db-subclass-to-dto/tests/BeforeAfter.Tests/AfterPersistenceTests.cs

using After;

namespace BeforeAfter.Tests;

/// <summary>
/// The after <see cref="DbContext"/> stores data-only persistence records
/// (<see cref="ClientData"/> / <see cref="OrderData"/>), never domain objects:
/// <see cref="DbContext"/>'s <c>Save</c> maps domain state into a row —
/// inserting on the first save, refreshing in place on later ones — and the
/// stored graph is flattened to ids.
/// </summary>
public class AfterPersistenceTests
{
    [Fact]
    public void Save_maps_domain_state_into_data_records()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        var order = new Order { Description = "one", TotalInCents = 15000 };
        client.Orders.Add(order);

        db.Save(client);
        db.Save(order);

        var clientRow = Assert.Single(db.Clients);
        Assert.Equal(client.Id, clientRow.Id);
        Assert.Equal("Acme", clientRow.Name);

        var orderRow = Assert.Single(db.Orders);
        Assert.Equal(order.Id, orderRow.Id);
        Assert.Equal("one", orderRow.Description);
        Assert.Equal(15000, orderRow.TotalInCents);
        Assert.Equal(client.Id, orderRow.ClientId);   // the graph is flattened to a key
    }

    [Fact]
    public void An_order_without_client_stores_an_empty_client_id()
    {
        var db = new DbContext();
        var order = new Order { Description = "orphan" };

        db.Save(order);

        Assert.Equal(Guid.Empty, Assert.Single(db.Orders).ClientId);
    }

    [Fact]
    public void Saving_again_refreshes_the_row_instead_of_duplicating_it()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        var order = new Order { Description = "one" };
        client.Orders.Add(order);
        db.Save(client);
        db.Save(order);

        order.Description = "one (edited)";
        order.TotalInCents = 9900;
        client.Name = "Acme GmbH";
        db.Save(order);
        db.Save(client);

        // One row per saved object, refreshed with the *current* state:
        var orderRow = Assert.Single(db.Orders);
        Assert.Equal(order.Id, orderRow.Id);
        Assert.Equal("one (edited)", orderRow.Description);
        Assert.Equal(9900, orderRow.TotalInCents);
        Assert.Equal(client.Id, orderRow.ClientId);

        var clientRow = Assert.Single(db.Clients);
        Assert.Equal("Acme GmbH", clientRow.Name);
    }

    [Fact]
    public void Rows_are_reachable_through_Set_and_Find()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        var order = new Order { Description = "one" };
        client.Orders.Add(order);
        db.Save(client);
        db.Save(order);

        Assert.Single(db.Set<ClientData>());
        Assert.Single(db.Set<OrderData>());

        var found = db.Find<OrderData>(row => row.Description == "one");
        Assert.Equal(order.Id, found!.Id);
        Assert.Null(db.Find<OrderData>(row => row.Description == "no such order"));
    }

    // ---------------------------------------------------------------------
    // Read-back: LoadOrder / LoadClient reassemble domain objects from the
    // stored rows (identity round-trip for now — OrderLines come later).
    // ---------------------------------------------------------------------

    [Fact]
    public void Loading_an_order_restores_its_state_and_its_client()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        var order = new Order { Description = "one", TotalInCents = 150_00 };
        client.Orders.Add(order);
        db.Save(client);
        db.Save(order);

        var loaded = db.LoadOrder(order.Id);

        Assert.NotNull(loaded);
        Assert.Equal(order.Id, loaded!.Id);
        Assert.Equal("one", loaded.Description);
        Assert.Equal(150_00, loaded.TotalInCents);

        // The graph is reassembled: the loaded order knows its client again,
        // and the client's collection holds the loaded order.
        Assert.NotNull(loaded.Client);
        Assert.Equal("Acme", loaded.Client!.Name);
        Assert.Same(loaded, Assert.Single(loaded.Client.Orders));
    }

    [Fact]
    public void Loading_a_client_restores_it_with_all_of_its_orders()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        client.Orders.Add(new Order { Description = "one", TotalInCents = 150_00 });
        client.Orders.Add(new Order { Description = "two", TotalInCents = 250_00 });
        db.Save(client);
        db.Save(client.Orders[0]);
        db.Save(client.Orders[1]);

        var loaded = db.LoadClient(client.Id);

        Assert.NotNull(loaded);
        Assert.Equal("Acme", loaded!.Name);
        Assert.Equal(2, loaded.Orders.Count);
        Assert.All(loaded.Orders, o => Assert.Same(loaded, o.Client));
    }

    [Fact]
    public void Loading_an_unknown_id_returns_null()
    {
        var db = new DbContext();

        Assert.Null(db.LoadOrder(Guid.NewGuid()));
        Assert.Null(db.LoadClient(Guid.NewGuid()));
    }
}