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ORM Event Interfaces
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<h1>SQLAlchemy 0.6.8 Documentation</h1>
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Version: <span class="versionnum">0.6.8</span> Last Updated: 06/05/2011 13:10:26
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ORM Event Interfaces
<h2>
ORM Event Interfaces
</h2>
<ul>
<li><a class="reference internal" href="#">ORM Event Interfaces</a><ul>
<li><a class="reference internal" href="#mapper-events">Mapper Events</a></li>
<li><a class="reference internal" href="#session-events">Session Events</a></li>
<li><a class="reference internal" href="#attribute-events">Attribute Events</a></li>
<li><a class="reference internal" href="#instrumentation-events-and-re-implementation">Instrumentation Events and Re-implementation</a></li>
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<div class="section" id="module-sqlalchemy.orm.interfaces">
<span id="orm-event-interfaces"></span><span id="events-orm-toplevel"></span><span id="interfaces-orm-toplevel"></span><h1>ORM Event Interfaces<a class="headerlink" href="#module-sqlalchemy.orm.interfaces" title="Permalink to this headline">¶</a></h1>
<p>This section describes the various categories of events which can be intercepted
within the SQLAlchemy ORM.</p>
<p>For non-ORM event documentation, see <a class="reference internal" href="../core/interfaces.html"><em>Core Event Interfaces</em></a>.</p>
<p>A new version of this API with a significantly more flexible and consistent
interface will be available in version 0.7.</p>
<div class="section" id="mapper-events">
<h2>Mapper Events<a class="headerlink" href="#mapper-events" title="Permalink to this headline">¶</a></h2>
<p>To use <a class="reference internal" href="#sqlalchemy.orm.interfaces.MapperExtension" title="sqlalchemy.orm.interfaces.MapperExtension"><tt class="xref py py-class docutils literal"><span class="pre">MapperExtension</span></tt></a>, make your own subclass of it and just send it off to a mapper:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">sqlalchemy.orm.interfaces</span> <span class="kn">import</span> <span class="n">MapperExtension</span>
<span class="k">class</span> <span class="nc">MyExtension</span><span class="p">(</span><span class="n">MapperExtension</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">before_insert</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">mapper</span><span class="p">,</span> <span class="n">connection</span><span class="p">,</span> <span class="n">instance</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"instance </span><span class="si">%s</span><span class="s"> before insert !"</span> <span class="o">%</span> <span class="n">instance</span>
<span class="n">m</span> <span class="o">=</span> <span class="n">mapper</span><span class="p">(</span><span class="n">User</span><span class="p">,</span> <span class="n">users_table</span><span class="p">,</span> <span class="n">extension</span><span class="o">=</span><span class="n">MyExtension</span><span class="p">())</span></pre></div>
</div>
<p>Multiple extensions will be chained together and processed in order; they are specified as a list:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">m</span> <span class="o">=</span> <span class="n">mapper</span><span class="p">(</span><span class="n">User</span><span class="p">,</span> <span class="n">users_table</span><span class="p">,</span> <span class="n">extension</span><span class="o">=</span><span class="p">[</span><span class="n">ext1</span><span class="p">,</span> <span class="n">ext2</span><span class="p">,</span> <span class="n">ext3</span><span class="p">])</span></pre></div>
</div>
<dl class="class">
<dt id="sqlalchemy.orm.interfaces.MapperExtension">
<em class="property">class </em><tt class="descclassname">sqlalchemy.orm.interfaces.</tt><tt class="descname">MapperExtension</tt><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension" title="Permalink to this definition">¶</a></dt>
<dd><p>Base implementation for customizing <tt class="docutils literal"><span class="pre">Mapper</span></tt> behavior.</p>
<p>New extension classes subclass <tt class="docutils literal"><span class="pre">MapperExtension</span></tt> and are specified
using the <tt class="docutils literal"><span class="pre">extension</span></tt> mapper() argument, which is a single
<tt class="docutils literal"><span class="pre">MapperExtension</span></tt> or a list of such. A single mapper
can maintain a chain of <tt class="docutils literal"><span class="pre">MapperExtension</span></tt> objects. When a
particular mapping event occurs, the corresponding method
on each <tt class="docutils literal"><span class="pre">MapperExtension</span></tt> is invoked serially, and each method
has the ability to halt the chain from proceeding further.</p>
<p>Each <tt class="docutils literal"><span class="pre">MapperExtension</span></tt> method returns the symbol
EXT_CONTINUE by default. This symbol generally means “move
to the next <tt class="docutils literal"><span class="pre">MapperExtension</span></tt> for processing”. For methods
that return objects like translated rows or new object
instances, EXT_CONTINUE means the result of the method
should be ignored. In some cases it’s required for a
default mapper activity to be performed, such as adding a
new instance to a result list.</p>
<p>The symbol EXT_STOP has significance within a chain
of <tt class="docutils literal"><span class="pre">MapperExtension</span></tt> objects that the chain will be stopped
when this symbol is returned. Like EXT_CONTINUE, it also
has additional significance in some cases that a default
mapper activity will not be performed.</p>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.after_delete">
<tt class="descname">after_delete</tt><big>(</big><em>mapper</em>, <em>connection</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.after_delete" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance after that instance is deleted.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.after_insert">
<tt class="descname">after_insert</tt><big>(</big><em>mapper</em>, <em>connection</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.after_insert" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance after that instance is inserted.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.after_update">
<tt class="descname">after_update</tt><big>(</big><em>mapper</em>, <em>connection</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.after_update" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance after that instance is updated.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.append_result">
<tt class="descname">append_result</tt><big>(</big><em>mapper</em>, <em>selectcontext</em>, <em>row</em>, <em>instance</em>, <em>result</em>, <em>**flags</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.append_result" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance before that instance is appended
to a result list.</p>
<p>If this method returns EXT_CONTINUE, result appending will proceed
normally. if this method returns any other value or None,
result appending will not proceed for this instance, giving
this extension an opportunity to do the appending itself, if
desired.</p>
<dl class="docutils">
<dt>mapper</dt>
<dd>The mapper doing the operation.</dd>
<dt>selectcontext</dt>
<dd>The QueryContext generated from the Query.</dd>
<dt>row</dt>
<dd>The result row from the database.</dd>
<dt>instance</dt>
<dd>The object instance to be appended to the result.</dd>
<dt>result</dt>
<dd>List to which results are being appended.</dd>
<dt>**flags</dt>
<dd>extra information about the row, same as criterion in
<tt class="docutils literal"><span class="pre">create_row_processor()</span></tt> method of
<tt class="xref py py-class docutils literal"><span class="pre">MapperProperty</span></tt></dd>
</dl>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.before_delete">
<tt class="descname">before_delete</tt><big>(</big><em>mapper</em>, <em>connection</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.before_delete" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance before that instance is deleted.</p>
<p>Note that <em>no</em> changes to the overall flush plan can be made
here; and manipulation of the <tt class="docutils literal"><span class="pre">Session</span></tt> will not have the
desired effect. To manipulate the <tt class="docutils literal"><span class="pre">Session</span></tt> within an
extension, use <tt class="docutils literal"><span class="pre">SessionExtension</span></tt>.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.before_insert">
<tt class="descname">before_insert</tt><big>(</big><em>mapper</em>, <em>connection</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.before_insert" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance before that instance is inserted
into its table.</p>
<p>This is a good place to set up primary key values and such
that aren’t handled otherwise.</p>
<p>Column-based attributes can be modified within this method
which will result in the new value being inserted. However
<em>no</em> changes to the overall flush plan can be made, and
manipulation of the <tt class="docutils literal"><span class="pre">Session</span></tt> will not have the desired effect.
To manipulate the <tt class="docutils literal"><span class="pre">Session</span></tt> within an extension, use
<tt class="docutils literal"><span class="pre">SessionExtension</span></tt>.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.before_update">
<tt class="descname">before_update</tt><big>(</big><em>mapper</em>, <em>connection</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.before_update" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance before that instance is updated.</p>
<p>Note that this method is called for all instances that are marked as
“dirty”, even those which have no net changes to their column-based
attributes. An object is marked as dirty when any of its column-based
attributes have a “set attribute” operation called or when any of its
collections are modified. If, at update time, no column-based
attributes have any net changes, no UPDATE statement will be issued.
This means that an instance being sent to before_update is <em>not</em> a
guarantee that an UPDATE statement will be issued (although you can
affect the outcome here).</p>
<p>To detect if the column-based attributes on the object have net
changes, and will therefore generate an UPDATE statement, use
<tt class="docutils literal"><span class="pre">object_session(instance).is_modified(instance,</span>
<span class="pre">include_collections=False)</span></tt>.</p>
<p>Column-based attributes can be modified within this method
which will result in the new value being updated. However
<em>no</em> changes to the overall flush plan can be made, and
manipulation of the <tt class="docutils literal"><span class="pre">Session</span></tt> will not have the desired effect.
To manipulate the <tt class="docutils literal"><span class="pre">Session</span></tt> within an extension, use
<tt class="docutils literal"><span class="pre">SessionExtension</span></tt>.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.create_instance">
<tt class="descname">create_instance</tt><big>(</big><em>mapper</em>, <em>selectcontext</em>, <em>row</em>, <em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.create_instance" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive a row when a new object instance is about to be
created from that row.</p>
<p>The method can choose to create the instance itself, or it can return
EXT_CONTINUE to indicate normal object creation should take place.</p>
<dl class="docutils">
<dt>mapper</dt>
<dd>The mapper doing the operation</dd>
<dt>selectcontext</dt>
<dd>The QueryContext generated from the Query.</dd>
<dt>row</dt>
<dd>The result row from the database</dd>
<dt>class_</dt>
<dd>The class we are mapping.</dd>
<dt>return value</dt>
<dd>A new object instance, or EXT_CONTINUE</dd>
</dl>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.init_failed">
<tt class="descname">init_failed</tt><big>(</big><em>mapper</em>, <em>class_</em>, <em>oldinit</em>, <em>instance</em>, <em>args</em>, <em>kwargs</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.init_failed" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an instance when it’s constructor has been called,
and raised an exception.</p>
<p>This method is only called during a userland construction of
an object. It is not called when an object is loaded from the
database.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.init_instance">
<tt class="descname">init_instance</tt><big>(</big><em>mapper</em>, <em>class_</em>, <em>oldinit</em>, <em>instance</em>, <em>args</em>, <em>kwargs</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.init_instance" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an instance when it’s constructor is called.</p>
<p>This method is only called during a userland construction of
an object. It is not called when an object is loaded from the
database.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.instrument_class">
<tt class="descname">instrument_class</tt><big>(</big><em>mapper</em>, <em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.instrument_class" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive a class when the mapper is first constructed, and has
applied instrumentation to the mapped class.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.populate_instance">
<tt class="descname">populate_instance</tt><big>(</big><em>mapper</em>, <em>selectcontext</em>, <em>row</em>, <em>instance</em>, <em>**flags</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.populate_instance" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an instance before that instance has
its attributes populated.</p>
<p>This usually corresponds to a newly loaded instance but may
also correspond to an already-loaded instance which has
unloaded attributes to be populated. The method may be called
many times for a single instance, as multiple result rows are
used to populate eagerly loaded collections.</p>
<p>If this method returns EXT_CONTINUE, instance population will
proceed normally. If any other value or None is returned,
instance population will not proceed, giving this extension an
opportunity to populate the instance itself, if desired.</p>
<p>As of 0.5, most usages of this hook are obsolete. For a
generic “object has been newly created from a row” hook, use
<tt class="docutils literal"><span class="pre">reconstruct_instance()</span></tt>, or the <tt class="docutils literal"><span class="pre">@orm.reconstructor</span></tt>
decorator.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.reconstruct_instance">
<tt class="descname">reconstruct_instance</tt><big>(</big><em>mapper</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.reconstruct_instance" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive an object instance after it has been created via
<tt class="docutils literal"><span class="pre">__new__</span></tt>, and after initial attribute population has
occurred.</p>
<p>This typically occurs when the instance is created based on
incoming result rows, and is only called once for that
instance’s lifetime.</p>
<p>Note that during a result-row load, this method is called upon
the first row received for this instance. Note that some
attributes and collections may or may not be loaded or even
initialized, depending on what’s present in the result rows.</p>
<p>The return value is only significant within the <tt class="docutils literal"><span class="pre">MapperExtension</span></tt>
chain; the parent mapper’s behavior isn’t modified by this method.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.MapperExtension.translate_row">
<tt class="descname">translate_row</tt><big>(</big><em>mapper</em>, <em>context</em>, <em>row</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.MapperExtension.translate_row" title="Permalink to this definition">¶</a></dt>
<dd><p>Perform pre-processing on the given result row and return a
new row instance.</p>
<p>This is called when the mapper first receives a row, before
the object identity or the instance itself has been derived
from that row. The given row may or may not be a
<tt class="docutils literal"><span class="pre">RowProxy</span></tt> object - it will always be a dictionary-like
object which contains mapped columns as keys. The
returned object should also be a dictionary-like object
which recognizes mapped columns as keys.</p>
<p>If the ultimate return value is EXT_CONTINUE, the row
is not translated.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="session-events">
<h2>Session Events<a class="headerlink" href="#session-events" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#sqlalchemy.orm.interfaces.SessionExtension" title="sqlalchemy.orm.interfaces.SessionExtension"><tt class="xref py py-class docutils literal"><span class="pre">SessionExtension</span></tt></a> applies plugin points for <a class="reference internal" href="session.html#sqlalchemy.orm.session.Session" title="sqlalchemy.orm.session.Session"><tt class="xref py py-class docutils literal"><span class="pre">Session</span></tt></a> objects:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">sqlalchemy.orm.interfaces</span> <span class="kn">import</span> <span class="n">SessionExtension</span>
<span class="k">class</span> <span class="nc">MySessionExtension</span><span class="p">(</span><span class="n">SessionExtension</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">before_commit</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">session</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"before commit!"</span>
<span class="n">Session</span> <span class="o">=</span> <span class="n">sessionmaker</span><span class="p">(</span><span class="n">extension</span><span class="o">=</span><span class="n">MySessionExtension</span><span class="p">())</span></pre></div>
</div>
<p>The same <a class="reference internal" href="#sqlalchemy.orm.interfaces.SessionExtension" title="sqlalchemy.orm.interfaces.SessionExtension"><tt class="xref py py-class docutils literal"><span class="pre">SessionExtension</span></tt></a> instance can be
used with any number of sessions.</p>
<dl class="class">
<dt id="sqlalchemy.orm.interfaces.SessionExtension">
<em class="property">class </em><tt class="descclassname">sqlalchemy.orm.interfaces.</tt><tt class="descname">SessionExtension</tt><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension" title="Permalink to this definition">¶</a></dt>
<dd><p>An extension hook object for Sessions. Subclasses may be
installed into a Session (or sessionmaker) using the <tt class="docutils literal"><span class="pre">extension</span></tt>
keyword argument.</p>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_attach">
<tt class="descname">after_attach</tt><big>(</big><em>session</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_attach" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after an instance is attached to a session.</p>
<p>This is called after an add, delete or merge.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_begin">
<tt class="descname">after_begin</tt><big>(</big><em>session</em>, <em>transaction</em>, <em>connection</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_begin" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after a transaction is begun on a connection</p>
<p><cite>transaction</cite> is the SessionTransaction. This method is called
after an engine level transaction is begun on a connection.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_bulk_delete">
<tt class="descname">after_bulk_delete</tt><big>(</big><em>session</em>, <em>query</em>, <em>query_context</em>, <em>result</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_bulk_delete" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after a bulk delete operation to the session.</p>
<p>This is called after a session.query(...).delete()</p>
<p><cite>query</cite> is the query object that this delete operation was
called on. <cite>query_context</cite> was the query context object.
<cite>result</cite> is the result object returned from the bulk operation.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_bulk_update">
<tt class="descname">after_bulk_update</tt><big>(</big><em>session</em>, <em>query</em>, <em>query_context</em>, <em>result</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_bulk_update" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after a bulk update operation to the session.</p>
<p>This is called after a session.query(...).update()</p>
<p><cite>query</cite> is the query object that this update operation was
called on. <cite>query_context</cite> was the query context object.
<cite>result</cite> is the result object returned from the bulk operation.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_commit">
<tt class="descname">after_commit</tt><big>(</big><em>session</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_commit" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after a commit has occured.</p>
<p>Note that this may not be per-flush if a longer running
transaction is ongoing.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_flush">
<tt class="descname">after_flush</tt><big>(</big><em>session</em>, <em>flush_context</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_flush" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after flush has completed, but before commit has been
called.</p>
<p>Note that the session’s state is still in pre-flush, i.e. ‘new’,
‘dirty’, and ‘deleted’ lists still show pre-flush state as well
as the history settings on instance attributes.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_flush_postexec">
<tt class="descname">after_flush_postexec</tt><big>(</big><em>session</em>, <em>flush_context</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_flush_postexec" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after flush has completed, and after the post-exec
state occurs.</p>
<p>This will be when the ‘new’, ‘dirty’, and ‘deleted’ lists are in
their final state. An actual commit() may or may not have
occured, depending on whether or not the flush started its own
transaction or participated in a larger transaction.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.after_rollback">
<tt class="descname">after_rollback</tt><big>(</big><em>session</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.after_rollback" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute after a rollback has occured.</p>
<p>Note that this may not be per-flush if a longer running
transaction is ongoing.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.before_commit">
<tt class="descname">before_commit</tt><big>(</big><em>session</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.before_commit" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute right before commit is called.</p>
<p>Note that this may not be per-flush if a longer running
transaction is ongoing.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.SessionExtension.before_flush">
<tt class="descname">before_flush</tt><big>(</big><em>session</em>, <em>flush_context</em>, <em>instances</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.SessionExtension.before_flush" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute before flush process has started.</p>
<p><cite>instances</cite> is an optional list of objects which were passed to
the <tt class="docutils literal"><span class="pre">flush()</span></tt> method.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="attribute-events">
<h2>Attribute Events<a class="headerlink" href="#attribute-events" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="#sqlalchemy.orm.interfaces.AttributeExtension" title="sqlalchemy.orm.interfaces.AttributeExtension"><tt class="xref py py-class docutils literal"><span class="pre">AttributeExtension</span></tt></a> is used to listen for set, remove, and append
events on individual mapped attributes. It is established on an individual
mapped attribute using the <cite>extension</cite> argument, available on
<a class="reference internal" href="mapper_config.html#sqlalchemy.orm.column_property" title="sqlalchemy.orm.column_property"><tt class="xref py py-func docutils literal"><span class="pre">column_property()</span></tt></a>, <a class="reference internal" href="relationships.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><tt class="xref py py-func docutils literal"><span class="pre">relationship()</span></tt></a>, and others:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">sqlalchemy.orm.interfaces</span> <span class="kn">import</span> <span class="n">AttributeExtension</span>
<span class="kn">from</span> <span class="nn">sqlalchemy.orm</span> <span class="kn">import</span> <span class="n">mapper</span><span class="p">,</span> <span class="n">relationship</span><span class="p">,</span> <span class="n">column_property</span>
<span class="k">class</span> <span class="nc">MyAttrExt</span><span class="p">(</span><span class="n">AttributeExtension</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">append</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">state</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">initiator</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"append event !"</span>
<span class="k">return</span> <span class="n">value</span>
<span class="k">def</span> <span class="nf">set</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">state</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">oldvalue</span><span class="p">,</span> <span class="n">initiator</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"set event !"</span>
<span class="k">return</span> <span class="n">value</span>
<span class="n">mapper</span><span class="p">(</span><span class="n">SomeClass</span><span class="p">,</span> <span class="n">sometable</span><span class="p">,</span> <span class="n">properties</span><span class="o">=</span><span class="p">{</span>
<span class="s">'foo'</span><span class="p">:</span><span class="n">column_property</span><span class="p">(</span><span class="n">sometable</span><span class="o">.</span><span class="n">c</span><span class="o">.</span><span class="n">foo</span><span class="p">,</span> <span class="n">extension</span><span class="o">=</span><span class="n">MyAttrExt</span><span class="p">()),</span>
<span class="s">'bar'</span><span class="p">:</span><span class="n">relationship</span><span class="p">(</span><span class="n">Bar</span><span class="p">,</span> <span class="n">extension</span><span class="o">=</span><span class="n">MyAttrExt</span><span class="p">())</span>
<span class="p">})</span></pre></div>
</div>
<p>Note that the <a class="reference internal" href="#sqlalchemy.orm.interfaces.AttributeExtension" title="sqlalchemy.orm.interfaces.AttributeExtension"><tt class="xref py py-class docutils literal"><span class="pre">AttributeExtension</span></tt></a> methods
<a class="reference internal" href="#sqlalchemy.orm.interfaces.AttributeExtension.append" title="sqlalchemy.orm.interfaces.AttributeExtension.append"><tt class="xref py py-meth docutils literal"><span class="pre">append()</span></tt></a> and <a class="reference internal" href="#sqlalchemy.orm.interfaces.AttributeExtension.set" title="sqlalchemy.orm.interfaces.AttributeExtension.set"><tt class="xref py py-meth docutils literal"><span class="pre">set()</span></tt></a> need
to return the <tt class="docutils literal"><span class="pre">value</span></tt> parameter. The returned value is used as the effective
value, and allows the extension to change what is ultimately persisted.</p>
<dl class="class">
<dt id="sqlalchemy.orm.interfaces.AttributeExtension">
<em class="property">class </em><tt class="descclassname">sqlalchemy.orm.interfaces.</tt><tt class="descname">AttributeExtension</tt><a class="headerlink" href="#sqlalchemy.orm.interfaces.AttributeExtension" title="Permalink to this definition">¶</a></dt>
<dd><p>An event handler for individual attribute change events.</p>
<p>AttributeExtension is assembled within the descriptors associated
with a mapped class.</p>
<dl class="attribute">
<dt id="sqlalchemy.orm.interfaces.AttributeExtension.active_history">
<tt class="descname">active_history</tt><a class="headerlink" href="#sqlalchemy.orm.interfaces.AttributeExtension.active_history" title="Permalink to this definition">¶</a></dt>
<dd><p>indicates that the set() method would like to receive the ‘old’ value,
even if it means firing lazy callables.</p>
<p>Note that <tt class="docutils literal"><span class="pre">active_history</span></tt> can also be set directly via
<a class="reference internal" href="mapper_config.html#sqlalchemy.orm.column_property" title="sqlalchemy.orm.column_property"><tt class="xref py py-func docutils literal"><span class="pre">column_property()</span></tt></a> and <a class="reference internal" href="relationships.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><tt class="xref py py-func docutils literal"><span class="pre">relationship()</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.AttributeExtension.append">
<tt class="descname">append</tt><big>(</big><em>state</em>, <em>value</em>, <em>initiator</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.AttributeExtension.append" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive a collection append event.</p>
<p>The returned value will be used as the actual value to be
appended.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.AttributeExtension.remove">
<tt class="descname">remove</tt><big>(</big><em>state</em>, <em>value</em>, <em>initiator</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.AttributeExtension.remove" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive a remove event.</p>
<p>No return value is defined.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.AttributeExtension.set">
<tt class="descname">set</tt><big>(</big><em>state</em>, <em>value</em>, <em>oldvalue</em>, <em>initiator</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.AttributeExtension.set" title="Permalink to this definition">¶</a></dt>
<dd><p>Receive a set event.</p>
<p>The returned value will be used as the actual value to be
set.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="instrumentation-events-and-re-implementation">
<h2>Instrumentation Events and Re-implementation<a class="headerlink" href="#instrumentation-events-and-re-implementation" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="#sqlalchemy.orm.interfaces.InstrumentationManager" title="sqlalchemy.orm.interfaces.InstrumentationManager"><tt class="xref py py-class docutils literal"><span class="pre">InstrumentationManager</span></tt></a> can be subclassed in order to receive class
instrumentation events as well as to change how class instrumentation
proceeds. This class exists for the purposes of integration with other object
management frameworks which would like to entirely modify the instrumentation
methodology of the ORM, and is not intended for regular usage. One possible
exception is the <a class="reference internal" href="#sqlalchemy.orm.interfaces.InstrumentationManager.post_configure_attribute" title="sqlalchemy.orm.interfaces.InstrumentationManager.post_configure_attribute"><tt class="xref py py-meth docutils literal"><span class="pre">InstrumentationManager.post_configure_attribute()</span></tt></a>
method, which can be useful for adding extensions to all mapped attributes,
though a much better way to do this will be available in a future release of
SQLAlchemy.</p>
<p>For an example of <a class="reference internal" href="#sqlalchemy.orm.interfaces.InstrumentationManager" title="sqlalchemy.orm.interfaces.InstrumentationManager"><tt class="xref py py-class docutils literal"><span class="pre">InstrumentationManager</span></tt></a>, see the example
<a class="reference internal" href="examples.html#examples-instrumentation"><em>Attribute Instrumentation</em></a>.</p>
<dl class="class">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager">
<em class="property">class </em><tt class="descclassname">sqlalchemy.orm.interfaces.</tt><tt class="descname">InstrumentationManager</tt><big>(</big><em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager" title="Permalink to this definition">¶</a></dt>
<dd><p>User-defined class instrumentation extension.</p>
<p>The API for this class should be considered as semi-stable,
and may change slightly with new releases.</p>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.__init__">
<tt class="descname">__init__</tt><big>(</big><em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.__init__" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.dict_getter">
<tt class="descname">dict_getter</tt><big>(</big><em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.dict_getter" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.dispose">
<tt class="descname">dispose</tt><big>(</big><em>class_</em>, <em>manager</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.dispose" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.get_instance_dict">
<tt class="descname">get_instance_dict</tt><big>(</big><em>class_</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.get_instance_dict" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.initialize_instance_dict">
<tt class="descname">initialize_instance_dict</tt><big>(</big><em>class_</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.initialize_instance_dict" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.install_descriptor">
<tt class="descname">install_descriptor</tt><big>(</big><em>class_</em>, <em>key</em>, <em>inst</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.install_descriptor" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.install_member">
<tt class="descname">install_member</tt><big>(</big><em>class_</em>, <em>key</em>, <em>implementation</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.install_member" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.install_state">
<tt class="descname">install_state</tt><big>(</big><em>class_</em>, <em>instance</em>, <em>state</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.install_state" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.instrument_attribute">
<tt class="descname">instrument_attribute</tt><big>(</big><em>class_</em>, <em>key</em>, <em>inst</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.instrument_attribute" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.instrument_collection_class">
<tt class="descname">instrument_collection_class</tt><big>(</big><em>class_</em>, <em>key</em>, <em>collection_class</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.instrument_collection_class" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.manage">
<tt class="descname">manage</tt><big>(</big><em>class_</em>, <em>manager</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.manage" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.manager_getter">
<tt class="descname">manager_getter</tt><big>(</big><em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.manager_getter" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.post_configure_attribute">
<tt class="descname">post_configure_attribute</tt><big>(</big><em>class_</em>, <em>key</em>, <em>inst</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.post_configure_attribute" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.remove_state">
<tt class="descname">remove_state</tt><big>(</big><em>class_</em>, <em>instance</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.remove_state" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.state_getter">
<tt class="descname">state_getter</tt><big>(</big><em>class_</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.state_getter" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.uninstall_descriptor">
<tt class="descname">uninstall_descriptor</tt><big>(</big><em>class_</em>, <em>key</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.uninstall_descriptor" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="sqlalchemy.orm.interfaces.InstrumentationManager.uninstall_member">
<tt class="descname">uninstall_member</tt><big>(</big><em>class_</em>, <em>key</em><big>)</big><a class="headerlink" href="#sqlalchemy.orm.interfaces.InstrumentationManager.uninstall_member" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
</dd></dl>
</div>
</div>
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