Entity Framework Core: Is it safe to delete Migration.Designer.cs if we will never Revert a migration?

Question

We have a database schema with ~200 tables. Model snapshot (Migration.Designer.cs) which is created for each migration is ~20K lines. So, having quite a number of migrations really slows down our build on CI (with ~30 migrations building a solution takes 6 minutes with migrations or 4 minutes without them).

So, to the question: is it safe to delete model snapshots for old migrations (that we know we will never Revert)? Are model snapshots used for anything else except Revert-Migration?

Answer 1

Are model snapshots used for anything else except Revert-Migration?

Yes. There are a few edge cases where it's needed. On SQL Server, those cases are:

• AlterColumn when the column is narrowed or the computed expression is changed and the indexes need to be rebuilt
• CreateIndex on a memory-optimized table when the index is unique and references nullable columns

So most of the time it's probably safe to delete, but please test that your migrations still work after doing so.

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The .Designer.cs file contains a partial class, with 2 attributes:

[DbContext...
[Migration...

Don't forget to copy these attributes to the class containing your migration code (the Up and Down methods of the same partial class). EF uses these attributes to determine which migrations are in the assembly.

After removing the .Designer.cs files from our project, dbContext.Database.GetPendingMigrations().Count() returned 0.

We solved this problem by adding these attributes.