Move source code into "Source" folder

Source/DataLayer/Configurations/LibraryBookConfig.cs

@@ -0,0 +1,32 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace DataLayer.Configurations
+{
+    internal class LibraryBookConfig : IEntityTypeConfiguration<LibraryBook>
+    {
+        public void Configure(EntityTypeBuilder<LibraryBook> entity)
+        {
+            // to allow same book (incl region) with diff acct.s:
+            //
+            // this file:
+            // - composite key:
+            //     entity.HasKey(b => new { b.BookId, b.Account });
+            //     entity.HasIndex(b => b.BookId);
+            //     entity.HasIndex(b => b.Account);
+            // - change the below relationship since Book+LibraryBook would no longer be 1:1
+            //
+            // other files:
+            // - change Book class since Book+LibraryBook would no longer be 1:1
+            // - update LibraryBook import code
+            // - would likely challenge assumptions throughout Libation which have been true up until now
+
+            entity.HasKey(lb => lb.BookId);
+
+            entity
+                .HasOne(lb => lb.Book)
+                .WithOne()
+                .HasForeignKey<LibraryBook>(lb => lb.BookId);
+        }
+    }
+}