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<h1 itemprop="name">DRF: How to handle arrays and nested objects in a multipart/form-data request?</h1>
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Thomas Loiret
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<span class="glyphicon glyphicon-calendar"></span> Wed 24 May 2023
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<h1>Tl;DR</h1>
<p>For array, use the following convention in your name <code>myfield[0]</code>, and for nested objects separate objects using a dot: <code>myfield.child</code>.</p>
<h1>Introduction</h1>
<p>This article is about Django Rest Framework handling multipart/form-data request. You might encounter such case if you design an endpoint that handles both files and data. Do to so, you will need to use the <a href="https://www.django-rest-framework.org/api-guide/parsers/">parser</a> <code>MultiPartParser</code>.</p>
<p>Things starts to be more complicated when you need to send complex fields: array and nested objects.</p>
<h1>The set up</h1>
<p>The view:</p>
<div class="highlight"><pre><span></span><code><span class="kn">from</span> <span class="nn">django.http</span> <span class="kn">import</span> <span class="n">JsonResponse</span>
<span class="kn">from</span> <span class="nn">books.serializers</span> <span class="kn">import</span> <span class="n">BookSerializer</span>
<span class="kn">from</span> <span class="nn">django.views.decorators.csrf</span> <span class="kn">import</span> <span class="n">csrf_exempt</span>
<span class="kn">from</span> <span class="nn">rest_framework.decorators</span> <span class="kn">import</span> <span class="n">api_view</span>
<span class="nd">@api_view</span><span class="p">([</span><span class="s1">'POST'</span><span class="p">])</span>
<span class="nd">@csrf_exempt</span>
<span class="k">def</span> <span class="nf">create_new_entry</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="nb">format</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
<span class="n">serializer</span> <span class="o">=</span> <span class="n">BookSerializer</span><span class="p">(</span><span class="n">data</span><span class="o">=</span><span class="n">request</span><span class="o">.</span><span class="n">data</span><span class="p">)</span>
<span class="k">if</span> <span class="n">serializer</span><span class="o">.</span><span class="n">is_valid</span><span class="p">():</span>
<span class="n">serializer</span><span class="o">.</span><span class="n">save</span><span class="p">()</span>
<span class="k">return</span> <span class="n">JsonResponse</span><span class="p">(</span><span class="n">serializer</span><span class="o">.</span><span class="n">data</span><span class="p">,</span> <span class="n">status</span><span class="o">=</span><span class="mi">201</span><span class="p">)</span>
<span class="k">return</span> <span class="n">JsonResponse</span><span class="p">(</span><span class="n">serializer</span><span class="o">.</span><span class="n">errors</span><span class="p">,</span> <span class="n">status</span><span class="o">=</span><span class="mi">400</span><span class="p">)</span>
</code></pre></div>
<p>The serializers:</p>
<div class="highlight"><pre><span></span><code><span class="kn">from</span> <span class="nn">rest_framework</span> <span class="kn">import</span> <span class="n">serializers</span>
<span class="k">class</span> <span class="nc">AuthorSerializer</span><span class="p">(</span><span class="n">serializers</span><span class="o">.</span><span class="n">Serializer</span><span class="p">):</span>
<span class="n">firstname</span> <span class="o">=</span> <span class="n">serializers</span><span class="o">.</span><span class="n">CharField</span><span class="p">()</span>
<span class="n">lastname</span> <span class="o">=</span> <span class="n">serializers</span><span class="o">.</span><span class="n">CharField</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">IntListField</span><span class="p">(</span><span class="n">serializers</span><span class="o">.</span><span class="n">ListField</span><span class="p">):</span>
<span class="n">child</span> <span class="o">=</span> <span class="n">serializers</span><span class="o">.</span><span class="n">IntegerField</span><span class="p">()</span>
<span class="k">class</span> <span class="nc">BookSerializer</span><span class="p">(</span><span class="n">serializers</span><span class="o">.</span><span class="n">Serializer</span><span class="p">):</span>
<span class="n">title</span> <span class="o">=</span> <span class="n">serializers</span><span class="o">.</span><span class="n">CharField</span><span class="p">()</span>
<span class="n">author</span> <span class="o">=</span> <span class="n">AuthorSerializer</span><span class="p">()</span>
<span class="n">ratings</span> <span class="o">=</span> <span class="n">IntListField</span><span class="p">()</span>
<span class="n">book</span> <span class="o">=</span> <span class="n">serializers</span><span class="o">.</span><span class="n">FileField</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">create</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">validated_data</span><span class="p">):</span>
<span class="c1"># Here you got everything as expected, validated_data looks like:</span>
<span class="c1"># {</span>
<span class="c1"># 'title': 'Les Fourmis', </span>
<span class="c1"># 'author': OrderedDict([</span>
<span class="c1"># ('firstname', 'Boris'), </span>
<span class="c1"># ('lastname', 'Vian')]</span>
<span class="c1"># ), </span>
<span class="c1"># 'ratings': [8, 9], </span>
<span class="c1"># 'book': <InMemoryUploadedFile: Les Fourmis.pdf (application/pdf)></span>
<span class="c1"># }</span>
</code></pre></div>
<h1>The request</h1>
<div class="highlight"><pre><span></span><code>curl -X POST \
http://127.0.0.1:8000/books/ \
-F 'title=Les Fourmis' \
-F 'author.firstname=Boris' \
-F 'author.lastname=Vian' \
-F 'ratings[0]=8' \
-F 'ratings[1]=9' \
-F 'book=@/Users/b0uh/Les Fourmis.pdf'
</code></pre></div>
<p>The two importants notations are:</p>
<ul>
<li><code>myfield[0]</code> for arrays</li>
<li><code>myfield.chdild</code> for nested objects</li>
</ul>
<p>I did not find any documentation about it while working on a similar use case so I hope this will help you!</p>
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