Classe « Column »

Constructeur sqlalchemy.Column.__init__

Signature de la constructeur __init__

def __init__(self, *args, **kwargs) 

Description

__init__.__doc__

        Construct a new ``Column`` object.

        :param name: The name of this column as represented in the database.
          This argument may be the first positional argument, or specified
          via keyword.

          Names which contain no upper case characters
          will be treated as case insensitive names, and will not be quoted
          unless they are a reserved word.  Names with any number of upper
          case characters will be quoted and sent exactly.  Note that this
          behavior applies even for databases which standardize upper
          case names as case insensitive such as Oracle.

          The name field may be omitted at construction time and applied
          later, at any time before the Column is associated with a
          :class:`_schema.Table`.  This is to support convenient
          usage within the :mod:`~sqlalchemy.ext.declarative` extension.

        :param type\_: The column's type, indicated using an instance which
          subclasses :class:`~sqlalchemy.types.TypeEngine`.  If no arguments
          are required for the type, the class of the type can be sent
          as well, e.g.::

            # use a type with arguments
            Column('data', String(50))

            # use no arguments
            Column('level', Integer)

          The ``type`` argument may be the second positional argument
          or specified by keyword.

          If the ``type`` is ``None`` or is omitted, it will first default to
          the special type :class:`.NullType`.  If and when this
          :class:`_schema.Column` is made to refer to another column using
          :class:`_schema.ForeignKey` and/or
          :class:`_schema.ForeignKeyConstraint`, the type
          of the remote-referenced column will be copied to this column as
          well, at the moment that the foreign key is resolved against that
          remote :class:`_schema.Column` object.

          .. versionchanged:: 0.9.0
            Support for propagation of type to a :class:`_schema.Column`
            from its
            :class:`_schema.ForeignKey` object has been improved and should be
            more reliable and timely.

        :param \*args: Additional positional arguments include various
          :class:`.SchemaItem` derived constructs which will be applied
          as options to the column.  These include instances of
          :class:`.Constraint`, :class:`_schema.ForeignKey`,
          :class:`.ColumnDefault`, :class:`.Sequence`, :class:`.Computed`
          :class:`.Identity`.  In some cases an
          equivalent keyword argument is available such as ``server_default``,
          ``default`` and ``unique``.

        :param autoincrement: Set up "auto increment" semantics for an integer
          primary key column.  The default value is the string ``"auto"``
          which indicates that a single-column primary key that is of
          an INTEGER type with no stated client-side or python-side defaults
          should receive auto increment semantics automatically;
          all other varieties of primary key columns will not.  This
          includes that :term:`DDL` such as PostgreSQL SERIAL or MySQL
          AUTO_INCREMENT will be emitted for this column during a table
          create, as well as that the column is assumed to generate new
          integer primary key values when an INSERT statement invokes which
          will be retrieved by the dialect.  When used in conjunction with
          :class:`.Identity` on a dialect that supports it, this parameter
          has no effect.

          The flag may be set to ``True`` to indicate that a column which
          is part of a composite (e.g. multi-column) primary key should
          have autoincrement semantics, though note that only one column
          within a primary key may have this setting.    It can also
          be set to ``True`` to indicate autoincrement semantics on a
          column that has a client-side or server-side default configured,
          however note that not all dialects can accommodate all styles
          of default as an "autoincrement".  It can also be
          set to ``False`` on a single-column primary key that has a
          datatype of INTEGER in order to disable auto increment semantics
          for that column.

          .. versionchanged:: 1.1 The autoincrement flag now defaults to
             ``"auto"`` which indicates autoincrement semantics by default
             for single-column integer primary keys only; for composite
             (multi-column) primary keys, autoincrement is never implicitly
             enabled; as always, ``autoincrement=True`` will allow for
             at most one of those columns to be an "autoincrement" column.
             ``autoincrement=True`` may also be set on a
             :class:`_schema.Column`
             that has an explicit client-side or server-side default,
             subject to limitations of the backend database and dialect.


          The setting *only* has an effect for columns which are:

          * Integer derived (i.e. INT, SMALLINT, BIGINT).

          * Part of the primary key

          * Not referring to another column via :class:`_schema.ForeignKey`,
            unless
            the value is specified as ``'ignore_fk'``::

                # turn on autoincrement for this column despite
                # the ForeignKey()
                Column('id', ForeignKey('other.id'),
                            primary_key=True, autoincrement='ignore_fk')

            It is typically not desirable to have "autoincrement" enabled on a
            column that refers to another via foreign key, as such a column is
            required to refer to a value that originates from elsewhere.

          The setting has these two effects on columns that meet the
          above criteria:

          * DDL issued for the column will include database-specific
            keywords intended to signify this column as an
            "autoincrement" column, such as AUTO INCREMENT on MySQL,
            SERIAL on PostgreSQL, and IDENTITY on MS-SQL.  It does
            *not* issue AUTOINCREMENT for SQLite since this is a
            special SQLite flag that is not required for autoincrementing
            behavior.

            .. seealso::

                :ref:`sqlite_autoincrement`

          * The column will be considered to be available using an
            "autoincrement" method specific to the backend database, such
            as calling upon ``cursor.lastrowid``, using RETURNING in an
            INSERT statement to get at a sequence-generated value, or using
            special functions such as "SELECT scope_identity()".
            These methods are highly specific to the DBAPIs and databases in
            use and vary greatly, so care should be taken when associating
            ``autoincrement=True`` with a custom default generation function.


        :param default: A scalar, Python callable, or
            :class:`_expression.ColumnElement` expression representing the
            *default value* for this column, which will be invoked upon insert
            if this column is otherwise not specified in the VALUES clause of
            the insert. This is a shortcut to using :class:`.ColumnDefault` as
            a positional argument; see that class for full detail on the
            structure of the argument.

            Contrast this argument to
            :paramref:`_schema.Column.server_default`
            which creates a default generator on the database side.

            .. seealso::

                :ref:`metadata_defaults_toplevel`

        :param doc: optional String that can be used by the ORM or similar
            to document attributes on the Python side.   This attribute does
            **not** render SQL comments; use the
            :paramref:`_schema.Column.comment`
            parameter for this purpose.

        :param key: An optional string identifier which will identify this
            ``Column`` object on the :class:`_schema.Table`.
            When a key is provided,
            this is the only identifier referencing the ``Column`` within the
            application, including ORM attribute mapping; the ``name`` field
            is used only when rendering SQL.

        :param index: When ``True``, indicates that a :class:`_schema.Index`
            construct will be automatically generated for this
            :class:`_schema.Column`, which will result in a "CREATE INDEX"
            statement being emitted for the :class:`_schema.Table` when the DDL
            create operation is invoked.

            Using this flag is equivalent to making use of the
            :class:`_schema.Index` construct explicitly at the level of the
            :class:`_schema.Table` construct itself::

                Table(
                    "some_table",
                    metadata,
                    Column("x", Integer),
                    Index("ix_some_table_x", "x")
                )

            To add the :paramref:`_schema.Index.unique` flag to the
            :class:`_schema.Index`, set both the
            :paramref:`_schema.Column.unique` and
            :paramref:`_schema.Column.index` flags to True simultaneously,
            which will have the effect of rendering the "CREATE UNIQUE INDEX"
            DDL instruction instead of "CREATE INDEX".

            The name of the index is generated using the
            :ref:`default naming convention <constraint_default_naming_convention>`
            which for the :class:`_schema.Index` construct is of the form
            ``ix_<tablename>_<columnname>``.

            As this flag is intended only as a convenience for the common case
            of adding a single-column, default configured index to a table
            definition, explicit use of the :class:`_schema.Index` construct
            should be preferred for most use cases, including composite indexes
            that encompass more than one column, indexes with SQL expressions
            or ordering, backend-specific index configuration options, and
            indexes that use a specific name.

            .. note:: the :attr:`_schema.Column.index` attribute on
               :class:`_schema.Column`
               **does not indicate** if this column is indexed or not, only
               if this flag was explicitly set here.  To view indexes on
               a column, view the :attr:`_schema.Table.indexes` collection
               or use :meth:`_reflection.Inspector.get_indexes`.

            .. seealso::

                :ref:`schema_indexes`

                :ref:`constraint_naming_conventions`

                :paramref:`_schema.Column.unique`

        :param info: Optional data dictionary which will be populated into the
            :attr:`.SchemaItem.info` attribute of this object.

        :param nullable: When set to ``False``, will cause the "NOT NULL"
            phrase to be added when generating DDL for the column.   When
            ``True``, will normally generate nothing (in SQL this defaults to
            "NULL"), except in some very specific backend-specific edge cases
            where "NULL" may render explicitly.
            Defaults to ``True`` unless :paramref:`_schema.Column.primary_key`
            is also ``True`` or the column specifies a :class:`_sql.Identity`,
            in which case it defaults to ``False``.
            This parameter is only used when issuing CREATE TABLE statements.

            .. note::

                When the column specifies a :class:`_sql.Identity` this
                parameter is in general ignored by the DDL compiler. The
                PostgreSQL database allows nullable identity column by
                setting this parameter to ``True`` explicitly.

        :param onupdate: A scalar, Python callable, or
            :class:`~sqlalchemy.sql.expression.ClauseElement` representing a
            default value to be applied to the column within UPDATE
            statements, which will be invoked upon update if this column is not
            present in the SET clause of the update. This is a shortcut to
            using :class:`.ColumnDefault` as a positional argument with
            ``for_update=True``.

            .. seealso::

                :ref:`metadata_defaults` - complete discussion of onupdate

        :param primary_key: If ``True``, marks this column as a primary key
            column. Multiple columns can have this flag set to specify
            composite primary keys. As an alternative, the primary key of a
            :class:`_schema.Table` can be specified via an explicit
            :class:`.PrimaryKeyConstraint` object.

        :param server_default: A :class:`.FetchedValue` instance, str, Unicode
            or :func:`~sqlalchemy.sql.expression.text` construct representing
            the DDL DEFAULT value for the column.

            String types will be emitted as-is, surrounded by single quotes::

                Column('x', Text, server_default="val")

                x TEXT DEFAULT 'val'

            A :func:`~sqlalchemy.sql.expression.text` expression will be
            rendered as-is, without quotes::

                Column('y', DateTime, server_default=text('NOW()'))

                y DATETIME DEFAULT NOW()

            Strings and text() will be converted into a
            :class:`.DefaultClause` object upon initialization.

            Use :class:`.FetchedValue` to indicate that an already-existing
            column will generate a default value on the database side which
            will be available to SQLAlchemy for post-fetch after inserts. This
            construct does not specify any DDL and the implementation is left
            to the database, such as via a trigger.

            .. seealso::

                :ref:`server_defaults` - complete discussion of server side
                defaults

        :param server_onupdate: A :class:`.FetchedValue` instance
            representing a database-side default generation function,
            such as a trigger. This
            indicates to SQLAlchemy that a newly generated value will be
            available after updates. This construct does not actually
            implement any kind of generation function within the database,
            which instead must be specified separately.


            .. warning:: This directive **does not** currently produce MySQL's
               "ON UPDATE CURRENT_TIMESTAMP()" clause.  See
               :ref:`mysql_timestamp_onupdate` for background on how to
               produce this clause.

            .. seealso::

                :ref:`triggered_columns`

        :param quote: Force quoting of this column's name on or off,
             corresponding to ``True`` or ``False``. When left at its default
             of ``None``, the column identifier will be quoted according to
             whether the name is case sensitive (identifiers with at least one
             upper case character are treated as case sensitive), or if it's a
             reserved word. This flag is only needed to force quoting of a
             reserved word which is not known by the SQLAlchemy dialect.

        :param unique: When ``True``, and the :paramref:`_schema.Column.index`
            parameter is left at its default value of ``False``,
            indicates that a :class:`_schema.UniqueConstraint`
            construct will be automatically generated for this
            :class:`_schema.Column`,
            which will result in a "UNIQUE CONSTRAINT" clause referring
            to this column being included
            in the ``CREATE TABLE`` statement emitted, when the DDL create
            operation for the :class:`_schema.Table` object is invoked.

            When this flag is ``True`` while the
            :paramref:`_schema.Column.index` parameter is simultaneously
            set to ``True``, the effect instead is that a
            :class:`_schema.Index` construct which includes the
            :paramref:`_schema.Index.unique` parameter set to ``True``
            is generated.  See the documentation for
            :paramref:`_schema.Column.index` for additional detail.

            Using this flag is equivalent to making use of the
            :class:`_schema.UniqueConstraint` construct explicitly at the
            level of the :class:`_schema.Table` construct itself::

                Table(
                    "some_table",
                    metadata,
                    Column("x", Integer),
                    UniqueConstraint("x")
                )

            The :paramref:`_schema.UniqueConstraint.name` parameter
            of the unique constraint object is left at its default value
            of ``None``; in the absence of a :ref:`naming convention <constraint_naming_conventions>`
            for the enclosing :class:`_schema.MetaData`, the UNIQUE CONSTRAINT
            construct will be emitted as unnamed, which typically invokes
            a database-specific naming convention to take place.

            As this flag is intended only as a convenience for the common case
            of adding a single-column, default configured unique constraint to a table
            definition, explicit use of the :class:`_schema.UniqueConstraint` construct
            should be preferred for most use cases, including composite constraints
            that encompass more than one column, backend-specific index configuration options, and
            constraints that use a specific name.

            .. note:: the :attr:`_schema.Column.unique` attribute on
                :class:`_schema.Column`
                **does not indicate** if this column has a unique constraint or
                not, only if this flag was explicitly set here.  To view
                indexes and unique constraints that may involve this column,
                view the
                :attr:`_schema.Table.indexes` and/or
                :attr:`_schema.Table.constraints` collections or use
                :meth:`_reflection.Inspector.get_indexes` and/or
                :meth:`_reflection.Inspector.get_unique_constraints`

            .. seealso::

                :ref:`schema_unique_constraint`

                :ref:`constraint_naming_conventions`

                :paramref:`_schema.Column.index`

        :param system: When ``True``, indicates this is a "system" column,
             that is a column which is automatically made available by the
             database, and should not be included in the columns list for a
             ``CREATE TABLE`` statement.

             For more elaborate scenarios where columns should be
             conditionally rendered differently on different backends,
             consider custom compilation rules for :class:`.CreateColumn`.

        :param comment: Optional string that will render an SQL comment on
             table creation.

             .. versionadded:: 1.2 Added the
                :paramref:`_schema.Column.comment`
                parameter to :class:`_schema.Column`.