🧱 Lesson 5 - Working with PostgreSQL (Multi-Database Setup)

#postgres #postgressql #csharp #entityframework

Series: From Code to Cloud: Building a Production-Ready .NET Application
By: Farrukh Rehman - Senior .NET Full Stack Developer / Team Lead
LinkedIn: https://linkedin.com/in/farrukh-rehman
GitHub: https://github.com/farrukh1212cs

Source Code Backend : https://github.com/farrukh1212cs/ECommerce-Backend.git

Source Code Frontend : https://github.com/farrukh1212cs/ECommerce-Frontend.git

PostgreSQL is a powerful open-source database widely used in enterprise and cloud systems.
In multi-tenant or SaaS environments, it’s common to support multiple database providers (e.g., MySQL, SQL Server, PostgreSQL) based on customer or deployment needs.

Our goal today:

🐳 Pull and run PostgreSQL via Docker
⚙️ Add PostgreSQL support in EF Core
🏗️ Create PostgresDbContext and design-time factory
🧱 Run migrations and verify setup

🐳 Step 1 — Pull PostgreSQL Docker Image and Run Container

Let’s start by running PostgreSQL locally inside Docker.
docker pull postgres

Run container
docker run -d --name postgres -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=Admin123! -p 5432:5432 postgres:latest

⚙️ Step 2 — Update appsettings.json

Add a new connection string for PostgreSQL in your ECommerce.API project.
"PostgreSQL":"Host=localhost;Port=5432;Database=ECommerceDb;Username=postgres;Password=Admin123!",
Now your application can dynamically choose the provider by changing:
"DatabaseProvider": "PostgreSQL"

🧱 Step 3 — Create PostgreSQL DbContext
Path : ECommerce.Infrastructure/Data/PostgresDbContext.cs

using Microsoft.EntityFrameworkCore;

namespace ECommerce.Infrastructure.Data;

public class PostgresDbContext : AppDbContext
{
    public PostgresDbContext(DbContextOptions<PostgresDbContext> options)
  : base(options)
    {
    }
}

Install Package

dotnet add ECommerce.Infrastructure package Npgsql.EntityFrameworkCore.PostgreSQL --version 8.0.11

🧩 Step 5 — Add Design-Time Factory

EF Core CLI needs this factory for dotnet ef migrations when it can’t build the host automatically.

Create PostgresDbContextFactory
Path : ECommerce.Infrastructure/Data/PostgresDbContextFactory.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.Extensions.Configuration;

namespace ECommerce.Infrastructure.Data;

public class PostgresDbContextFactory : IDesignTimeDbContextFactory<PostgresDbContext>
{
    public PostgresDbContext CreateDbContext(string[] args)
    {
        var basePath = Path.Combine(Directory.GetCurrentDirectory(), "../ECommerce.API");
        var configuration = new ConfigurationBuilder()
            .SetBasePath(basePath)
            .AddJsonFile("appsettings.json", optional: false)
            .AddJsonFile("appsettings.Development.json", optional: true)
            .Build();

        var connectionString = configuration.GetConnectionString("PostgreSQL");

        var optionsBuilder = new DbContextOptionsBuilder<PostgresDbContext>();
        optionsBuilder.UseNpgsql(connectionString);

        return new PostgresDbContext(optionsBuilder.Options);
    }
}

Update Dependency Injection
Path : ECommerce.Infrastructure/DependencyInjection.cs

using ECommerce.Infrastructure.Data;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

namespace ECommerce.Infrastructure;

public static class DependencyInjection
{
    public static IServiceCollection AddInfrastructure(
        this IServiceCollection services,
        IConfiguration configuration)
    {
        var provider = configuration["DatabaseProvider"] ?? "MySQL";

        if (string.Equals(provider, "SqlServer", StringComparison.OrdinalIgnoreCase))
        {
            var conn = configuration.GetConnectionString("SqlServer");
            services.AddDbContext<AppDbContext, SqlServerDbContext>(options =>
                options.UseSqlServer(conn));
        }
        else if (string.Equals(provider, "MySQL", StringComparison.OrdinalIgnoreCase))
        {
            var conn = configuration.GetConnectionString("MySQL");
            services.AddDbContext<AppDbContext, MySqlDbContext>(options =>
                options.UseMySql(conn, ServerVersion.AutoDetect(conn)));
        }
        else if (string.Equals(provider, "PostgreSQL", StringComparison.OrdinalIgnoreCase))
        {

            var conn = configuration.GetConnectionString("PostgreSQL");
            services.AddDbContext<AppDbContext, PostgresDbContext>(options =>
                options.UseNpgsql(conn));
        }
        else
        {
            throw new InvalidOperationException($"Unsupported provider: {provider}");
        }

        return services;
    }
}

🧱 Step 6 — Create Migrations
Now you can generate a separate migration folder for PostgreSQL.

dotnet ef migrations add InitPostgres -p ECommerce.Infrastructure -s ECommerce.API --context PostgresDbContext --output-dir "Migrations/PostgreSQL"
dotnet ef database update -p ECommerce.Infrastructure -s ECommerce.API --context PostgresDbContext