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<h1>Wrong Approach</h1>
<p>The wrong approach is to try to store disconnected objects. db4o manages object by their <a href="../../basics/identity_concept.htm">object-identity</a> and doesn't recognize objects which have been serialized or loaded by another object container instance. This example shows, that instead of updating the object, db4o will store a new instance of the object. </p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">Pilot joe;
using (IObjectContainer container = OpenDatabase())
{
joe = QueryByName(container, "Joe");
}
// The update on another object
joe.Name = "Joe New";
using (IObjectContainer otherContainer = OpenDatabase())
{
otherContainer.Store(joe);
}
using (IObjectContainer container = OpenDatabase())
{
// instead of updating the existing pilot,
// a new instance was stored.
IList<Pilot> pilots = container.Query<Pilot>();
Console.WriteLine("Amount of pilots: " + pilots.Count);
foreach (Pilot pilot in pilots)
{
Console.WriteLine(pilot);
}
}</pre>
<div class="codesnippet-meta">ObjectIdentityExamples.cs: Update doesn't works when using the different object containers
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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 joe As Pilot
Using container As IObjectContainer = OpenDatabase()
joe = QueryByName(container, "Joe")
End Using
' The update on another object
joe.Name = "Joe New"
Using otherContainer As IObjectContainer = OpenDatabase()
otherContainer.Store(joe)
End Using
Using container As IObjectContainer = OpenDatabase()
' instead of updating the existing pilot,
' a new instance was stored.
Dim pilots As IList(Of Pilot) = container.Query(Of Pilot)()
Console.WriteLine("Amount of pilots: " & pilots.Count)
For Each pilot As Pilot In pilots
Console.WriteLine(pilot)
Next
End Using</pre>
<div class="codesnippet-meta">ObjectIdentityExamples.vb: Update doesn't works when using the different object containers
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</div>
<p>So in order to update an object, you need to load and store it in the same object-container. If you cannot do this, you need to merge to object-changes. <a href="example_merge_changes.htm" target="" title="" alt="" class="MCXref" xrefformat="See "{paratext}"">See "Example Merge Changes"</a></p>
<div class="codesnippet" MadCap:conditions="Primary.c#">
<pre class="prettyprint" xml:space="preserve">using (IObjectContainer container = OpenDatabase())
{
Pilot joe = QueryByName(container, "Joe");
joe.Name = "Joe New";
container.Store(joe);
}
using (IObjectContainer container = OpenDatabase())
{
IList<Pilot> pilots = container.Query<Pilot>();
Console.WriteLine("Amount of pilots: " + pilots.Count);
foreach (Pilot pilot in pilots)
{
Console.WriteLine(pilot);
}
}</pre>
<div class="codesnippet-meta">ObjectIdentityExamples.cs: Update works when using the same object container
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</div>
<div class="codesnippet" MadCap:conditions="Primary.VB.NET">
<pre class="prettyprint lang-vb" MadCap:conditions="Primary.Online" xml:space="preserve">Using container As IObjectContainer = OpenDatabase()
Dim joe As Pilot = QueryByName(container, "Joe")
joe.Name = "Joe New"
container.Store(joe)
End Using
Using container As IObjectContainer = OpenDatabase()
Dim pilots As IList(Of Pilot) = container.Query(Of Pilot)()
Console.WriteLine("Amount of pilots: " & pilots.Count)
For Each pilot As Pilot In pilots
Console.WriteLine(pilot)
Next
End Using</pre>
<div class="codesnippet-meta">ObjectIdentityExamples.vb: Update works when using the same object container
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