This topic applies to .NET version only
Db4o uses full class name to distinguish classes within the database file. In .NET full class name has the following format:
Namespace.ClassName, AssemblyName
Effectively that means that the same class definition within different assemblies (applications or libraries) will be recognized as two different classes by db4o. You should keep this in mind in the following cases:
Let's use an example to see what happens in these cases. We will create 2 applications Test1.exe and Test2.exe. Both will have a simplest class definition:
01/* Copyright (C) 2004 - 2007 db4objects Inc. http://www.db4o.com */ 02
namespace Db4objects.Db4odoc.ClassNameFormat 03
{ 04
class Test 05
{ 06
public override string ToString() 07
{ 08
return "Test"; 09
} 10
} 11
}
01' Copyright (C) 2004 - 2007 db4objects Inc. http://www.db4o.com 02
Namespace Db4objects.Db4odoc.ClassNameFormat 03
04
Class Test 05
06
Public Overloads Overrides Function ToString() As String 07
Return "Test" 08
End Function 09
End Class 10
End Namespace
Test1 application will store one object of Test class to the database:
01private static void StoreObjects() 02
{ 03
File.Delete(Db4oFileName); 04
IObjectContainer container = Db4oFactory.OpenFile(Db4oFileName); 05
try 06
{ 07
// Store a simple class to the database 08
Test test = new Test(); 09
container.Set(test); 10
} 11
finally 12
{ 13
container.Commit(); 14
} 15
}
01Private Shared Sub StoreObjects() 02
File.Delete(Db4oFileName) 03
Dim container As IObjectContainer = Db4oFactory.OpenFile(Db4oFileName) 04
Try 05
' Store a simple class to the database 06
Dim test As Test = New Test 07
container.Set(test) 08
Finally 09
container.Commit() 10
End Try 11
End Sub
Another application (Test2) will try to read this object from the same database file. To check how the Test object was actually stored in the database we will use StoredClass API:
01public static void CheckDatabase() 02
{ 03
IObjectContainer container = Db4oFactory.OpenFile(Db4oFileName); 04
try 05
{ 06
// Read db4o contents from another application 07
IObjectSet result = container.Get(typeof(Test)); 08
ListResult(result); 09
// Check what classes are actualy stored in the database 10
IStoredClass[] storedClasses = container.Ext().StoredClasses(); 11
foreach (IStoredClass storedClass in storedClasses) 12
{ 13
System.Console.WriteLine("Stored class: " + storedClass.GetName()); 14
} 15
} 16
finally 17
{ 18
container.Commit(); 19
} 20
}
01Private Shared Sub CheckDatabase() 02
Dim container As IObjectContainer = Db4oFactory.OpenFile(Db4oFileName) 03
Try 04
' Read db4o contents from another application 05
Dim result As IObjectSet = container.Get(GetType(Test)) 06
ListResult(result) 07
' Check what classes are actualy stored in the database 08
Dim storedClasses As IStoredClass() = container.Ext.StoredClasses 09
Dim storedClass As IStoredClass 10
For Each storedClass In storedClasses 11
System.Console.WriteLine("Stored class: " + storedClass.GetName) 12
Next 13
Finally 14
container.Commit() 15
End Try 16
End Sub
From the example we can see that though the class has been stored to the database, it cannot be retrieved from the Test2 application, as the assembly name is different from the original.
In order to make your classes readable from another assembly you should use one of the existing workarounds: