实体框架 6 映射外键问题

Question

我有 3 个实体：问题public enum QuestionType{    Scenario,    Step}public class Question{    public int Id { get; set; }    public int CategoryId { get; set; }    [Required] [MaxLength(255)] public string Text { get; set; }    [MaxLength(255)] public string FrameText { get; set; }    public int Order { get; set; }    public QuestionType Type { get; set; }    public DefaultAnswer DefaultAnswer { get; set; }    public IList<Answer> Answers { get; set; }}回答public class Answer{    public int Id { get; set; }    public int QuestionId { get; set; }    [Required] [MaxLength(255)] public string Text { get; set; }    public int Order { get; set; }    public Scenario Scenario { get; set; }    public IList<Formula> Formulas { get; set; }    public IList<Image> Images { get; set; }}最后，DefaultAnswer：public class DefaultAnswer{    public int QuestionId { get; set; }    public int AnswerId { get; set; }    public Answer Answer { get; set; }    public Question Question { get; set; }}之间的关系问题和答案是显而易见的。我想为一个问题设置一个DefaultAnswer，所以我DefaultAnswer在Question模型中添加了一个导航属性。这是可选的，因为它可以为空。所以，我试图建立这样的关系：modelBuilder.Entity<DefaultAnswer>().HasKey(m => new { m.QuestionId, m.AnswerId });modelBuilder.Entity<Question>().HasOptional(m => m.DefaultAnswer).WithRequired(m => m.Question);modelBuilder.Entity<DefaultAnswer>().HasRequired(m => m.Answer).WithMany().HasForeignKey(m => m.AnswerId);但这不起作用，它会Question_Id在DefaultAnswers表中创建另一个名为的字段..... 这就是 EF 生成的内容：public override void Up(){    CreateTable(        "dbo.DefaultAnswers",        c => new            {                QuestionId = c.Int(nullable: false),                AnswerId = c.Int(nullable: false),                Question_Id = c.Int(nullable: false),            })        .PrimaryKey(t => new { t.QuestionId, t.AnswerId })        .ForeignKey("dbo.Answers", t => t.AnswerId, cascadeDelete: true)        .ForeignKey("dbo.Questions", t => t.Question_Id)        .Index(t => t.AnswerId)        .Index(t => t.Question_Id);}有谁知道我如何创建这种关系，同时仍将导航属性保留在Question 中？

Answer 1

我不确定引入 DefaultAnswer 实体的意图是什么。但是这种关系可以在没有它的情况下建模。例如：

public enum QuestionType

{

    Scenario,

    Step

}

public class Question

{

    public int Id { get; set; }

    public int CategoryId { get; set; }

    [Required] [MaxLength(255)] public string Text { get; set; }

    [MaxLength(255)] public string FrameText { get; set; }

    public int Order { get; set; }

    public QuestionType Type { get; set; }

    public int? DefaultAnswerId { get; set; }

    [ForeignKey("Id,DefaultAnswerId")]

    public Answer DefaultAnswer { get; set; }

    public IList<Answer> Answers { get; set; }

}

public class Answer

{

    public int Id { get; set; }

    public int QuestionId { get; set; }

    [Required] [MaxLength(255)] public string Text { get; set; }

    public int Order { get; set; }

    public virtual Question Question { get; set; }

    //public Scenario Scenario { get; set; }

    //public IList<Formula> Formulas { get; set; }

    //public IList<Image> Images { get; set; }

}

class Db: DbContext

{

    public DbSet<Question> Question { get; set; }

    public DbSet<Answer> Answer { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)

    {

        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Answer>().HasKey(m => new { m.QuestionId, m.Id });

        modelBuilder.Entity<Answer>().HasRequired(m => m.Question).WithMany(q => q.Answers).HasForeignKey( m => m.QuestionId);

        modelBuilder.Entity<Question>().HasOptional(m => m.DefaultAnswer);

    }

}

Answer 2

首先，建议简单地将答案标记为“默认”的评论听起来不错，但试图帮助解决实际问题......

好的，我认为可以为您提供所需的编辑....

所以，我在这里使用的模型：

public enum QuestionType

{

    Scenario,

    Step

}

public class Question

{

    public int Id { get; set; }

    public int CategoryId { get; set; }

    [Required] [MaxLength(255)]

    public string Text { get; set; }

    [MaxLength(255)]

    public string FrameText { get; set; }

    public int Order { get; set; }

    public QuestionType Type { get; set; }

    public DefaultAnswer DefaultAnswer { get; set; }

    public IList<Answer> Answers { get; set; }

}

public class Answer

{

    public int Id { get; set; }

    public int QuestionId { get; set; }

    [Required]

    [MaxLength(255)]

    public string Text { get; set; }

    public int Order { get; set; }

    public Scenario Scenario { get; set; }

    public Question Question { get; set; }

    //commented these out for the sake of this

    //example

   /*public IList<Formula> Formulas { get; set; }

    public IList<Image> Images { get; set; }*/

}

public class DefaultAnswer

{

    public int QuestionId { get; set; }

    public int AnswerId { get; set; }

    public Answer Answer { get; set; }

    public Question Question { get; set; }

}

如此定义的关系：

//don't need a compound key for answers... 

//easier to just let each answer be entirely unique.            

modelBuilder.Entity<Answer>().HasKey(m => m.Id );

modelBuilder.Entity<Answer>().HasRequired(m => m.Question)

    .WithMany(q => q.Answers).HasForeignKey(m => m.QuestionId);

modelBuilder.Entity<Question>()

    .HasOptional(m => m.DefaultAnswer)

    .WithOptionalDependent(m => m.Question);

//default answer is basically a mapping table between questions and answers.

//so it has a compound key.  In fact the table should consist of ONLY these two key

//fields...

modelBuilder.Entity<DefaultAnswer>()

    .HasKey(m => new { m.AnswerId, m.QuestionId });              

这为我产生了这个：

CreateTable(

            "dbo.DefaultAnswers",

            c => new

                {

                    AnswerId = c.Int(nullable: false),

                    QuestionId = c.Int(nullable: false),

                })

            .PrimaryKey(t => new { t.AnswerId, t.QuestionId })

            .ForeignKey("dbo.Answers", t => t.AnswerId, cascadeDelete: true)

            .Index(t => t.AnswerId);

唯一让我无法理解的是级联删除行为是如何设置的......有点担心删除“DefaultAnswer”记录会删除答案 - 当天太晚了，我的大脑无法解决这个问题我'我害怕！