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<span class="productTitle">Json.NET - Quick Starts & API Documentation</span><br />
<span class="topicTitle">Serialization and Preserving Object References</span></div>
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<p>By default Json.NET will serialize all objects it encounters by value. If a list
contains two Person references, and both references point to the same object
then the JsonSerializer will write out all the names and values for each
reference.</p>
<div class="overflowpanel"> <div class="code">
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<pre style="margin: 0px;"><span style="color: #2b91af;">Person</span> p = <span style="color: blue;">new</span> <span style="color: #2b91af;">Person</span></pre>
<pre style="margin: 0px;"> {</pre>
<pre style="margin: 0px;"> BirthDate = <span style="color: blue;">new</span> <span style="color: #2b91af;">DateTime</span>(1980, 12, 23, 0, 0, 0, <span style="color: #2b91af;">DateTimeKind</span>.Utc),</pre>
<pre style="margin: 0px;"> LastModified = <span style="color: blue;">new</span> <span style="color: #2b91af;">DateTime</span>(2009, 2, 20, 12, 59, 21, <span style="color: #2b91af;">DateTimeKind</span>.Utc),</pre>
<pre style="margin: 0px;"> Name = <span style="color: #a31515;">"James"</span></pre>
<pre style="margin: 0px;"> };</pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">List</span><<span style="color: #2b91af;">Person</span>> people = <span style="color: blue;">new</span> <span style="color: #2b91af;">List</span><<span style="color: #2b91af;">Person</span>>();</pre>
<pre style="margin: 0px;">people.Add(p);</pre>
<pre style="margin: 0px;">people.Add(p);</pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: blue;">string</span> json = <span style="color: #2b91af;">JsonConvert</span>.SerializeObject(people, <span style="color: #2b91af;">Formatting</span>.Indented);</pre>
<pre style="margin: 0px;"><span style="color: green;">//[</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// {</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "Name": "James",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "BirthDate": "\/Date(346377600000)\/",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "LastModified": "\/Date(1235134761000)\/"</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// },</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// {</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "Name": "James",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "BirthDate": "\/Date(346377600000)\/",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "LastModified": "\/Date(1235134761000)\/"</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// }</span></pre>
<pre style="margin: 0px;"><span style="color: green;">//]</span></pre>
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<p>In most cases this is the desired result but in certain scenarios writing the second item in the list as a reference to the first is a better solution.
If the above JSON was deserialized now then the returned list would contain two
completely separate Person objects with the same values. Writing references by value will also cause problems on objects where a
circular reference occurs.</p>
<h3>PreserveReferencesHandling</h3>
<p>Settings PreserveReferencesHandling will track object references when serializing
and deserializing JSON.</p>
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<pre style="margin: 0px;"><span style="color: blue;">string</span> json = <span style="color: #2b91af;">JsonConvert</span>.SerializeObject(people, <span style="color: #2b91af;">Formatting</span>.Indented,</pre>
<pre style="margin: 0px;"> <span style="color: blue;">new</span> <span style="color: #2b91af;">JsonSerializerSettings</span> { PreserveReferencesHandling = <span style="color: #2b91af;">PreserveReferencesHandling</span>.Objects });</pre>
<pre style="margin: 0px;"><span style="color: green;">//[</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// {</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "$id": "1",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "Name": "James",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "BirthDate": "\/Date(346377600000)\/",</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "LastModified": "\/Date(1235134761000)\/"</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// },</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// {</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// "$ref": "1"</span></pre>
<pre style="margin: 0px;"><span style="color: green;">// }</span></pre>
<pre style="margin: 0px;"><span style="color: green;">//]</span></pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">List</span><<span style="color: #2b91af;">Person</span>> deserializedPeople = <span style="color: #2b91af;">JsonConvert</span>.DeserializeObject<<span style="color: #2b91af;">List</span><<span style="color: #2b91af;">Person</span>>>(json,</pre>
<pre style="margin: 0px;"> <span style="color: blue;">new</span> <span style="color: #2b91af;">JsonSerializerSettings</span> { PreserveReferencesHandling = <span style="color: #2b91af;">PreserveReferencesHandling</span>.Objects });</pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(deserializedPeople.Count);</pre>
<pre style="margin: 0px;"><span style="color: green;">// 2</span></pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">Person</span> p1 = deserializedPeople[0];</pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">Person</span> p2 = deserializedPeople[1];</pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(p1.Name);</pre>
<pre style="margin: 0px;"><span style="color: green;">// James</span></pre>
<pre style="margin: 0px;"><span style="color: #2b91af;">Console</span>.WriteLine(p2.Name);</pre>
<pre style="margin: 0px;"><span style="color: green;">// James</span></pre>
<pre style="margin: 0px;"> </pre>
<pre style="margin: 0px;"><span style="color: blue;">bool</span> equal = <span style="color: #2b91af;">Object</span>.ReferenceEquals(p1, p2);</pre>
<pre style="margin: 0px;"><span style="color: green;">// true</span></pre>
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<p>The first Person in the list is serizlied with the addition of an object Id. The
second Person in JSON is now only a reference to the first.</p>
<p>With PreserveReferencesHandling on now only one Person object is created on
deserialization and the list contains two references to it, mirroring what we
started with.</p>
<h3>IsReference on JsonObjectAttribute, JsonArrayAttribute and JsonPropertyAttribute</h3>
<p>The PreserveReferencesHandling setting on the JsonSerializer will change
how all objects are serialized and deserialized. For fine grain control over which
objects and members should be serialized as a reference there is the IsReference property on
the JsonObjectAttribute, JsonArrayAttribute and JsonPropertyAttribute.</p>
<p>Setting IsReference on JsonObjectAttribute or JsonArrayAttribute to true will
mean the JsonSerializer will always serialize the type the attribute is against
as a reference. Setting IsReference on the JsonPropertyAttribute to true will
serialize only that property as a reference.</p>
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<pre style="margin: 0px;">[<span style="color: #2b91af;">JsonObject</span>(IsReference = <span style="color: blue;">true</span>)]</pre>
<pre style="margin: 0px;"><span style="color: blue;">public</span> <span style="color: blue;">class</span> <span style="color: #2b91af;">EmployeeReference</span></pre>
<pre style="margin: 0px;">{</pre>
<pre style="margin: 0px;"> <span style="color: blue;">public</span> <span style="color: blue;">string</span> Name { <span style="color: blue;">get</span>; <span style="color: blue;">set</span>; }</pre>
<pre style="margin: 0px;"> <span style="color: blue;">public</span> <span style="color: #2b91af;">EmployeeReference</span> Manager { <span style="color: blue;">get</span>; <span style="color: blue;">set</span>; }</pre>
<pre style="margin: 0px;">}</pre>
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<h3>IReferenceResolver</h3>
<p>To customize how references are generated and resolved the <a href="./html/T_Newtonsoft_Json_Serialization_IReferenceResolver.htm">IReferenceResolver</a> interface is available to inherit from and use with the JsonSerializer.</p>
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