EF核心中的多对多关系问题

Question

我正在尝试在实体Project 和实体Resource 之间建立多对多关系。我创建了一个关系实体：ProjectResource。我已经使用这样的 fluent API 设置了关系：

modelBuilder.Entity<ProjectResource>()
    .HasKey(pr => new { pr.ProjectId, pr.ResourceId });

modelBuilder.Entity<ProjectResource>()
    .HasOne(pr => pr.Project)
    .WithMany(p => p.ProjectResources)
    .HasForeignKey(pr => pr.ProjectId);

modelBuilder.Entity<ProjectResource>()
    .HasOne(pr => pr.Resource)
    .WithMany(r => r.ProjectResources)
    .HasForeignKey(pr => pr.ResourceId);

以下是我的课程Project 和Resources 的简要定义（我只包括那种关系）：

public class Resource
{
    public Guid DepartmentId { get; set; }
    public Department Department { get; set; }

    public Guid? ManagerId { get; set; }
    public Resource Manager { get; set; }

    public ICollection<Resource> Resources { get; set; }
    public ICollection<ProjectResource> ProjectResources { get; set; }
    public ICollection<ChangeLog> ChangeLogs { get; set; }
    public ICollection<Requirement> Requirements { get; set; }
    public ICollection<UseCase> UseCases { get; set; }  
}

public class Project
{
    public Guid ResponsibleId { get; set; }
    public Resource Responsible { get; set; }

    public ICollection<ProjectResource> ProjectResources { get; set; }
    public ICollection<BusinessNeed> BusinessNeeds { get; set; }
    public ICollection<SuccessCriteria> SuccessCriterias { get; set; }
    public ICollection<Requirement> Requirements { get; set; }
    public ICollection<UseCase> UseCases { get; set; }
    public ICollection<ChangeLog> ChangeLogs { get; set; }
    public ICollection<GlossaryWord> GlossaryWords { get; set; }
}

public class ProjectResource
{
    public Guid ProjectId { get; set; }
    public Project Project { get; set; }
    public Guid ResourceId { get; set; }
    public Resource Resource { get; set; }
}

我已经研究了这个问题，但似乎找不到解决方案。我已经按照here 中描述的指南完成了。

我收到以下错误：

在表“ProjectResources”上引入 FOREIGN KEY 约束“FK_ProjectResources_Resources_ResourceId”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。

我到底做错了什么？

Answer 1

问题是由Resource和Project之间现有的required（因此cascade delete）一对多关系引起的，由Responsible中的Responsible/ResponsibleId属性表示。

这是从Resource 到ProjectResource 的多个级联路径：

Resource (Id) -> (ResponsibleId) Project (Id) -> (ProjectId) ProjectResource
Resource (Id) -> (ResourceId) ProjectResource

解决多个级联路径的唯一方法是通过关闭至少一个关系的级联删除来打破循环，并手动或通过数据库触发器处理删除。

对于这个具体模型，可能最简单的方法是关闭 Resource -> Project 关系的删除级联：

modelBuilder.Entity<Project>()
    .HasOne(p => p.Responsible)
    .WithMany()
    .OnDelete(DeleteBehavior.Restrict);