实体框架代码首先是多对多关系和继承

Question

请原谅我,如果这个问题已在某个地方得到解答,我一直很难找到解决这个问题的方法.

我正在尝试在MVC4项目上设置EF Code First.我有一个继承自Person的用户和客户.然后我有一个Template对象,它与Customer有多对多的关系,与User有一对多的关系.以下是我设置的方法:

楷模

public class Person
{
    [Key]
    public int PersonID { get; set; }

    public string LastName { get; set; }
    public string FirstName { get; set; }

    public string FullName
    {
        get
        {
            return String.Format("{0} {1}", FirstName, LastName);
        }
    }

    public string Email { get; set; }

    public virtual List<Template> Templates { get; set; }
}

public class User : Person
{
    .... 
}

public class Customer : Person
{
    ....
}

public class Template
{
    public int TemplateId { get; set; }
    public string TemplateName { get; set; }

    public virtual List<Customer> Customers { get; set; }

    [ForeignKey("User")]
    public int UserId { get; set; }
    public virtual User User { get; set; }
}

CONTEXT

public class ProjectContext : DbContext
{
    public ProjectContext()
        : base("name=ProjectDB")
    {
    }

    public DbSet<Template> Templates { get; set; }
    public DbSet<User> Users { get; set; }
    public DbSet<Customer> Customers { get; set; }
    public DbSet<Person> People { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Conventions
            .Remove<PluralizingTableNameConvention>();

        modelBuilder.Entity<Template>()
            .HasMany(x => x.Customers)
            .WithMany(x => x.Templates)
            .Map(x => x.MapLeftKey("TemplateId")
                .MapRightKey("PersonId")
                .ToTable("TemplateCustomer")
            );
    }
}

如果我从上下文中删除Person DBSet,这可以正常工作但设置TPT继承.我想使用TPH继承,但是当我在上下文中启用Person DBSet的迁移时,它会阻塞:

NavigationProperty"模板"无效.FromRole在AssociationType"MvcProject.Models.Template_Customers" Template_Customers_Target'类型"MvcProject.Models.Customer"必须完全匹配与此NavigationProperty声明的类型"MvcProject.Models.Person".

我在哪里错了？

Answer 1

您无法从基础实体继承导航属性.它们总是必须在关系的另一端引用的类中声明.

• Template.Customers引用Customer(而不是Person),因此Templates必须在Customer(不在Person)中声明反向导航属性
• Template.User引用User(而不是Person),因此Templates必须在User(不在Person)中声明反向导航属性

所以,基本上你必须将Templates集合从Person两个派生类中移出:

public class Person
{
    // no Templates collection here
}

public class User : Person
{
    //... 
    public virtual List<Template> Templates { get; set; }
}

public class Customer : Person
{
    //...
    public virtual List<Template> Templates { get; set; }
}

然后,您可以使用Fluent API定义两个关系,如下所示:

modelBuilder.Entity<Template>()
    .HasMany(t => t.Customers)
    .WithMany(c => c.Templates) // = Customer.Templates
    .Map(x => x.MapLeftKey("TemplateId")
               .MapRightKey("PersonId")
               .ToTable("TemplateCustomer"));

modelBuilder.Entity<Template>()
    .HasRequired(t => t.User)
    .WithMany(u => u.Templates) // = User.Templates
    .HasForeignKey(t => t.UserId);