实体框架多对多关系错误

Posted 2023-02-26

【中文标题】实体框架多对多关系错误

【英文标题】：Entity Framework many to many relation error

【发布时间】：2018-05-11 05:15:46

【问题描述】：

我正在尝试在我的两个表之间创建多对多关系，但是当我运行 Update-Database 命令时出现此错误：

在表“ExamQuestions”上引入 FOREIGN KEY 约束“FK_dbo.ExamQuestions_dbo.Questions_Question_Id”可能会导致循环或多个级联路径。指定 ON DELETE NO ACTION 或 ON UPDATE NO ACTION，或修改其他 FOREIGN KEY 约束。 无法创建约束或索引。查看以前的错误。

我的第一个实体是：

public class Question

   public Question()
   
       this.Exams = new HashSet<Exam>();
   

   [Key]
   public int Id  get; set; 

   [Required(ErrorMessage="Question is Required")]
   [Display(Name="Question")]
   [Allowhtml]
   public string QuestionText  get; set; 

   // public bool IsMultiSelect  get; set; 
   public string Hint  get; set; 
   public string HelpLink  get; set; 

   public int Marks  get; set; 
   public byte[] ImageData  get; set; 
   [StringLength(50)]
   public string MimeType  get; set; 
   public byte[] Audio  get; set; 

   public int QuestionTypeId  get; set; 
   public int TopicId  get; set; 
   public int DifficulityLevelId  get; set; 
   public int SubjectId  get; set; 

   public DifficultyLevel QuestionDifficulity  get; set; 
   public Topic Topic  get; set; 

   public virtual ICollection<Option> Options  get; set; 
   public ICollection<Exam> Exams  get; set; 

第二个实体是：

public class Exam

   public Exam()
   
       this.Questions = new HashSet<Question>();
   

   [Key]
   public int Id  get; set; 

   [Required]
   public string Name  get; set; 
   [Required]
   public int Duration  get; set; 
   [Required]
   public int TotalQuestion  get; set; 
   [Required]
   public int TotalMarks  get; set; 
   public bool SectionWiseTime  get; set; 
   public bool QuestionWiseTime  get; set; 
   public bool AllQustionRequired  get; set; 
   public bool AllowBackForward  get; set; 
   public bool SuffleSubjectWise  get; set; 
   public bool SuffleOptionWise  get; set; 
   public bool GroupSubjectWise  get; set; 

   [Required]
   public int ExamTypeId  get; set; 
   [Required]
   public int ExamInstructionId  get; set; 
   [Required]
   public int DifficultyLevelId  get; set; 

   public virtual ExamType ExamType  get; set; 
   public virtual ExamInstruction ExamInstruction  get; set; 
   public virtual DifficultyLevel DifficultyLevel  get; set; 

   public virtual  ICollection<Question> Questions  get; set; 
   //public virtual ICollection<ExamSchedule> ExamSchedules  get; set; 

谁能告诉我哪里出错了？

【问题讨论】：

实体似乎没问题。你也有映射吗？该错误是从 SQL Server 引发的。开始迁移时您的数据库是否为空？

没有其他错误。就这一个。

关于映射？

【参考方案1】：

默认情况下，EF 设置了级联删除。此错误警告您，这可能会导致具有多对多关系的级联删除。并且可能不是您打算在删除/更新时发生的事情。

您可以在OnModelCreating 方法中删除OneToManyCascadeDeleteConvention，或者在每个实体的流利映射上删除。

Details are provided in this SO Answer