How Can I Integrate EF 4.0 Data Models Without Physical Primary Keys?

EF data model exclusion due to missing primary key

When integrating an existing database into Entity Framework (EF) 4.0, it is common for some tables to be missing primary keys. This issue occurs when creating a new entity data model, resulting in an error message stating that the primary key is missing and the table is subsequently excluded.

It is generally believed that a physical primary key must be added to the affected table to resolve this issue. However, there is a workaround that allows you to use these tables without modifying their schema.

As Tillito suggested, this workaround involves modifying the SELECT statement for the offending view in a new SELECT statement. By wrapping the original SELECT statement in this way, you can use the ISNULL function to specify the column to be used as the primary key. Instead, you can use the NULLIF function to prevent a column from being designated as a primary key.

Example:

Consider the following example:

<code class="language-sql">SELECT
  ISNULL(MyPrimaryID,-999) MyPrimaryID,
  NULLIF(AnotherProperty,'') AnotherProperty
FROM ( ... ) AS temp</code>

In this example, the ISNULL function forces EF to recognize "MyPrimaryID" as a primary key, while the NULLIF function ensures that "AnotherProperty" is not considered a primary key.

By applying this technique, you avoid the need to modify the database schema and seamlessly integrate existing tables into your EF data model, allowing data manipulation without modifications to physical primary keys.

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