Classe « VARCHAR »

Constructeur sqlalchemy.VARCHAR.__init__

Signature de la constructeur __init__

def __init__(self, length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False) 

Description

__init__.__doc__

        Create a string-holding type.

        :param length: optional, a length for the column for use in
          DDL and CAST expressions.  May be safely omitted if no ``CREATE
          TABLE`` will be issued.  Certain databases may require a
          ``length`` for use in DDL, and will raise an exception when
          the ``CREATE TABLE`` DDL is issued if a ``VARCHAR``
          with no length is included.  Whether the value is
          interpreted as bytes or characters is database specific.

        :param collation: Optional, a column-level collation for
          use in DDL and CAST expressions.  Renders using the
          COLLATE keyword supported by SQLite, MySQL, and PostgreSQL.
          E.g.::

            >>> from sqlalchemy import cast, select, String
            >>> print(select(cast('some string', String(collation='utf8'))))
            SELECT CAST(:param_1 AS VARCHAR COLLATE utf8) AS anon_1

        :param convert_unicode: When set to ``True``, the
          :class:`.String` type will assume that
          input is to be passed as Python Unicode objects under Python 2,
          and results returned as Python Unicode objects.
          In the rare circumstance that the DBAPI does not support
          Python unicode under Python 2, SQLAlchemy will use its own
          encoder/decoder functionality on strings, referring to the
          value of the :paramref:`_sa.create_engine.encoding` parameter
          parameter passed to :func:`_sa.create_engine` as the encoding.

          .. deprecated:: 1.3 The :paramref:`.String.convert_unicode` parameter is deprecated and will be removed in a future release.  All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary.



          For the extremely rare case that Python Unicode
          is to be encoded/decoded by SQLAlchemy on a backend
          that *does* natively support Python Unicode,
          the string value ``"force"`` can be passed here which will
          cause SQLAlchemy's encode/decode services to be
          used unconditionally.

          .. note::

            SQLAlchemy's unicode-conversion flags and features only apply
            to Python 2; in Python 3, all string objects are Unicode objects.
            For this reason, as well as the fact that virtually all modern
            DBAPIs now support Unicode natively even under Python 2,
            the :paramref:`.String.convert_unicode` flag is inherently a
            legacy feature.

          .. note::

            In the vast majority of cases, the :class:`.Unicode` or
            :class:`.UnicodeText` datatypes should be used for a
            :class:`_schema.Column` that expects to store non-ascii data.
            These
            datatypes will ensure that the correct types are used on the
            database side as well as set up the correct Unicode behaviors
            under Python 2.

          .. seealso::

            :paramref:`_sa.create_engine.convert_unicode` -
            :class:`_engine.Engine`-wide parameter

        :param unicode_error: Optional, a method to use to handle Unicode
          conversion errors. Behaves like the ``errors`` keyword argument to
          the standard library's ``string.decode()`` functions, requires
          that :paramref:`.String.convert_unicode` is set to
          ``"force"``

          .. deprecated:: 1.3 The :paramref:`.String.unicode_errors` parameter is deprecated and will be removed in a future release.  This parameter is unnecessary for modern Python DBAPIs and degrades performance significantly.