EF Core外键配置问题代码优先问题答案

【问题标题】：EF Core Foreign Key configuration problem Code First ProblemEF Core外键配置问题代码优先问题
【发布时间】：2022-01-01 06:28:51
【问题描述】：

我在应用中有 4 个表格。

User 表（来自 IdentityUser）-UserId 是 PK
Club 表：PK 为 club_id。
必须属于Club 的Team 表。 PK 为team_id + club_id。
作为用户的表Player (PK UserID)。
必须属于一个团队的表Team_Players：PK 为team_id + club_id + UserId。

当我尝试添加迁移时，我收到以下错误：

具有外键属性 {'Team_Id' : string} 的从 'Team_Players.Team' 到 'Team' 的关系不能以主键 {'Team_Id' : string, 'Club_Id' : string} 为目标，因为它不兼容。为此关系配置一个主键或一组兼容的外键属性。

非常感谢您的帮助。

这是类的代码：

public class Club : BaseModel
{
        [Display(Name = "ID")]
        [Required]
        [Key]
        public string Club_id { get; set; }
}

public class Team : BaseModel
{
        [Display(Name = "ID")]
        [Required]
        public string Team_Id { get; set; }

        [ForeignKey("Club_Id")]
        public Club Club { get; set; }

        [Required]
        [Display(Name = "Club")]
        [MaxLength(50, ErrorMessage = "Field cannot be more than 50 Characters")]
        public string Club_Id  { get; set; }
}    

public class Player : BaseModel
{
        [Required]
        [Display(Name = "ID")]
        public string UserId { get; set; }
     
        [ForeignKey("Club_Id")]
        public Team Club { get; set; }

        [Required]
        [Display(Name = "Club ID")]
        [MaxLength(50, ErrorMessage = "Field cannot be more than 50 Characters")]
        public string Club_Id { get; set; }
}

public class Team_Players:BaseModel
{
        [Required]
        [Display(Name = "ID")]
        public string UserId { get; set; }

        [ForeignKey("Club_Id")]
        public Club Club { get; set; }

        [Display(Name = "Club ID")]
        [MaxLength(50, ErrorMessage = "Field cannot be more than 50 Characters")]
        public string Club_Id { get; set; }

        [ForeignKey("Team_Id")]
        public Team Team { get; set; }
        [Display(Name = "Team ID")]
        public string Team_Id { get; set; }
}

最后我的OnModelCreating 方法有以下代码：

modelBuilder.Entity<Team>()
                .HasKey(e => new { e.Team_Id, e.Club_Id});

modelBuilder.Entity<Coach>()
                .HasKey(e => new { e.UserId, e.Club_Id });

modelBuilder.Entity<Player>()
               .HasKey(e => new { e.UserId, e.Club_Id });

modelBuilder.Entity<Team_Players>()
               .HasKey(e => new { e.UserId, e.Club_Id ,e.Team_Id});

【问题讨论】：

标签： entity-framework ef-code-first

【解决方案1】：

外键以键为目标，而不仅仅是键的一部分。所以

[ForeignKey("Team_Id")]
public Team Team { get; set; }

应该是

[ForeignKey("Team_Id, Club_Id")]
public Team Team { get; set; }

因为

Entity<Team>().HasKey(e => new { e.Team_Id, e.Club_Id});

【讨论】：