model-defined function

.NET Framework (current version)
 

A model-defined function is a function that is defined in a conceptual model. The body of a model-defined function is expressed in Entity SQL, which allows for the function to be expressed independently of rules or languages supported in the data source.

A definition for a model-defined function contains the following information:

  • A function name. (Required)

  • The type of the return value. (Optional)

    System_CAPS_ICON_note.jpg Note

    If no return type is specified, the return value is void.

  • Parameter information. (Optional)

  • An Entity SQL expression that defines the body of the function.

Note that model-defined functions do not support output parameters. This restriction is in place so that model-defined functions can be composed.

The diagram below shows a conceptual model with three entity types: Book, Publisher, and Author.

Model With Published Date

The ADO.NET Entity Framework uses a domain-specific language (DSL) called conceptual schema definition language (CSDL) to define conceptual models. The following CSDL defines a function in the conceptual model that returns the numbers of years since an instance of a Book (in the diagram above) was published.

	<Function Name="GetYearsInPrint" ReturnType="Edm.Int32" >
          <Parameter Name="book" Type="BooksModel.Book" />
          <DefiningExpression>
            Year(CurrentDateTime()) - Year(cast(book.PublishedDate as DateTime))
          </DefiningExpression>
        </Function>

Entity Data Model Key Concepts
Entity Data Model
Entity Data Model: Primitive Data Types

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