How to show combobox display value

[wallytax]

Suppose I have a data source for products that has the field supplier_id. When opening the form for an existing product, I want to see the name of the supplier. I want to send this name from the server together with this ID (so that no extra query is necessary to retrieve the supplier). Therefore I use a SQL statement like this:

  SELECT     products.id,
             products.supplier_id,
             suppliers.name AS supplier_name
  FROM       products
  INNER JOIN suppliers ON suppliers.id = products.supplier_id

To change the supplier, I show a combo box and only then a query needs to be done to retrieve the suppliers. On the server it should be a SQL like:

  SELECT id,
         name
  FROM   suppliers

I was hoping to be able to do something like this (like in a ListGrid):

  isc.DynamicForm.create({
    fields: [
      { name: 'supplier_id', displayField: 'supplier_name' }
    ]
  });

And then I need to specify different values for displayField and valueField when the combo box is pressed.

I don't think this is possible, so I'm looking for a suitable "work-around" / solution. I've also tried to do something with setting the foreignKey property on the supplier_id field in the data source of products. This causes an extra query, which is not that big of a deal, but I have an extra issue there. In reality all my records have a field "shop_code" indicating the shop the product belongs to (so one database is used for multiple shops). So when retrieving the supplier, it also needs to send the shop_code of the product (which is the same). My SQL statement in fact needs to be something like this:

  SELECT     products.id,
             products.supplier_id,
             suppliers.name AS supplier_name
  FROM       products
  INNER JOIN suppliers ON suppliers.id = products.supplier_id AND suppliers.shop_code = products.shop_code

I don't know where or when to specify this extra request parameter (if possible at all). It basically means I have a composed foreign key relation and reading the Quick Start Guide gives me the feeling this is not possible.

[wallytax]

Although I still have issues figuring out what the best way is to work with combo boxes for suppliers, I do have one question in particular.

When I open an existing product it will fire a request to get the current supplier. I'm doing some trickery to convert the url the data source will use on a per-request base. For this trickery it is necessary that I set a value on the request object before have the suppliers data source performing an request. Is this possible and if so where?

Some background: my product record has a field "shop_code" that needs to be passed to the request object before requesting a supplier (both need to be records of the same shop).

Any help will very much be appreciated.

[wallytax]

For people interested in knowing a solution: I found the right property and it is "optionCriteria". Each form in my application is specific for a shop, so I instantiate them with a property "shop_code". Based on that, I created the following component:

    // custom form item class for combo box properties (for my application)
    isc.defineClass('MyComboBoxItem', isc.ComboBoxItem).addProperties({
        addUnknownValues: false,
        cachePickListResults: false,
        displayField: 'name',
        minimumSearchLength: 2,
        valueField: 'id',

        init: function () {
            this.optionCriteria = isc.addProperties({
                site_code: this.form.shop_code
            }, this.optionCriteria);
            this.Super('init', arguments);
        }
    });

    // the form defines a combo box as follows:
    var form = isc.DynamicForm.create({
        fields: [
            { name: 'supplier_id', editorType: 'myComboBox', optionsDataSource: 'suppliers' }
        ]
    });

In my custom DataSource class I perform some trickery in the getDataURL() method to create an URL with the shop code in it (thus not as query string parameter) but this is up to you.