src/Db/DataMappers.cs

@@ -0,0 +1,46 @@
+using Domain;
+
+namespace Db;
+
+/// <summary>Hand-written mappers between domain objects and persistence records; each method maps one direction and never mutates its input.</summary>
+public static class DataMappers
+{
+    /// <summary>Map a <see cref="Client"/> to its persistence record <see cref="ClientData"/>.</summary>
+    public static ClientData ToClientData(Client client)
+    {
+        ArgumentNullException.ThrowIfNull(client);
+        return new ClientData { Id = client.Id, Name = client.Name };
+    }
+
+    /// <summary>Map an <see cref="Order"/> to its persistence record <see cref="OrderData"/>; the client back-reference becomes a foreign key.</summary>
+    public static OrderData ToOrderData(Order order)
+    {
+        ArgumentNullException.ThrowIfNull(order);
+        return new OrderData
+        {
+            Id = order.Id,
+            Description = order.Description,
+            TotalInCents = order.TotalInCents.Cents,   // value object → plain int for the row
+            ClientId = order.Client?.Id ?? Guid.Empty,
+        };
+    }
+
+    /// <summary>Map a <see cref="ClientData"/> record back to a <see cref="Client"/>.</summary>
+    public static Client FromClientData(ClientData row)
+    {
+        ArgumentNullException.ThrowIfNull(row);
+        return new Client { Id = row.Id, Name = row.Name };
+    }
+
+    /// <summary>Map an <see cref="OrderData"/> record back to an <see cref="Order"/>; the context reassembles the graph.</summary>
+    public static Order FromOrderData(OrderData row)
+    {
+        ArgumentNullException.ThrowIfNull(row);
+        return new Order
+        {
+            Id = row.Id,
+            Description = row.Description,
+            TotalInCents = OrderMoney.From(row.TotalInCents),   // plain int from the row → value object
+        };
+    }
+}