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Classe « ColumnDefault »

Constructeur sqlalchemy.ColumnDefault.__new__

Signature de la constructeur __new__

def __new__(cls, arg: 'Any' = None, for_update: 'bool' = False) -> 'ColumnDefault' 

Description

help(ColumnDefault.__new__)

Construct a new :class:`.ColumnDefault`.


:param arg: argument representing the default value.
 May be one of the following:

 * a plain non-callable Python value, such as a
   string, integer, boolean, or other simple type.
   The default value will be used as is each time.
 * a SQL expression, that is one which derives from
   :class:`_expression.ColumnElement`.  The SQL expression will
   be rendered into the INSERT or UPDATE statement,
   or in the case of a primary key column when
   RETURNING is not used may be
   pre-executed before an INSERT within a SELECT.
 * A Python callable.  The function will be invoked for each
   new row subject to an INSERT or UPDATE.
   The callable must accept exactly
   zero or one positional arguments.  The one-argument form
   will receive an instance of the :class:`.ExecutionContext`,
   which provides contextual information as to the current
   :class:`_engine.Connection` in use as well as the current
   statement and parameters.

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