Entity Framework: Must I Add Primary Keys to Existing Tables for Data Manipulation?

Entity Framework and Existing Databases: The Primary Key Question

Working with Entity Framework (EF) and a pre-existing database often presents challenges, especially when tables lack primary keys. Creating an Entity Data Model might result in errors, excluding tables without them. This raises a crucial question: Is adding primary keys to these tables absolutely necessary for data manipulation within EF, or are there alternative approaches?

A Workaround: Leveraging ISNULL and NULLIF

A practical solution, as highlighted by Tillito, involves a clever workaround for SQL Server views. By encapsulating the original view's SELECT statement within another SELECT statement, you can manipulate data without modifying the underlying table structure.

To designate a column as a primary key for EF's purposes, wrap it with the ISNULL function. For example:

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

Conversely, to prevent EF from treating a column as a primary key, use the NULLIF function:

SELECT NULLIF(AnotherProperty, '') AS AnotherProperty,
       ...
FROM ( ... ) AS temp

Real-World Application

Consider a scenario where your application uses multiple tables from an existing database, and you wish to avoid altering the original table schemas. By implementing this technique within your view definitions, incorporating ISNULL and NULLIF as demonstrated, EF will correctly identify the needed primary keys without requiring any schema modifications.

This method enables seamless integration of your existing database tables into your EF application, even without pre-existing primary keys, providing a flexible and efficient solution.

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