ASP.NET Core 2.x – Add a DbContext

Index:

1. Example entity model
2. Install NuGet packages
3. Create context class
4. Update Startup.cs
5. Example connection string
6. Add-Migration
7. Update-Database
8. Seed data

Example entity model

using System.ComponentModel.DataAnnotations;

namespace MyProject.Models
{
    public class Customer
    {
        [Key]
        public long CustomerId { get; set; }
        public string Name { get; set; }
        public DateTime? FirstPurchaseDate { get; set; }
    }
}

Read about the [Key] annotation and others here

Install NuGet packages (the Identity packages are only necessary if your app is managing identities, I think)

<PackageReference Include="Microsoft.AspNetCore.App" />
<PackageReference Include="Microsoft.AspNetCore.Identity" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="2.2.0" />
<PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.2.0" />

Create your context class that inherits from DbContext. I like to put my context class in a folder named “Data” at the root of my project.

using Microsoft.EntityFrameworkCore;
using MyProject.Models;

namespace MyProject.Data
{
    public class ApplicationDbContext : DbContext
    {
        public MyProjectDbContext(DbContextOptions<MyProjectDbContext> options) : base(options)
        {

        }

        // Add DbSet for each entity class
        public DbSet<Customer> Customer { get; set; }
    }
}

Call services.AddDbContext<>(...); in Startup.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using System;
using MyProject.Data;

namespace MyProject
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            // ...

            services.AddDbContext<MyProjectDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

            // ...
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ...)
        {
            // ...
        }

    }
}

Example appsettings.json connection string (the database it points to doesn’t need to exist, but the connection string needs to exist for Add-Migration to work )

"ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\\MSSQLLocalDB;Database=_CHANGE_ME;Trusted_Connection=True;MultipleActiveResultSets=true"
 }

TODO: Add-Migration

TODO: Update-Database

TODO: Initialization code, like seed data