Database Reset for Testing

Weasel provides an FK-aware database cleaner for EF Core that makes integration testing straightforward. Inspired by Respawn and Marten's ResetAllData(), the cleaner discovers tables from your DbContext metadata, resolves foreign key ordering, and generates provider-specific SQL to safely truncate all data.

Setup

Register the cleaner and optional seed data in your DI container:

var builder = Host.CreateDefaultBuilder();
builder.ConfigureServices(services =>
{
    services.AddDbContext<ShopDbContext>(options =>
        options.UseNpgsql("Host=localhost;Database=mydb"));

    // Register the Weasel migrator for your database provider
    services.AddSingleton<Migrator, Weasel.Postgresql.PostgresqlMigrator>();

    // Register the database cleaner
    services.AddDatabaseCleaner<ShopDbContext>();

    // Register seed data (optional, runs after ResetAllDataAsync)
    services.AddInitialData<ShopDbContext, TestOrderSeedData>();
});

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Deleting All Data

Use DeleteAllDataAsync() to truncate all tables in FK-safe order (children before parents):

var cleaner = host.Services.GetRequiredService<IDatabaseCleaner<ShopDbContext>>();

// Delete all data from tables managed by the DbContext
// Tables are truncated in FK-safe order (children first)
await cleaner.DeleteAllDataAsync();

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Behind the scenes, the cleaner generates provider-specific SQL:

• PostgreSQL: TRUNCATE TABLE t1, t2, t3 RESTART IDENTITY CASCADE;
• SQL Server: DELETE FROM each table in dependency order, then DBCC CHECKIDENT to reseed
• SQLite: DELETE FROM each table in dependency order, then clears sqlite_sequence

Reset with Seed Data

Use ResetAllDataAsync() to delete all data and then run all registered IInitialData<TContext> seeders:

var cleaner = host.Services.GetRequiredService<IDatabaseCleaner<ShopDbContext>>();

// Delete all data, then run all registered IInitialData<T> seeders
await cleaner.ResetAllDataAsync();

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IInitialData

Implement IInitialData<TContext> to define seed data applied after a reset. Multiple seeders execute in registration order.

public class TestOrderSeedData : IInitialData<ShopDbContext>
{
    public async Task Populate(ShopDbContext context, CancellationToken cancellation)
    {
        context.Customers.Add(new ShopCustomer { Name = "Test Customer" });
        context.Orders.Add(new ShopOrder { CustomerId = 1, Status = "Pending" });
        await context.SaveChangesAsync(cancellation);
    }
}

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Multi-Tenancy

For multi-tenant scenarios where each tenant has its own database, pass an explicit DbConnection to target a specific tenant:

var cleaner = host.Services.GetRequiredService<IDatabaseCleaner<ShopDbContext>>();

// For multi-tenant scenarios, pass an explicit connection
// to target a specific tenant database
await using var tenantConnection = new Npgsql.NpgsqlConnection(
    "Host=localhost;Database=tenant_abc");

await cleaner.DeleteAllDataAsync(tenantConnection);
// or with seeding:
await cleaner.ResetAllDataAsync(tenantConnection);

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Performance

The cleaner memoizes the table dependency graph and generated SQL on first use. The EF Core model is immutable, so the SQL never changes. This means subsequent calls in a test suite reuse the cached SQL with zero overhead — critical when running hundreds of tests.

Supported Providers

Provider	Strategy	Identity Reset
PostgreSQL	TRUNCATE ... CASCADE RESTART IDENTITY	Automatic
SQL Server	DELETE FROM in FK order	DBCC CHECKIDENT
SQLite	DELETE FROM in FK order	Clears sqlite_sequence
MySQL	TRUNCATE TABLE with FOREIGN_KEY_CHECKS=0	Automatic
Oracle	DELETE FROM in FK order	N/A (uses sequences)