I'm writing a warehouse management module and I came to the inventory step.

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class wh_inventory(osv.osv): _name = 'wh.inventory'

_columns = {
        'date' : fields.datetime('Date),
        'warehouse_id' : fields.many2one('wh.warehouse', 'Warehouse Name,required=True),
        'inventory_line_ids':fields.one2many('wh.inventory.line','inventory_id','Inventory),
        'notes':fields.char('Notes),
        'balance_track':fields.boolean('Balance Track')

}

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class wh_inventory_line(osv.osv):

_name = 'wh.inventory.line'

_columns = {

        'inventory_id':fields.many2one('wh.inventory', 'Inventory'),

        'warehouse_id':fields.related('inventory_id','warehouse_id'),

        'material_id' : fields.many2one('wh.material' ,'Material Name'),

        'balance':fields.float('Balance'),

        'previous_balance':fields.float('Previous Balance'),

}

I need to make an inventory every now and then for each warehouse separately and each inventory operation will be kept in the database as a master-detail relation, ie:

one record for the basic data such as id, date, warehouse_id etc. and this will be recorded in a table created by (inventory) object.

many records will keep the details of the operation (one record for each material) recording the material id, inventory id, balance, etc. and this will be recorded in the table (inventory_lines).

During the data entry, when the user selects a material, I need to check its current balance and display it in the balance field. In order to do this, I'll need to know the warehouse id because every warehouse shall have separate inventories.

I have many materials stored in many warehouses. For example: I can have a quantity of 5 pens in warehouse A and 10 pens in warehouse B and 6 pens in warehouse C.

First, I select the warehouse (A or B or C) --- let's say warehouse B

Then I select the material (Pen or notebook or whatever) --- let's say Pen

Now, I want to search the database to find the balance of (Pen) in (Warehouse B)

I can write something like this:

select balance from inventory_lines where material_id=mmmmmm and warehouse_id=wwwwww

So, I need to get the material id (mmmmm) and the warehouse id (wwwww)

And that will be done with each material I choose.

The warehouse id is in the column: inventory_id in the object: inventory 'warehouse_id' : fields.many2one('makhazen.warehouse', 'Warehouse Name',required=True),

The material id is in the column: material_id of the object inventory_line as in the picture in the question 'material_id' : fields.many2one('makhazen.material' ,'Material Name'),

I faced the following problem:

I could use the (on_change) method in the form view on the material_id field and could trigger a method to search for the balance in the database but I needed the warehouse_id which I couldn't get. The questions are: - How are this master-detail relationship is handled in openerp? how values are passed between the master table and the details table? - How can we extend the scope of the warehouse_id so that it can be seen from any method in the module? - I could change the values of the fields by calling a method and returning the desired values in a dictionary, but how to do the opposite (read them)?

It's very critical matter to me.