Resolving Microsoft.Data.SqlClient.SqlException When Working with Entity Framework Migrations

Discover how to troubleshoot and resolve the `SqlException` error in Entity Framework Core migrations while preserving existing tables and their structure.
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Troubleshooting Microsoft.Data.SqlClient.SqlException in Entity Framework Core Migrations

When working with Entity Framework Core (EF Core), developers may encounter a perplexing issue: the Microsoft.Data.SqlClient.SqlException. This often arises during the migration phase, particularly when trying to create a new table that references an existing one. In this post, we'll take a closer look at this problem and explore an effective solution to ensure a smooth migration experience while preserving your legacy database tables.

The Problem

Imagine you are in the middle of reworking your website's database structure. You've generated new entities and created a migration accordingly. However, there’s a catch: you want to keep the legacy tables unchanged while introducing new ones. Your initial migrations appear to be successful, but then you try to run the command:

[[See Video to Reveal this Text or Code Snippet]]

Only to be greeted with an error message indicating that the new table (let’s say ProjetDossierModel) cannot reference an existing table (DossierModel) due to an invalid reference.

This problem arises primarily because the excluded tables' auto-generated names do not match the actual table names in the database, leading to broken foreign key relationships.

The Solution

After troubleshooting, the solution is straightforward. The error appeared because the migration script generated a foreign key that incorrectly referenced DossierModel instead of the correct existing table name, which is Dossier. Here’s how to fix this problem step-by-step.

Step 1: Locate the Migration File

Step 2: Update the Foreign Key Reference

Within the Up method of your migration file, find the section that defines the new table ProjetDossier. It should resemble the following code snippet:

[[See Video to Reveal this Text or Code Snippet]]

Change the principalTable from DossierModel to Dossier, as follows:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Apply the Changes

Once you have made the changes in your migration file, save the file and run the migration command again:

[[See Video to Reveal this Text or Code Snippet]]

If everything is set correctly, the migration should work without throwing any exceptions.

Conclusion

Handling migrations in Entity Framework Core, especially when dealing with legacy databases, can sometimes lead to confusing SqlExceptions. However, by ensuring that your foreign key relationships point to the correct table names, you can successfully navigate these challenges. In typing this out, it becomes clear how important attention to detail is in maintaining data integrity while working with migrations.

If you find yourself stuck again, remember to check your migration files for naming conventions and references carefully. Happy coding!