如何在 EF Core 中创建关系？

Question

我正在构建一个带有 Web API 后端和 Angular 5 前端的 ASP.NET Core 2.0 应用程序。对于我的数据访问层，我使用的是 Entity Framework Core。

例如，我下面有两个模型有关系。

 public class Project 
{
    [Key]
    public int Id { get; set; }

    public string project_name { get; set; }

    [ForeignKey("Person")]
    public int? pm_person_id { get; set; }

    [ForeignKey("Person")]
    public int? ptl_person_id { get; set; }

    [ForeignKey("pm_person_id")]
    public virtual Person pm_person { get; set; }

    [ForeignKey("ptl_person_id")]
    public virtual Person ptl_person { get; set; }
}



public class Person 
{
    public Person()
    {
        pm_projects = new HashSet<Project>();
        ptl_projects = new HashSet<Project>();
    }

    [Key]
    public int Id { get; set; }

    public string full_name { get; set; }

    [ForeignKey("pm_person_id")]
    public virtual ICollection<Project> pm_projects { get; set; }

    [ForeignKey("ptl_person_id")]
    public virtual ICollection<Project> ptl_projects { get; set; }
}

但是，当我尝试连接到数据库并检索这些以显示时，EF Core 表示它不理解 Project.pm_person_id 和 Person 之间的关系。

我遵循了 EF Core 上的 Microsoft 文档，它建议使用 ForeignKey 属性，而不是在 ModelBuilder 中定义这些属性。我是否完全正确地建立了关系？

Answer 1

在类 Project 中你必须添加 using

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

类Project应该这样建模：

[ForeignKey("pm_person_id")]
public int pm_person_id { get; set; }
public Person Person { get; set; }

并在 Person 类中添加 collection

public ICollection<Project> Project { get; set; }

试试这个！

Answer 2

为每个外键放置一个 id 属性和一个具有外键类数据类型的属性，您不需要任何注释实体框架会理解它是一个外键

public class Project 
{
  public int ID { get; set; }

  public string projectName { get; set; }

  public int? pmPersonID { get; set; }
  public Person pmPerson { get; set; }

  public int? ptlPersonID { get; set; }
  public Person ptlPerson { get; set; }
}



public class Person 
{
    public Person()
  {
    pm_projects = new HashSet<Project>();
    ptl_projects = new HashSet<Project>();
  }

  public int ID { get; set; }

  public string fullName { get; set; }

  public int pmPersonId { get; set; }
  public virtual ICollection<Project> pmProjects { get; set; }

  public int ptlProjectsId { get; set; }
  public virtual ICollection<Project> ptlProjects { get; set; }

}

Answer 3

不确定您在此处寻找的确切内容，但这是一个更深入的示例，可能会有所帮助。

public class Person
{
    public Person()
    {
        PM_Projects = new HashSet<Project>();
        PTL_Projects = new HashSet<Project>();
    }

    [Key]
    [Required]
    public int Id { get; set; }

    public string Full_Name { get; set; }

    public virtual ICollection<Project> PM_Projects { get; set; }

    public virtual ICollection<Project> PTL_Projects { get; set; }
}

public class Project
{
    [Key]
    [Required]
    public int Id { get; set; }

    public string Project_Name { get; set; }

    [ForeignKey("PM_Person")]
    public int PM_Person_Id { get; set; }

    [ForeignKey("PTL_Person")]
    public int PTL_Person_Id { get; set; }

    public virtual Person PM_Person { get; set; }

    public virtual Person PTL_Person { get; set; }
}

一些映射的类

public class PersonMap : IEntityTypeConfiguration<Person>
{
    public void Configure(EntityTypeBuilder<Person> builder)
    {

        builder.Property(t => t.Full_Name);

        //table  
        builder.ToTable("People");

        //relationships
        builder.HasMany(s => s.PM_Projects).WithOne(o=>o.PM_Person).OnDelete(DeleteBehavior.Restrict);
        builder.HasMany(s => s.PTL_Projects).WithOne(o => o.PTL_Person).OnDelete(DeleteBehavior.Restrict);
    }
}

public class ProjectMap : IEntityTypeConfiguration<Project>
{
    public void Configure(EntityTypeBuilder<Project> builder)
    {

        builder.Property(t => t.Project_Name);

        //table  
        builder.ToTable("Projects");

        //relationships
        builder.HasOne(s => s.PM_Person).WithMany(d=>d.PM_Projects).OnDelete(DeleteBehavior.Restrict);
        builder.HasOne(s => s.PTL_Person).WithMany(d => d.PTL_Projects).OnDelete(DeleteBehavior.Restrict);

    }
}

关于模型创建

protected override void OnModelCreating(ModelBuilder builder)
{
        base.OnModelCreating(builder);


        // Customize the ASP.NET Identity model and override the defaults if needed.
        // For example, you can rename the ASP.NET Identity table names and more.
        // Add your customizations after calling base.OnModelCreating(builder);

        //Build identity
        BuildIdentity(builder);

        builder.ApplyConfiguration(new PersonMap());
        builder.ApplyConfiguration(new ProjectMap());
}

添加并运行你的迁移