---
name: migrations
description: 'Implementation details for EF Core migrations. Use when changing MigrationsSqlGenerator, model diffing, migration operations, HistoryRepository, the Migrator or related classes.'
user-invocable: false
---

# Migrations

## Pipeline

**Add migration**: `MigrationsScaffolder.ScaffoldMigration()` → `MigrationsModelDiffer.GetDifferences()` → list of `MigrationOperation` → `CSharpMigrationsGenerator` and `CSharpSnapshotGenerator` produce Up/Down/Snapshot code

**Apply migration**: `Migrator.MigrateAsync()` → reads `__EFMigrationsHistory` → per pending: `MigrationsSqlGenerator.Generate(operations)` → `MigrationCommandExecutor` executes

## Model Snapshot

- Model snapshots use `typeof(Dictionary<string, object>)` (property bag format), not the actual CLR type. When examining the `ClrType` in a snapshot, don't assume it matches the real entity type.
- `SnapshotModelProcessor.Process()` is used at design-time to fixup older model snapshots for backward compatibility.
- `MigrationsModelDiffer` uses provider-agnostic structural comparison between relational models to determine what migration operations are necessary.

## Testing

Migration operation tests: `test/EFCore.Relational.Tests/Migrations/`. Functional tests: `test/EFCore.{Provider}.FunctionalTests/Migrations/`. Model differ tests: `test/EFCore.Relational.Tests/Migrations/Internal/MigrationsModelDifferTest*.cs`.

To simulate a snapshot model use `ModelBuilder` calls without conventions.