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<h1>Native Query Examples</h1>
<p>Here's a collection of native query examples. These queries assume that there's a Pilot class with a name and age and a Car class with a pilot and name.</p>
<p MadCap:conditions="Primary..NET">Note that for .NET 3.5 or newer we recommend to use <a href="../linq.htm">LINQ</a> instead of native queries.</p>
<h2><a name="Equality"></a>Equality</h2>
<p>This query shows you how compare a <span class="Primarygetter/setter">property</span> for equality. In this example we compare the name of a person.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<Pilot> result = container.Query(
delegate(Pilot pilot) { return pilot.Name == "John"; });</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Check for equality of the name
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 result As IList(Of Pilot) = container.Query(Of Pilot)(AddressOf QueryJohns)</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Check for equality of the name
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 Shared Function QueryJohns(ByVal pilot As Pilot)
Return pilot.Name = "John"
End Function</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Query for John
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<h2><a name="Comparison"></a>Comparison</h2>
<p>You can compare values with the usual comparison operators.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<Pilot> result = container.Query(
delegate(Pilot pilot) { return pilot.Age < 18; });</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Compare values to each other
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 result As IList(Of Pilot) = container.Query(Of Pilot)(AddressOf QueryAdults)</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Compare values to each other
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 Shared Function QueryAdults(ByVal pilot As Pilot)
Return pilot.Age < 18
End Function</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Query for adults
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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<h2><a name="ValueRange"></a>Query For Value Range</h2>
<p>Of course you can combine different comparisons. For example you can combine the greater and smaller than operators to check for a range of values.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<Pilot> result = container.Query(
delegate(Pilot pilot) { return pilot.Age > 18 && pilot.Age < 30; });</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Query for a particular rage of values
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 result As IList(Of Pilot) = container.Query(Of Pilot)(AddressOf QueryRange)</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Query for a particular rage of values
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 Shared Function QueryRange(ByVal pilot As Pilot)
Return pilot.Age > 18 AndAlso pilot.Age < 30
End Function</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Query for range
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<h2><a name="LogicalOperators"></a>Combine Check With Logical Operators</h2>
<p>Of course you can combine a arbitrary set of conditions with logical operators.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<Pilot> result = container.Query(
delegate(Pilot pilot)
{
return (pilot.Age > 18 && pilot.Age < 30)
|| pilot.Name == "John";
});</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Combine different comparisons with the logical operators
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 result As IList(Of Pilot) = container.Query(Of Pilot)(AddressOf CombineCriterias)</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Combine different comparisons with the logical operators
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 Shared Function CombineCriterias(ByVal pilot As Pilot)
Return (pilot.Age > 18 AndAlso pilot.Age < 30) OrElse pilot.Name = "John"
End Function</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Combine criterias
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<h2><a name="SeperateQueryUnit"></a>Query In Separate<span MadCap:conditions="Primary..NET"> Method</span></h2>
<p>You can implement your query in a separate<span MadCap:conditions="Primary..NET"> method</span> and then just us it where you need it. This is especially useful when you reuse the same query multiple times. Or you want to give your query a clear name for documentation purposes.</p>
<p>First write your <span MadCap:conditions="Primary..NET"> method</span>:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">private static bool AllJohns(Pilot pilot)
{
return pilot.Name == "John";
}
</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Query as method
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 Shared Function AllJohns(ByVal pilot As Pilot) As Boolean
Return pilot.Name = "John"
End Function
</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Query as method
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<p>And then use it:</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<Pilot> result = container.Query(new Predicate<Pilot>(AllJohns));</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Use the predefined query
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 result As IList(Of Pilot) = container.Query(Of Pilot)(AddressOf AllJohns)</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Use the predefined query
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
</div>
<h2><a name="ArbitraryCode"></a>Arbitrary Code</h2>
<p>In principal your query can contain any code and can do the most complex comparisons. However in practice the are limitations. The simple queries are <a href="native_query_optimization.htm">optimized and translated to SODA-queries</a>. This is not possible for complex queries. If the query cannot be optimized, db4o will instantiate all objects and pass it to your query-object. This is a order of magnitude slower than a optimized native query and only feasible for smaller data sets.</p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">IList<int> allowedAges = Array.AsReadOnly(new int[] {18, 20, 35});
IList<Pilot> result = container.Query(
delegate(Pilot pilot)
{
return allowedAges.Contains(pilot.Age) ||
pilot.Name.ToLowerInvariant() == "John";
});</pre>
<div class="codesnippet-meta">NativeQueryExamples.cs: Arbitrary code
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-csharp.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 result As IList(Of Pilot) = container.Query(Of Pilot)(AddressOf QueryWithAnyCode)</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Arbitrary code
<div class="codedownload"><a href="../../../CodeExamples/query/nq/Example-query-nq-vb.zip" class="codedownload" MadCap:conditions="Primary.Online">Download Code</a></div><div class="codedownload copylink-marker" MadCap:conditions="Primary.Online"><a href="#copy">Copy Code</a></div></div>
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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 Shared Function QueryWithAnyCode(ByVal pilot As Pilot)
Dim allowedAges As IList(Of Integer) = Array.AsReadOnly(New Integer() {18, 20, 35})
Return allowedAges.Contains(Pilot.Age) _
OrElse Pilot.Name.ToLowerInvariant() = "John"
End Function</pre>
<div class="codesnippet-meta">NativeQueryExamples.vb: Query with arbitrary code
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