How Can I Use Entity Framework with Tables Lacking Primary Keys?

Entity Framework with tables missing primary keys

When using Entity Framework to deal with existing databases, you often encounter tables that do not have a primary key defined. In this case, the creation of the entity data model may result in an error message stating that the primary key cannot be inferred and the table is excluded.

In order to solve this problem and use related entities, there are two main methods:

1. Add primary key:

The traditional method is to add a primary key to the table in the database. This ensures that Entity Framework can correctly identify and manage the table's entities. However, depending on the nature of the data and the requirements of the application, this may not be feasible.

2. Workarounds using ISNULL and NULLIF:

Another solution proposed by Tillito is to use the ISNULL and NULLIF functions to force or prevent Entity Framework from using a specific column as a primary key. By wrapping the view's select statement in another select statement, you can apply these functions as follows:

SELECT
  ISNULL(MyPrimaryID,-999) MyPrimaryID,
  NULLIF(AnotherProperty,'') AnotherProperty
  FROM ( ... ) AS temp

Using ISNULL, you can force Entity Framework to treat non-existent primary key values ​​as defined (-999 in the example). In contrast, using NULLIF, you prevent a column from being treated as a primary key by converting any non-null value to NULL.

This workaround provides a way to use tables without primary keys in Entity Framework while maintaining data integrity and functionality in your application.

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