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

code/MessengerApi.Db.Npg.Migrator/DesignTimeDbContextFactory.cs

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+using MessengerApi.Db.Npg;
+using Microsoft.EntityFrameworkCore.Design;
+
+namespace MessengerApi.Db.Sql.Migrator
+{
+    public partial class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<MessengerNpgDbContext>
+    {
+        public MessengerNpgDbContext CreateDbContext(string[] args)
+        {
+            return new MessengerNpgDbContext(this.ConnectionString);
+        }
+    }
+}

code/MessengerApi.Db.Npg.Migrator/MessengerApi.Db.Npg.Migrator.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="9.0.6">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MessengerApi.Db.Npg\MessengerApi.Db.Npg.csproj" />
+  </ItemGroup>
+
+</Project>

code/MessengerApi.Db.Npg.Migrator/Program.cs

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+namespace MessengerApi.Db.Npg.Migrator
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            // You can use empty string to build the context when adding a migration - adding a migration does not hit the DB.
+
+            // DesignTimeDbFactory.ConnectionString.cs is not versioned on purposed. Add missing property file for this partial class and then run this command:
+            // Add-Migration YourMigration -Project MessengerApi.Db.Npg -StartupProject MessengerApi.Db.Npg.Migrator -Verbose -Context MessengerNpgDbContext
+
+            // To update the database, make sure your connection string is correct and run this command:
+            // Update-Database -Project MessengerApi.Db.Npg -StartupProject MessengerApi.Db.Npg.Migrator -Verbose -Context MessengerNpgDbContext
+        }
+    }
+}