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2009-08-21

Avoid "Tall" DAO Factories

A "tall" DAO factory can be defined as a big class that contains too much methods for each business class that compounds your domain model.

public class DAOFactory
{
IClass1DAO GetClass1DAO() { ... }
IClass2DAO GetClass2DAO() { ... }
IClass3DAO GetClass3DAO() { ... }
IClass4DAO GetClass4DAO() { ... }
IClass5DAO GetClass5DAO() { ... }
IClass6DAO GetClass6DAO() { ... }
IClass7DAO GetClass7DAO() { ... }
IClass8DAO GetClass8DAO() { ... }
IClass9DAO GetClass9DAO() { ... }
IClass10DAO GetClass10DAO() { ... }
: : : :
}


Besides big, these kind of class should be modified every time a new domain class is added to your system.
In order to avoid that to happen, one good option is to use a generic method for all DAO interfaces.

public class DAOFactory
{
ICommonDAO GetDAO < I > ( ) where I : ICommonDAO { ... }
}


The action of searching the corresponding DAO interface implementation can be easily achieved by using .NET reflection support for Assemblies and Types.
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