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Summary: - Move docs script to `scripts/` - Add small note on README about regenerating docs - Re-gen docs (doing this because of all the recent spelling, etc. fixes -- note, no breaking changes have landed, so we're good to re-gen.) Closes https://github.com/Instagram/IGListKit/pull/797 Differential Revision: D5162705 Pulled By: rnystrom fbshipit-source-id: 83cb0f171c10526a8a4b5d8a746fc2226987f256
392 lines
27 KiB
HTML
392 lines
27 KiB
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<article class="main-content">
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<section>
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<section class="section">
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<h1 id='working-with-core-data' class='heading'>Working with Core Data</h1>
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<p>This guide provides details on how to work with <a href="https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/CoreData/index.html">Core Data</a> and <code>IGListKit</code>.</p>
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<h2 id='background' class='heading'>Background</h2>
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<p>The main difference in the setup and architecture of a Core Data and <code>IGListKit</code> application is the configuration of the model layer. Core Data operates with a mutable model layer, where objects are always passed by reference and the same instance is modified when an object is edited.</p>
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<p><code>IGListKit</code> requires an immutable model in order to correctly calculate the diffing between model snapshots and to correctly animate the <code>UICollectionView</code>.</p>
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<p>In order to satisfy these prerequisites, Core Data <code>NSManagedObject</code>s should not be used directly as <code>ListDiffable</code> objects. Instead, a view model (or some sort of token object) should be used to mimic (or act as a placeholder for) the data that will be displayed in the collection view.</p>
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<h2 id='further-discussion' class='heading'>Further discussion</h2>
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<p>There are further discussions on this topic at <a href="https://github.com/Instagram/IGListKit/issues/460">#460</a>, <a href="https://github.com/Instagram/IGListKit/issues/461">#461</a>, <a href="https://github.com/Instagram/IGListKit/issues/407">#407</a>.</p>
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<h2 id='basic-setup' class='heading'>Basic Setup</h2>
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<p>The basic setup for Core Data and <code>IGListKit</code> is the same as the normal setup that is found in the <a href="https://instagram.github.io/IGListKit/getting-started.html">Getting Started Guide</a>. The main difference will be in the setup of the model in the datasource.</p>
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<h2 id='working-with-view-model' class='heading'>Working with view model</h2>
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<h3 id='creating-a-view-model' class='heading'>Creating a view model</h3>
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<p>Suppose the Core Data model consist of:</p>
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<pre class="highlight swift"><code><span class="kd">extension</span> <span class="kt">User</span> <span class="p">{</span>
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<span class="kd">@NSManaged</span> <span class="k">var</span> <span class="nv">firstName</span><span class="p">:</span> <span class="kt">String</span>
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<span class="kd">@NSManaged</span> <span class="k">var</span> <span class="nv">lastName</span><span class="p">:</span> <span class="kt">String</span>
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<span class="kd">@NSManaged</span> <span class="k">var</span> <span class="nv">address</span><span class="p">:</span> <span class="kt">String</span>
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<span class="kd">@NSManaged</span> <span class="k">var</span> <span class="nv">someVariableNotNeededInUI</span><span class="p">:</span> <span class="kt">String</span>
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<span class="p">}</span>
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</code></pre>
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<p>A <code>ViewModel</code> object will contain only the necessary information needed to build UI. The properties of the <code>ViewModel</code> will be immutable:</p>
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<pre class="highlight swift"><code><span class="kd">class</span> <span class="kt">UserViewModel</span><span class="p">:</span> <span class="kt">NSObject</span> <span class="p">{</span>
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<span class="k">let</span> <span class="nv">firstName</span><span class="p">:</span> <span class="kt">String</span>
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<span class="k">let</span> <span class="nv">lastName</span><span class="p">:</span> <span class="kt">String</span>
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<span class="k">let</span> <span class="nv">address</span><span class="p">:</span> <span class="kt">String</span>
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<span class="p">}</span>
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</code></pre>
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<p>We recommend writing a helper method to translate Core Data objects into <code>ViewModel</code> objects:</p>
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<pre class="highlight swift"><code><span class="kd">extension</span> <span class="kt">UserViewModel</span> <span class="p">{</span>
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<span class="kd">static</span> <span class="kd">func</span> <span class="nf">fromCoreData</span><span class="p">(</span><span class="nv">user</span><span class="p">:</span> <span class="kt">User</span><span class="p">)</span> <span class="o">-></span> <span class="kt">UserViewModel</span> <span class="p">{</span>
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<span class="c1">// - Note: For avoiding Core Data threading violation, the following code should be wrapped in a</span>
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<span class="c1">// user.managedObjectContext?.performAndWait {}</span>
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<span class="k">return</span> <span class="kt">UserViewModel</span><span class="p">(</span><span class="nv">firstName</span><span class="p">:</span> <span class="n">user</span><span class="o">.</span><span class="n">firstName</span><span class="p">,</span> <span class="nv">lastName</span><span class="p">:</span> <span class="n">user</span><span class="o">.</span><span class="n">lastName</span><span class="p">,</span> <span class="nv">address</span><span class="p">:</span> <span class="n">user</span><span class="o">.</span><span class="n">lastName</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</code></pre>
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<p>The <code>IGListDiffable</code> protocol is implemented on the <code>ViewModel</code> layer:</p>
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<pre class="highlight swift"><code><span class="kd">extension</span> <span class="kt">UserViewModel</span><span class="p">:</span> <span class="kt">ListDiffable</span> <span class="p">{</span>
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<span class="kd">public</span> <span class="kd">func</span> <span class="nf">diffIdentifier</span><span class="p">()</span> <span class="o">-></span> <span class="kt">NSObjectProtocol</span> <span class="p">{</span>
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<span class="k">return</span> <span class="kt">NSString</span><span class="p">(</span><span class="nv">string</span><span class="p">:</span> <span class="n">firstName</span> <span class="o">+</span> <span class="n">lastName</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="kd">public</span> <span class="kd">func</span> <span class="nf">isEqual</span><span class="p">(</span><span class="n">toDiffableObject</span> <span class="nv">object</span><span class="p">:</span> <span class="kt">ListDiffable</span><span class="p">?)</span> <span class="o">-></span> <span class="kt">Bool</span> <span class="p">{</span>
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<span class="k">guard</span> <span class="k">let</span> <span class="nv">toObject</span> <span class="o">=</span> <span class="n">object</span> <span class="k">as?</span> <span class="kt">UserViewModel</span> <span class="k">else</span> <span class="p">{</span> <span class="k">return</span> <span class="kc">false</span> <span class="p">}</span>
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<span class="k">return</span> <span class="k">self</span><span class="o">.</span><span class="n">firstName</span> <span class="o">==</span> <span class="n">toObject</span><span class="o">.</span><span class="n">firstName</span>
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<span class="o">&&</span> <span class="k">self</span><span class="o">.</span><span class="n">lastName</span> <span class="o">==</span> <span class="n">toObject</span><span class="o">.</span><span class="n">lastName</span>
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<span class="o">&&</span> <span class="k">self</span><span class="o">.</span><span class="n">address</span> <span class="o">==</span> <span class="n">toObject</span><span class="o">.</span><span class="n">address</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</code></pre>
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<h2 id='setting-up-the-view-model-in-the-adapter-data-source' class='heading'>Setting up the view model in the adapter data source</h2>
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<p>Steps to configure the <code>UICollectionView</code> with the <code>ViewModel</code>:</p>
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<ul>
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<li>Retrieve Core Data objects</li>
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<li>Transform Core Data objects into ViewModel objects and return them</li>
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<li>Track changes to Core Data objects and update the datasource with them</li>
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</ul>
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<h3 id='retrieve-core-data-objects' class='heading'>Retrieve Core Data objects</h3>
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<p>The way objects are retrieved from Core Data is depends on the project. </p>
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<p>Example: Suppose there is a delegate <code>Provider</code> class with the role of fetching Core Data objects and checking for updates. It can use an <code>NSFetchedResultsController</code> to leverage on the Core Data framework and rely on automatic notifications for updates.</p>
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<pre class="highlight swift"><code><span class="kd">final</span> <span class="kd">class</span> <span class="kt">UserProvider</span><span class="p">:</span> <span class="kt">NSObject</span> <span class="p">{</span>
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<span class="kd">private</span> <span class="kd">lazy</span> <span class="k">var</span> <span class="nv">userFetchResultController</span><span class="p">:</span> <span class="kt">NSFetchedResultsController</span><span class="o"><</span><span class="kt">User</span><span class="o">></span> <span class="o">=</span> <span class="p">{</span>
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<span class="k">let</span> <span class="nv">fetchRequest</span><span class="p">:</span> <span class="kt">NSFetchRequest</span><span class="o"><</span><span class="kt">User</span><span class="o">></span> <span class="o">=</span> <span class="kt">NSFetchRequest</span><span class="p">(</span><span class="nv">entityName</span><span class="p">:</span> <span class="s">"User"</span><span class="p">)</span>
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<span class="c1">// sort descriptors and predicates </span>
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<span class="c1">// ...</span>
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<span class="k">let</span> <span class="nv">fetchResultController</span> <span class="o">=</span> <span class="kt">NSFetchedResultsController</span><span class="p">(</span>
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<span class="nv">fetchRequest</span><span class="p">:</span> <span class="n">tripsFetchRequest</span><span class="p">,</span>
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<span class="nv">managedObjectContext</span><span class="p">:</span> <span class="k">self</span><span class="o">.</span><span class="n">coreDataStack</span><span class="o">.</span><span class="n">mainQueueManagedObjectContext</span><span class="p">,</span>
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<span class="nv">sectionNameKeyPath</span><span class="p">:</span> <span class="kc">nil</span><span class="p">,</span>
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<span class="nv">cacheName</span><span class="p">:</span> <span class="kc">nil</span><span class="p">)</span>
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|
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|
<span class="c1">// Set delegate to track CoreData changes</span>
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<span class="n">fetchResultController</span><span class="o">.</span><span class="n">delegate</span> <span class="o">=</span> <span class="k">self</span>
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<span class="k">return</span> <span class="n">fetchResultController</span>
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<span class="p">}()</span>
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<span class="nf">init</span><span class="p">(</span><span class="nv">coreDataStack</span><span class="p">:</span> <span class="kt">CoreDataStack</span><span class="p">)</span> <span class="p">{</span>
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|
<span class="k">self</span><span class="o">.</span><span class="n">coreDataStack</span> <span class="o">=</span> <span class="n">coreDataStack</span>
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<span class="k">super</span><span class="o">.</span><span class="nf">init</span><span class="p">()</span>
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<span class="k">do</span> <span class="p">{</span>
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<span class="k">try</span> <span class="n">userFetchResultController</span><span class="o">.</span><span class="nf">performFetch</span><span class="p">()</span>
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<span class="p">}</span>
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<span class="k">catch</span> <span class="p">{</span>
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<span class="nf">fatalError</span><span class="p">(</span><span class="s">"Cannot Fetch! </span><span class="se">\(</span><span class="n">error</span><span class="se">)</span><span class="s">"</span><span class="p">)</span>
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|
<span class="p">}</span>
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|
<span class="p">}</span>
|
|
<span class="p">}</span>
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|
</code></pre>
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|
<h3 id='transform-core-data-objects-into-view-models' class='heading'>Transform Core Data objects into view models</h3>
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<pre class="highlight swift"><code><span class="kd">func</span> <span class="nf">getUsers</span><span class="p">()</span> <span class="o">-></span> <span class="p">[</span><span class="kt">UserViewModel</span><span class="p">]?</span> <span class="p">{</span>
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|
<span class="k">guard</span> <span class="k">let</span> <span class="nv">users</span> <span class="o">=</span> <span class="k">self</span><span class="o">.</span><span class="n">userFetchResultController</span><span class="o">.</span><span class="n">fetchedObjects</span> <span class="k">else</span> <span class="p">{</span> <span class="k">return</span> <span class="kc">nil</span> <span class="p">}</span>
|
|
<span class="c1">// Here we transform and return ViewModel objects!</span>
|
|
<span class="k">return</span> <span class="n">users</span><span class="o">.</span><span class="n">flatMap</span> <span class="p">{</span> <span class="kt">UserViewModel</span><span class="o">.</span><span class="nf">fromCoreData</span><span class="p">(</span><span class="nv">user</span><span class="p">:</span> <span class="nv">$0</span><span class="p">)</span> <span class="p">}</span>
|
|
<span class="p">}</span>
|
|
</code></pre>
|
|
<h3 id='track-changes-to-core-data' class='heading'>Track changes to Core Data</h3>
|
|
|
|
<p>The <code>Provider</code> will track changes to the Core Data model by listening to the <code>NSFetchedResultsController</code> methods and inform the application about this changes via KVO, notifications, delegation, etc.</p>
|
|
<pre class="highlight swift"><code><span class="kd">extension</span> <span class="kt">UserProvider</span><span class="p">:</span> <span class="kt">NSFetchedResultsControllerDelegate</span> <span class="p">{</span>
|
|
<span class="kd">func</span> <span class="nf">controllerDidChangeContent</span><span class="p">(</span><span class="n">_</span> <span class="nv">controller</span><span class="p">:</span> <span class="kt">NSFetchedResultsController</span><span class="o"><</span><span class="kt">NSFetchRequestResult</span><span class="o">></span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="k">self</span><span class="o">.</span><span class="n">delegate</span><span class="p">?</span><span class="o">.</span><span class="nf">performUpdatesForCoreDataChange</span><span class="p">(</span><span class="nv">animated</span><span class="p">:</span> <span class="kc">true</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
<span class="p">}</span>
|
|
</code></pre>
|
|
<h3 id='configure-the-datasource' class='heading'>Configure the datasource</h3>
|
|
|
|
<p>The data source retrieves ViewModels and configures the <code>IGListSectionController</code> with them:</p>
|
|
<pre class="highlight swift"><code><span class="kd">func</span> <span class="nf">objects</span><span class="p">(</span><span class="k">for</span> <span class="nv">listAdapter</span><span class="p">:</span> <span class="kt">ListAdapter</span><span class="p">)</span> <span class="o">-></span> <span class="p">[</span><span class="kt">ListDiffable</span><span class="p">]</span> <span class="p">{</span>
|
|
<span class="k">return</span> <span class="k">self</span><span class="o">.</span><span class="n">userProvider</span><span class="o">.</span><span class="nf">getUsers</span><span class="p">()</span>
|
|
<span class="p">}</span>
|
|
</code></pre>
|
|
<h3 id='reacting-to-core-data-changes-in-ui' class='heading'>Reacting to Core Data changes in UI</h3>
|
|
|
|
<p>The <code>UIViewController</code> containing the <code>UICollectionView</code>, will react to the <code>NSFetchedResultController</code> messages by updating the UI:</p>
|
|
<pre class="highlight swift"><code><span class="kd">func</span> <span class="nf">performUpdatesForCoreDataChange</span><span class="p">(</span><span class="nv">animated</span><span class="p">:</span> <span class="kt">Bool</span><span class="p">)</span> <span class="p">{</span>
|
|
<span class="c1">// Updating contents of collection view</span>
|
|
<span class="k">self</span><span class="o">.</span><span class="n">adapter</span><span class="o">.</span><span class="nf">performUpdates</span><span class="p">(</span><span class="nv">animated</span><span class="p">:</span> <span class="n">animated</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
</code></pre>
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</section>
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<p>© 2017 <a class="link" href="https://twitter.com/fbOpenSource" target="_blank" rel="external">Instagram</a>. All rights reserved. (Last updated: 2017-05-26)</p>
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<p>Generated by <a class="link" href="https://github.com/realm/jazzy" target="_blank" rel="external">jazzy ♪♫ v0.8.2</a>, a <a class="link" href="http://realm.io" target="_blank" rel="external">Realm</a> project.</p>
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