<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>
Ordering List
—
SQLAlchemy 1.2 Documentation
</title>
<!-- begin iterate through site-imported + sphinx environment css_files -->
<link rel="stylesheet" href="../../_static/pygments.css" type="text/css" />
<link rel="stylesheet" href="../../_static/docs.css" type="text/css" />
<link rel="stylesheet" href="../../_static/changelog.css" type="text/css" />
<link rel="stylesheet" href="../../_static/sphinx_paramlinks.css" type="text/css" />
<!-- end iterate through site-imported + sphinx environment css_files -->
<!-- begin layout.mako headers -->
<link rel="index" title="Index" href="../../genindex.html" />
<link rel="search" title="Search" href="../../search.html" />
<link rel="copyright" title="Copyright" href="../../copyright.html" />
<link rel="top" title="SQLAlchemy 1.2 Documentation" href="../../index.html" />
<link rel="up" title="ORM Extensions" href="index.html" />
<link rel="next" title="Horizontal Sharding" href="horizontal_shard.html" />
<link rel="prev" title="Mutation Tracking" href="mutable.html" />
<!-- end layout.mako headers -->
</head>
<body>
<div id="docs-container">
<div id="docs-top-navigation-container" class="body-background">
<div id="docs-header">
<div id="docs-version-header">
Release: <span class="version-num">1.2.19</span>
| Release Date: April 15, 2019
</div>
<h1>SQLAlchemy 1.2 Documentation</h1>
</div>
</div>
<div id="docs-body-container">
<div id="fixed-sidebar" class="withsidebar">
<div id="docs-sidebar-popout">
<h3><a href="../../index.html">SQLAlchemy 1.2 Documentation</a></h3>
<p id="sidebar-topnav">
<a href="../../contents.html">Contents</a> |
<a href="../../genindex.html">Index</a>
</p>
<div id="sidebar-search">
<form class="search" action="../../search.html" method="get">
<label>
Search terms:
<input type="text" placeholder="search..." name="q" size="12" />
</label>
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
</div>
<div id="docs-sidebar">
<div id="sidebar-banner">
</div>
<div id="docs-sidebar-inner">
<h3>
<a href="../index.html" title="SQLAlchemy ORM">SQLAlchemy ORM</a>
</h3>
<ul>
<li><span class="link-container"><a class="reference external" href="../tutorial.html">Object Relational Tutorial</a></span></li>
<li><span class="link-container"><a class="reference external" href="../mapper_config.html">Mapper Configuration</a></span></li>
<li><span class="link-container"><a class="reference external" href="../relationships.html">Relationship Configuration</a></span></li>
<li><span class="link-container"><a class="reference external" href="../loading_objects.html">Loading Objects</a></span></li>
<li><span class="link-container"><a class="reference external" href="../session.html">Using the Session</a></span></li>
<li><span class="link-container"><a class="reference external" href="../extending.html">Events and Internals</a></span></li>
<li><span class="link-container"><a class="reference external" href="index.html">ORM Extensions</a></span><ul>
<li><span class="link-container"><a class="reference external" href="associationproxy.html">Association Proxy</a></span></li>
<li><span class="link-container"><a class="reference external" href="automap.html">Automap</a></span></li>
<li><span class="link-container"><a class="reference external" href="baked.html">Baked Queries</a></span></li>
<li><span class="link-container"><a class="reference external" href="declarative/index.html">Declarative</a></span></li>
<li><span class="link-container"><a class="reference external" href="mutable.html">Mutation Tracking</a></span></li>
<li class="selected"><span class="link-container"><strong>Ordering List</strong><a class="paramlink headerlink reference internal" href="#">¶</a></span><ul>
<li><span class="link-container"><a class="reference external" href="#api-reference">API Reference</a></span></li>
</ul>
</li>
<li><span class="link-container"><a class="reference external" href="horizontal_shard.html">Horizontal Sharding</a></span></li>
<li><span class="link-container"><a class="reference external" href="hybrid.html">Hybrid Attributes</a></span></li>
<li><span class="link-container"><a class="reference external" href="indexable.html">Indexable</a></span></li>
<li><span class="link-container"><a class="reference external" href="instrumentation.html">Alternate Class Instrumentation</a></span></li>
</ul>
</li>
<li><span class="link-container"><a class="reference external" href="../examples.html">ORM Examples</a></span></li>
</ul>
</div>
</div>
</div>
<div id="docs-body" class="withsidebar" >
<div class="section" id="module-sqlalchemy.ext.orderinglist">
<span id="ordering-list"></span><h1>Ordering List<a class="headerlink" href="#module-sqlalchemy.ext.orderinglist" title="Permalink to this headline">¶</a></h1>
<p>A custom list that manages index/position information for contained
elements.</p>
<dl class="field-list simple">
<dt class="field-odd">author</dt>
<dd class="field-odd"><p>Jason Kirtland</p>
</dd>
</dl>
<p><code class="docutils literal notranslate"><span class="pre">orderinglist</span></code> is a helper for mutable ordered relationships. It will
intercept list operations performed on a <a class="reference internal" href="../relationship_api.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><code class="xref py py-func docutils literal notranslate"><span class="pre">relationship()</span></code></a>-managed
collection and
automatically synchronize changes in list position onto a target scalar
attribute.</p>
<p>Example: A <code class="docutils literal notranslate"><span class="pre">slide</span></code> table, where each row refers to zero or more entries
in a related <code class="docutils literal notranslate"><span class="pre">bullet</span></code> table. The bullets within a slide are
displayed in order based on the value of the <code class="docutils literal notranslate"><span class="pre">position</span></code> column in the
<code class="docutils literal notranslate"><span class="pre">bullet</span></code> table. As entries are reordered in memory, the value of the
<code class="docutils literal notranslate"><span class="pre">position</span></code> attribute should be updated to reflect the new sort order:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Base</span> <span class="o">=</span> <span class="n">declarative_base</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">Slide</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s1">'slide'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">primary_key</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">String</span><span class="p">)</span>
<span class="n">bullets</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s2">"Bullet"</span><span class="p">,</span> <span class="n">order_by</span><span class="o">=</span><span class="s2">"Bullet.position"</span><span class="p">)</span>
<span class="k">class</span> <span class="nc">Bullet</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s1">'bullet'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">primary_key</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="n">slide_id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">ForeignKey</span><span class="p">(</span><span class="s1">'slide.id'</span><span class="p">))</span>
<span class="n">position</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">)</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">String</span><span class="p">)</span></pre></div>
</div>
<p>The standard relationship mapping will produce a list-like attribute on each
<code class="docutils literal notranslate"><span class="pre">Slide</span></code> containing all related <code class="docutils literal notranslate"><span class="pre">Bullet</span></code> objects,
but coping with changes in ordering is not handled automatically.
When appending a <code class="docutils literal notranslate"><span class="pre">Bullet</span></code> into <code class="docutils literal notranslate"><span class="pre">Slide.bullets</span></code>, the <code class="docutils literal notranslate"><span class="pre">Bullet.position</span></code>
attribute will remain unset until manually assigned. When the <code class="docutils literal notranslate"><span class="pre">Bullet</span></code>
is inserted into the middle of the list, the following <code class="docutils literal notranslate"><span class="pre">Bullet</span></code> objects
will also need to be renumbered.</p>
<p>The <a class="reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList" title="sqlalchemy.ext.orderinglist.OrderingList"><code class="xref py py-class docutils literal notranslate"><span class="pre">OrderingList</span></code></a> object automates this task, managing the
<code class="docutils literal notranslate"><span class="pre">position</span></code> attribute on all <code class="docutils literal notranslate"><span class="pre">Bullet</span></code> objects in the collection. It is
constructed using the <a class="reference internal" href="#sqlalchemy.ext.orderinglist.ordering_list" title="sqlalchemy.ext.orderinglist.ordering_list"><code class="xref py py-func docutils literal notranslate"><span class="pre">ordering_list()</span></code></a> factory:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">sqlalchemy.ext.orderinglist</span> <span class="k">import</span> <span class="n">ordering_list</span>
<span class="n">Base</span> <span class="o">=</span> <span class="n">declarative_base</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">Slide</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s1">'slide'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">primary_key</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">String</span><span class="p">)</span>
<span class="n">bullets</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s2">"Bullet"</span><span class="p">,</span> <span class="n">order_by</span><span class="o">=</span><span class="s2">"Bullet.position"</span><span class="p">,</span>
<span class="n">collection_class</span><span class="o">=</span><span class="n">ordering_list</span><span class="p">(</span><span class="s1">'position'</span><span class="p">))</span>
<span class="k">class</span> <span class="nc">Bullet</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s1">'bullet'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">primary_key</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="n">slide_id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">ForeignKey</span><span class="p">(</span><span class="s1">'slide.id'</span><span class="p">))</span>
<span class="n">position</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">)</span>
<span class="n">text</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">String</span><span class="p">)</span></pre></div>
</div>
<p>With the above mapping the <code class="docutils literal notranslate"><span class="pre">Bullet.position</span></code> attribute is managed:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">s</span> <span class="o">=</span> <span class="n">Slide</span><span class="p">()</span>
<span class="n">s</span><span class="o">.</span><span class="n">bullets</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">Bullet</span><span class="p">())</span>
<span class="n">s</span><span class="o">.</span><span class="n">bullets</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">Bullet</span><span class="p">())</span>
<span class="n">s</span><span class="o">.</span><span class="n">bullets</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">position</span>
<span class="o">>>></span> <span class="mi">1</span>
<span class="n">s</span><span class="o">.</span><span class="n">bullets</span><span class="o">.</span><span class="n">insert</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">Bullet</span><span class="p">())</span>
<span class="n">s</span><span class="o">.</span><span class="n">bullets</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="o">.</span><span class="n">position</span>
<span class="o">>>></span> <span class="mi">2</span></pre></div>
</div>
<p>The <a class="reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList" title="sqlalchemy.ext.orderinglist.OrderingList"><code class="xref py py-class docutils literal notranslate"><span class="pre">OrderingList</span></code></a> construct only works with <strong>changes</strong> to a
collection, and not the initial load from the database, and requires that the
list be sorted when loaded. Therefore, be sure to specify <code class="docutils literal notranslate"><span class="pre">order_by</span></code> on the
<a class="reference internal" href="../relationship_api.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><code class="xref py py-func docutils literal notranslate"><span class="pre">relationship()</span></code></a> against the target ordering attribute, so that the
ordering is correct when first loaded.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p><a class="reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList" title="sqlalchemy.ext.orderinglist.OrderingList"><code class="xref py py-class docutils literal notranslate"><span class="pre">OrderingList</span></code></a> only provides limited functionality when a primary
key column or unique column is the target of the sort. Operations
that are unsupported or are problematic include:</p>
<blockquote>
<div><ul class="simple">
<li><p>two entries must trade values. This is not supported directly in the
case of a primary key or unique constraint because it means at least
one row would need to be temporarily removed first, or changed to
a third, neutral value while the switch occurs.</p></li>
<li><p>an entry must be deleted in order to make room for a new entry.
SQLAlchemy’s unit of work performs all INSERTs before DELETEs within a
single flush. In the case of a primary key, it will trade
an INSERT/DELETE of the same primary key for an UPDATE statement in order
to lessen the impact of this limitation, however this does not take place
for a UNIQUE column.
A future feature will allow the “DELETE before INSERT” behavior to be
possible, alleviating this limitation, though this feature will require
explicit configuration at the mapper level for sets of columns that
are to be handled in this way.</p></li>
</ul>
</div></blockquote>
</div>
<p><a class="reference internal" href="#sqlalchemy.ext.orderinglist.ordering_list" title="sqlalchemy.ext.orderinglist.ordering_list"><code class="xref py py-func docutils literal notranslate"><span class="pre">ordering_list()</span></code></a> takes the name of the related object’s ordering
attribute as an argument. By default, the zero-based integer index of the
object’s position in the <a class="reference internal" href="#sqlalchemy.ext.orderinglist.ordering_list" title="sqlalchemy.ext.orderinglist.ordering_list"><code class="xref py py-func docutils literal notranslate"><span class="pre">ordering_list()</span></code></a> is synchronized with the
ordering attribute: index 0 will get position 0, index 1 position 1, etc. To
start numbering at 1 or some other integer, provide <code class="docutils literal notranslate"><span class="pre">count_from=1</span></code>.</p>
<div class="section" id="api-reference">
<h2>API Reference<a class="headerlink" href="#api-reference" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="sqlalchemy.ext.orderinglist.ordering_list">
<code class="descclassname">sqlalchemy.ext.orderinglist.</code><code class="descname">ordering_list</code><span class="sig-paren">(</span><em>attr</em>, <em>count_from=None</em>, <em>**kw</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.ordering_list" title="Permalink to this definition">¶</a></dt>
<dd><p>Prepares an <a class="reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList" title="sqlalchemy.ext.orderinglist.OrderingList"><code class="xref py py-class docutils literal notranslate"><span class="pre">OrderingList</span></code></a> factory for use in mapper definitions.</p>
<p>Returns an object suitable for use as an argument to a Mapper
relationship’s <code class="docutils literal notranslate"><span class="pre">collection_class</span></code> option. e.g.:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">sqlalchemy.ext.orderinglist</span> <span class="k">import</span> <span class="n">ordering_list</span>
<span class="k">class</span> <span class="nc">Slide</span><span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">__tablename__</span> <span class="o">=</span> <span class="s1">'slide'</span>
<span class="nb">id</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">Integer</span><span class="p">,</span> <span class="n">primary_key</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">Column</span><span class="p">(</span><span class="n">String</span><span class="p">)</span>
<span class="n">bullets</span> <span class="o">=</span> <span class="n">relationship</span><span class="p">(</span><span class="s2">"Bullet"</span><span class="p">,</span> <span class="n">order_by</span><span class="o">=</span><span class="s2">"Bullet.position"</span><span class="p">,</span>
<span class="n">collection_class</span><span class="o">=</span><span class="n">ordering_list</span><span class="p">(</span><span class="s1">'position'</span><span class="p">))</span></pre></div>
</div>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><ul class="simple">
<li><p><span class="target" id="sqlalchemy.ext.orderinglist.ordering_list.params.attr"></span><strong>attr</strong><a class="paramlink headerlink reference internal" href="#sqlalchemy.ext.orderinglist.ordering_list.params.attr">¶</a> – Name of the mapped attribute to use for storage and retrieval of
ordering information</p></li>
<li><p><span class="target" id="sqlalchemy.ext.orderinglist.ordering_list.params.count_from"></span><strong>count_from</strong><a class="paramlink headerlink reference internal" href="#sqlalchemy.ext.orderinglist.ordering_list.params.count_from">¶</a> – Set up an integer-based ordering, starting at <code class="docutils literal notranslate"><span class="pre">count_from</span></code>. For
example, <code class="docutils literal notranslate"><span class="pre">ordering_list('pos',</span> <span class="pre">count_from=1)</span></code> would create a 1-based
list in SQL, storing the value in the ‘pos’ column. Ignored if
<code class="docutils literal notranslate"><span class="pre">ordering_func</span></code> is supplied.</p></li>
</ul>
</dd>
</dl>
<p>Additional arguments are passed to the <a class="reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList" title="sqlalchemy.ext.orderinglist.OrderingList"><code class="xref py py-class docutils literal notranslate"><span class="pre">OrderingList</span></code></a> constructor.</p>
</dd></dl>
<dl class="function">
<dt id="sqlalchemy.ext.orderinglist.count_from_0">
<code class="descclassname">sqlalchemy.ext.orderinglist.</code><code class="descname">count_from_0</code><span class="sig-paren">(</span><em>index</em>, <em>collection</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.count_from_0" title="Permalink to this definition">¶</a></dt>
<dd><p>Numbering function: consecutive integers starting at 0.</p>
</dd></dl>
<dl class="function">
<dt id="sqlalchemy.ext.orderinglist.count_from_1">
<code class="descclassname">sqlalchemy.ext.orderinglist.</code><code class="descname">count_from_1</code><span class="sig-paren">(</span><em>index</em>, <em>collection</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.count_from_1" title="Permalink to this definition">¶</a></dt>
<dd><p>Numbering function: consecutive integers starting at 1.</p>
</dd></dl>
<dl class="function">
<dt id="sqlalchemy.ext.orderinglist.count_from_n_factory">
<code class="descclassname">sqlalchemy.ext.orderinglist.</code><code class="descname">count_from_n_factory</code><span class="sig-paren">(</span><em>start</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.count_from_n_factory" title="Permalink to this definition">¶</a></dt>
<dd><p>Numbering function: consecutive integers starting at arbitrary start.</p>
</dd></dl>
<dl class="class">
<dt id="sqlalchemy.ext.orderinglist.OrderingList">
<em class="property">class </em><code class="descclassname">sqlalchemy.ext.orderinglist.</code><code class="descname">OrderingList</code><span class="sig-paren">(</span><em>ordering_attr=None</em>, <em>ordering_func=None</em>, <em>reorder_on_append=False</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList" title="Permalink to this definition">¶</a></dt>
<dd><p>Bases: <code class="xref py py-class docutils literal notranslate"><span class="pre">builtins.list</span></code></p>
<p>A custom list that manages position information for its children.</p>
<p>The <a class="reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList" title="sqlalchemy.ext.orderinglist.OrderingList"><code class="xref py py-class docutils literal notranslate"><span class="pre">OrderingList</span></code></a> object is normally set up using the
<a class="reference internal" href="#sqlalchemy.ext.orderinglist.ordering_list" title="sqlalchemy.ext.orderinglist.ordering_list"><code class="xref py py-func docutils literal notranslate"><span class="pre">ordering_list()</span></code></a> factory function, used in conjunction with
the <a class="reference internal" href="../relationship_api.html#sqlalchemy.orm.relationship" title="sqlalchemy.orm.relationship"><code class="xref py py-func docutils literal notranslate"><span class="pre">relationship()</span></code></a> function.</p>
<dl class="method">
<dt id="sqlalchemy.ext.orderinglist.OrderingList.__init__">
<code class="descname">__init__</code><span class="sig-paren">(</span><em>ordering_attr=None</em>, <em>ordering_func=None</em>, <em>reorder_on_append=False</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList.__init__" title="Permalink to this definition">¶</a></dt>
<dd><p>A custom list that manages position information for its children.</p>
<p><code class="docutils literal notranslate"><span class="pre">OrderingList</span></code> is a <code class="docutils literal notranslate"><span class="pre">collection_class</span></code> list implementation that
syncs position in a Python list with a position attribute on the
mapped objects.</p>
<p>This implementation relies on the list starting in the proper order,
so be <strong>sure</strong> to put an <code class="docutils literal notranslate"><span class="pre">order_by</span></code> on your relationship.</p>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><ul class="simple">
<li><p><span class="target" id="sqlalchemy.ext.orderinglist.OrderingList.params.ordering_attr"></span><strong>ordering_attr</strong><a class="paramlink headerlink reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList.params.ordering_attr">¶</a> – Name of the attribute that stores the object’s order in the
relationship.</p></li>
<li><p><span class="target" id="sqlalchemy.ext.orderinglist.OrderingList.params.ordering_func"></span><strong>ordering_func</strong><a class="paramlink headerlink reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList.params.ordering_func">¶</a> – <p>Optional. A function that maps the position in
the Python list to a value to store in the
<code class="docutils literal notranslate"><span class="pre">ordering_attr</span></code>. Values returned are usually (but need not be!)
integers.</p>
<p>An <code class="docutils literal notranslate"><span class="pre">ordering_func</span></code> is called with two positional parameters: the
index of the element in the list, and the list itself.</p>
<p>If omitted, Python list indexes are used for the attribute values.
Two basic pre-built numbering functions are provided in this module:
<code class="docutils literal notranslate"><span class="pre">count_from_0</span></code> and <code class="docutils literal notranslate"><span class="pre">count_from_1</span></code>. For more exotic examples
like stepped numbering, alphabetical and Fibonacci numbering, see
the unit tests.</p>
</p></li>
<li><p><span class="target" id="sqlalchemy.ext.orderinglist.OrderingList.params.reorder_on_append"></span><strong>reorder_on_append</strong><a class="paramlink headerlink reference internal" href="#sqlalchemy.ext.orderinglist.OrderingList.params.reorder_on_append">¶</a> – <p>Default False. When appending an object with an existing (non-None)
ordering value, that value will be left untouched unless
<code class="docutils literal notranslate"><span class="pre">reorder_on_append</span></code> is true. This is an optimization to avoid a
variety of dangerous unexpected database writes.</p>
<p>SQLAlchemy will add instances to the list via append() when your
object loads. If for some reason the result set from the database
skips a step in the ordering (say, row ‘1’ is missing but you get
‘2’, ‘3’, and ‘4’), reorder_on_append=True would immediately
renumber the items to ‘1’, ‘2’, ‘3’. If you have multiple sessions
making changes, any of whom happen to load this collection even in
passing, all of the sessions would try to “clean up” the numbering
in their commits, possibly causing all but one to fail with a
concurrent modification error.</p>
<p>Recommend leaving this with the default of False, and just call
<code class="docutils literal notranslate"><span class="pre">reorder()</span></code> if you’re doing <code class="docutils literal notranslate"><span class="pre">append()</span></code> operations with
previously ordered instances or when doing some housekeeping after
manual sql operations.</p>
</p></li>
</ul>
</dd>
</dl>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.ext.orderinglist.OrderingList.append">
<code class="descname">append</code><span class="sig-paren">(</span><em>entity</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList.append" title="Permalink to this definition">¶</a></dt>
<dd><p>Append object to the end of the list.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.ext.orderinglist.OrderingList.insert">
<code class="descname">insert</code><span class="sig-paren">(</span><em>index</em>, <em>entity</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList.insert" title="Permalink to this definition">¶</a></dt>
<dd><p>Insert object before index.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.ext.orderinglist.OrderingList.pop">
<code class="descname">pop</code><span class="sig-paren">(</span><em>index=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList.pop" title="Permalink to this definition">¶</a></dt>
<dd><p>Remove and return item at index (default last).</p>
<p>Raises IndexError if list is empty or index is out of range.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.ext.orderinglist.OrderingList.remove">
<code class="descname">remove</code><span class="sig-paren">(</span><em>entity</em><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList.remove" title="Permalink to this definition">¶</a></dt>
<dd><p>Remove first occurrence of value.</p>
<p>Raises ValueError if the value is not present.</p>
</dd></dl>
<dl class="method">
<dt id="sqlalchemy.ext.orderinglist.OrderingList.reorder">
<code class="descname">reorder</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#sqlalchemy.ext.orderinglist.OrderingList.reorder" title="Permalink to this definition">¶</a></dt>
<dd><p>Synchronize ordering for the entire collection.</p>
<p>Sweeps through the list and ensures that each object has accurate
ordering information set.</p>
</dd></dl>
</dd></dl>
</div>
</div>
</div>
</div>
<div id="docs-bottom-navigation" class="docs-navigation-links, withsidebar">
Previous:
<a href="mutable.html" title="previous chapter">Mutation Tracking</a>
Next:
<a href="horizontal_shard.html" title="next chapter">Horizontal Sharding</a>
<div id="docs-copyright">
© <a href="../../copyright.html">Copyright</a> 2007-2019, the SQLAlchemy authors and contributors.
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.0.1.
</div>
</div>
</div>
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: '../../',
VERSION: '1.2.19',
COLLAPSE_MODINDEX: false,
FILE_SUFFIX: '.html'
};
</script>
<script type="text/javascript" id="documentation_options" data-url_root="../../" src="../../_static/documentation_options.js"></script>
<!-- begin iterate through sphinx environment script_files -->
<script type="text/javascript" src="../../_static/jquery.js"></script>
<script type="text/javascript" src="../../_static/underscore.js"></script>
<script type="text/javascript" src="../../_static/doctools.js"></script>
<script type="text/javascript" src="../../_static/language_data.js"></script>
<!-- end iterate through sphinx environment script_files -->
<script type="text/javascript" src="../../_static/detectmobile.js"></script>
<script type="text/javascript" src="../../_static/init.js"></script>
</body>
</html>
distrib
>
Mageia
>
7
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
b0b6ffab06cbeede296e36ce94734bf8
>
files
>
840
