Basic ASP.NET Core Web API Connected To PostgreSQL via Docker

This is a guide to create a ASP.NET Core Web API using Visual Studio and connect it to PostgreSQL database using Docker

In order to brush up on my .NET skills, I didn’t know where to start. My friend, Paul, asked me to make build a .NET Core Web API and connect it to PostgreSQL database. It sounded fun for two reasons…

  • It’s programming (obviously)

  • I never worked with PostgresSQL so, an opportunity to learn a new database

Let’s begin!!

What you will need

  • Visual Studio For Mac (VS)

  • DBeaver

  • Docker

  • Docker-Compose

Let the exciting journey begin

Create docker-compose.yml

If you don’t know, docker-compose.yml is a configuration file for Docker-Compose (tool for defining and running multiple containers) used to configure application’s services.

NOTE: This file must be in the root of your project, otherwise, it won’t work.

Create a file and name it docker-compose.yml and add the below code in it

version: '3'
    image: postgres:latest
      - "5432:5432"
    container_name: database
      - POSTGRES_PASSWORD=password

Code Explanation:

version - which version is used

services - what services we are running

postgres - service name

image - name of the image to be used

ports - which port(s) to be used

container_name - name of the container

environemnt - consist of environment variables


Create a new Project

  1. Open Visual Studio

  2. Click New

  3. Under Web and Console, click App

  4. Under ASP.NET Core, select API

  5. Click Next

  6. Ensure .NET Core 3.1. is select for Target Framework

  7. Give project a name like YourProjectName

  8. Click Create

  9. Your project folder structure should look like the below:

Note: If you can’t see the view Solution View, go to View on the menubar and select Design.

Create A Model

A model represent the data to be managed for the application. Our model will be call UserInfo because we are saving users’ information in it.

  1. Right click on YourProjectName in the Solution ExplorerAddNew Folder

  2. Name it as Models

  3. Right click on Models > Add > New Class

  4. Name it as UserInfo

  5. Add the below code

    public class UserInfo
        public long id { get; set; }
        public string email { get; set; }
        public string firstName { get; set; }
        public string lastName { get; set; }
        public string occupation { get; set; }
        public string title { get; set; }
        public string url_Blogs { get; set; }
        public string url_Github { get; set; }
        public string url_Linked { get; set; }

    The classes in the Model’s folder can be placed anywhere in the project, however, the structure above is used as best practice to keep project organised and structured

Create A Database Context

This is the class which is an a vital part of Entity Framework. It inherits from DbContext which represents a session with the database and then can be used as querying and saving to the database

  1. Right click on Models > Add > New Class

  2. Name is as UserInfoDbConext

  3. import Microsoft.EntityFrameworkCor

  4. Derive it from DbContext

  5. Add the below code:

using Microsoft.EntityFrameworkCore;

namespace YourProjecName.Models
    public class UserInfoContext : DbContext
        public UserInfoContext(DbContextOptions<UserInfoContext> options)
            : base(options)

        public DbSet<UserInfo> UserInfo { get; set; }


Register The Above Database Context

For the database context we just created, it needs to be registered with the Dependency Injection container for it work. We will also be connecting to PostgreSQL database using a connection string.

  1. Open Startup.cs (should be in the project’s root)

  2. Add the code (shown by prefixing and suffixing ***)

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
***using Microsoft.EntityFrameworkCore;***
***using YourProjectName.Models;***

namespace YourProjectName
    public class Startup
        public Startup(IConfiguration configuration)
            Configuration = configuration;

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
            ***services.AddDbContext<UserInfoContext>(options =>

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
            if (env.IsDevelopment())




            app.UseEndpoints(endpoints =>

Code Explanation

Specifies to use the connection string from the config to connect to PostgreSQL database. We haven’t added the connection string in the config yet. That’s what we will do now.

Adding Database Connection String

This string will specify the credentials and details of PostgreSQL database for the application to connect to.

Open appsettings.json and the below JSON under AllowedHosts: ”*”

 "ConnectionStrings": {
    "DefaultConnection": "Host=localhost;Port=5432;Username=postgres;Password=password;Database=postgres;"

Make sure the connection details match your docker-compose.yml

ALERT - In production you should NEVER hardcode sensitive information in the files. Instead they should be encapsulated in environment variables

Scaffolding Controller

  1. Add the following NuGet packages in your project
    dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL
    dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL.Design
    dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
    dotnet add package Microsoft.EntityFrameworkCore.Design
    dotnet tool install --global dotnet-aspnet-codegenerator

    dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design - Installs the scaffolding (code generation of CRUD operations) engine

  2. Create a controller
  • Right clicking Project itself in the Solution Explorer

  • Add > New Scaffolding > Click Next

  • Model class to be used would be UserInfo (if you have been following from the start)

  • DbContext class to be used would be UserInfoDbContext (if you have been following from the start)

  • Give controller a name UserInfoController > click Finish

After a few moment, you should see your controller with CRUD (create, remove, update, delete) operation in the Controllers folders

Customise GET and POST Methods

  1. Open the new created controller, UserInfoController in Controllers folder
  2. Replace the exisiting code with the below:
using System.Collections.Generic;
using System.Linq;
using Microsoft.AspNetCore.Mvc;
using RoarcoderUserInfoApi.Models;

namespace RoarcoderUserInfoApi.Controllers
    public class UserInfoController : ControllerBase
        private readonly UserInfoContext _context;

        public UserInfoController(UserInfoContext context)
            _context = context;

        // GET: api/UserInfo
        public ActionResult<List<UserInfo>> GetAll()
            return _context.UserInfo.ToList();

        // GET: api/UserInfo/5
        public ActionResult<UserInfo> GetUserInfo(long id)
            var userInfo = _context.UserInfo.Find(id);

            if (userInfo == null)
                return NotFound();

            return userInfo;

        public void Post([FromBody] UserInfo userInfo)


Code Explanation

Line 8:

[Route("api/[controller]")] - specifies the route for the controller. That means when you want to access the controller from the browser, you will suffix api/the-controller-name to your localhost and port number.

For example: https://localhost:5000/api/userinfo

Line 9

[ApiController] - attribute means that the controller listens to web api requests

Line 20 to 24

[HttpGet] - attribute means when the get request is sent by client, this attributes receives it and invokes GET method.

This methods get all the record from the database table as a list and display it

Line 27 to 38

[Http({“id“})] - attribute means that when a user request is sent with an id (a unique identifier), this method is invoked and the id from the url is passed into it.

This method takes in an id and returns a single record corresponding to that id.

Line 40 to 46

[HttpPost] - attribute means when the post request is sent by client, this attributes receives it and invoke POST method

[FromBody] - means to take the content to be posted from the body

This methods take the content form the body and inserts in the database

Add EF Migrations

Run the below command in the project folder in CLI to add Entity Framework Migration

dotnet ef migrations add InitialMigration

This generates the code that create the database from scratch. The generated file is named as **_InitialMigration** and is located in **Migrations** folder.

It contains of two methods:

Up - Create the database table(s) mentioned in the DbContext and columns from the model class UserInfo

Down - Deletes what’s created

Updating Database

dotnet ef database update

This updates the database to the latest or particular migrations

Connecting to Database with PostgreSQL DB Management Tool

  1. Open PostgresSQL database management tool → Select PostgreSQL → Click Next

  1. Fill in the details appropriately

  2. If all the details were correct, you should see Connected upon clicking est Connection.

  3. Click OK > Finish

  1. Insert a record in your database table

Please note: If your table name consists on mixed of upper and lower case letter, ensure to include quotesaround, otherwise, PostgreSQL will consider it lowercase by default and it won’t work

Testing API Using Postman

Open terminal and go to your project’s folder and run docker-compose up The above command starts all docker services.

Build and run your project in VS

Open Post man and do the following:

GET Request:

1 - URL where application is listening

2 - Type of Request

3 - Send the request (moment of truth)

4 - You should get 200 OK in response

5 - The data from the database is shown

Post Request:

1 - URL where application is listening

2 - Type of Request

3 - Switch to body

4 - Enter the content in JSON you want to insert in the database

5 - Send the request (moment of truth)

6 - You should get 200 OK in response

Now to confirm, go to the PostgreSQL DB Tool and check

As you can see, we already had one record in the table. We inserted one more (id=2) and it’s inserted successfully.

Hope, it’s working for you as well. If it’s not, feel free to get in touch and i’ll help you.

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