Jul 8, 2009

Limitation of Entity Data Model Designer

The disigner does not support all the features of the EDM. With some of less frequently used EDM features, you will have to work with the XML after all.

  • Stored procedures

    The Designer supports a narrow use of stored procedures. Using the Designer, you can override the Entity Framework's automatic generation of Insert, Update, and Delete commands by mapping an entity to a set of stored procedures with two important rules. The first is that the stored procedure must line up with the entity. For inserts and updates, that means the values for the stored procedure parameters must come from an entity's property. The second rule is that you have to override the Insert, Update, and Delete commands, or no commands at all, so you'll need to map all three functions.

    In addition, the Designer supports read queries as long as the query results map directly to an entity. If you have a query that returns random data, you will need to manually create an entity for it to map to. That's not too hard in the Designer, but there's another requirement that will necessitate doing some work in the XML.

  • Unsupported EDM types

    The EDM has a very rich set of modeling capabilities. But the Designer does not support all of these advanced modeling techniques, requiring you to handcode some of them in the XML. In most cases, you can continue to work with the model in the Designer even though you won't see these particular model types, though you can leverage them in your code. However, there are a few model types, such as the very useful complex type, that, when included in the XML, will make it impossible to open the model in the Designer. The Designer is well aware of these limitations, and at least provides an alternative view that displays a message explaining why the model can't be opened.

  • Generating a database from the model

    The EDM is based on a data-driven design with the assumption that there is an existing database for the model to map back to. This makes a lot of sense if you are building an application for an existing database. Domain-driven developers prefer to create their object model first and have a database generated from that. The current designer does not support this capability. However, model first development will be possible in the next version of the Entity Framework tools, which will ship in Visual Studio 2010. In the meantime, developers in the community and at Microsoft are playing with a code generator called T4 Templates (Text Template Transformation Toolkit) to read the model and generate SQL script files to generate database objects for you.

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