Migrations

Weasel's EF Core integration provides methods to detect schema differences and apply migrations using the same delta-detection engine that powers Weasel's core migration infrastructure.

Creating a Migration

The CreateMigrationAsync() extension method on IServiceProvider compares the EF Core model against the actual database state and returns a DbContextMigration that can be inspected or applied.

// Detect schema changes
await using var migration = await serviceProvider.CreateMigrationAsync(dbContext, ct);

// Check if anything changed
if (migration.Migration.Difference != SchemaPatchDifference.None)
{
    // Apply the migration
    await migration.ExecuteAsync(AutoCreate.CreateOrUpdate, ct);
}

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The DbContextMigration record wraps three components:

• Connection -- A DbConnection with full credentials for executing DDL.
• Migrator -- The database-specific Migrator (e.g., PostgresqlMigrator).
• Migration -- A SchemaMigration containing the detected deltas and DDL patches.

DbContextMigration implements IAsyncDisposable and disposes the connection when done.

Creating an IDatabase

For deeper integration with Weasel's IDatabase infrastructure (including the CLI tools), use CreateDatabase():

// Create an IDatabaseWithTables for use with Weasel's migration infrastructure
var database = serviceProvider.CreateDatabase(dbContext);

// The database identifier defaults to the DbContext's full type name
// You can also provide a custom identifier:
var customDatabase = serviceProvider.CreateDatabase(dbContext, "my-read-models");

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This is useful when composing multiple schema sources (e.g., Marten documents plus EF Core tables) into a single migration pipeline.

Finding the Right Migrator

FindMigratorForDbContext() resolves the correct Migrator from the DI container by matching it against the DbContext's connection type:

// Register migrators in DI
var services = new ServiceCollection();
services.AddSingleton<Migrator>(new PostgresqlMigrator());
// or: services.AddSingleton<Migrator>(new SqlServerMigrator());

// Later, resolve automatically
var (connection, migrator) = serviceProvider.FindMigratorForDbContext(dbContext);

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If no registered Migrator matches the connection type, an InvalidOperationException is thrown listing the available migrators.

Connection Handling

EF Core sometimes strips credentials from connection strings (e.g., after EnsureCreatedAsync() or when using DbDataSource). The integration handles this with two internal helpers:

• FindDataSource() -- Extracts the DbDataSource from EF Core's options extensions. When available, connections created from the data source retain full credentials.
• GetConnectionWithCredentials() -- Falls back through the DbContext's connection string and data source to find a connection with credentials intact.

The CreateDatabase() method prefers the data source path when available, which is particularly important for PostgreSQL with NpgsqlDataSource where connection pooling and authentication are managed by the data source.

AutoCreate Options

The ExecuteAsync() method accepts an AutoCreate enum that controls migration behavior:

Value	Behavior
AutoCreate.None	No action taken
AutoCreate.CreateOnly	Create new objects only, skip updates
AutoCreate.CreateOrUpdate	Create new objects and update existing ones
AutoCreate.All	Full migration including destructive changes