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<div class="section" id="s-writing-a-custom-storage-system">
<span id="writing-a-custom-storage-system"></span><h1>Writing a custom storage system<a class="headerlink" href="#writing-a-custom-storage-system" title="Permalink to this headline">¶</a></h1>
<p>If you need to provide custom file storage – a common example is storing files
on some remote system – you can do so by defining a custom storage class.
You’ll need to follow these steps:</p>
<ol class="arabic">
<li><p class="first">Your custom storage system must be a subclass of
<code class="docutils literal"><span class="pre">django.core.files.storage.Storage</span></code>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">django.core.files.storage</span> <span class="k">import</span> <span class="n">Storage</span>
<span class="k">class</span> <span class="nc">MyStorage</span><span class="p">(</span><span class="n">Storage</span><span class="p">):</span>
<span class="o">...</span>
</pre></div>
</div>
</li>
<li><p class="first">Django must be able to instantiate your storage system without any arguments.
This means that any settings should be taken from <code class="docutils literal"><span class="pre">django.conf.settings</span></code>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">django.conf</span> <span class="k">import</span> <span class="n">settings</span>
<span class="kn">from</span> <span class="nn">django.core.files.storage</span> <span class="k">import</span> <span class="n">Storage</span>
<span class="k">class</span> <span class="nc">MyStorage</span><span class="p">(</span><span class="n">Storage</span><span class="p">):</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">option</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">option</span><span class="p">:</span>
<span class="n">option</span> <span class="o">=</span> <span class="n">settings</span><span class="o">.</span><span class="n">CUSTOM_STORAGE_OPTIONS</span>
<span class="o">...</span>
</pre></div>
</div>
</li>
<li><p class="first">Your storage class must implement the <a class="reference internal" href="#django.core.files.storage._open" title="django.core.files.storage._open"><code class="xref py py-meth docutils literal"><span class="pre">_open()</span></code></a> and <a class="reference internal" href="#django.core.files.storage._save" title="django.core.files.storage._save"><code class="xref py py-meth docutils literal"><span class="pre">_save()</span></code></a>
methods, along with any other methods appropriate to your storage class. See
below for more on these methods.</p>
<p>In addition, if your class provides local file storage, it must override
the <code class="docutils literal"><span class="pre">path()</span></code> method.</p>
</li>
<li><p class="first">Your storage class must be <a class="reference internal" href="../topics/migrations.html#custom-deconstruct-method"><span class="std std-ref">deconstructible</span></a>
so it can be serialized when it’s used on a field in a migration. As long
as your field has arguments that are themselves
<a class="reference internal" href="../topics/migrations.html#migration-serializing"><span class="std std-ref">serializable</span></a>, you can use the
<code class="docutils literal"><span class="pre">django.utils.deconstruct.deconstructible</span></code> class decorator for this
(that’s what Django uses on FileSystemStorage).</p>
</li>
</ol>
<p>By default, the following methods raise <cite>NotImplementedError</cite> and will
typically have to be overridden:</p>
<ul class="simple">
<li><a class="reference internal" href="../ref/files/storage.html#django.core.files.storage.Storage.delete" title="django.core.files.storage.Storage.delete"><code class="xref py py-meth docutils literal"><span class="pre">Storage.delete()</span></code></a></li>
<li><a class="reference internal" href="../ref/files/storage.html#django.core.files.storage.Storage.exists" title="django.core.files.storage.Storage.exists"><code class="xref py py-meth docutils literal"><span class="pre">Storage.exists()</span></code></a></li>
<li><a class="reference internal" href="../ref/files/storage.html#django.core.files.storage.Storage.listdir" title="django.core.files.storage.Storage.listdir"><code class="xref py py-meth docutils literal"><span class="pre">Storage.listdir()</span></code></a></li>
<li><a class="reference internal" href="../ref/files/storage.html#django.core.files.storage.Storage.size" title="django.core.files.storage.Storage.size"><code class="xref py py-meth docutils literal"><span class="pre">Storage.size()</span></code></a></li>
<li><a class="reference internal" href="../ref/files/storage.html#django.core.files.storage.Storage.url" title="django.core.files.storage.Storage.url"><code class="xref py py-meth docutils literal"><span class="pre">Storage.url()</span></code></a></li>
</ul>
<p>Note however that not all these methods are required and may be deliberately
omitted. As it happens, it is possible to leave each method unimplemented and
still have a working Storage.</p>
<p>By way of example, if listing the contents of certain storage backends turns
out to be expensive, you might decide not to implement <cite>Storage.listdir</cite>.</p>
<p>Another example would be a backend that only handles writing to files. In this
case, you would not need to implement any of the above methods.</p>
<p>Ultimately, which of these methods are implemented is up to you. Leaving some
methods unimplemented will result in a partial (possibly broken) interface.</p>
<p>You’ll also usually want to use hooks specifically designed for custom storage
objects. These are:</p>
<dl class="method">
<dt id="django.core.files.storage._open">
<code class="descname">_open</code>(<em>name</em>, <em>mode='rb'</em>)<a class="headerlink" href="#django.core.files.storage._open" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<p><strong>Required</strong>.</p>
<p>Called by <code class="docutils literal"><span class="pre">Storage.open()</span></code>, this is the actual mechanism the storage class
uses to open the file. This must return a <code class="docutils literal"><span class="pre">File</span></code> object, though in most cases,
you’ll want to return some subclass here that implements logic specific to the
backend storage system.</p>
<dl class="method">
<dt id="django.core.files.storage._save">
<code class="descname">_save</code>(<em>name</em>, <em>content</em>)<a class="headerlink" href="#django.core.files.storage._save" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<p>Called by <code class="docutils literal"><span class="pre">Storage.save()</span></code>. The <code class="docutils literal"><span class="pre">name</span></code> will already have gone through
<code class="docutils literal"><span class="pre">get_valid_name()</span></code> and <code class="docutils literal"><span class="pre">get_available_name()</span></code>, and the <code class="docutils literal"><span class="pre">content</span></code> will be a
<code class="docutils literal"><span class="pre">File</span></code> object itself.</p>
<p>Should return the actual name of name of the file saved (usually the <code class="docutils literal"><span class="pre">name</span></code>
passed in, but if the storage needs to change the file name return the new name
instead).</p>
<dl class="method">
<dt id="django.core.files.storage.get_valid_name">
<code class="descname">get_valid_name</code>(<em>name</em>)<a class="headerlink" href="#django.core.files.storage.get_valid_name" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<p>Returns a filename suitable for use with the underlying storage system. The
<code class="docutils literal"><span class="pre">name</span></code> argument passed to this method is the original filename sent to the
server, after having any path information removed. Override this to customize
how non-standard characters are converted to safe filenames.</p>
<p>The code provided on <code class="docutils literal"><span class="pre">Storage</span></code> retains only alpha-numeric characters, periods
and underscores from the original filename, removing everything else.</p>
<dl class="method">
<dt id="django.core.files.storage.get_available_name">
<code class="descname">get_available_name</code>(<em>name</em>, <em>max_length=None</em>)<a class="headerlink" href="#django.core.files.storage.get_available_name" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<p>Returns a filename that is available in the storage mechanism, possibly taking
the provided filename into account. The <code class="docutils literal"><span class="pre">name</span></code> argument passed to this method
will have already cleaned to a filename valid for the storage system, according
to the <code class="docutils literal"><span class="pre">get_valid_name()</span></code> method described above.</p>
<p>The length of the filename will not exceed <code class="docutils literal"><span class="pre">max_length</span></code>, if provided. If a
free unique filename cannot be found, a <a class="reference internal" href="../ref/exceptions.html#django.core.exceptions.SuspiciousOperation" title="django.core.exceptions.SuspiciousOperation"><code class="xref py py-exc docutils literal"><span class="pre">SuspiciousFileOperation</span></code></a> exception is raised.</p>
<p>If a file with <code class="docutils literal"><span class="pre">name</span></code> already exists, an underscore plus a random 7 character
alphanumeric string is appended to the filename before the extension.</p>
<div class="versionchanged">
<span class="title">Changed in Django 1.7:</span> <p>Previously, an underscore followed by a number (e.g. <code class="docutils literal"><span class="pre">"_1"</span></code>, <code class="docutils literal"><span class="pre">"_2"</span></code>,
etc.) was appended to the filename until an available name in the destination
directory was found. A malicious user could exploit this deterministic
algorithm to create a denial-of-service attack. This change was also made
in Django 1.6.6, 1.5.9, and 1.4.14.</p>
</div>
<div class="versionchanged">
<span class="title">Changed in Django 1.8:</span> <p>The <code class="docutils literal"><span class="pre">max_length</span></code> argument was added.</p>
</div>
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