EF Core Fluent API

多对多配置

先安装 Install-Package MySql.Data.EntityFrameworkCore

创建3个表

创建类

    public class Role
    {
        public long Id { get; set; }

        public string Name { get; set; }
    }
	
	 public class User
    {
        public long Id { get; set; }

        public string Name { get; set; }
    }
	
	 public class UserRoleRelation
    {
        public long Id { get; set; }

        public long UserId { get; set; }

        public long RoleId { get; set; }

        public User User { get; set; }

        public Role Role { get; set; }
    }

编写DbContext，ef core的DbContext等EF的核心类在using Microsoft.EntityFrameworkCore;

public class MyDbContext : DbContext
    {
        public DbSet<User> Users { get; set; }

        public DbSet<Role> Roles { get; set; }

        public DbSet<UserRoleRelation> UserRoleRelations { get; set; }

        public DbSet<weixin_userinfo> WeixinUserinfo { get; set; }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            base.OnConfiguring(optionsBuilder);
            
            optionsBuilder.UseMySQL("Server=127.0.0.1;database=test;uid=root;pwd=123456");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);

            var typeUser = modelBuilder.Entity<User>();
            typeUser.ToTable("T_Users");

            var typeRole = modelBuilder.Entity<Role>();
            typeRole.ToTable("T_Roles");

            var typeUserRoleRelation = modelBuilder.Entity<UserRoleRelation>();
            typeUserRoleRelation.ToTable("T_UserRoleRelations");

            /**
             * 多对多:不用中间实体的多对多还不支持，要自己拆成用中间实体的两对一对多。
             * EF中（一对多）写法：builder.HasRequired(e => e.Role).WithMany();
             */
            typeUserRoleRelation.HasOne(e=>e.Role).WithMany().HasForeignKey(e=>e.RoleId).IsRequired();
            typeUserRoleRelation.HasOne(e=>e.User).WithMany().HasForeignKey(e=>e.UserId).IsRequired();

        }
    }

通过UseMySQL这样的扩展方法来配置连接字符串，这是.Net core的风格！可以把连接字符串写到配置文件中，然后再读取。

运行：

            using (MyDbContext ctx = new MyDbContext())
            {

                var user = ctx.Users.First();

                long userId = user.Id;

                var relactions = ctx.UserRoleRelations.Include(e => e.Role) 
                .Where(r => r.UserId == userId);

                foreach (var relation in relactions)
                {
                    Console.WriteLine(relation.Role.Name);
                }
            }

链接：EF Fluent API https://www.cnblogs.com/tangge/p/9831957.html

EntityTypeConfiguration

ef core 1.1

没有内置EntityTypeConfiguration，需要手动自己注册一个

IEntityTypeConfiguration.cs

using Microsoft.EntityFrameworkCore;

namespace Entity.Config
{
    public interface IEntityTypeConfiguration
    {
        void Map(ModelBuilder builder);
    }

    public interface IEntityTypeConfiguration<T> : IEntityTypeConfiguration where T : class
    {
        void Map(ModelBuilder builder);
    }
}

EntityTypeConfiguration.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace Entity.Config
{
    public abstract class EntityTypeConfiguration<T> : IEntityTypeConfiguration<T> where T : class
    {
        public abstract void Map(EntityTypeBuilder<T> builder);

        public void Map(ModelBuilder builder)
        {
            Map(builder.Entity<T>());
        }
    }
}

ModelBuilderExtenions.cs

using Microsoft.EntityFrameworkCore;

namespace Entity.Config
{
    public static class ModelBuilderExtenions
    {
        private static IEnumerable<Type> GetMappingTypes(this Assembly assembly, Type mappingInterface)
        {
            return assembly.GetTypes().Where(x => !x.GetTypeInfo().IsAbstract &&
                                                  x.GetInterfaces().Any(y => y.GetTypeInfo().IsGenericType
                                                                             && y.GetGenericTypeDefinition() ==
                                                                             mappingInterface));
        }


        public static void AddEntityConfigurationsFromAssembly(this ModelBuilder modelBuilder, Assembly assembly)
        {
            var mappingTypes = assembly.GetMappingTypes(typeof(IEntityTypeConfiguration<>));

            foreach (var config in mappingTypes.Select(Activator.CreateInstance).Cast<IEntityTypeConfiguration>())
            {
                config.Map(modelBuilder);
            }
        }
    }
}

修改MyDbContext.cs

protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);

            //modelBuilder.AddEntityConfigurationsFromAssembly(Assembly.GetEntryAssembly());//参数表示config类所在的程序集
            modelBuilder.AddEntityConfigurationsFromAssembly(Assembly.Load("Entity"));//这里加载的是 Entity程序集
			...
	    }

下面示例创建一个UserRoleRelationConfig.cs，其他自己建

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace Entity.Config
{
    public class UserRoleRelationConfig:EntityTypeConfiguration<UserRoleRelation>
    {
        public override void Map(EntityTypeBuilder<UserRoleRelation> builder)
        {
            builder.ToTable("T_UserRoleRelations");

            /**
             * 多对多:不用中间实体的多对多还不支持，要自己拆成用中间实体的两对一对多。
             * EF中（一对多）写法：builder.HasRequired(e => e.Role).WithMany();
             */
            builder.HasOne(e => e.Role).WithMany().HasForeignKey(e => e.RoleId).IsRequired();
            builder.HasOne(e => e.User).WithMany().HasForeignKey(e => e.UserId).IsRequired();
        }
    }
}

ef core 2.0

EF Core 2.0 中内置了 IEntityTypeConfiguration

  public class UserRoleRelationConfig:IEntityTypeConfiguration<UserRoleRelation>
   {
       public void Configure(EntityTypeBuilder<UserRoleRelation> builder)
       {
            builder.ToTable("T_UserRoleRelations");

            /**
             * 多对多:不用中间实体的多对多还不支持，要自己拆成用中间实体的两对一对多。
             * EF中（一对多）写法：builder.HasRequired(e => e.Role).WithMany();
             */
            builder.HasOne(e => e.Role).WithMany().HasForeignKey(e => e.RoleId).IsRequired();
            builder.HasOne(e => e.User).WithMany().HasForeignKey(e => e.UserId).IsRequired();
        }
   }