other options passed to the dialect’s get_check_constraints() method.

    New in version 1.1.0.

  `get_columns`(connection, table_name, schema=None, **kw)

    inherited from the `get_columns()` method of `Dialect`

    Return information about columns in table_name.

    Given a `Connection`, a string table_name, and an optional string schema, return column information as a list of dictionaries with these keys:

    name

      the column’s name

    type

      [sqlalchemy.types#TypeEngine]

    nullable

      boolean

    default

      the column’s default value

    autoincrement

      boolean

    sequence
      a dictionary of the form
        {‘name’str, ‘start’ :int, ‘increment’: int, ‘minvalue’: int,

          ‘maxvalue’: int, ‘nominvalue’: bool, ‘nomaxvalue’: bool, ‘cycle’: bool, ‘cache’: int, ‘order’: bool}

    Additional column attributes may be present.

  classmethod `get_dialect_cls`(url)

    inherited from the `get_dialect_cls()` method of `Dialect`

    Given a URL, return the `Dialect` that will be used.

    This is a hook that allows an external plugin to provide functionality around an existing dialect, by allowing the plugin to be loaded from the url based on an entrypoint, and then the plugin returns the actual dialect to be used.

    By default this just returns the cls.

    New in version 1.0.3.

  `get_foreign_keys`(connection, table_name, schema=None, **kw)

    inherited from the `get_foreign_keys()` method of `Dialect`

    Return information about foreign_keys in table_name.

    Given a `Connection`, a string table_name, and an optional string schema, return foreign key information as a list of dicts with these keys:

    name

      the constraint’s name

    constrained_columns

      a list of column names that make up the foreign key

    referred_schema

      the name of the referred schema

    referred_table

      the name of the referred table

    referred_columns

      a list of column names in the referred table that correspond to constrained_columns

  `get_indexes`(connection, table_name, schema=None, **kw)

    inherited from the `get_indexes()` method of `Dialect`

    Return information about indexes in table_name.

    Given a `Connection`, a string table_name and an optional string schema, return index information as a list of dictionaries with these keys:

    name

      the index’s name

    column_names

      list of column names in order

    unique

      boolean

  `get_isolation_level`(dbapi_conn)

    inherited from the `get_isolation_level()` method of `Dialect`

    Given a DBAPI connection, return its isolation level.

    When working with a `Connection` object, the corresponding DBAPI connection may be procured using the `Connection.connection` accessor.

    Note that this is a dialect-level method which is used as part of the implementation of the `Connection` and `Engine` isolation level facilities; these APIs should be preferred for most typical use cases.

    See also

    `Connection.get_isolation_level()` - view current level

    `Connection.default_isolation_level` - view default level

    `Connection.execution_options.isolation_level` - set per `Connection` isolation level

    `create_engine.isolation_level` - set per `Engine` isolation level

  `get_pk_constraint`(conn, table_name, schema=None, **kw)

    Compatibility method, adapts the result of get_primary_keys() for those dialects which don’t implement get_pk_constraint().

  `get_primary_keys`(connection, table_name, schema=None, **kw)

    inherited from the `get_primary_keys()` method of `Dialect`

    Return information about primary keys in table_name.

    Deprecated since version 0.8: The `Dialect.get_primary_keys()` method is deprecated and will be removed in a future release. Please refer to the `Dialect.get_pk_constraint()` method.

  `get_table_comment`(connection, table_name, schema=None, **kw)

    inherited from the `get_table_comment()` method of `Dialect`

    Return the “comment” for the table identified by table_name.

    Given a string table_name and an optional string schema, return table comment information as a dictionary with this key:

    text

      text of the comment

    Raises `NotImplementedError` for dialects that don’t support comments.

    New in version 1.2.

  `get_table_names`(connection, schema=None, **kw)

    inherited from the `get_table_names()` method of `Dialect`

    Return a list of table names for schema.

  `get_temp_table_names`(connection, schema=None, **kw)

    inherited from the `get_temp_table_names()` method of `Dialect`

    Return a list of temporary table names on the given connection, if supported by the underlying backend.

  `get_temp_view_names`(connection, schema=None, **kw)

    inherited from the `get_temp_view_names()` method of `Dialect`

    Return a list of temporary view names on the given connection, if supported by the underlying backend.

  `get_unique_constraints`(connection, table_name, schema=None, **kw)

    inherited from the `get_unique_constraints()` method of `Dialect`

    Return information about unique constraints in table_name.

    Given a string table_name and an optional string schema, return unique constraint information as a list of dicts with these keys:

    name

      the unique constraint’s name

    column_names

      list of column names in order

    **kw

      other options passed to the dialect’s get_unique_constraints() method.

    New in version 0.9.0.

  `get_view_definition`(connection, view_name, schema=None, **kw)

    inherited from the `get_view_definition()` method of `Dialect`

    Return view definition.

    Given a `Connection`, a string view_name, and an optional string schema, return the view definition.

  `get_view_names`(connection, schema=None, **kw)

    inherited from the `get_view_names()` method of `Dialect`

    Return a list of all view names available in the database.

    schema:

      Optional, retrieve names from a non-default schema.

  `has_sequence`(connection, sequence_name, schema=None)

    inherited from the `has_sequence()` method of `Dialect`

    Check the existence of a particular sequence in the database.

    Given a `Connection` object and a string sequence_name, return True if the given sequence exists in the database, False otherwise.

  `has_table`(connection, table_name, schema=None)

    inherited from the `has_table()` method of `Dialect`

    Check the existence of a particular table in the database.

    Given a `Connection` object and a string table_name, return True if the given table (possibly within the specified schema) exists in the database, False otherwise.

  `initialize`(connection)

    Called during strategized creation of the dialect with a connection.

    Allows dialects to configure options based on server version info or other properties.

    The connection passed here is a SQLAlchemy Connection object, with full capabilities.

    The initialize() method of the base dialect should be called via super().

  `is_disconnect`(e, connection, cursor)

    Return True if the given DB-API error indicates an invalid connection

  `normalize_name`(name)

    inherited from the `normalize_name()` method of `Dialect`

    convert the given name to lowercase if it is detected as case insensitive.

    this method is only used if the dialect defines requires_name_normalize=True.

  `on_connect`()

    return a callable which sets up a newly created DBAPI connection.

    This is used to set dialect-wide per-connection options such as isolation modes, unicode modes, etc.

    If a callable is returned, it will be assembled into a pool listener that receives the direct DBAPI connection, with all wrappers removed.

    If None is returned, no listener will be generated.

  `preparer`

    alias of `sqlalchemy.sql.compiler.IdentifierPreparer`

  `reflecttable`(connection, table, include_columns, exclude_columns, **opts)

    Load table description from the database.

    Given a `Connection` and a `Table` object, reflect its columns and properties from the database.

    The implementation of this method is provided by `DefaultDialect.reflecttable()`, which makes use of `Inspector` to retrieve column information.

    Dialects should not seek to implement this method, and should instead implement individual schema inspection operations such as `Dialect.get_columns()`, `Dialect.get_pk_constraint()`, etc.

  `reset_isolation_level`(dbapi_conn)

    Given a DBAPI connection, revert its isolation to the default.

    Note that this is a dialect-level method which is used as part of the implementation of the `Connection` and `Engine` isolation level facilities; these APIs should be preferred for most typical use cases.

    See also

    `Connection.get_isolation_level()` - view current level

    `Connection.default_isolation_level` - view default level

    `Connection.execution_options.isolation_level` - set per `Connection` isolation level

    `create_engine.isolation_level` - set per `Engine` isolation level

  `set_isolation_level`(dbapi_conn, level)

    inherited from the `set_isolation_level()` method of `Dialect`

    Given a DBAPI connection, set its isolation level.

    Note that this is a dialect-level method which is used as part of the implementation of the `Connection` and `Engine` isolation level facilities; these APIs should be preferred for most typical use cases.

    See also

    `Connection.get_isolation_level()` - view current level

    `Connection.default_isolation_level` - view default level

    `Connection.execution_options.isolation_level` - set per `Connection` isolation level

    `create_engine.isolation_level` - set per `Engine` isolation level

  `statement_compiler`

    alias of `sqlalchemy.sql.compiler.SQLCompiler`

  `type_compiler`

    alias of `sqlalchemy.sql.compiler.GenericTypeCompiler`

  `type_descriptor`(typeobj)

    Provide a database-specific `TypeEngine` object, given the generic object which comes from the types module.

    This method looks for a dictionary called `colspecs` as a class or instance-level variable, and passes on to `types.adapt_type()`.

class `sqlalchemy.engine.interfaces.` `Dialect`

  Define the behavior of a specific database and DB-API combination.

  Any aspect of metadata definition, SQL query generation, execution, result-set handling, or anything else which varies between databases is defined under the general category of the Dialect. The Dialect acts as a factory for other database-specific object implementations including ExecutionContext, Compiled, DefaultGenerator, and TypeEngine.

  All Dialects implement the following attributes:

  name

    identifying name for the dialect from a DBAPI-neutral point of view (i.e. ‘sqlite’)

  driver

    identifying name for the dialect’s DBAPI

  positional

    True if the paramstyle for this Dialect is positional.

  paramstyle

    the paramstyle to be used (some DB-APIs support multiple paramstyles).

  convert_unicode

    True if Unicode conversion should be applied to all `str` types.

  encoding

    type of encoding to use for unicode, usually defaults to ‘utf-8’.

  statement_compiler

    a `Compiled` class used to compile SQL statements

  ddl_compiler

    a `Compiled` class used to compile DDL statements

  server_version_info

    a tuple containing a version number for the DB backend in use. This value is only available for supporting dialects, and is typically populated during the initial connection to the database.

  default_schema_name

    the name of the default schema. This value is only available for supporting dialects, and is typically populated during the initial connection to the database.

  execution_ctx_cls

    a `ExecutionContext` class used to handle statement execution

  execute_sequence_format

    either the ‘tuple’ or ‘list’ type, depending on what cursor.execute() accepts for the second argument (they vary).

  preparer

    a `IdentifierPreparer` class used to quote identifiers.

  supports_alter

    `True` if the database supports `ALTER TABLE`.

  max_identifier_length

    The maximum length of identifier names.

  supports_unicode_statements

    Indicate whether the DB-API can receive SQL statements as Python unicode strings

  supports_unicode_binds

    Indicate whether the DB-API can receive string bind parameters as Python unicode strings

  supports_sane_rowcount

    Indicate whether the dialect properly implements rowcount for `UPDATE` and `DELETE` statements.

  supports_sane_multi_rowcount

    Indicate whether the dialect properly implements rowcount for `UPDATE` and `DELETE` statements when executed via executemany.

  preexecute_autoincrement_sequences

    True if ‘implicit’ primary key functions must be executed separately in order to get their value. This is currently oriented towards PostgreSQL.

  implicit_returning

    use RETURNING or equivalent during INSERT execution in order to load newly generated primary keys and other column defaults in one execution, which are then available via inserted_primary_key. If an insert statement has returning() specified explicitly, the “implicit” functionality is not used and inserted_primary_key will not be available.

  colspecs

    A dictionary of TypeEngine classes from sqlalchemy.types mapped to subclasses that are specific to the dialect class. This dictionary is class-level only and is not accessed from the dialect instance itself.

  supports_default_values

    Indicates if the construct `INSERT INTO tablename DEFAULT VALUES` is supported

  supports_sequences

    Indicates if the dialect supports CREATE SEQUENCE or similar.

  sequences_optional

    If True, indicates if the “optional” flag on the Sequence() construct should signal to not generate a CREATE SEQUENCE. Applies only to dialects that support sequences. Currently used only to allow PostgreSQL SERIAL to be used on a column that specifies Sequence() for usage on other backends.

  supports_native_enum

    Indicates if the dialect supports a native ENUM construct. This will prevent types.Enum from generating a CHECK constraint when that type is used.

  supports_native_boolean

    Indicates if the dialect supports a native boolean construct. This will prevent types.Boolean from generating a CHECK constraint when that type is used.

  dbapi_exception_translation_map

    A dictionary of names that will contain as values the names of pep-249 exceptions (“IntegrityError”, “OperationalError”, etc) keyed to alternate class names, to support the case where a DBAPI has exception classes that aren’t named as they are referred to (e.g. IntegrityError = MyException). In the vast majority of cases this dictionary is empty.

    New in version 1.0.5.

  `connect`()

    return a callable which sets up a newly created DBAPI connection.

    The callable accepts a single argument “conn” which is the DBAPI connection itself. It has no return value.

    This is used to set dialect-wide per-connection options such as isolation modes, unicode modes, etc.

    If a callable is returned, it will be assembled into a pool listener that receives the direct DBAPI connection, with all wrappers removed.

    If None is returned, no listener will be generated.

  `create_connect_args`(url)

    Build DB-API compatible connection arguments.

    Given a `URL` object, returns a tuple consisting of a *args/**kwargs suitable to send directly to the dbapi’s connect function.

  `create_xid`()

    Create a two-phase transaction ID.

    This id will be passed to do_begin_twophase(), do_rollback_twophase(), do_commit_twophase(). Its format is unspecified.

  `denormalize_name`(name)

    convert the given name to a case insensitive identifier for the backend if it is an all-lowercase name.

    this method is only used if the dialect defines requires_name_normalize=True.

  `do_begin`(dbapi_connection)

    Provide an implementation of `connection.begin()`, given a DB-API connection.

    The DBAPI has no dedicated “begin” method and it is expected that transactions are implicit. This hook is provided for those DBAPIs that might need additional help in this area.

    Note that `Dialect.do_begin()` is not called unless a `Transaction` object is in use. The `Dialect.do_autocommit()` hook is provided for DBAPIs that need some extra commands emitted after a commit in order to enter the next transaction, when the SQLAlchemy `Connection` is used in its default “autocommit” mode.

    Parameters

      dbapi_connection – a DBAPI connection, typically proxied within a `ConnectionFairy`.

  `do_begin_twophase`(connection, xid)

    Begin a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

  `do_close`(dbapi_connection)

    Provide an implementation of `connection.close()`, given a DBAPI connection.

    This hook is called by the `Pool` when a connection has been detached from the pool, or is being returned beyond the normal capacity of the pool.

  `do_commit`(dbapi_connection)

    Provide an implementation of `connection.commit()`, given a DB-API connection.

    Parameters

      dbapi_connection – a DBAPI connection, typically proxied within a `ConnectionFairy`.

  `do_commit_twophase`(connection, xid, is_prepared=True, recover=False)

    Commit a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

      - is_prepared – whether or not `TwoPhaseTransaction.prepare()` was called.

      - recover – if the recover flag was passed.

  `do_execute`(cursor, statement, parameters, context=None)

    Provide an implementation of `cursor.execute(statement, parameters)`.

  `do_execute_no_params`(cursor, statement, parameters, context=None)

    Provide an implementation of `cursor.execute(statement)`.

    The parameter collection should not be sent.

  `do_executemany`(cursor, statement, parameters, context=None)

    Provide an implementation of `cursor.executemany(statement, parameters)`.

  `do_prepare_twophase`(connection, xid)

    Prepare a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

  `do_recover_twophase`(connection)

    Recover list of uncommitted prepared two phase transaction identifiers on the given connection.

    Parameters

      connection – a `Connection`.

  `do_release_savepoint`(connection, name)

    Release the named savepoint on a connection.

    Parameters

      - connection – a `Connection`.

      - name – savepoint name.

  `do_rollback`(dbapi_connection)

    Provide an implementation of `connection.rollback()`, given a DB-API connection.

    Parameters

      dbapi_connection – a DBAPI connection, typically proxied within a `ConnectionFairy`.

  `do_rollback_to_savepoint`(connection, name)

    Rollback a connection to the named savepoint.

    Parameters

      - connection – a `Connection`.

      - name – savepoint name.

  `do_rollback_twophase`(connection, xid, is_prepared=True, recover=False)

    Rollback a two phase transaction on the given connection.

    Parameters

      - connection – a `Connection`.

      - xid – xid

      - is_prepared – whether or not `TwoPhaseTransaction.prepare()` was called.

      - recover – if the recover flag was passed.

  `do_savepoint`(connection, name)

    Create a savepoint with the given name.

    Parameters

      - connection – a `Connection`.

      - name – savepoint name.

  classmethod `engine_created`(engine)

    A convenience hook called before returning the final `Engine`.

    If the dialect returned a different class from the `get_dialect_cls()` method, then the hook is called on both classes, first on the dialect class returned by the `get_dialect_cls()` method and then on the class on which the method was called.

    The hook should be used by dialects and/or wrappers to apply special events to the engine or its components. In particular, it allows a dialect-wrapping class to apply dialect-level events.

    New in version 1.0.3.

  `get_check_constraints`(connection, table_name, schema=None, **kw)

    Return information about check constraints in table_name.

    Given a string table_name and an optional string schema, return check constraint information as a list of dicts with these keys:

    name

      the check constraint’s name

    sqltext

      the check constraint’s SQL expression

    **kw

      other options passed to the dialect’s get_check_constraints() method.

    New in version 1.1.0.

  `get_columns`(connection, table_name, schema=None, **kw)

    Return information about columns in table_name.

    Given a `Connection`, a string table_name, and an optional string schema, return column information as a list of dictionaries with these keys:

    name

      the column’s name

    type

      [sqlalchemy.types#TypeEngine]

    nullable

      boolean

    default

      the column’s default value

    autoincrement

      boolean

    sequence
      a dictionary of the form
        {‘name’str, ‘start’ :int, ‘increment’: int, ‘minvalue’: int,

          ‘maxvalue’: int, ‘nominvalue’: bool, ‘nomaxvalue’: bool, ‘cycle’: bool, ‘cache’: int, ‘order’: bool}

    Additional column attributes may be present.

  classmethod `get_dialect_cls`(url)

    Given a URL, return the `Dialect` that will be used.

    This is a hook that allows an external plugin to provide functionality around an existing dialect, by allowing the plugin to be loaded from the url based on an entrypoint, and then the plugin returns the actual dialect to be used.

    By default this just returns the cls.

    New in version 1.0.3.

  `get_foreign_keys`(connection, table_name, schema=None, **kw)

    Return information about foreign_keys in table_name.

    Given a `Connection`, a string table_name, and an optional string schema, return foreign key information as a list of dicts with these keys:

    name

      the constraint’s name

    constrained_columns

      a list of column names that make up the foreign key

    referred_schema

      the name of the referred schema

    referred_table

      the name of the referred table

    referred_columns

      a list of column names in the referred table that correspond to constrained_columns

  `get_indexes`(connection, table_name, schema=None, **kw)

    Return information about indexes in table_name.

    Given a `Connection`, a string table_name and an optional string schema, return index information as a list of dictionaries with these keys:

    name

      the index’s name

    column_names

      list of column names in order

    unique

      boolean

  `get_isolation_level`(dbapi_conn)

    Given a DBAPI connection, return its isolation level.

    When working with a `Connection` object, the corresponding DBAPI connection may be procured using the `Connection.connection` accessor.

    Note that this is a dialect-level method which is used as part of the implementation of the `Connection` and `Engine` isolation level facilities; these APIs should be preferred for most typical use cases.

    See also

    `Connection.get_isolation_level()` - view current level

    `Connection.default_isolation_level` - view default level

    `Connection.execution_options.isolation_level` - set per `Connection` isolation level

    `create_engine.isolation_level` - set per `Engine` isolation level

  `get_pk_constraint`(connection, table_name, schema=None, **kw)

    Return information about the primary key constraint on table_name`.

    Given a `Connection`, a string table_name, and an optional string schema, return primary key information as a dictionary with these keys:

    constrained_columns

      a list of column names that make up the primary key

    name

      optional name of the primary key constraint.

  `get_primary_keys`(connection, table_name, schema=None, **kw)

    Return information about primary keys in table_name.

    Deprecated since version 0.8: The `Dialect.get_primary_keys()` method is deprecated and will be removed in a future release. Please refer to the `Dialect.get_pk_constraint()` method.

  `get_table_comment`(connection, table_name, schema=None, **kw)

    Return the “comment” for the table identified by table_name.

    Given a string table_name and an optional string schema, return table comment information as a dictionary with this key:

    text

      text of the comment

    Raises `NotImplementedError` for dialects that don’t support comments.

    New in version 1.2.

  `get_table_names`(connection, schema=None, **kw)

    Return a list of table names for schema.

  `get_temp_table_names`(connection, schema=None, **kw)

    Return a list of temporary table names on the given connection, if supported by the underlying backend.

  `get_temp_view_names`(connection, schema=None, **kw)

    Return a list of temporary view names on the given connection, if supported by the underlying backend.

  `get_unique_constraints`(connection, table_name, schema=None, **kw)

    Return information about unique constraints in table_name.

    Given a string table_name and an optional string schema, return unique constraint information as a list of dicts with these keys:

    name

      the unique constraint’s name

    column_names

      list of column names in order

    **kw

      other options passed to the dialect’s get_unique_constraints() method.

    New in version 0.9.0.

  `get_view_definition`(connection, view_name, schema=None, **kw)

    Return view definition.

    Given a `Connection`, a string view_name, and an optional string schema, return the view definition.

  `get_view_names`(connection, schema=None, **kw)

    Return a list of all view names available in the database.

    schema:

      Optional, retrieve names from a non-default schema.

  `has_sequence`(connection, sequence_name, schema=None)

    Check the existence of a particular sequence in the database.

    Given a `Connection` object and a string sequence_name, return True if the given sequence exists in the database, False otherwise.

  `has_table`(connection, table_name, schema=None)

    Check the existence of a particular table in the database.

    Given a `Connection` object and a string table_name, return True if the given table (possibly within the specified schema) exists in the database, False otherwise.

  `initialize`(connection)

    Called during strategized creation of the dialect with a connection.

    Allows dialects to configure options based on server version info or other properties.

    The connection passed here is a SQLAlchemy Connection object, with full capabilities.

    The initialize() method of the base dialect should be called via super().

  `is_disconnect`(e, connection, cursor)

    Return True if the given DB-API error indicates an invalid connection

  `normalize_name`(name)

    convert the given name to lowercase if it is detected as case insensitive.

    this method is only used if the dialect defines requires_name_normalize=True.

  `reflecttable`(connection, table, include_columns, exclude_columns)

    Load table description from the database.

    Given a `Connection` and a `Table` object, reflect its columns and properties from the database.

    The implementation of this method is provided by `DefaultDialect.reflecttable()`, which makes use of `Inspector` to retrieve column information.

    Dialects should not seek to implement this method, and should instead implement individual schema inspection operations such as `Dialect.get_columns()`, `Dialect.get_pk_constraint()`, etc.

  `reset_isolation_level`(dbapi_conn)

    Given a DBAPI connection, revert its isolation to the default.

    Note that this is a dialect-level method which is used as part of the implementation of the `Connection` and `Engine` isolation level facilities; these APIs should be preferred for most typical use cases.

    See also

    `Connection.get_isolation_level()` - view current level

    `Connection.default_isolation_level` - view default level

    `Connection.execution_options.isolation_level` - set per `Connection` isolation level

    `create_engine.isolation_level` - set per `Engine` isolation level

  `set_isolation_level`(dbapi_conn, level)

    Given a DBAPI connection, set its isolation level.

    Note that this is a dialect-level method which is used as part of the implementation of the `Connection` and `Engine` isolation level facilities; these APIs should be preferred for most typical use cases.

    See also

    `Connection.get_isolation_level()` - view current level

    `Connection.default_isolation_level` - view default level

    `Connection.execution_options.isolation_level` - set per `Connection` isolation level

    `create_engine.isolation_level` - set per `Engine` isolation level

  classmethod `type_descriptor`(typeobj)

    Transform a generic type to a dialect-specific type.

    Dialect classes will usually use the `types.adapt_type()` function in the types module to accomplish this.

    The returned result is cached per dialect class so can contain no dialect-instance state.

class `sqlalchemy.engine.default.` `DefaultExecutionContext`

  Bases: `sqlalchemy.engine.interfaces.ExecutionContext`

  `create_cursor`()

    Return a new cursor generated from this ExecutionContext’s connection.

    Some dialects may wish to change the behavior of connection.cursor(), such as postgresql which may return a PG “server side” cursor.

  `current_parameters` = None

    A dictionary of parameters applied to the current row.

    This attribute is only available in the context of a user-defined default generation function, e.g. as described at Context-Sensitive Default Functions. It consists of a dictionary which includes entries for each column/value pair that is to be part of the INSERT or UPDATE statement. The keys of the dictionary will be the key value of each `Column`, which is usually synonymous with the name.

    Note that the `DefaultExecutionContext.current_parameters` attribute does not accommodate for the “multi-values” feature of the `Insert.values()` method. The `DefaultExecutionContext.get_current_parameters()` method should be preferred.

    See also

    `DefaultExecutionContext.get_current_parameters()`

    Context-Sensitive Default Functions

  `get_current_parameters`(isolate_multiinsert_groups=True)

    Return a dictionary of parameters applied to the current row.

    This method can only be used in the context of a user-defined default generation function, e.g. as described at Context-Sensitive Default Functions. When invoked, a dictionary is returned which includes entries for each column/value pair that is part of the INSERT or UPDATE statement. The keys of the dictionary will be the key value of each `Column`, which is usually synonymous with the name.

    Parameters

      isolate_multiinsert_groups=True – indicates that multi-valued INSERT constructs created using `Insert.values()` should be handled by returning only the subset of parameters that are local to the current column default invocation. When `False`, the raw parameters of the statement are returned including the naming convention used in the case of multi-valued INSERT.

    New in version 1.2: added `DefaultExecutionContext.get_current_parameters()` which provides more functionality over the existing `DefaultExecutionContext.current_parameters` attribute.

    See also

    `DefaultExecutionContext.current_parameters`

    Context-Sensitive Default Functions

  `get_lastrowid`()

    return self.cursor.lastrowid, or equivalent, after an INSERT.

    This may involve calling special cursor functions, issuing a new SELECT on the cursor (or a new one), or returning a stored value that was calculated within post_exec().

    This function will only be called for dialects which support “implicit” primary key generation, keep preexecute_autoincrement_sequences set to False, and when no explicit id value was bound to the statement.

    The function is called once, directly after post_exec() and before the transaction is committed or ResultProxy is generated. If the post_exec() method assigns a value to self._lastrowid, the value is used in place of calling get_lastrowid().

    Note that this method is not equivalent to the `lastrowid` method on `ResultProxy`, which is a direct proxy to the DBAPI `lastrowid` accessor in all cases.

  `get_result_processor`(type_, colname, coltype)

    Return a ‘result processor’ for a given type as present in cursor.description.

    This has a default implementation that dialects can override for context-sensitive result type handling.

  `handle_dbapi_exception`(e)

    Receive a DBAPI exception which occurred upon execute, result fetch, etc.

  `lastrow_has_defaults`()

    Return True if the last INSERT or UPDATE row contained inlined or database-side defaults.

  `post_exec`()

    Called after the execution of a compiled statement.

    If a compiled statement was passed to this ExecutionContext, the last_insert_ids, last_inserted_params, etc. datamembers should be available after this method completes.

  `pre_exec`()

    Called before an execution of a compiled statement.

    If a compiled statement was passed to this ExecutionContext, the statement and parameters datamembers must be initialized after this statement is complete.

  `set_input_sizes`(translate=None, include_types=None, exclude_types=None)

    Given a cursor and ClauseParameters, call the appropriate style of `setinputsizes()` on the cursor, using DB-API types from the bind parameter’s `TypeEngine` objects.

    This method only called by those dialects which require it, currently cx_oracle.

  `should_autocommit_text`(statement)

    Parse the given textual statement and return True if it refers to a “committable” statement

class `sqlalchemy.engine.interfaces.` `ExecutionContext`

  A messenger object for a Dialect that corresponds to a single execution.

  ExecutionContext should have these data members:

  connection

    Connection object which can be freely used by default value generators to execute SQL. This Connection should reference the same underlying connection/transactional resources of root_connection.

  root_connection

    Connection object which is the source of this ExecutionContext. This Connection may have close_with_result=True set, in which case it can only be used once.

  dialect

    dialect which created this ExecutionContext.

  cursor

    DB-API cursor procured from the connection,

  compiled

    if passed to constructor, sqlalchemy.engine.base.Compiled object being executed,

  statement

    string version of the statement to be executed. Is either passed to the constructor, or must be created from the sql.Compiled object by the time pre_exec() has completed.

  parameters

    bind parameters passed to the execute() method. For compiled statements, this is a dictionary or list of dictionaries. For textual statements, it should be in a format suitable for the dialect’s paramstyle (i.e. dict or list of dicts for non positional, list or list of lists/tuples for positional).

  isinsert

    True if the statement is an INSERT.

  isupdate

    True if the statement is an UPDATE.

  should_autocommit

    True if the statement is a “committable” statement.

  prefetch_cols

    a list of Column objects for which a client-side default was fired off. Applies to inserts and updates.

  postfetch_cols

    a list of Column objects for which a server-side default or inline SQL expression value was fired off. Applies to inserts and updates.

  `create_cursor`()

    Return a new cursor generated from this ExecutionContext’s connection.

    Some dialects may wish to change the behavior of connection.cursor(), such as postgresql which may return a PG “server side” cursor.

  `exception` = None

    A DBAPI-level exception that was caught when this ExecutionContext attempted to execute a statement.

    This attribute is meaningful only within the `ConnectionEvents.dbapi_error()` event.

    New in version 0.9.7.

    See also

    `ExecutionContext.is_disconnect`

    `ConnectionEvents.dbapi_error()`

  `get_rowcount`()

    Return the DBAPI `cursor.rowcount` value, or in some cases an interpreted value.

    See `ResultProxy.rowcount` for details on this.

  `handle_dbapi_exception`(e)

    Receive a DBAPI exception which occurred upon execute, result fetch, etc.

  `is_disconnect` = None

    Boolean flag set to True or False when a DBAPI-level exception is caught when this ExecutionContext attempted to execute a statement.

    This attribute is meaningful only within the `ConnectionEvents.dbapi_error()` event.

    New in version 0.9.7.

    See also

    `ExecutionContext.exception`

    `ConnectionEvents.dbapi_error()`

  `lastrow_has_defaults`()

    Return True if the last INSERT or UPDATE row contained inlined or database-side defaults.

  `post_exec`()

    Called after the execution of a compiled statement.

    If a compiled statement was passed to this ExecutionContext, the last_insert_ids, last_inserted_params, etc. datamembers should be available after this method completes.

  `pre_exec`()

    Called before an execution of a compiled statement.

    If a compiled statement was passed to this ExecutionContext, the statement and parameters datamembers must be initialized after this statement is complete.

  `result`()

    Return a result object corresponding to this ExecutionContext.

    Returns a ResultProxy.

  `should_autocommit_text`(statement)

    Parse the given textual statement and return True if it refers to a “committable” statement

class `sqlalchemy.log.` `Identified`

class `sqlalchemy.sql.compiler.` `IdentifierPreparer`(dialect, initial_quote='"', final_quote=None, escape_quote='"', quote_case_sensitive_collations=True, omit_schema=False)

  Handle quoting and case-folding of identifiers based on options.

  `__init__`(dialect, initial_quote='"', final_quote=None, escape_quote='"', quote_case_sensitive_collations=True, omit_schema=False)

    Construct a new `IdentifierPreparer` object.

    initial_quote

      Character that begins a delimited identifier.

    final_quote

      Character that ends a delimited identifier. Defaults to initial_quote.

    omit_schema

      Prevent prepending schema name. Useful for databases that do not support schemae.

  `format_column`(column, use_table=False, name=None, table_name=None, use_schema=False)

    Prepare a quoted column name.

  `format_schema`(name, quote=None)

    Prepare a quoted schema name.

  `format_table`(table, use_schema=True, name=None)

    Prepare a quoted table and schema name.

  `format_table_seq`(table, use_schema=True)

    Format table name and schema as a tuple.

  `quote`(ident, force=None)

    Conditionally quote an identfier.

    The identifier is quoted if it is a reserved word, contains quote-necessary characters, or is an instance of `quoted_name` which includes `quote` set to `True`.

    Subclasses can override this to provide database-dependent quoting behavior for identifier names.

    Parameters

      - ident – string identifier

      - force –

        this parameter is no longer used.

        Deprecated since version 0.9: The `IdentifierPreparer.force` parameter is deprecated and will be removed in a future release. Quoting preference is now intrinsic to the string being quoted by making use of the `quoted_name` class.

  `quote_identifier`(value)

    Quote an identifier.

    Subclasses should override this to provide database-dependent quoting behavior.

  `quote_schema`(schema, force=None)

    Conditionally quote a schema name.

    The name is quoted if it is a reserved word, contains quote-necessary characters, or is an instance of `quoted_name` which includes `quote` set to `True`.

    Subclasses can override this to provide database-dependent quoting behavior for schema names.

    Parameters

      - schema – string schema name

      - force –

        this parameter is no longer used.

        Deprecated since version 0.9: The `IdentifierPreparer.force` parameter is deprecated and will be removed in a future release. Quoting preference is now intrinsic to the string being quoted by making use of the `quoted_name` class.

  `unformat_identifiers`(identifiers)

    Unpack ‘schema.table.column’-like strings into components.

class `sqlalchemy.sql.compiler.` `SQLCompiler`(dialect, statement, column_keys=None, inline=False, **kwargs)

  Bases: `sqlalchemy.sql.compiler.Compiled`

  Default implementation of `Compiled`.

  Compiles `ClauseElement` objects into SQL strings.

  `__init__`(dialect, statement, column_keys=None, inline=False, **kwargs)

    Construct a new `SQLCompiler` object.

    Parameters

      - dialect – `Dialect` to be used

      - statement – `ClauseElement` to be compiled

      - column_keys – a list of column names to be compiled into an INSERT or UPDATE statement.

      - inline – whether to generate INSERT statements as “inline”, e.g. not formatted to return any generated defaults

      - kwargs – additional keyword arguments to be consumed by the superclass.

  `ansi_bind_rules` = False

    SQL 92 doesn’t allow bind parameters to be used in the columns clause of a SELECT, nor does it allow ambiguous expressions like “? = ?”. A compiler subclass can set this flag to False if the target driver/DB enforces this

  `construct_params`(params=None, _group_number=None, _check=True)

    return a dictionary of bind parameter keys and values

  `contains_expanding_parameters` = False

    True if we’ve encountered bindparam(…, expanding=True).

    These need to be converted before execution time against the string statement.

  `default_from`()

    Called when a SELECT statement has no froms, and no FROM clause is to be appended.

    Gives Oracle a chance to tack on a `FROM DUAL` to the string output.

  `delete_extra_from_clause`(update_stmt, from_table, extra_froms, from_hints, **kw)

    Provide a hook to override the generation of an DELETE..FROM clause.

    This can be used to implement DELETE..USING for example.

    MySQL and MSSQL override this.

  `get_select_precolumns`(select, **kw)

    Called when building a `SELECT` statement, position is just before column list.

  `group_by_clause`(select, **kw)

    allow dialects to customize how GROUP BY is rendered.

  `isdelete` = False

    class-level defaults which can be set at the instance level to define if this Compiled instance represents INSERT/UPDATE/DELETE

  `order_by_clause`(select, **kw)

    allow dialects to customize how ORDER BY is rendered.

  `params`

    Return the bind param dictionary embedded into this compiled object, for those values that are present.

  `render_literal_value`(value, type_)

    Render the value of a bind parameter as a quoted literal.

    This is used for statement sections that do not accept bind parameters on the target driver/database.

    This should be implemented by subclasses using the quoting services of the DBAPI.

  `render_table_with_column_in_update_from` = False

    set to True classwide to indicate the SET clause in a multi-table UPDATE statement should qualify columns with the table name (i.e. MySQL only)

  `returning` = None

    holds the “returning” collection of columns if the statement is CRUD and defines returning columns either implicitly or explicitly

  `returning_precedes_values` = False

    set to True classwide to generate RETURNING clauses before the VALUES or WHERE clause (i.e. MSSQL)

  `sql_compiler`

    Return a Compiled that is capable of processing SQL expressions.

    If this compiler is one, it would likely just return ‘self’.

  `update_from_clause`(update_stmt, from_table, extra_froms, from_hints, **kw)

    Provide a hook to override the generation of an UPDATE..FROM clause.

    MySQL and MSSQL override this.

  `update_limit_clause`(update_stmt)

    Provide a hook for MySQL to add LIMIT to the UPDATE

  `update_tables_clause`(update_stmt, from_table, extra_froms, **kw)

    Provide a hook to override the initial table clause in an UPDATE statement.

    MySQL overrides this.

class `sqlalchemy.sql.compiler.` `StrSQLCompiler`(dialect, statement, column_keys=None, inline=False, **kwargs)

  Bases: `sqlalchemy.sql.compiler.SQLCompiler`

  A `SQLCompiler` subclass which allows a small selection of non-standard SQL features to render into a string value.

  The `StrSQLCompiler` is invoked whenever a Core expression element is directly stringified without calling upon the `ClauseElement.compile()` method. It can render a limited set of non-standard SQL constructs to assist in basic stringification, however for more substantial custom or dialect-specific SQL constructs, it will be necessary to make use of `ClauseElement.compile()` directly.

  See also

  How do I render SQL expressions as strings, possibly with bound parameters inlined?

  `delete_extra_from_clause`(update_stmt, from_table, extra_froms, from_hints, **kw)

    Provide a hook to override the generation of an DELETE..FROM clause.

    This can be used to implement DELETE..USING for example.

    MySQL and MSSQL override this.

  `update_from_clause`(update_stmt, from_table, extra_froms, from_hints, **kw)

    Provide a hook to override the generation of an UPDATE..FROM clause.

    MySQL and MSSQL override this.