Add LinkedChildren database table for normalized relationships

Introduces a new database table to store linked child relationships for
boxsets, playlists, and video alternate versions. This replaces the
JSON-serialized Data column approach with a proper relational structure.

- Add LinkedChildEntity and LinkedChildType enum
- Add entity configuration with proper foreign keys
- Add EF Core migration for SQLite

1 files changed, 33 insertions, 0 deletions

diff --git a/src/Jellyfin.Database/Jellyfin.Database.Implementations/ModelConfiguration/LinkedChildConfiguration.cs b/src/Jellyfin.Database/Jellyfin.Database.Implementations/ModelConfiguration/LinkedChildConfiguration.cs
new file mode 100644
index 0000000000..44bd01ad63
--- /dev/null
+++ b/src/Jellyfin.Database/Jellyfin.Database.Implementations/ModelConfiguration/LinkedChildConfiguration.cs
@@ -0,0 +1,33 @@
+using Jellyfin.Database.Implementations.Entities;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace Jellyfin.Database.Implementations.ModelConfiguration;
+
+/// <summary>
+/// LinkedChildEntity configuration.
+/// </summary>
+public class LinkedChildConfiguration : IEntityTypeConfiguration<LinkedChildEntity>
+{
+    /// <inheritdoc/>
+    public void Configure(EntityTypeBuilder<LinkedChildEntity> builder)
+    {
+        builder.ToTable("LinkedChildren");
+        builder.HasKey(e => new { e.ParentId, e.ChildId });
+        builder.HasIndex(e => e.ParentId);
+        builder.HasIndex(e => e.ChildId);
+        builder.HasIndex(e => new { e.ParentId, e.SortOrder });
+        builder.HasIndex(e => new { e.ParentId, e.ChildType });
+        builder.HasIndex(e => new { e.ChildId, e.ChildType });
+
+        builder.HasOne(e => e.Parent)
+            .WithMany(e => e.LinkedChildEntities)
+            .HasForeignKey(e => e.ParentId)
+            .OnDelete(DeleteBehavior.NoAction);
+
+        builder.HasOne(e => e.Child)
+            .WithMany(e => e.LinkedChildOfEntities)
+            .HasForeignKey(e => e.ChildId)
+            .OnDelete(DeleteBehavior.NoAction);
+    }
+}