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<h1><a name="kanchor7"></a>LINQ</h1>
<p>Of course, db4o supports .NET LINQ to query the database.</p>
<p>First, you need to add the <i>Db4objects.Db4o.Linq.dll</i>-assembly to your project. This assembly contains db4o LINQ-Implementation. Make also sure that Mono.Reflection.dll is aside it. <a href="../../dependency_overview.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Dependency Overview"</a></p>
<p>Note that LINQ requires .NET 3.5 or newer!</p>
<h2>LINQ Queries</h2>
<p>Writing a query is simple. You write the LINQ query against the object-container. First you need to import the LINQ-namespaces.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">using System.Linq;
using Db4objects.Db4o.Linq;</pre>
<div class="codesnippet-meta">LinqExamples.cs: Use the LINQ namespace
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<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Imports System.Linq
Imports Db4objects.Db4o.Linq</pre>
<div class="codesnippet-meta">LinqExamples.vb: Use the LINQ namespace
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<p>After that, you can start to write a LINQ-Query against the object container.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">var allPersons = from Person p in container
select p;</pre>
<div class="codesnippet-meta">LinqExamples.cs: Simple query
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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 allPersons = From p In container _
Select p</pre>
<div class="codesnippet-meta">LinqExamples.vb: Simple query
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<p>In order to learn LINQ, take a look a the LINQ-resources and tutorial out on the Internet. For example the <a href="http://msdn.microsoft.com/en-us/library/bb397926.aspx" target="_blank">LINQ-Overview at MSDN</a>or at <a href="http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx" target="_blank">this example-collection.</a></p>
<p>There are also a few simple <a href="linq/linq_examples.htm">LINQ query examples for db4o here</a>.</p>
<h2><a name="kanchor8"></a>IQueryable</h2>
<p>db4o also support the .NET IQueryable interface. This is useful when you want to build an abstraction layer for db4o or integrate db4o with other frameworks.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IQueryable<Person> personQuerable = container.AsQueryable<Person>();
var adults = from p in personQuerable
where p.Age > 18
orderby p.Name
select p;</pre>
<div class="codesnippet-meta">LinqExamples.cs: Get a IQueryable-instance
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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 personQuerable As IQueryable(Of Person) = container.AsQueryable(Of Person)()
Dim adults = From p In personQuerable _
Where p.Age > 18 _
Order By p.Name _
Select p</pre>
<div class="codesnippet-meta">LinqExamples.vb: Get a IQueryable-instance
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<h2>More on db4o's LINQ Provider</h2>
<p>db4o LINQ provider translates the LINQ queries into db4o's low level query <a href="soda_query.htm">API</a>. Read what this query optimization need and what its limits are. <a href="linq/optimization.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "LINQ Optimization"</a></p>
<p>Also read how LINQ is supported on the .NET Compact Framework. <a href="linq/linq_for_compact_framework.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "LINQ For Compact Framework"</a></p>
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