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<h1>Example ID-Generator</h1>
<p>This example demonstrates how you can use an ID-generator to identify objects across objects containers. Take a look advantages and disadvantages of ID-generators: <a href="comparison_of_ids.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Comparison Of Different IDs"</a></p>
<p>This example assumes that all object have a common super-class, IDHolder, which holds the id.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">private int id;
public int Id
{
get { return id; }
set { id = value; }
}
</pre>
<div class="codesnippet-meta">IDHolder.cs: id holder
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Private m_id As Integer
Public Property Id() As Integer
Get
Return m_id
End Get
Set(ByVal value As Integer)
m_id = value
End Set
End Property
</pre>
<div class="codesnippet-meta">IDHolder.vb: id holder
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<p>Don't forget to index the id-field. Otherwise finding objects by id will be slow.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">configuration.Common.ObjectClass(typeof (IDHolder)).ObjectField("id").Indexed(true);</pre>
<div class="codesnippet-meta">AutoIncrementExample.cs: index the id-field
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">configuration.Common.ObjectClass(GetType(IDHolder)).ObjectField("id").Indexed(True)</pre>
<div class="codesnippet-meta">AutoIncrementExample.vb: index the id-field
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<p>The hard part is to write an efficient ID-Generator. For this example a very simple <a href="../../advanced_topics/callbacks/possible_usecases/autoincrement.htm">auto increment generator</a> is used. Use the <a href="../../advanced_topics/callbacks/event_registry_api.htm">creating-callback-event</a> in order to add the ids to the object. When committing, store the state of the id-generator.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">AutoIncrement increment = new AutoIncrement(container);
IEventRegistry eventRegistry = EventRegistryFactory.ForObjectContainer(container);
eventRegistry.Creating+=
delegate(object sender, CancellableObjectEventArgs args)
{
if (args.Object is IDHolder)
{
IDHolder idHolder = (IDHolder)args.Object;
idHolder.Id = increment.GetNextID(idHolder.GetType());
}
};
eventRegistry.Committing +=
delegate(object sender, CommitEventArgs args)
{
increment.StoreState();
};</pre>
<div class="codesnippet-meta">AutoIncrementExample.cs: use events to assign the ids
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Dim increment As New AutoIncrement(container)
Dim eventRegistry As IEventRegistry = EventRegistryFactory.ForObjectContainer(container)
AddHandler eventRegistry.Creating, AddressOf increment.HandleCreating
AddHandler eventRegistry.Committing, AddressOf increment.HandleCommiting</pre>
<div class="codesnippet-meta">AutoIncrementExample.vb: use events to assign the ids
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<p>The id is hold by the object itself, so you can get it directly.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IDHolder idHolder = (IDHolder) obj;
int id = idHolder.Id;</pre>
<div class="codesnippet-meta">AutoIncrementExample.cs: get the id
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Dim idHolder As IDHolder = DirectCast(obj, IDHolder)
Dim id As Integer = idHolder.Id</pre>
<div class="codesnippet-meta">AutoIncrementExample.vb: get the id
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<p>You can get the object you can by a regular query.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">object instance = container.Query(delegate(IDHolder o) { return o.Id == id; })[0];</pre>
<div class="codesnippet-meta">AutoIncrementExample.cs: get an object by its id
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Dim instance As Object = container.Query(Function(o As IDHolder) o.Id = id)(0)</pre>
<div class="codesnippet-meta">AutoIncrementExample.vb: get an object by its id
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