Why Am I Getting the 'Cannot Insert Explicit Value for Identity Column' Error in Entity Framework?

Understanding "Cannot Insert Explicit Value for Identity Column" Error in Entity Framework

Error:
The "Cannot insert explicit value for identity column in table" error occurs when attempting to insert a value into an identity column (auto-increment columns) while the IDENTITY_INSERT database option is set to OFF.

Cause:
This error indicates that Entity Framework is trying to insert a specific value for an identity column, which is not allowed when the database manages the value generation.

Solution:

1. Check database and EF model:

   • Ensure that the identity column in the database is set to be auto-incremented.
   • In the Entity Framework model, the StoreGeneratedPattern property for the identity column should be set to "Identity."

2. Update EDMX file (Entity Data Model):

   • If the database has been modified, it's recommended to update the Entity Data Model (EDMX) file to reflect the changes. This ensures that the model matches the database structure.

3. Check for "IsDbGenerated" attribute:

   • Open the EDMX file and navigate to the table containing the identity column.
   • Look for the "IsDbGenerated" attribute for the identity property. If it's not present, add it manually and set it to "true."

4. Disable auto-generated values in code:

   • Avoid manually assigning values to identity columns in your code. This may interfere with the auto-increment behavior.

Code Sample:

GroupMember groupMember = new GroupMember();
groupMember.GroupId = group.Id;
groupMember.UserId = new UserId(group.Owner);
// Remove this line, as it manually assigns an ID
// groupMember.Id = _groupContext.GroupMembers.Count();
group.GroupMembers.Add(groupMember);

By following these steps, the error should be resolved, and Entity Framework will correctly insert values into the identity column based on the database configuration.

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