Swevo.EFCore.Seeding 1.0.1

Swevo.EFCore.Seeding

Fluent, idempotent, dependency-ordered seed data for EF Core. Define IEntitySeed<T> classes, declare run-order dependencies, then call SeedDatabaseAsync() on startup. Seeds that find existing data skip themselves automatically.

// 1. Define seeds
public class RolesSeed : IEntitySeed<Role>
{
    public IEnumerable<Role> GetData() =>
    [
        new Role { Id = 1, Name = "Admin" },
        new Role { Id = 2, Name = "User" },
    ];
}

public class UsersSeed : IEntitySeed<User>
{
    public IEnumerable<User> GetData() =>
    [
        new User { Id = 1, Email = "admin@example.com", RoleId = 1 },
    ];
}

// 2. Register
builder.Services.AddEFCoreSeeding<AppDbContext>(seeds =>
{
    seeds.Add<RolesSeed, Role>();
    seeds.Add<UsersSeed, User>().DependsOn<RolesSeed>(); // roles run first
});

// 3. Apply once the host is built
await app.SeedDatabaseAsync();

Install

dotnet add package Swevo.EFCore.Seeding

How idempotency works

Before inserting, the runner calls DbSet<T>.AnyAsync(). If the set already contains rows the entire seed is skipped. This means:

• Safe to call SeedDatabaseAsync() on every startup
• Re-deploying never duplicates reference data
• Production and test environments stay in sync

Dependency ordering

Declare which seeds must complete before another starts using .DependsOn<TSeed>():

seeds.Add<PermissionsSeed, Permission>();
seeds.Add<RolesSeed, Role>();
seeds.Add<UserRoleSeed, UserRole>()
    .DependsOn<PermissionsSeed>()
    .DependsOn<RolesSeed>();

The runner performs a topological sort (Kahn's algorithm) and executes seeds in a valid order. Circular dependencies throw InvalidOperationException at startup, not at runtime.

Unregistered dependency detection

seeds.Add<UsersSeed, User>().DependsOn<RolesSeed>(); // RolesSeed not registered → throws

InvalidOperationException: Seed 'UsersSeed' declares a dependency on 'RolesSeed',
but 'RolesSeed' is not registered. Call .Add<RolesSeed, Role>() first.

Manual trigger

If you prefer to seed on demand rather than at startup:

using var scope = app.Services.CreateScope();
var runner = scope.ServiceProvider.GetRequiredService<ISeedRunner>();
await runner.RunAsync();

Testing

The runner is registered as ISeedRunner — mock or stub it in unit tests:

// In integration tests with EF Core InMemory:
builder.Services.AddEFCoreSeeding<TestDbContext>(seeds =>
    seeds.Add<RolesSeed, Role>());

await host.SeedDatabaseAsync();
// db.Roles is now populated

Part of the Swevo EF Core toolkit

License

MIT © 2026 Justin Bannister