Initial commit carried over from private repo. This is V2.

code/MessengerApi.Db.Npg/MessengerNpgDbContext.cs

@@ -0,0 +1,31 @@
+using MessengerApi.Db.Entities;
+using Microsoft.EntityFrameworkCore;
+
+namespace MessengerApi.Db.Npg
+{
+    public class MessengerNpgDbContext : MessengerDbContext
+    {
+        private readonly string connectionString;
+
+        public MessengerNpgDbContext(string connectionString)
+        {
+            this.connectionString = connectionString;
+        }
+
+        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
+        {
+            base.OnConfiguring(optionsBuilder);
+            optionsBuilder.UseNpgsql(this.connectionString);
+        }
+
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            base.OnModelCreating(modelBuilder);
+
+            // https://stackoverflow.com/questions/26464357/what-is-the-purpose-of-non-unique-indexes-in-a-database
+            // https://stackoverflow.com/questions/40767980/generate-a-composite-unique-constraint-index-in-ef-core
+            // https://www.geeksforgeeks.org/difference-between-clustered-and-non-clustered-index/
+            modelBuilder.Entity<Message>().HasIndex(e => new { e.ToId, e.IsDelivered }).IsUnique(false);
+        }
+    }
+}