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I am in the middle of trying to complete a design for a project and have basically come to a fork in the road. I have made up my mind that I want to use EF4 as my data persistence layer, but my existing database is causing me some pains. Changing or augmenting the database is not an option. I have a single table that really serves multiple purposes and contains 120 columns (I didn't design this table!!! - it is a DB2 carryover after a SQL Server conversion long ago). I have designed a class diagram that creates five entities from this table, at varying levels of aggregation. In my research of what to do in these situations, I have narrowed it down to either using a “QueryView” in my MSL layer or a “DefiningQuery” in my SSDL layer to create the entities I need from this monolith table. The resultant data will only need to be read-only. I’d prefer getting back a proper entity, but anonymous types or dbdatarecord would be okay.

I have attempted to use a QueryView in MSL with my entity defined in my CSDL but the MSL keeps getting regenerated and my changes lost when I compile. Why?

Can anyone provide input as to what I should do here? Is using a DefiningQuery or QueryView preferable in this situation? Any input as to keeping these changes after updating my model from the database or compiling would be also very appreciated.

EverettEvola
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QueryView should not be regenerated. I'm not sure how QueryView behaves when you do update from database. I'm sure that DefiningQuery will be deleted when doing Update from database because DefiningQuery is defined in SSDL which is completely deleted during Update from database. I have some workaround for custom DefiningQueries by using two different EDMXs - one just for queries and second for entities updated from database. General concept is described here.

Difference between QueryView and DefiningQuery is the level where these constructs are included. QueryView is MSL element built as custom ESQL query on top of existing entity so your 120 columns entity must exists in EDMX. From unknown reason QueryView has no support for aggregations. DefiningQuery is SSDL element build as custom SQL query. It is by default used for database views (btw. probably best choice for you).

Community
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Ladislav Mrnka
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