EF Code First with Dependency Injection

Demonstrates how to add DI to IDesignTimeDbContextFactory implementation so that the EF Core CLI will pick up the connection string via DI and Config.

Prerequisites

• .NET Core SDK
  • https://dotnet.microsoft.com/download/
  • This demo uses .NET Core 2.2.

ASPNET Core Web API Setup

1. Create a new Visual Studio solution and add a global.json file with the SDK version.

   • Open a command prompt at the solution root.
   • Enter and run: dotnet new globaljson
   • Add an existing item to the solution and select the global.json file.
   • Verify that the SDK version matches that which you previously installed.

2. Add an ASP.NET Core Web API project.

   • Use .Web suffix.

3. Add a .NET Standard Class Library project for entities.

   • Use .Entities suffix.
   • Add a Product class.

   public class Product
   {
       public int Id { get; set; }
       public string ProductName { get; set; }
       public decimal UnitPrice { get; set; }
   }

4. Add a .NET Standard Class Library project for repository interfaces.

   • Use .Abstractions suffix.
   • Reference the Entities project.
   • Add IProductRepository interface.

   public interface IProductRepository
   {
       Task<Product> GetProduct(int id);
   }

5. Add a .NET Standard Class Library for EF context and repositories.

   • Use .EF suffix.
   • Reference Entities and Abstractions projects.
   • Add Microsoft.EntityFrameworkCore.Sql NuGet package.
   • Add ProductsDbContext class.
     • Include ctor that accepts DbContextOptions.
     • Override OnModelCreating to seed data.

   public class ProductsDbContext : DbContext
   {
       public ProductsDbContext(DbContextOptions options) : base(options) { }
   
       public DbSet<Product> Products { get; set; }
   
       protected override void OnModelCreating(ModelBuilder modelBuilder)
       {
           var product = new Product
           {
               Id = 1,
               ProductName = "Chai",
               UnitPrice = 10
           };
           modelBuilder.Entity<Product>().HasData(product);
       }
   }

   • Add ProductRepository class.
     • Add ctor accepting ProductsDbContext.

   public class ProductRepository : IProductRepository
   {
       public ProductsDbContext Context { get; }
   
       public ProductRepository(ProductsDbContext context)
       {
           Context = context;
       }
   
       public async Task<Product> GetProduct(int id)
       {
           return await Context.Products.SingleOrDefaultAsync(e => e.Id == id);
       }
   }

6. Add a connection string to the appsettings files in the Web project.

   • Use different database names to simulate Dev vs Prod deployments.
   • Add the following to appsettings.json:

   "ConnectionStrings": {
       "ProductsDbContext": "Data Source=(localdb)\\MsSqlLocalDb;initial catalog=ProductsDbProd;Integrated Security=True; MultipleActiveResultSets=True"
   }

   • Add the following to appsettings.Development.json:

   "ConnectionStrings": {
       "ProductsDbContext": "Data Source=(localdb)\\MsSqlLocalDb;initial catalog=ProductsDbPDev;Integrated Security=True; MultipleActiveResultSets=True"
   }

7. Configure DI in the Web project.

   • Add Microsoft.EntityFrameworkCore.Sql NuGet package.
   • Add references to the Entities, Abstractions and EF projects.
   • Update ConfigureServices in Startup to register ProductsDbContext with the DI system.

   services.AddDbContext<ProductsDbContext>(options =>
       options.UseSqlServer(Configuration.GetConnectionString(nameof(ProductsDbContext))));
   services.AddScoped<IProductRepository, ProductRepository>();

8. Refactor ValuesController in the Web project to use IProductRepository to retrieve a product by id.

   • Rename to ProductsController
   • Add ctor accepting IProductRepository.

   public IProductRepository ProductsRepo { get; }
   
   public ProductsController(IProductRepository productsRepo)
   {
       ProductsRepo = productsRepo;
   }

   • Remove all methods except Get(int id).
   • Refactor Get method.

   // GET api/products/5
   [HttpGet("{id}")]
   public async Task<ActionResult<Product>> Get(int id)
   {
       var product = await ProductsRepo.GetProduct(id);
       return Ok(product);
   }

Initial EF Core Code First Setup

1. Add a .NET Core Class Library project with a .EF.Design suffix.

   • This needs to be a .NET Core, versus .NET Standard, project in order to support the EF Core CLI tooling.

   • Add the following NuGet packages:
     Microsoft.EntityFrameworkCore.Design
     Microsoft.EntityFrameworkCore.SqlServer

   • Add a ProductsDbContextFactory class that implements IDesignTimeDbContextFactory<ProductsDbContext>.

   public class ProductsDbContextFactory : IDesignTimeDbContextFactory<ProductsDbContext>
   {
       public ProductsDbContext CreateDbContext(string[] args)
       {
           var optionsBuilder = new DbContextOptionsBuilder<ProductsDbContext>();
           var connectionString = "Data Source=(localdb)\\MsSqlLocalDb;initial catalog=ProductsDbDev;Integrated Security=True; MultipleActiveResultSets=True";
           optionsBuilder.UseSqlServer(connectionString, b => b.MigrationsAssembly("EfDesignDemo.EF.Design"));
           return new ProductsDbContext(optionsBuilder.Options);
       }
   }

2. This should be sufficient to generage a code migration and create a database.

   • Run the following from the EF.Design project directory.

   dotnet ef migrations add initial
   

   • Then run the following to create the database.

   dotnet ef database update
   

3. Try running the application.

   • First cd into the Web application directory.

   dotnet run
   

   • Then browse to: http://localhost:5000/api/products/1
     • A product should be retrieved from the database.

   {
       id: 1,
       productName: "Chai",
       unitPrice: 10
   }

   • Press Ctrl+C to terminate the running app.

Refactored EF Core Code First Setup

1. Refactor ProductsDbContextFactory to retrieve the connection string from the appsettings.*.json file.

   • This depends on the value of the ASPNETCORE_ENVIRONMENT environment variable.

   public class ProductsDbContextFactory : IDesignTimeDbContextFactory<ProductsDbContext>
   {
       public ProductsDbContext CreateDbContext(string[] args)
       {
           // Get environment
           string environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
   
           // Build config
           IConfiguration config = new ConfigurationBuilder()
               .SetBasePath(Path.Combine(Directory.GetCurrentDirectory(), "../EfDesignDemo"))
               .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
               .AddJsonFile($"appsettings.{environment}.json", optional: true)
               .AddEnvironmentVariables()
               .Build();
   
           // Get connection string
           var optionsBuilder = new DbContextOptionsBuilder<ProductsDbContext>();
           var connectionString = config.GetConnectionString(nameof(ProductsDbContext));
           optionsBuilder.UseSqlServer(connectionString, b => b.MigrationsAssembly("EfDesignDemo.EF.Design"));
           return new ProductsDbContext(optionsBuilder.Options);
       }
   }

2. From the EF.Design project directory run dotnet ef database update.

   • This time the ProductsDbProd database should be created from the connection string in appsettings.json.
   • This is because the ASPNETCORE_ENVIRONMENT environment variable is not set.

3. Try setting ASPNETCORE_ENVIRONMENT on the command line before running dotnet ef database update.

   set ASPNETCORE_ENVIRONMENT=Development
   dotnet ef database update
   

   • First delete the ProductsDbDev database.
   • This time the ProductsDbDev database should be created.

Add Some DI Love

1. Add some interfaces to the to the .Abstractions project.

   • Add a IConfigurationService interface.
     • Add the Microsoft.Extensions.Configuration.Abstractions NuGet package.

   public interface IConfigurationService
   {
       IConfiguration GetConfiguration();
   }

   • Add a IEnvironmentService interface.

   public interface IEnvironmentService
   {
       string EnvironmentName { get; set; }
   }

2. Add a .Configuration .NET Standard Class Library project to the solution.

   • Add the following NuGet packages:

   Microsoft.Extensions.Configuration
   Microsoft.Extensions.Configuration.EnvironmentVariables
   Microsoft.Extensions.Configuration.Json
   

   • Reference the .Abstractions project.
   • Add an EnvironmentService class.

   public class EnvironmentService : IEnvironmentService
   {
       public EnvironmentService()
       {
           EnvironmentName = Environment.GetEnvironmentVariable(Constants.EnvironmentVariables.AspnetCoreEnvironment)
               ?? Constants.Environments.Production;
       }
   
       public string EnvironmentName { get; set; }
   }

   • Add an ConfigurationService class.

   public class ConfigurationService : IConfigurationService
   {
       public IEnvironmentService EnvService { get; }
       public string CurrentDirectory { get; set; }
   
       public ConfigurationService(IEnvironmentService envService)
       {
           EnvService = envService;
       }
   
       public IConfiguration GetConfiguration()
       {
           CurrentDirectory = CurrentDirectory ?? Directory.GetCurrentDirectory();
           return new ConfigurationBuilder()
               .SetBasePath(CurrentDirectory)
               .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
               .AddJsonFile($"appsettings.{EnvService.EnvironmentName}.json", optional: true)
               .AddEnvironmentVariables()
               .Build();
       }
   }

3. Add a .DI .NET Standard Class Library project.

   • Add the following NuGet packages.

   Microsoft.EntityFrameworkCore.Design
   Microsoft.EntityFrameworkCore.SqlServer
   

   • Add references to the .EF,** .Abstractions**, .Configuration projects.
   • Add a DependencyResolver class.

   public class DependencyResolver
   {
       public IServiceProvider ServiceProvider { get; }
       public string CurrentDirectory { get; set; }
   
       public DependencyResolver()
       {
           // Set up Dependency Injection
           IServiceCollection services = new ServiceCollection();
           ConfigureServices(services);
           ServiceProvider = services.BuildServiceProvider();
       }
   
       private void ConfigureServices(IServiceCollection services)
       {
           // Register env and config services
           services.AddTransient<IEnvironmentService, EnvironmentService>();
           services.AddTransient<IConfigurationService, ConfigurationService>
               (provider => new ConfigurationService(provider.GetService<IEnvironmentService>())
               {
                   CurrentDirectory = CurrentDirectory
               });
   
           // Register DbContext class
           services.AddTransient(provider =>
           {
               var configService = provider.GetService<IConfigurationService>();
               var connectionString = configService.GetConfiguration().GetConnectionString(nameof(ProductsDbContext));
               var optionsBuilder = new DbContextOptionsBuilder<ProductsDbContext>();
               optionsBuilder.UseSqlServer(connectionString, builder => builder.MigrationsAssembly("EfDesignDemo.EF.Design"));
               return new ProductsDbContext(optionsBuilder.Options);
           });
       }
   }

4. Add a reference from the .EF.Design project to the .DI project.

   • Refactor the ProductsDbContextFactory to use the DependencyResolver to create the DbContext.

   public class ProductsDbContextFactory : IDesignTimeDbContextFactory<ProductsDbContext>
   {
       public ProductsDbContext CreateDbContext(string[] args)
       {
           // Get DbContext from DI system
           var resolver = new DependencyResolver
           {
               CurrentDirectory = Path.Combine(Directory.GetCurrentDirectory(), "../EfDesignDemo.Web")
           };
           return resolver.ServiceProvider.GetService(typeof(ProductsDbContext)) as ProductsDbContext;
       }
   }