准备三个Model

League

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text;
namespace Demo.Domain
{
    public class League
    {
        public int Id { get; set; }
        [Required]
        [MaxLength(100)]
        public string Name { get; set; }
        [Required,MaxLength(100)]
        public string Country { get; set; }
    }
}

Club

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;
namespace Demo.Domain
{
    public class Club
    {
        public Club()
        {
            Players = new List<Player>();
        }
        public int Id { get; set; }
        public string Name { get; set; }
        public string City { get; set; }
        [Column(TypeName ="date")]
        public DateTime DateOfEstablishment { get; set; }
        public string History { get; set; }
        public League League { get; set; }
        public List<Player> Players { get; set; }
    }
}

Player

using System;
using System.Collections.Generic;
namespace Demo.Domain
{
    public class Player
    {
        public Player()
        {
            GamePlayers = new List<GamePlayer>();   //避免空指针异常
        }
        public int Id { get; set; }
        public string Name { get; set; }
        public DateTime DateOfBirth { get; set; }
        public List<GamePlayer> GamePlayers { get; set; }
        //与Resume建立一对一的关系
        public int ResumeId { get; set; }
        public Resume Resume { get; set; }
    }
}

源代码EFCoreDemo3.x.zip