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<div class="section" id="module-mptt.managers">
<span id="mptt-managers"></span><h1><tt class="docutils literal"><span class="pre">mptt.managers</span></tt><a class="headerlink" href="#module-mptt.managers" title="Permalink to this headline">¶</a></h1>
<p>A custom manager for working with trees of objects.</p>
<dl class="class">
<dt id="mptt.managers.TreeManager">
<em class="property">class </em><tt class="descclassname">mptt.managers.</tt><tt class="descname">TreeManager</tt><a class="headerlink" href="#mptt.managers.TreeManager" title="Permalink to this definition">¶</a></dt>
<dd><p>A manager for working with trees of objects.</p>
<dl class="method">
<dt id="mptt.managers.TreeManager.add_related_count">
<tt class="descname">add_related_count</tt><big>(</big><em>queryset</em>, <em>rel_model</em>, <em>rel_field</em>, <em>count_attr</em>, <em>cumulative=False</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.add_related_count" title="Permalink to this definition">¶</a></dt>
<dd><p>Adds a related item count to a given <tt class="docutils literal"><span class="pre">QuerySet</span></tt> using its
<tt class="docutils literal"><span class="pre">extra</span></tt> method, for a <tt class="docutils literal"><span class="pre">Model</span></tt> class which has a relation to
this <tt class="docutils literal"><span class="pre">Manager</span></tt>‘s <tt class="docutils literal"><span class="pre">Model</span></tt> class.</p>
<p>Arguments:</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">rel_model</span></tt></dt>
<dd>A <tt class="docutils literal"><span class="pre">Model</span></tt> class which has a relation to this <cite>Manager`</cite>‘s
<tt class="docutils literal"><span class="pre">Model</span></tt> class.</dd>
<dt><tt class="docutils literal"><span class="pre">rel_field</span></tt></dt>
<dd>The name of the field in <tt class="docutils literal"><span class="pre">rel_model</span></tt> which holds the
relation.</dd>
<dt><tt class="docutils literal"><span class="pre">count_attr</span></tt></dt>
<dd>The name of an attribute which should be added to each item in
this <tt class="docutils literal"><span class="pre">QuerySet</span></tt>, containing a count of how many instances
of <tt class="docutils literal"><span class="pre">rel_model</span></tt> are related to it through <tt class="docutils literal"><span class="pre">rel_field</span></tt>.</dd>
<dt><tt class="docutils literal"><span class="pre">cumulative</span></tt></dt>
<dd>If <tt class="docutils literal"><span class="pre">True</span></tt>, the count will be for each item and all of its
descendants, otherwise it will be for each item itself.</dd>
</dl>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.delay_mptt_updates">
<tt class="descname">delay_mptt_updates</tt><big>(</big><em>*args</em>, <em>**kwds</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.delay_mptt_updates" title="Permalink to this definition">¶</a></dt>
<dd><p>Context manager. Delays mptt updates until the end of a block of bulk processing.</p>
<p>NOTE that this context manager causes inconsistencies! MPTT model methods are
not guaranteed to return the correct results until the end of the context block.</p>
<dl class="docutils">
<dt>When to use this method:</dt>
<dd><p class="first">If used correctly, this method can be used to speed up bulk updates.
This is best for updates in a localised area of the db table, especially if all
the updates happen in a single tree and the rest of the forest is left untouched.
No subsequent rebuild is necessary.</p>
<p>delay_mptt_updates does a partial rebuild of the modified trees (not the whole table).
If used indiscriminately, this can actually be much slower than just letting the updates
occur when they’re required.</p>
<p>The worst case occurs when every tree in the table is modified just once.
That results in a full rebuild of the table, which can be <em>very</em> slow.</p>
<p class="last">If your updates will modify most of the trees in the table (not a small number of trees),
you should consider using TreeManager.disable_mptt_updates, as it does much fewer
queries.</p>
</dd>
<dt>Transactions:</dt>
<dd>This doesn’t enforce any transactional behavior.
You should wrap this in a transaction to ensure database consistency.</dd>
<dt>Exceptions:</dt>
<dd>If an exception occurs before the processing of the block, delayed updates
will not be applied.</dd>
</dl>
<p>Usage:</p>
<div class="highlight-python"><pre>with transaction.commit_on_success():
with MyNode.objects.delay_mptt_updates():
## bulk updates.</pre>
</div>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.disable_mptt_updates">
<tt class="descname">disable_mptt_updates</tt><big>(</big><em>*args</em>, <em>**kwds</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.disable_mptt_updates" title="Permalink to this definition">¶</a></dt>
<dd><p>Context manager. Disables mptt updates.</p>
<p>NOTE that this context manager causes inconsistencies! MPTT model methods are
not guaranteed to return the correct results.</p>
<dl class="docutils">
<dt>When to use this method:</dt>
<dd><p class="first">If used correctly, this method can be used to speed up bulk updates.</p>
<p>This doesn’t do anything clever. It <em>will</em> mess up your tree.
You should follow this method with a call to TreeManager.rebuild() to ensure your
tree stays sane, and you should wrap both calls in a transaction.</p>
<p class="last">This is best for updates that span a large part of the table.
If you are doing localised changes (1 tree, or a few trees) consider
using delay_mptt_updates.
If you are making only minor changes to your tree, just let the updates happen.</p>
</dd>
<dt>Transactions:</dt>
<dd>This doesn’t enforce any transactional behavior.
You should wrap this in a transaction to ensure database consistency.</dd>
</dl>
<p>If updates are already disabled on the model, this is a noop.</p>
<p>Usage:</p>
<div class="highlight-python"><pre>with transaction.commit_on_success():
with MyNode.objects.disable_mptt_updates():
## bulk updates.
MyNode.objects.rebuild()</pre>
</div>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.get_query_set">
<tt class="descname">get_query_set</tt><big>(</big><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.get_query_set" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a <tt class="docutils literal"><span class="pre">QuerySet</span></tt> which contains all tree items, ordered in
such a way that that root nodes appear in tree id order and
their subtrees appear in depth-first order.</p>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.get_queryset_descendants">
<tt class="descname">get_queryset_descendants</tt><big>(</big><em>queryset</em>, <em>include_self=False</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.get_queryset_descendants" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a queryset containing the descendants of all nodes in the
given queryset.</p>
<p>If <tt class="docutils literal"><span class="pre">include_self=True</span></tt>, nodes in <tt class="docutils literal"><span class="pre">queryset</span></tt> will also
be included in the result.</p>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.init_from_model">
<tt class="descname">init_from_model</tt><big>(</big><em>model</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.init_from_model" title="Permalink to this definition">¶</a></dt>
<dd><p>Sets things up. This would normally be done in contribute_to_class(),
but Django calls that before we’ve created our extra tree fields on the
model (which we need). So it’s done here instead, after field setup.</p>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.insert_node">
<tt class="descname">insert_node</tt><big>(</big><em>node</em>, <em>target</em>, <em>position=u'last-child'</em>, <em>save=False</em>, <em>allow_existing_pk=False</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.insert_node" title="Permalink to this definition">¶</a></dt>
<dd><p>Sets up the tree state for <tt class="docutils literal"><span class="pre">node</span></tt> (which has not yet been
inserted into in the database) so it will be positioned relative
to a given <tt class="docutils literal"><span class="pre">target</span></tt> node as specified by <tt class="docutils literal"><span class="pre">position</span></tt> (when
appropriate) it is inserted, with any neccessary space already
having been made for it.</p>
<p>A <tt class="docutils literal"><span class="pre">target</span></tt> of <tt class="docutils literal"><span class="pre">None</span></tt> indicates that <tt class="docutils literal"><span class="pre">node</span></tt> should be
the last root node.</p>
<p>If <tt class="docutils literal"><span class="pre">save</span></tt> is <tt class="docutils literal"><span class="pre">True</span></tt>, <tt class="docutils literal"><span class="pre">node</span></tt>‘s <tt class="docutils literal"><span class="pre">save()</span></tt> method will be
called before it is returned.</p>
<p>NOTE: This is a low-level method; it does NOT respect <tt class="docutils literal"><span class="pre">MPTTMeta.order_insertion_by</span></tt>.
In most cases you should just set the node’s parent and let mptt call this during save.</p>
</dd></dl>
<dl class="attribute">
<dt id="mptt.managers.TreeManager.left_attr">
<tt class="descname">left_attr</tt><a class="headerlink" href="#mptt.managers.TreeManager.left_attr" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="attribute">
<dt id="mptt.managers.TreeManager.level_attr">
<tt class="descname">level_attr</tt><a class="headerlink" href="#mptt.managers.TreeManager.level_attr" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.move_node">
<tt class="descname">move_node</tt><big>(</big><em>node</em>, <em>target</em>, <em>position=u'last-child'</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.move_node" title="Permalink to this definition">¶</a></dt>
<dd><p>Moves <tt class="docutils literal"><span class="pre">node</span></tt> relative to a given <tt class="docutils literal"><span class="pre">target</span></tt> node as specified
by <tt class="docutils literal"><span class="pre">position</span></tt> (when appropriate), by examining both nodes and
calling the appropriate method to perform the move.</p>
<p>A <tt class="docutils literal"><span class="pre">target</span></tt> of <tt class="docutils literal"><span class="pre">None</span></tt> indicates that <tt class="docutils literal"><span class="pre">node</span></tt> should be
turned into a root node.</p>
<p>Valid values for <tt class="docutils literal"><span class="pre">position</span></tt> are <tt class="docutils literal"><span class="pre">'first-child'</span></tt>,
<tt class="docutils literal"><span class="pre">'last-child'</span></tt>, <tt class="docutils literal"><span class="pre">'left'</span></tt> or <tt class="docutils literal"><span class="pre">'right'</span></tt>.</p>
<p><tt class="docutils literal"><span class="pre">node</span></tt> will be modified to reflect its new tree state in the
database.</p>
<p>This method explicitly checks for <tt class="docutils literal"><span class="pre">node</span></tt> being made a sibling
of a root node, as this is a special case due to our use of tree
ids to order root nodes.</p>
<p>NOTE: This is a low-level method; it does NOT respect <tt class="docutils literal"><span class="pre">MPTTMeta.order_insertion_by</span></tt>.
In most cases you should just move the node yourself by setting node.parent.</p>
</dd></dl>
<dl class="attribute">
<dt id="mptt.managers.TreeManager.parent_attr">
<tt class="descname">parent_attr</tt><a class="headerlink" href="#mptt.managers.TreeManager.parent_attr" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.partial_rebuild">
<tt class="descname">partial_rebuild</tt><big>(</big><em>tree_id</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.partial_rebuild" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.rebuild">
<tt class="descname">rebuild</tt><big>(</big><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.rebuild" title="Permalink to this definition">¶</a></dt>
<dd><p>Rebuilds whole tree in database using <cite>parent</cite> link.</p>
</dd></dl>
<dl class="attribute">
<dt id="mptt.managers.TreeManager.right_attr">
<tt class="descname">right_attr</tt><a class="headerlink" href="#mptt.managers.TreeManager.right_attr" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.root_node">
<tt class="descname">root_node</tt><big>(</big><em>tree_id</em><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.root_node" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns the root node of the tree with the given id.</p>
</dd></dl>
<dl class="method">
<dt id="mptt.managers.TreeManager.root_nodes">
<tt class="descname">root_nodes</tt><big>(</big><big>)</big><a class="headerlink" href="#mptt.managers.TreeManager.root_nodes" title="Permalink to this definition">¶</a></dt>
<dd><p>Creates a <tt class="docutils literal"><span class="pre">QuerySet</span></tt> containing root nodes.</p>
</dd></dl>
<dl class="attribute">
<dt id="mptt.managers.TreeManager.tree_id_attr">
<tt class="descname">tree_id_attr</tt><a class="headerlink" href="#mptt.managers.TreeManager.tree_id_attr" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
</dd></dl>
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