EF Core Fluent API

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();

        }
    }

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

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