C#&.NET Core应用程序中EF Core是否可以通过一个方法返回不同类型的对象？

1 个回答

• 0

  按照问题的描述，可以创建一个泛型的方法来实现一个方法返回不同类型的对象，这是一种泛型仓储的架构模式。
  这里我用EF Core InMemoryDatabase数据提供程序做了一个简单的示例。

  1.安装NuGet程序包

  在项目中使用NuGet程序包管理工具或命令行安装依赖包：Microsoft.EntityFrameworkCore.InMemory

  2.创建MyDbContext.cs数据库连接上下文

  using ConsoleApp2.Models;
  using Microsoft.EntityFrameworkCore;
  
  namespace ConsoleApp2
  {
      internal class MyDbContext : DbContext
      {
          public MyDbContext()
          {
          }
  
          protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
          {
              optionsBuilder.UseInMemoryDatabase("DemoDatabase");
          }
  
          public virtual DbSet<Customer> Customers { get; set; }
          public virtual DbSet<Order> Orders { get; set; }
          public virtual DbSet<Address> Addresses { get; set; }
      }
  }
  

  3.创建实体类

  Address.cs

  namespace ConsoleApp2.Models
  {
      public class Address
      {
          public int Id { get; set; }
          public string Province { get; set; }
          public string City { get; set; }
          public string District { get; set; }
          public string Street1 { get; set; }
          public string Street2 { get; set; }
          public string MobilePhone { get; set; }
      }
  }
  

  Customer.cs

  using System;
  using System.Collections.Generic;
  
  namespace ConsoleApp2.Models
  {
      public class Customer
      {
          public Customer()
          {
              CreatedAt = DateTime.Now;
              Addresses = new HashSet<Address>();
          }
          public int Id { get; set; }
          public string FirstName { get; set; }
          public string LastName { get; set; }
          public string Username { get; set; }
          public string Gender { get; set; }
          public DateTime CreatedAt { get; set; }
          public ICollection<Address> Addresses { get; set; }
      }
  }
  

  Order.cs

  using System;
  
  namespace ConsoleApp2.Models
  {
      public class Order
      {
          public long Id { get; set; }
          public string OrderNo { get; set; }
          public DateTime PurchasedAt { get; set; }
          public double Amount { get; set; }
          public virtual Customer Customer { get; set; }
      }
  }
  

  4.添加示例数据

  DataGenerator.cs

  using ConsoleApp2.Models;
  using System;
  using System.Collections.Generic;
  
  namespace ConsoleApp2
  {
      public class DataGenerator
      {
          public static void Init()
          {
              using var db = new MyDbContext();
              var addresses = new List<Address>
              {
                  new Address { Province = "重庆", City = "重庆", District="江北区",Id=1,Street1="观音桥",MobilePhone="10000"}
              };
              db.Addresses.AddRange(addresses);
              var customer = new Customer
              {
                  Id = 1,
                  FirstName = "刘",
                  LastName = "先生",
                  Username = "rector",
                  Gender = "男",
                  Addresses = addresses
              };
              db.Customers.Add(customer);
              db.Orders.Add(new Order
              {
                  Id = 10000,
                  OrderNo = DateTime.Now.ToString("yyyyMMddHHmmssfff"),
                  Customer = customer,
                  Amount = 3999.99,
                  PurchasedAt = DateTime.Now
              });
              var i = db.SaveChanges(true);
              Console.WriteLine("数据初始化完成.");
          }
      }
  }
  

  最后，再创建一个DbContext的静态类，并在其中创建泛型静态扩展方法，如下：

  using Microsoft.EntityFrameworkCore;
  
  namespace ConsoleApp2
  {
      public static class DbContextExtension
      {
          /// <summary>
          /// 根据ID获取实体对象
          /// </summary>
          /// <typeparam name="TEntity"></typeparam>
          /// <param name="context"></param>
          /// <param name="id"></param>
          /// <returns></returns>
          public static TEntity GetById<TEntity>(this DbContext context, object id) where TEntity : class
          {
              return context.Set<TEntity>().Find(id);
          }
      }
  }
  

  这里只创建了一个名为GetById<TEntity>()的泛型方法，在调用此方法中，指定的TEntity是什么类型，返回的即为什么类型，测试代码如下：

  using ConsoleApp2.Models;
  using System;
  using System.Text.Encodings.Web;
  using System.Text.Json;
  using System.Text.Unicode;
  
  namespace ConsoleApp2
  {
      internal class Program
      {
          static void Main(string[] args)
          {
              DataGenerator.Init();
              JsonSerializerOptions options = new JsonSerializerOptions
              {
                  Encoder = JavaScriptEncoder.Create(UnicodeRanges.BasicLatin, UnicodeRanges.CjkUnifiedIdeographs)
              };
              using var db = new MyDbContext();
              var address = db.GetById<Address>(1);
              Console.WriteLine(JsonSerializer.Serialize(address, options));
  
              var customer = db.GetById<Customer>(1);
              Console.WriteLine(JsonSerializer.Serialize(customer, options));
  
              var order = db.GetById<Order>(10000L);
              Console.WriteLine(JsonSerializer.Serialize(order, options));
  
              Console.ReadKey();
          }
      }
  }
  

  运行结果如图：

  

  评论 分享

  

  Rector

  2021-10-14 回答