範例：ASP.NET Core 2.0 DI & EntityFrameworkCore & Repository Pattern

假設建立了一個 DbContext 叫做 TempDbContext

    public class TempDbContext : DbContext
    {
        public TempDbContext(DbContextOptions<TempDbContext> options)  : base(options)
        {

        }

        public DbSet<Product> Products { get; set; }
    }

IRepository<T> 為一些常用操作(例如CRUD)的 interface

IProductRepository 為操作 Product 的 interface，並包含了IRepository<T>

    public interface IRepository<T> where T : class
    {
        IEnumerable<T> GetAll();
        IEnumerable<T> Find(Func<T, bool> predicate);
        T GetById(int id);
        void Create(T entity);
        void Update(T entity);
        void Detele(T entity);
        int Count(Func<T, bool> predicate);
    }

    public interface IProductRepository : IRepository<Product>
    {
        // 一些操作 Product 的方法
        Product GetProductByName(string name);
    }

實作 IRepository<T>

    public class Repository<T> : IRepository<T> where T : class
    {
        // 會利用 ASP.NET Core 2.0 的 DI 注入實例
        protected readonly TempDbContext _context;
        public Repository(TempDbContext context)
        {
            _context = context;
        }
        public void Save() => _context.SaveChanges();

        public int Count(Func<T, bool> predicate)
        {
            return _context.Set<T>().Where(predicate).Count();
        }

        public void Create(T entity)
        {
            _context.Add(entity);
            Save();
        }

        public void Detele(T entity)
        {
            _context.Remove(entity);
            Save();
        }

        public IEnumerable<T> Find(Func<T, bool> predicate)
        {
            return _context.Set<T>().Where(predicate);
        }

        public IEnumerable<T> GetAll()
        {
            return _context.Set<T>();
        }

        public T GetById(int id)
        {
            return _context.Set<T>().Find(id);
        }

        public void Update(T entity)
        {
            _context.Entry(entity).State = EntityState.Modified;
            Save();
        }
    }

實作 IProductRepository，也繼承 Repository<Product>

    public class ProductRepository : Repository<Product>, IProductRepository
    {
        public ProductRepository(TempDbContext context) : base(context)
        {
        }

        public Product GetProductByName(string name)
        {
            return _context
                .Products
                .Where(p => p.Name == name)
                .FirstOrDefault();
        }
    }

ASP.NET Core 2.0 DI 設定(Startup)

        public void ConfigureServices(IServiceCollection services)
        {
            // Repository 建構子需要 DbContext
            services.AddDbContext<TempDbContext>(options => options.UseInMemoryDatabase("TempContext"));
            services.AddTransient<IProductRepository, ProductRepository>();
            services.AddMvc();
        }

在 Controller 中使用 Repository

    [Route("api/[controller]")]
    public class ProductController : Controller
    {
        private readonly IProductRepository _productRepository;

        public ProductController(IProductRepository productRepository)
        {
            _productRepository = productRepository;
        }
    }

==========
Debug：
在執行時發生了這個錯誤

Additional information: No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions object in its constructor and passes it to the base constructor for DbContext.

確定在ConfigureServices有設定DbContext的注入，後來發現是TempDbContext的建構子忘了呼叫base(options)