I have the following code:

class product_product(osv.osv):
    _name = 'product.product'
    _inherit = 'product.product'

    def test(self, cr, uid, ids, field_names=None, arg=None, context=None):
        result = {}
        if not ids: return result

        context['only_with_stock'] = True

        for id in ids:
            context['product_id'] = id
            location_obj = self.pool.get('stock.location')
            result[id] = location_obj.search(cr, uid, [('usage', '=', 'internal')], context=context)

        return result


    _columns = {
        'test': fields.function(test, type='one2many', relation='stock.location', string='Stock by Location'),
    }

product_product()

and:

<openerp>
    <data>

        <act_window
            context="{'product_id': active_id, 'only_with_stock': True}"
            id="act_stock_product_location_open"
            name="Stock by Location"
            res_model="stock.location"
            src_model="product.product"/>


        <record id="nfx_view_normal_procurement_locations_form" model="ir.ui.view">
            <field name="name">nfx_product.normal.procurement.locations.inherit</field>
            <field name="model">product.product</field>
            <field name="inherit_id" ref="stock.view_normal_procurement_locations_form"/>
            <field name="arch" type="xml">
                <group name="lot" position="before" version="7.0">
                    <group string="Locations" attrs="{'invisible': [('type', '=', 'service')]}" groups="base.group_user">
                        <field name="test" nolabel="1" context="{'product_id': active_id, 'only_with_stock': True}">
                            <tree string="Stock Location">
                                <field name="complete_name"/>
                                <field name="stock_real"/>
                                <field name="stock_virtual" invisible="'product_id' not in context"/>
                            </tree>
                        </field>
                    </group>
                </group>

            </field>
        </record>

    </data>
</openerp>

The test() function works well. It creates a one2many field with the stock locations. The complete_name field in the treeview is ok but the stock_real and stock_virtual fields are empty(0.00). I think because this fields calls _product_value() from stock/stock.py and _product_value() needs the product_id passed in the context. But it is not passed.

What I'm doing wrong?