adding entries to the "Relational" table in entity model? how do i do that?

Question

so the story is very simple.

I have one table called Products and another Called categories. In addition, i have another table called ProductCategories that hold the relationship of catetories to their corresponding products (i.e, the table has two columns, ProductId, ColumnId).

For some reason, after adding all those table to my entity model, i don't have "Access" to it, hence i can do myentityModel.ProductCategories, so i could relational items between those two tables.

And yes, the ProductCategores table is added as "Association" to the entity model. i don't really understand that.

EDIT:

I do see that as part of creating new "Product" i can pass EntityCollection of "Category". So i do query from my entity model for a list of the matching categories that the user selected (on the webpage). so for example, i get (after query the model), an Objectset of "Category". However, i encountered two issues:

the 'AddObject' accept only EntityCollection, hence i need to re-create a set and then add all the objects from the ObjectSet to the entityCollection, in this process i need to detach it from the previous model and add it to the new collection. if not, i get an exception.
when i do the SaveChanges, i see that i get an exception that it was actually trying to Create new Category rather than adding new ProductCategory. again, am i missing something here?

Thanks.

score 0 · Answer 1 · answered Jul 28 '11 at 17:16

This sounds like a Many-to-Many relationship. In your entity model, you don't need to declare the join table as a separate entity. Instead, you configure the relationship between the Products and the Categories as a Many-to-Many and add metadata about the join table. In Hibernate, you would have:

    @ManyToMany(targetEntity=Categories.class, cascade={CascadeType.ALL}, fetch = FetchType.LAZY)
    @JoinTable(name="tb_products_categories",
        joinColumns=@JoinColumn(name="category_id"),
        inverseJoinColumns=@JoinColumn(name="product_id")
    )
    @IndexColumn(name="join_id")
    public List<Categories> getCategories() {
        return categories;
    }

When you query, the ORM layer takes care of determining SQL and traversing table joins.

adding entries to the "Relational" table in entity model? how do i do that?

1 Answers1