DKNet

Seed missing rows through EF Core callbacks

Part of DKNet.EfCore.Extensions. Discover IDataSeedingConfiguration implementations and run them through EF Core native seeding callbacks.

Use the console-project setup in the Quick Start, then replace Program.cs with this example.

using Microsoft.EntityFrameworkCore;
using DKNet.EfCore.Extensions.Configurations;
using DKNet.EfCore.Extensions.Extensions;

using var connection = new Microsoft.Data.Sqlite.SqliteConnection("Data Source=:memory:");
connection.Open();
var o = new DbContextOptionsBuilder<DemoDb>();
o.UseSqlite(connection).UseAutoDataSeeding([typeof(DemoDb).Assembly]);
await using var db = new DemoDb(o.Options);
await db.Database.EnsureCreatedAsync();
await db.Database.EnsureCreatedAsync();
Console.WriteLine(await db.Items.CountAsync()); // 1

public sealed class DemoDb(DbContextOptions<DemoDb> options) : DbContext(options)
{
    public DbSet<Item> Items => Set<Item>();
}
public sealed class ItemSeed : DataSeedingConfiguration<Item>
{
    protected override ValueTask<ICollection<Item>> GetDataAsync(CancellationToken cancellation = default)
        => ValueTask.FromResult<ICollection<Item>>([new Item { Id = 7, Name = "Coffee" }]);
}
public sealed class Item
{
    public int Id { get; set; }
    public string Name { get; set; } = "";
}

UseAutoDataSeeding discovers ItemSeed, hooks EF Core seeding, compares candidate primary keys and adds only missing rows before SaveChangesAsync.

DataSeedingConfiguration<TEntity> loads existing primary-key projections, including composite and shadow keys. Explicit non-default keys are compared by values, independent of entity equality. Empty candidates or no missing rows cause no save.

⚙️ Configuration reference

Option	Type	Default	Effect
`assemblies`	`Assembly[]`	required	Scan seed configurations; an empty array finds none. Null throws.
`Order`	`int`	`0`	Metadata only; discovery does not sort it.
`EntityType`	`Type`	`typeof(TEntity)`	Exposes the targeted CLR type.
`SeedAsync`	nullable callback on interface	base implementation	Base loads GetDataAsync and inserts missing keys. Null callbacks are skipped.

⚠️ Gotchas & limits

Seeding is a separate opt-in from model configuration. Implementations are instantiated once with parameterless constructors when options are configured.
Order is declared but not sorted or otherwise read by the discovery runner. Combine dependent operations in one seeder.
All-default keys count as unset and always new. Use stable explicit keys for repeatable seeding. Candidate duplicates are not removed within one seed batch.
This inserts missing rows; it does not update existing rows or delete obsolete data. Query filters on the DbSet affect which existing keys are seen.
The synchronous callback blocks on SeedAsync with CancellationToken.None; the async callback forwards its cancellation token.

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