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  <div class="section" id="intermediate-usage">
<span id="intermediate"></span><h1>Intermediate Usage<a class="headerlink" href="#intermediate-usage" title="Permalink to this headline"></a></h1>
<p>This page covers building a slightly more complex Flask-RESTful app that will
cover out some best practices when setting up a real-world Flask-RESTful-based
API. The <a class="reference internal" href="quickstart.html#quickstart"><span class="std std-ref">Quickstart</span></a> section is great for getting started with your first
Flask-RESTful app, so if you&#8217;re new to Flask-RESTful you&#8217;d be better off
checking that out first.</p>
<div class="section" id="project-structure">
<h2>Project Structure<a class="headerlink" href="#project-structure" title="Permalink to this headline"></a></h2>
<p>There are many different ways to organize your Flask-RESTful app, but here
we&#8217;ll describe one that scales pretty well with larger apps and maintains
a nice level organization.</p>
<p>The basic idea is to split your app into three main parts: the routes, the
resources, and any common infrastructure.</p>
<p>Here&#8217;s an example directory structure:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">myapi</span><span class="o">/</span>
    <span class="fm">__init__</span><span class="o">.</span><span class="n">py</span>
    <span class="n">app</span><span class="o">.</span><span class="n">py</span>          <span class="c1"># this file contains your app and routes</span>
    <span class="n">resources</span><span class="o">/</span>
        <span class="fm">__init__</span><span class="o">.</span><span class="n">py</span>
        <span class="n">foo</span><span class="o">.</span><span class="n">py</span>      <span class="c1"># contains logic for /Foo</span>
        <span class="n">bar</span><span class="o">.</span><span class="n">py</span>      <span class="c1"># contains logic for /Bar</span>
    <span class="n">common</span><span class="o">/</span>
        <span class="fm">__init__</span><span class="o">.</span><span class="n">py</span>
        <span class="n">util</span><span class="o">.</span><span class="n">py</span>     <span class="c1"># just some common infrastructure</span>
</pre></div>
</div>
<p>The common directory would probably just contain a set of helper functions
to fulfill common needs across your application. It could also contain, for
example, any custom input/output types your resources need to get the job done.</p>
<p>In the resource files, you just have your resource objects. So here&#8217;s what
<code class="docutils literal"><span class="pre">foo.py</span></code> might look like:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flask_restful</span> <span class="k">import</span> <span class="n">Resource</span>

<span class="k">class</span> <span class="nc">Foo</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">get</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">pass</span>
    <span class="k">def</span> <span class="nf">post</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">pass</span>
</pre></div>
</div>
<p>The key to this setup lies in <code class="docutils literal"><span class="pre">app.py</span></code>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flask</span> <span class="k">import</span> <span class="n">Flask</span>
<span class="kn">from</span> <span class="nn">flask_restful</span> <span class="k">import</span> <span class="n">Api</span>
<span class="kn">from</span> <span class="nn">myapi.resources.foo</span> <span class="k">import</span> <span class="n">Foo</span>
<span class="kn">from</span> <span class="nn">myapi.resources.bar</span> <span class="k">import</span> <span class="n">Bar</span>
<span class="kn">from</span> <span class="nn">myapi.resources.baz</span> <span class="k">import</span> <span class="n">Baz</span>

<span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="vm">__name__</span><span class="p">)</span>
<span class="n">api</span> <span class="o">=</span> <span class="n">Api</span><span class="p">(</span><span class="n">app</span><span class="p">)</span>

<span class="n">api</span><span class="o">.</span><span class="n">add_resource</span><span class="p">(</span><span class="n">Foo</span><span class="p">,</span> <span class="s1">&#39;/Foo&#39;</span><span class="p">,</span> <span class="s1">&#39;/Foo/&lt;str:id&gt;&#39;</span><span class="p">)</span>
<span class="n">api</span><span class="o">.</span><span class="n">add_resource</span><span class="p">(</span><span class="n">Bar</span><span class="p">,</span> <span class="s1">&#39;/Bar&#39;</span><span class="p">,</span> <span class="s1">&#39;/Bar/&lt;str:id&gt;&#39;</span><span class="p">)</span>
<span class="n">api</span><span class="o">.</span><span class="n">add_resource</span><span class="p">(</span><span class="n">Baz</span><span class="p">,</span> <span class="s1">&#39;/Baz&#39;</span><span class="p">,</span> <span class="s1">&#39;/Baz/&lt;str:id&gt;&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p>As you can imagine with a particularly large or complex API, this file ends up
being very valuable as a comprehensive list of all the routes and resources in
your API. You would also use this file to set up any config values
(<a class="reference external" href="/usr/share/doc/python-flask-doc/html/api.html#flask.Flask.before_request" title="(in Flask v0.12)"><code class="xref py py-meth docutils literal"><span class="pre">before_request()</span></code></a>, <a class="reference external" href="/usr/share/doc/python-flask-doc/html/api.html#flask.Flask.after_request" title="(in Flask v0.12)"><code class="xref py py-meth docutils literal"><span class="pre">after_request()</span></code></a>).
Basically, this file configures your entire API.</p>
<p>The things in the common directory are just things you&#8217;d want to support your
resource modules.</p>
</div>
<div class="section" id="use-with-blueprints">
<h2>Use With Blueprints<a class="headerlink" href="#use-with-blueprints" title="Permalink to this headline"></a></h2>
<p>See <a class="reference external" href="/usr/share/doc/python-flask-doc/html/blueprints.html#blueprints" title="(in Flask v0.12)"><span>Modular Applications with Blueprints</span></a> in the Flask documentation for what blueprints are and
why you should use them. Here&#8217;s an example of how to link an <a class="reference internal" href="api.html#flask_restful.Api" title="flask_restful.Api"><code class="xref py py-class docutils literal"><span class="pre">Api</span></code></a>
up to a <a class="reference external" href="/usr/share/doc/python-flask-doc/html/api.html#flask.Blueprint" title="(in Flask v0.12)"><code class="xref py py-class docutils literal"><span class="pre">Blueprint</span></code></a>.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flask</span> <span class="k">import</span> <span class="n">Flask</span><span class="p">,</span> <span class="n">Blueprint</span>
<span class="kn">from</span> <span class="nn">flask_restful</span> <span class="k">import</span> <span class="n">Api</span><span class="p">,</span> <span class="n">Resource</span><span class="p">,</span> <span class="n">url_for</span>

<span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="vm">__name__</span><span class="p">)</span>
<span class="n">api_bp</span> <span class="o">=</span> <span class="n">Blueprint</span><span class="p">(</span><span class="s1">&#39;api&#39;</span><span class="p">,</span> <span class="vm">__name__</span><span class="p">)</span>
<span class="n">api</span> <span class="o">=</span> <span class="n">Api</span><span class="p">(</span><span class="n">api_bp</span><span class="p">)</span>

<span class="k">class</span> <span class="nc">TodoItem</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">get</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">id</span><span class="p">):</span>
        <span class="k">return</span> <span class="p">{</span><span class="s1">&#39;task&#39;</span><span class="p">:</span> <span class="s1">&#39;Say &quot;Hello, World!&quot;&#39;</span><span class="p">}</span>

<span class="n">api</span><span class="o">.</span><span class="n">add_resource</span><span class="p">(</span><span class="n">TodoItem</span><span class="p">,</span> <span class="s1">&#39;/todos/&lt;int:id&gt;&#39;</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">register_blueprint</span><span class="p">(</span><span class="n">api_bp</span><span class="p">)</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Calling <a class="reference internal" href="api.html#flask_restful.Api.init_app" title="flask_restful.Api.init_app"><code class="xref py py-meth docutils literal"><span class="pre">Api.init_app()</span></code></a> is not required here because registering the
blueprint with the app takes care of setting up the routing for the
application.</p>
</div>
</div>
<div class="section" id="full-parameter-parsing-example">
<h2>Full Parameter Parsing Example<a class="headerlink" href="#full-parameter-parsing-example" title="Permalink to this headline"></a></h2>
<p>Elsewhere in the documentation, we&#8217;ve described how to use the reqparse example
in detail. Here we&#8217;ll set up a resource with multiple input parameters that
exercise a larger amount of options. We&#8217;ll define a resource named &#8220;User&#8221;.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flask_restful</span> <span class="k">import</span> <span class="n">fields</span><span class="p">,</span> <span class="n">marshal_with</span><span class="p">,</span> <span class="n">reqparse</span><span class="p">,</span> <span class="n">Resource</span>

<span class="k">def</span> <span class="nf">email</span><span class="p">(</span><span class="n">email_str</span><span class="p">):</span>
    <span class="sd">&quot;&quot;&quot;Return email_str if valid, raise an exception in other case.&quot;&quot;&quot;</span>
    <span class="k">if</span> <span class="n">valid_email</span><span class="p">(</span><span class="n">email_str</span><span class="p">):</span>
        <span class="k">return</span> <span class="n">email_str</span>
    <span class="k">else</span><span class="p">:</span>
        <span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">{}</span><span class="s1"> is not a valid email&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">email_str</span><span class="p">))</span>

<span class="n">post_parser</span> <span class="o">=</span> <span class="n">reqparse</span><span class="o">.</span><span class="n">RequestParser</span><span class="p">()</span>
<span class="n">post_parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
    <span class="s1">&#39;username&#39;</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">&#39;username&#39;</span><span class="p">,</span>
    <span class="n">location</span><span class="o">=</span><span class="s1">&#39;form&#39;</span><span class="p">,</span> <span class="n">required</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span>
    <span class="n">help</span><span class="o">=</span><span class="s1">&#39;The user</span><span class="se">\&#39;</span><span class="s1">s username&#39;</span><span class="p">,</span>
<span class="p">)</span>
<span class="n">post_parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
    <span class="s1">&#39;email&#39;</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">&#39;email&#39;</span><span class="p">,</span>
    <span class="nb">type</span><span class="o">=</span><span class="n">email</span><span class="p">,</span> <span class="n">location</span><span class="o">=</span><span class="s1">&#39;form&#39;</span><span class="p">,</span>
    <span class="n">required</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="n">help</span><span class="o">=</span><span class="s1">&#39;The user</span><span class="se">\&#39;</span><span class="s1">s email&#39;</span><span class="p">,</span>
<span class="p">)</span>
<span class="n">post_parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
    <span class="s1">&#39;user_priority&#39;</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">&#39;user_priority&#39;</span><span class="p">,</span>
    <span class="nb">type</span><span class="o">=</span><span class="nb">int</span><span class="p">,</span> <span class="n">location</span><span class="o">=</span><span class="s1">&#39;form&#39;</span><span class="p">,</span>
    <span class="n">default</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">choices</span><span class="o">=</span><span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">),</span> <span class="n">help</span><span class="o">=</span><span class="s1">&#39;The user</span><span class="se">\&#39;</span><span class="s1">s priority&#39;</span><span class="p">,</span>
<span class="p">)</span>

<span class="n">user_fields</span> <span class="o">=</span> <span class="p">{</span>
    <span class="s1">&#39;id&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Integer</span><span class="p">,</span>
    <span class="s1">&#39;username&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">String</span><span class="p">,</span>
    <span class="s1">&#39;email&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">String</span><span class="p">,</span>
    <span class="s1">&#39;user_priority&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Integer</span><span class="p">,</span>
    <span class="s1">&#39;custom_greeting&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">FormattedString</span><span class="p">(</span><span class="s1">&#39;Hey there </span><span class="si">{username}</span><span class="s1">!&#39;</span><span class="p">),</span>
    <span class="s1">&#39;date_created&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">DateTime</span><span class="p">,</span>
    <span class="s1">&#39;date_updated&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">DateTime</span><span class="p">,</span>
    <span class="s1">&#39;links&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Nested</span><span class="p">({</span>
        <span class="s1">&#39;friends&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_friends&#39;</span><span class="p">),</span>
        <span class="s1">&#39;posts&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_posts&#39;</span><span class="p">),</span>
    <span class="p">}),</span>
<span class="p">}</span>

<span class="k">class</span> <span class="nc">User</span><span class="p">(</span><span class="n">Resource</span><span class="p">):</span>

    <span class="nd">@marshal_with</span><span class="p">(</span><span class="n">user_fields</span><span class="p">)</span>
    <span class="k">def</span> <span class="nf">post</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="n">args</span> <span class="o">=</span> <span class="n">post_parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">()</span>
        <span class="n">user</span> <span class="o">=</span> <span class="n">create_user</span><span class="p">(</span><span class="n">args</span><span class="o">.</span><span class="n">username</span><span class="p">,</span> <span class="n">args</span><span class="o">.</span><span class="n">email</span><span class="p">,</span> <span class="n">args</span><span class="o">.</span><span class="n">user_priority</span><span class="p">)</span>
        <span class="k">return</span> <span class="n">user</span>

    <span class="nd">@marshal_with</span><span class="p">(</span><span class="n">user_fields</span><span class="p">)</span>
    <span class="k">def</span> <span class="nf">get</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">id</span><span class="p">):</span>
        <span class="n">args</span> <span class="o">=</span> <span class="n">post_parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">()</span>
        <span class="n">user</span> <span class="o">=</span> <span class="n">fetch_user</span><span class="p">(</span><span class="nb">id</span><span class="p">)</span>
        <span class="k">return</span> <span class="n">user</span>
</pre></div>
</div>
<p>As you can see, we create a <code class="docutils literal"><span class="pre">post_parser</span></code> specifically to handle the parsing
of arguments provided on POST. Let&#8217;s step through the definition of each
argument.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">post_parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
    <span class="s1">&#39;username&#39;</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">&#39;username&#39;</span><span class="p">,</span>
    <span class="n">location</span><span class="o">=</span><span class="s1">&#39;form&#39;</span><span class="p">,</span> <span class="n">required</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span>
    <span class="n">help</span><span class="o">=</span><span class="s1">&#39;The user</span><span class="se">\&#39;</span><span class="s1">s username&#39;</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">username</span></code> field is the most normal out of all of them. It takes
a string from the POST body and converts it to a string type. This argument
is required (<code class="docutils literal"><span class="pre">required=True</span></code>), which means that if it isn&#8217;t provided,
Flask-RESTful will automatically return a 400 with a message along the lines
of &#8216;the username field is required&#8217;.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">post_parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
    <span class="s1">&#39;email&#39;</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">&#39;email&#39;</span><span class="p">,</span>
    <span class="nb">type</span><span class="o">=</span><span class="n">email</span><span class="p">,</span> <span class="n">location</span><span class="o">=</span><span class="s1">&#39;form&#39;</span><span class="p">,</span>
    <span class="n">required</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="n">help</span><span class="o">=</span><span class="s1">&#39;The user</span><span class="se">\&#39;</span><span class="s1">s email&#39;</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">email</span></code> field has a custom type of <code class="docutils literal"><span class="pre">email</span></code>. A few lines earlier we
defined an <code class="docutils literal"><span class="pre">email</span></code> function that takes a string and returns it if the type is
valid, else it raises an exception, exclaiming that the email type was
invalid.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">post_parser</span><span class="o">.</span><span class="n">add_argument</span><span class="p">(</span>
    <span class="s1">&#39;user_priority&#39;</span><span class="p">,</span> <span class="n">dest</span><span class="o">=</span><span class="s1">&#39;user_priority&#39;</span><span class="p">,</span>
    <span class="nb">type</span><span class="o">=</span><span class="nb">int</span><span class="p">,</span> <span class="n">location</span><span class="o">=</span><span class="s1">&#39;form&#39;</span><span class="p">,</span>
    <span class="n">default</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">choices</span><span class="o">=</span><span class="nb">range</span><span class="p">(</span><span class="mi">5</span><span class="p">),</span> <span class="n">help</span><span class="o">=</span><span class="s1">&#39;The user</span><span class="se">\&#39;</span><span class="s1">s priority&#39;</span><span class="p">,</span>
<span class="p">)</span>
</pre></div>
</div>
<p>The <code class="docutils literal"><span class="pre">user_priority</span></code> type takes advantage of the <code class="docutils literal"><span class="pre">choices</span></code> argument. This
means that if the provided <cite>user_priority</cite> value doesn&#8217;t fall in the range
specified by the <code class="docutils literal"><span class="pre">choices</span></code> argument (in this case <code class="docutils literal"><span class="pre">[0,</span> <span class="pre">1,</span> <span class="pre">2,</span> <span class="pre">3,</span> <span class="pre">4]</span></code>),
Flask-RESTful will automatically respond with a 400 and a descriptive error
message.</p>
<p>That covers the inputs. We also defined some interesting field types in the
<code class="docutils literal"><span class="pre">user_fields</span></code> dictionary to showcase a couple of the more exotic types.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">user_fields</span> <span class="o">=</span> <span class="p">{</span>
    <span class="s1">&#39;id&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Integer</span><span class="p">,</span>
    <span class="s1">&#39;username&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">String</span><span class="p">,</span>
    <span class="s1">&#39;email&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">String</span><span class="p">,</span>
    <span class="s1">&#39;user_priority&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Integer</span><span class="p">,</span>
    <span class="s1">&#39;custom_greeting&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">FormattedString</span><span class="p">(</span><span class="s1">&#39;Hey there </span><span class="si">{username}</span><span class="s1">!&#39;</span><span class="p">),</span>
    <span class="s1">&#39;date_created&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">DateTime</span><span class="p">,</span>
    <span class="s1">&#39;date_updated&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">DateTime</span><span class="p">,</span>
    <span class="s1">&#39;links&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Nested</span><span class="p">({</span>
        <span class="s1">&#39;friends&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_friends&#39;</span><span class="p">,</span> <span class="n">absolute</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
        <span class="s1">&#39;posts&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_friends&#39;</span><span class="p">,</span> <span class="n">absolute</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
    <span class="p">}),</span>
<span class="p">}</span>
</pre></div>
</div>
<p>First up, there&#8217;s <a class="reference internal" href="api.html#fields.FormattedString" title="fields.FormattedString"><code class="xref py py-class docutils literal"><span class="pre">fields.FormattedString</span></code></a>.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="s1">&#39;custom_greeting&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">FormattedString</span><span class="p">(</span><span class="s1">&#39;Hey there </span><span class="si">{username}</span><span class="s1">!&#39;</span><span class="p">),</span>
</pre></div>
</div>
<p>This field is primarily used to interpolate values from the response into
other values. In this instance, <code class="docutils literal"><span class="pre">custom_greeting</span></code> will always contain the
value returned from the <code class="docutils literal"><span class="pre">username</span></code> field.</p>
<p>Next up, check out <a class="reference internal" href="api.html#fields.Nested" title="fields.Nested"><code class="xref py py-class docutils literal"><span class="pre">fields.Nested</span></code></a>.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="s1">&#39;links&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Nested</span><span class="p">({</span>
    <span class="s1">&#39;friends&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_friends&#39;</span><span class="p">,</span> <span class="n">absolute</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
    <span class="s1">&#39;posts&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_posts&#39;</span><span class="p">,</span> <span class="n">absolute</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
<span class="p">}),</span>
</pre></div>
</div>
<p>This field is used to create a sub-object in the response. In this case,
we want to create a <code class="docutils literal"><span class="pre">links</span></code> sub-object to contain urls of related objects.
Note that we passed <cite>fields.Nested</cite> another dict which is built in such a
way that it would be an acceptable argument to <a class="reference internal" href="api.html#flask_restful.marshal" title="flask_restful.marshal"><code class="xref py py-func docutils literal"><span class="pre">marshal()</span></code></a> by itself.</p>
<p>Finally, we used the <a class="reference internal" href="api.html#fields.Url" title="fields.Url"><code class="xref py py-class docutils literal"><span class="pre">fields.Url</span></code></a> field type.</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="s1">&#39;friends&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_friends&#39;</span><span class="p">,</span> <span class="n">absolute</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
<span class="s1">&#39;posts&#39;</span><span class="p">:</span> <span class="n">fields</span><span class="o">.</span><span class="n">Url</span><span class="p">(</span><span class="s1">&#39;user_friends&#39;</span><span class="p">,</span> <span class="n">absolute</span><span class="o">=</span><span class="kc">True</span><span class="p">),</span>
</pre></div>
</div>
<p>It takes as its first parameter the name of the endpoint associated with the
urls of the objects in the <code class="docutils literal"><span class="pre">links</span></code> sub-object.  Passing <code class="docutils literal"><span class="pre">absolute=True</span></code>
ensures that the generated urls will have the hostname included.</p>
</div>
<div class="section" id="passing-constructor-parameters-into-resources">
<h2>Passing Constructor Parameters Into Resources<a class="headerlink" href="#passing-constructor-parameters-into-resources" title="Permalink to this headline"></a></h2>
<p>Your <a class="reference internal" href="api.html#flask_restful.Resource" title="flask_restful.Resource"><code class="xref py py-class docutils literal"><span class="pre">Resource</span></code></a> implementation may require outside dependencies. Those
dependencies are best passed-in through the constructor to loosely couple each
other. The <a class="reference internal" href="api.html#flask_restful.Api.add_resource" title="flask_restful.Api.add_resource"><code class="xref py py-meth docutils literal"><span class="pre">Api.add_resource()</span></code></a> method has two keyword arguments:
<code class="docutils literal"><span class="pre">resource_class_args</span></code> and <code class="docutils literal"><span class="pre">resource_class_kwargs</span></code>. Their values will be forwarded
and passed into your Resource implementation&#8217;s constructor.</p>
<p>So you could have a <a class="reference internal" href="api.html#flask_restful.Resource" title="flask_restful.Resource"><code class="xref py py-class docutils literal"><span class="pre">Resource</span></code></a>:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">flask_restful</span> <span class="k">import</span> <span class="n">Resource</span>

<span class="k">class</span> <span class="nc">TodoNext</span><span class="p">(</span><span class="n">Resource</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="o">**</span><span class="n">kwargs</span><span class="p">):</span>
        <span class="c1"># smart_engine is a black box dependency</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">smart_engine</span> <span class="o">=</span> <span class="n">kwargs</span><span class="p">[</span><span class="s1">&#39;smart_engine&#39;</span><span class="p">]</span>

    <span class="k">def</span> <span class="nf">get</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">smart_engine</span><span class="o">.</span><span class="n">next_todo</span><span class="p">()</span>
</pre></div>
</div>
<p>You can inject the required dependency into TodoNext like so:</p>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">smart_engine</span> <span class="o">=</span> <span class="n">SmartEngine</span><span class="p">()</span>

<span class="n">api</span><span class="o">.</span><span class="n">add_resource</span><span class="p">(</span><span class="n">TodoNext</span><span class="p">,</span> <span class="s1">&#39;/next&#39;</span><span class="p">,</span>
    <span class="n">resource_class_kwargs</span><span class="o">=</span><span class="p">{</span> <span class="s1">&#39;smart_engine&#39;</span><span class="p">:</span> <span class="n">smart_engine</span> <span class="p">})</span>
</pre></div>
</div>
<p>Same idea applies for forwarding <cite>args</cite>.</p>
</div>
</div>


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  <h3><a href="index.html">Table Of Contents</a></h3>
  <ul>
<li><a class="reference internal" href="#">Intermediate Usage</a><ul>
<li><a class="reference internal" href="#project-structure">Project Structure</a></li>
<li><a class="reference internal" href="#use-with-blueprints">Use With Blueprints</a></li>
<li><a class="reference internal" href="#full-parameter-parsing-example">Full Parameter Parsing Example</a></li>
<li><a class="reference internal" href="#passing-constructor-parameters-into-resources">Passing Constructor Parameters Into Resources</a></li>
</ul>
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