c# - EF Code First 中自引用实体的映射

Question

在我的数据库中，我有一个表 Category，其中包含列 Id、CategoryName、ParentCategoryId，其中 ParentCategoryId 对 Category.Id 有约束。

我首先使用实体​​框架代码，其中实体看起来像:

public class Category
{
   public long Id { get; private set; }
   public string CategoryName { get; private set; }
   public long? ParentCategoryId { get; private set; }
   public Category ParentCategory { get; private set; }       
   public virtual ICollection<Category> SubCategories { get; private set; }
}

如果我尝试对此运行查询，我会得到异常:

 The relationship 'ComplaintModel.FK_Complaint_Category' was not loaded because the type 'ComplaintModel.Category' is not available.\r\nThe following information may be useful in resolving the previous error:\r\nThe required property 'Category1' does not exist on the type 'EC.Complaint.Services.Command.Domain.Entities.Category'.\r\n\r\n"}    System.Exception {System.Data.MetadataException}

所以它似乎需要导航属性，如果我添加这些:

 public ICollection<Category> Category1 { get; private set; }
 public long? Category2Id { get; private set; }
 public Category Category2 { get; private set; }

查询有效。

当然，我不想要 Category1 和 Category2 属性，我想要使用 ParentCategory 和 SubCategories 属性。

如何让代码首先使用正确的导航属性？

Answer 1

你的 POCO 类应该是这样的......

public class Category
{
   public long Id { get; private set; }
   public string CategoryName { get; private set; }
   public long? ParentCategoryId { get; private set; }
   public virtual Category ParentCategory { get; private set; }       
   public virtual ICollection<Category> SubCategories { get; private set; }
}

public class CategoryConfiguration : EntityTypeConfiguration<Category>
{
    public CategoryConfiguration()
    {
        this.HasKey(x => x.Id);

        this.HasMany(category => category.SubCategories)
            .WithOptional(category => category.ParentCategoryId)
            .HasForeignKey(course => course.UserId)
            .WillCascadeOnDelete(false);
    }
}