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Classe « Session »

Méthode sqlalchemy.orm.Session.is_modified

Signature de la méthode is_modified

def is_modified(self, instance: 'object', include_collections: 'bool' = True) -> 'bool' 

Description

help(Session.is_modified)

Return ``True`` if the given instance has locally
modified attributes.

This method retrieves the history for each instrumented
attribute on the instance and performs a comparison of the current
value to its previously flushed or committed value, if any.

It is in effect a more expensive and accurate
version of checking for the given instance in the
:attr:`.Session.dirty` collection; a full test for
each attribute's net "dirty" status is performed.

E.g.::

    return session.is_modified(someobject)

A few caveats to this method apply:

* Instances present in the :attr:`.Session.dirty` collection may
  report ``False`` when tested with this method.  This is because
  the object may have received change events via attribute mutation,
  thus placing it in :attr:`.Session.dirty`, but ultimately the state
  is the same as that loaded from the database, resulting in no net
  change here.
* Scalar attributes may not have recorded the previously set
  value when a new value was applied, if the attribute was not loaded,
  or was expired, at the time the new value was received - in these
  cases, the attribute is assumed to have a change, even if there is
  ultimately no net change against its database value. SQLAlchemy in
  most cases does not need the "old" value when a set event occurs, so
  it skips the expense of a SQL call if the old value isn't present,
  based on the assumption that an UPDATE of the scalar value is
  usually needed, and in those few cases where it isn't, is less
  expensive on average than issuing a defensive SELECT.

  The "old" value is fetched unconditionally upon set only if the
  attribute container has the ``active_history`` flag set to ``True``.
  This flag is set typically for primary key attributes and scalar
  object references that are not a simple many-to-one.  To set this
  flag for any arbitrary mapped column, use the ``active_history``
  argument with :func:`.column_property`.

:param instance: mapped instance to be tested for pending changes.
:param include_collections: Indicates if multivalued collections
 should be included in the operation.  Setting this to ``False`` is a
 way to detect only local-column based properties (i.e. scalar columns
 or many-to-one foreign keys) that would result in an UPDATE for this
 instance upon flush.

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