Why Does Entity Framework Auto-Increment Keys Even When Manually Specified?

Entity Framework and Manually Assigned Keys: A Troubleshooting Guide

A common challenge when using Entity Framework's code-first approach involves the framework's tendency to auto-increment keys, even when keys are manually assigned. This article details a solution and its potential pitfalls.

A developer recently encountered this issue. Despite explicitly setting key values, Entity Framework continued to auto-increment. The typical solution, using HasDatabaseGeneratedOption(DatabaseGeneratedOption.None):

modelBuilder.Entity<event>().Property(e => e.EventID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

...resulted in the following error:

<code>Unhandled Exception:
System.Data.Entity.Infrastructure.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---
System.Data.UpdateException: An error occurred while updating the entries. See the inner exception for details. --->
System.Data.SqlClient.SqlException: Cannot insert explicit value for identity column in table 'Events' when IDENTITY_INSERT is set to OFF.</code>

This error arises because IDENTITY_INSERT for the 'Events' table was set to OFF. To resolve this, IDENTITY_INSERT must be explicitly set to ON before inserting data with manually-specified keys. This allows the database to accept the pre-assigned key values.

Alternatively, attributes can achieve the same outcome:

[Key]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int EventID { get; set; }

This approach functions in both Entity Framework and Entity Framework Core. The key is to correctly manage the database's IDENTITY_INSERT setting to avoid conflicts when manually assigning primary key values. Remember to set it back to OFF after your insertion is complete for standard database behavior.

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