首先使用EF Core 2.0代码将2个外键作为主键

问题描述

我有两个表：评论和赞。

。

4) The User and Comment classes also have navigation properties (since it's one side of one-to-many relations): Likes.
 5）最后，总是使用 Table 属性可避免出现复数问题，因为将其关闭。
5) Finally, always use Table attribute to avoid problems with pluralizations because there's no way to turn it off.
[Table("Comment")]
public class Comment
{
    public int CommentID { get; set; }
    public List<Like> Likes { get; set; }
}

[Table("User")]
public class User
{
    public int UserId { get; set; }
    public List<Like> Likes { get; set; }
}

[Table("Like")]
public class Like
{
    [Key]
    [Column(Order = 1)]
    public int CommentID { get; set; }
    [Key]
    [Column(Order = 2)]
    public int UserID { get; set; }

    [ForeignKey("CommentId")]
    public Comment Comment { get; set; }
    [ForeignKey("UserId")]
    public User User { get; set; }
}
 更新 
 在EF Core中设置复合键 
 键（和 Column ）属性（用于指定复合主键）实际上在EF Core中不起作用-它们在EF6中起作用。要在EF Core中配置组合键，您需要使用Fluent Configuration。
The Key (and Column) attributes, used to designate composite primary key, actually, don't work in EF Core - they work in EF6. To configure composite key in EF Core, you need to use Fluent Configuration.
您有两种选择。
 选项1。在 OnModelCreatingMethod 中进行所有配置：
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Like>().HasKey(l => new { l.CommentID, l.UserID });
}
 选项2。将所有配置移到单独的位置类并将其应用于 OnModelCreating ：
OPTION 2. Move all the configuration into separate class and apply it in OnModelCreating:
 1）创建用于配置的单独类
1) Create separate class for configuration
class LikeConfiguration : IEntityTypeConfiguration<Like>
{
    public void Configure(EntityTypeBuilder<Like> builder)
    {
        builder.HasKey(l => new { l.CommentID, l.UserID });
    }
}
 2）应用配置：
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.ApplyConfiguration(new LikeConfiguration());
}
选择任何您喜欢的选项。
Choose any option you like.
如您所见，要在Fluent Configuration中配置组合键，您需要使用。同样，属性的顺序很重要。
As you see, to configure composite key in Fluent Configuration, you need to use anonymous type. And again, the order of properties matters.
                        
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