entity-framework - Code First - 两个外键作为主键，无法添加迁移

Question

我的用户表:

public class User
    {
        [Key]
        public int UserId { get; set; }

        public virtual ICollection<PollVote> PollVotes { get; set; }
    }

我的投票表:

public class Poll
    {
        [Key]
        public int PollId { get; set; }

        public virtual ICollection<PollVote> PollVotes { get; set; }
    }

我的投票表

public class PollVote
    {
        [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]        
        public int VoteId { get; set; }

        [Key]
        public int PollId { get; set; }

        [Key]
        public int UserId { get; set; }

        public DateTime TimeVoted { get; set; }
        public int Answer { get; set; }

        public virtual Poll Poll { get; set; }
        public virtual User User { get; set; }
    }

我的配置:

//User config:
             this.HasMany(x => x.PollVotes)
                .WithRequired()
                .HasForeignKey(x => x.UserId)
                .WillCascadeOnDelete(false);

//Poll Config
            this.HasMany(x => x.PollVotes)
                .WithRequired()
                .HasForeignKey(x => x.PollId)
                .WillCascadeOnDelete(false);

//PollVote Config
            this.HasKey(x => x.UserId)
                .HasRequired(x => x.User)
                .WithMany()
                .HasForeignKey(x => x.UserId);
            this.HasKey(x => x.PollId)
                .HasRequired(x => x.Poll)
                .WithMany()
                .HasForeignKey(x => x.PollId);

关系是:一次投票可以有很多票，但是一个用户每次投票只能投一票。

当我尝试在 PM-Console 中 Add-Migration 时出现此错误

\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'PollVote_Poll_Source' in relationship 'PollVote_Poll'. Because the Dependent Role refers to the key properties, the upper bound of the multiplicity of the Dependent Role must be '1'. \tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'Poll_PollVotes_Target' in relationship 'Poll_PollVotes'. Because the Dependent Role refers to the key properties, the upper bound of the multiplicity of the Dependent Role must be '1'.

有什么建议吗？

Answer 1

您可以通过添加 [Column] 来指定复合键属性到数据注释...

    [Key, Column(Order = 1)]
    public int PollId { get; set; }

    [Key, Column(Order = 2)]
    public int UserId { get; set; }

...或者通过 Fluent API 使用匿名对象:

this.HasKey(x => new { x.UserId, x.PollId });

this.HasRequired(x => x.User)
    .WithMany(u => u.PollVotes)
    .HasForeignKey(x => x.UserId);

this.HasRequired(x => x.Poll)
    .WithMany(p => p.PollVotes)
    .HasForeignKey(x => x.PollId);

不要忘记 WithMany 中反向导航属性的 lambda 表达式，如上图，去掉UserConfig中多余的配置和 PollConfig .