实体框架代码一个实体的“多对多”

Question

I have model Category:

public class Category
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
    }

I want to create a new model DependencyCategory something like this to store many to many child parent relationship.

public class DependencyCategory
    {
        public int Id { get; set; }
        public Category Child { get; set; }
        public Category Parent { get; set; }
    }

How to create now relationship with ICollection<DependencyCategory> Children, Parent in Category model? I want for example when access a category parent to see all children or if is child to see all parent available.

Answer 1

Based on what I understand, your classes should be defined like this.

public class Category
{
    public int Id {get; set; }
    public string Name {get; set; }
    public string Description {get; set; }

    public List<Category> ParentCategories {get; set; }
    public List<Category> ChildCategories {get; set; }
}

public class CategoryRelationships
{
    public int ParentCategoryId {get; set; }
    public int ChildCategoryId {get; set; }
}

I haven't included all the plumbing as Code-First isn't my strong point, but it should point you in the right direction and improve your database structure slightly. Note the CategoryRelationship class defines your relationships, put a composite-primary-key on both ParentCategoryId and ChildCategoryId and you have no need for a separate Id column, whilst also ensuring that the same two Categories cannot be linked twice.

Hope it helps.

Answer 2

This solved

HasRequired(a => a.ParentProduct)
                .WithMany(b => b.ChildProducts)
                .HasForeignKey(c => c.ParentId) // FK_RelatedProductParentID
                .WillCascadeOnDelete(false);
HasRequired(a => a.ChildProduct)
                .WithMany(b => b.ParentProducts)
                .HasForeignKey(c => c.ChildId); // FK_RelatedProductChildID
public class CategoryDependency
    {
        [Key, Column(Order = 0)]
        public int ParentId { get; set; } // ParentID
        [Key, Column(Order = 1)]
        public int ChildId { get; set; } // ChildID

        // Foreign keys
        public virtual Product ParentProduct { get; set; } //  FK_RelatedProductParentID
        public virtual Product ChildProduct { get; set; } //  FK_RelatedProductChildID
    }
public class Product
    {
        [Key]
        public int ProductId { get; set; } // ProductID (Primary key)
        public string ProductName { get; set; } // ProductName


        // Reverse navigation
        public virtual ICollection<RelatedProduct> ParentProducts { get; set; } // RelatedProduct.FK_RelatedProductChildID
        public virtual ICollection<RelatedProduct> ChildProducts { get; set; } // RelatedProduct.FK_RelatedProductParentID
    }