.net core 1.1 entityframework 和 mysql 数据库连接

Question

我正在安装 vs 2017 并尝试使用 .net core 1.1、entity framework 和我的 sql 数据库创建一个测试 Web api 项目。

下面是我正在使用的包列表

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Folder Include="wwwroot\" />
  </ItemGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.ApplicationInsights.AspNetCore" Version="2.0.0" />
    <PackageReference Include="Microsoft.AspNetCore" Version="1.1.2" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="1.1.3" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="1.1.2" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.0.0-preview1-final" />
    <PackageReference Include="Microsoft.Extensions.Logging.Debug" Version="1.1.2" />
    <PackageReference Include="MySql.Data.EntityFrameworkCore" Version="7.0.7-m61" />
    <PackageReference Include="Pomelo.EntityFrameworkCore.MySql" Version="1.1.2" />
  </ItemGroup>
  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="1.0.1" />
  </ItemGroup>

</Project>

并且 dbcontext class 是

public class NorthWindDBContext : DbContext
    {
        public NorthWindDBContext()
        //: base(options)
        { }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            var builder = new ConfigurationBuilder()
                       .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);

            var configuration = builder.Build();

            string connectionString = configuration.GetConnectionString("northwindConnection");
            optionsBuilder.UseMySql(connectionString);
        }


        public virtual DbSet<Customers> Customers { get; set; }
        public virtual DbSet<Categories> Categories { get; set; }
        public virtual DbSet<Products> Products { get; set; }
        public virtual DbSet<Orders> Orders { get; set; }
        public virtual DbSet<Order_Details> Order_Details { get; set; }



    }

但是当我尝试 运行 时发生异常

System.InvalidOperationException: 'The entity type 'Categories' requires a primary key to be defined.'

我不明白怎么回事。

请帮忙

更新 1 下面是类别模型

public class Categories
    {
        [Key]
        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
        public string Description { get; set; }
        public byte Picture { get; set; }  

    }

我已经在 MySql 中创建了数据库。

更新 2

 public class Categories
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]        
        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
        public string Description { get; set; }
        public byte Picture { get; set; }


    }

更新 3

public class Categories
    {
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        [Key]
        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
        public string Description { get; set; }
        public byte Picture { get; set; }
    }

Answer 1

The entity type 'Categories' requires a primary key to be defined.

Entity Framework 需要主键才能工作。有两种方法可以做到这一点（据我所知）。

• Data Annotations
• Fluent API

例如

//Data Annotations
public class EmployeeEntity : BaseEntity
{
    // Denotes the primary key column
    [Key]
    // Add this if your column is not auto-generated
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public short Id { get; set; }

    public string Name { get; set; }

    // more fields, probably
}

// Fluent API
public partial class EmployeeMap : EntityTypeConfiguration<EmployeeEntity>
{
    public EmployeeMap()
    {
        ToTable("employee");
        HasKey(emp => emp.Id)
          .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
    }
}

请注意，如果您的主键不是自动生成的，您需要使用您选择的任何方法告诉 EF。

注解：[DatabaseGenerated(DatabaseGeneratedOption.None)]
流利：HasKey(emp => emp.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);