C＃Nhibernate-将新项目添加到多对多关系

Question

So i have the two tables (Product and Supplier) connected through a many-to-many relationship. They're coded as follows:

class Product
{
    public virtual uint id { get; set; }
    public virtual string name { get; set; }
    public virtual float stock { get; set; }
    public virtual float value { get; set; }
    public virtual Category category { get; set; }

    public virtual ISet suppliers { get; set; }
    public virtual ISet saleItems { get; set; }
    public virtual ISet stockInlets { get; set; }
}

-

class Supplier
{
    public virtual uint id { get; set; }
    public virtual string name { get; set; }
    public virtual string CNPJ { get; set; }
    public virtual string addressLine1 { get; set; }
    public virtual string addressLine2 { get; set; }
    public virtual string telephone1 { get; set; }
    public virtual string telephone2 { get; set; }

    public virtual ISet products { get; set; }
    public virtual ISet stockInlets { get; set; }
}

And this is how I mapped their relationship:

<set name="suppliers" table="product_x_supplier" fetch="join" lazy="false">
  <key column="product_id" />
  <many-to-many class="Supplier" column="supplier_id" />
</set>

-

<set name="products" table="product_x_supplier" fetch="join" lazy="false">
  <key column="supplier_id" />
  <many-to-many class="Product" column="product_id" />
</set>

Now, I'm having a problem when inserting a new Product and trying to link the correspondent Suppliers to it. I did manage to Update an already existing one, but not to create a new one. Here's the (simplified) code I'm trying to use:

Product p = new Product()
{
    name = "Test product",
    stock = 0,
    value = 2,
    category = (Category)cats[0]
};

for (int i = 0; i < suppliers.Length; i++)
{
    p.suppliers.Add(suppliers[i]);
}

repository.Add(p);

It tells me Object reference not set to an instance of an object. . I tried to instantiate the object, doing something like p.suppliers = new IList<Supplier>(); but then it complained it Cannot create an instance of the abstract class or interface 'System.Collections.Generic.IList<TCC.Hibernate.Domain.Classes.Supplier>' .

Any help is appreciated.

Answer 1

Use...

p.suppliers = new List<Supplier>();

Your list needs to be initialized prior to adding items to it. IList is an interface, not a class, you need to use List , the default implementation of IList .

As an aside, it seems you may not be that familiar with the C# language or the built-in .NET libraries. I would suggest becoming more familiar with basic C# development before playing with third-party libraries like Hibernate. Hibernate is an especially complex library that will be the cause of many headaches for you if you have troubles diagnosing even simple errors like these.

Good luck!

UPDATE:

Sorry, I didn't notice that your field types were ISet , not IList . You will have to use an ISet implementation like HashSet or SortedSet as Sly has demonstrated in their answer.

You can browse the MSDN to learn more about these collection types...

http://msdn.microsoft.com/en-us/library/0sbxh9x2

Answer 2

Use

 class Supplier
 {
      public Supplier()
      {
          this.suppliers = new HashedSet<Supplier>();
      }

      public virtual ICollection<Product> products { get; private set; }
 }

This way you will ensure that collection is always initialized and nobody can replace it.