实体框架代码首先对现有表进行多个安装 [英] Entity Framework Code First Many to Many Setup For Existing Tables

问题描述

我有以下表格 Essence ， EssenseSet 和 Essense2EssenceSet

Essense2EssenceSet 是创建M：M关系的链接表。

Essense2EssenceSet is the linking table that creates the M:M relationship.

我已经无法通过EF代码获得M：M关系。

I've been unable to get the M:M relationship working though in EF code first though.

这是我的代码： p>

Here's my code:

[Table("Essence", Schema = "Com")]
    public class Essence
    {
        public int EssenceID { get; set; }
        public string Name { get; set; }
        public int EssenceTypeID { get; set; }
        public string DescLong { get; set; }
        public string DescShort { get; set; }
        public virtual ICollection<EssenceSet> EssenceSets { get; set; }
        public virtual EssenceType EssenceType { get; set; }
    }

    [Table("EssenceSet", Schema = "Com")]
    public class EssenceSet
    {
        public int EssenceSetID { get; set; }
        public int EssenceMakerID { get; set; }
        public string Name { get; set; }
        public string DescLong { get; set; }
        public string DescShort { get; set; }

        public virtual ICollection<Essence> Essences { get; set; }
    }

[Table("Essence2EssenceSet", Schema = "Com")]
    public class Essence2EssenceSet
    {
        //(PK / FK)
        [Key] [Column(Order = 0)] [ForeignKey("Essence")] public int EssenceID { get; set; }
        [Key] [Column(Order = 1)] [ForeignKey("EssenceSet")] public int EssenceSetID { get; set; }

        //Navigation
        public virtual Essence Essence { get; set; }
        public virtual EssenceSet EssenceSet { get; set; }
    }
            public class EssenceContext : DbContext
            {
                public DbSet<Essence> Essences { get; set; }
                public DbSet<EssenceSet> EssenceSets { get; set; }
                public DbSet<Essence2EssenceSet> Essence2EssenceSets { get; set; }

                protected override void OnModelCreating(DbModelBuilder mb)
                {
                    mb.Entity<Essence>()
                        .HasMany(e => e.EssenceSets)
                        .WithMany(set => set.Essences)
                        .Map(mc =>
                            {
                                mc.ToTable("Essence2EssenceSet");
                                mc.MapLeftKey("EssenceID");
                                mc.MapRightKey("EssenceSetID");
                            });
                }
        }

这是我要运行的代码：

This is the code I'm trying to run:

    Essence e = new Essence();
                            e.EssenceTypeID = (int)(double)dr[1];
                            e.Name          = dr[2].ToString();
                            e.DescLong      = dr[3].ToString();

                            //Get Essence Set
                            int setID = (int)(double)dr[0];
                            var set = ctx.EssenceSets.Find(setID);
                            e.EssenceSets = new HashSet<EssenceSet>();
                            e.EssenceSets.Add(set);
                            ctx.Essences.Add(e);
ctx.SaveChanges();

这里是错误：

strong>在保存不暴露其关系的外键属性的实体时发生错误。 EntityEntries属性将返回null，因为单个实体不能被识别为异常的来源。

An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception.

我无法找到问题。我非常感谢帮助设置正确。
谢谢！

I'm not able to find the problem. I'd greatly appreciate help setting this up right. Thanks!

推荐答案

删除您的 Essence2EssenceSet 表。如果连接表仅包含参与多对多关系的相关实体的关键字，则不需要将其映射为实体。还要确保你对多对多关系的流畅映射指定表的模式：

Remove your Essence2EssenceSet table. If junction table contains only keys of related entities participating in many-to-many relations it is not needed to map it as entity. Also make sure that your fluent mapping of many-to-many relations specifies schema for table:

mb.Entity<Essence>()
  .HasMany(e => e.EssenceSets)
  .WithMany(set => set.Essences)
  .Map(mc =>
      {
          mc.ToTable("Essence2EssenceSet", "Com");
          mc.MapLeftKey("EssenceID");
          mc.MapRightKey("EssenceSetID");
      });

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