EF Core 5.x 如何配置两实体间多个带关联实体的多对多关系

实现方案 #

你可以利用EF Core的共享实体类型特性，仅定义一个通用关联类，同时映射为两个独立的数据库关联表，完全消除代码冗余。

步骤1：定义通用关联实体 #

public class GameCard
{
    public int GameId { get; set; }
    public Game Game { get; set; }
    
    public int Order { get; set; }

    public int CardId { get; set; }
    public Card Card { get; set; }
}

步骤2：调整业务实体属性 #

public class Game
{
    [Key]
    public int Id { get; set; }
    
    // 直接使用通用关联类作为导航属性类型
    public ICollection<GameCard> Deck { get; set; }
    public ICollection<GameCard> OnTable { get; set; }
    
    [Required]
    public int CardIndex { get; set; }
    
    [Required]
    public int PlayerId { get; set; }
    [Required]
    public Player Player { get; set; }
}

public class Card : IEntity
{
    [Key]
    public int Id { get; set; }

    [Required]
    public Shape Shape { get; set; }
    [Required]
    public Fill Fill { get; set; }
    [Required]
    public Color Color { get; set; }
    [Required]
    public int NrOfShapes { get; set; }
    
    // 分别对应两组多对多关系的导航
    public ICollection<GameCard> DeckCards { get; set; }
    public ICollection<GameCard> TableCards { get; set; }
}

步骤3：配置模型映射 #

在OnModelCreating中把同一个GameCard类分别映射为两个不同的数据库实体，对应两张独立的关联表：

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

    // 配置第一组：牌堆关联，映射到DeckGameCards表
    modelBuilder.Entity<GameCard>("DeckGameCard", builder =>
    {
        builder.ToTable("DeckGameCards");
        builder.HasKey(x => new {x.GameId, x.CardId});
        builder.HasOne(gc => gc.Card)
            .WithMany(c => c.DeckCards)
            .HasForeignKey(gc => gc.CardId);
        builder.HasOne(gc => gc.Game)
            .WithMany(g => g.Deck)
            .HasForeignKey(gc => gc.GameId);
    });

    // 配置第二组：桌面关联，映射到TableGameCards表
    modelBuilder.Entity<GameCard>("TableGameCard", builder =>
    {
        builder.ToTable("TableGameCards");
        builder.HasKey(x => new {x.GameId, x.CardId});
        builder.HasOne(gc => gc.Card)
            .WithMany(c => c.TableCards)
            .HasForeignKey(gc => gc.CardId);
        builder.HasOne(gc => gc.Game)
            .WithMany(g => g.OnTable)
            .HasForeignKey(gc => gc.GameId);
    });
}

配置完成后生成迁移，EF会自动创建两张结构完全独立的关联表，使用方式和你之前两套关联实体的用法完全一致。

内容的提问来源于stack exchange，提问作者Joris L