I made a template to facilitate POS inheritance, easy to use with the command scaffold. You can find it here https://github.com/haroldtamo/Odoo-Pos-Inheritance-Template

Sorry, I don't have enough karma to post it as answer, so i posted it here. The original question begin here :

Hi,

I want to override the PosModel in model.js (begin on line 17) by adding a new field in the fetch of products (product.product class) like this :

return self.fetch(
                        'product.product', 
                        ['name', 'field_to_add','list_price','price','pos_categ_id', 'taxes_id', 'ean13', 'default_code',
                         'to_weight', 'uom_id', 'uos_id', 'uos_coeff', 'mes_type', 'description_sale', 'description'],
                        [['sale_ok','=',true],['available_in_pos','=',true]],
                        {pricelist: self.get('shop').pricelist_id[0]} // context for price
                    );

Unfortunately, i think i use a wrong method for inheritance : in fact, i copy all the class PosModel and i add my field in a new addons so, when the POS session is loaded, products are loaded twice : first when odoo call the original class and second when it call mine. The consequence is that the loading of the pos session is very slow. So i want to know the right method to override or inherit that class (PosModel)

Here is my code for inheritance (sorry i don't see the [CODE] tag ) (look the part in bold) :

function openerp_pos_price_control_models(instance, module){ var module = instance.point_of_sale; var QWeb = instance.web.qweb; _t = instance.web._t; var round_di = instance.web.round_decimals; var round_pr = instance.web.round_precision; module.PosModel = Backbone.Model.extend({ initialize: function(session, attributes) { Backbone.Model.prototype.initialize.call(this, attributes); var self = this; this.session = session; this.ready = $.Deferred(); // used to notify the GUI that the PosModel has loaded all resources this.flush_mutex = new $.Mutex(); // used to make sure the orders are sent to the server once at time this.barcode_reader = new module.BarcodeReader({'pos': this}); // used to read barcodes this.proxy = new module.ProxyDevice(); // used to communicate to the hardware devices via a local proxy this.db = new module.PosLS(); // a database used to store the products and categories this.db.clear('products','categories'); this.debug = jQuery.deparam(jQuery.param.querystring()).debug !== undefined; //debug mode // default attributes values. If null, it will be loaded below. this.set({ 'nbr_pending_operations': 0, 'currency': {symbol: '$', position: 'after'}, 'shop': null, 'company': null, 'user': null, // the user that loaded the pos 'user_list': null, // list of all users 'partner_list': null, // list of all partners with an ean 'cashier': null, // the logged cashier, if different from user 'orders': new module.OrderCollection(), //this is the product list as seen by the product list widgets, it will change based on the category filters 'products': new module.ProductCollection(), 'cashRegisters': null, 'bank_statements': null, 'taxes': null, 'pos_session': null, 'pos_config': null, 'units': null, 'units_by_id': null, 'pricelist': null, 'selectedOrder': null, }); this.get('orders').bind('remove', function(){ self.on_removed_order(); }); // We fetch the backend data on the server asynchronously. this is done only when the pos user interface is launched, // Any change on this data made on the server is thus not reflected on the point of sale until it is relaunched. // when all the data has loaded, we compute some stuff, and declare the Pos ready to be used. $.when(this.load_server_data()) .done(function(){ //self.log_loaded_data(); //Uncomment if you want to log the data to the console for easier debugging self.ready.resolve(); }).fail(function(){ //we failed to load some backend data, or the backend was badly configured. //the error messages will be displayed in PosWidget self.ready.reject(); }); }, // helper function to load data from the server fetch: function(model, fields, domain, ctx){ return new instance.web.Model(model).query(fields).filter(domain).context(ctx).all() }, // loads all the needed data on the sever. returns a deferred indicating when all the data has loaded. load_server_data: function(){ var self = this; var loaded = self.fetch('res.users',['name','company_id'],[['id','=',this.session.uid]]) .then(function(users){ self.set('user',users[0]); return self.fetch('res.company', [ 'currency_id', 'email', 'website', 'company_registry', 'vat', 'name', 'phone', 'partner_id', ], [['id','=',users[0].company_id[0]]]); }).then(function(companies){ self.set('company',companies[0]); return self.fetch('res.partner',['contact_address'],[['id','=',companies[0].partner_id[0]]]); }).then(function(company_partners){ self.get('company').contact_address = company_partners[0].contact_address; return self.fetch('product.uom', null, null); }).then(function(units){ self.set('units',units); var units_by_id = {}; for(var i = 0, len = units.length; i < len; i++){ units_by_id[units[i].id] = units[i]; } self.set('units_by_id',units_by_id); return self.fetch('product.packaging', null, null); }).then(function(packagings){ self.set('product.packaging',packagings); return self.fetch('res.users', ['name','ean13'], [['ean13', '!=', false]]); }).then(function(users){ self.set('user_list',users); return self.fetch('res.partner', ['name','ean13'], [['ean13', '!=', false]]); }).then(function(partners){ self.set('partner_list',partners); return self.fetch('account.tax', ['amount', 'price_include', 'type']); }).then(function(taxes){ self.set('taxes', taxes); return self.fetch( 'pos.session', ['id', 'journal_ids','name','user_id','config_id','start_at','stop_at'], [['state', '=', 'opened'], ['user_id', '=', self.session.uid]] ); }).then(function(sessions){ self.set('pos_session', sessions[0]); return self.fetch( 'pos.config', ['name','journal_ids','shop_id','journal_id', 'iface_self_checkout', 'iface_led', 'iface_cashdrawer', 'iface_payment_terminal', 'iface_electronic_scale', 'iface_barscan', 'iface_vkeyboard', 'iface_print_via_proxy','iface_cashdrawer','state','sequence_id','session_ids'], [['id','=', self.get('pos_session').config_id[0]]] ); }).then(function(configs){ var pos_config = configs[0]; self.set('pos_config', pos_config); self.iface_electronic_scale = !!pos_config.iface_electronic_scale; self.iface_print_via_proxy = !!pos_config.iface_print_via_proxy; self.iface_vkeyboard = !!pos_config.iface_vkeyboard; self.iface_self_checkout = !!pos_config.iface_self_checkout; self.iface_cashdrawer = !!pos_config.iface_cashdrawer; return self.fetch('sale.shop',[],[['id','=',pos_config.shop_id[0]]]); }).then(function(shops){ self.set('shop',shops[0]); return self.fetch('product.pricelist',['currency_id'],[['id','=',self.get('shop').pricelist_id[0]]]); }).then(function(pricelists){ self.set('pricelist',pricelists[0]); return self.fetch('res.currency',['symbol','position','rounding','accuracy'],[['id','=',self.get('pricelist').currency_id[0]]]); }).then(function(currencies){ self.set('currency',currencies[0]); return self.fetch('product.packaging',['ean','product_id']); }).then(function(packagings){ self.db.add_packagings(packagings); return self.fetch('pos.category', ['id','name','parent_id','child_id','image']) }).then(function(categories){ self.db.add_categories(categories); return self.fetch( 'product.product', ['name', 'min_sale_price', 'list_price','price','pos_categ_id', 'taxes_id', 'ean13', 'default_code', 'to_weight', 'uom_id', 'uos_id', 'uos_coeff', 'mes_type', 'description_sale', 'description'], [['sale_ok','=',true],['available_in_pos','=',true]], {pricelist: self.get('shop').pricelist_id[0]} // context for price ); }).then(function(products){ self.db.add_products(products); return self.fetch( 'account.bank.statement', ['account_id','currency','journal_id','state','name','user_id','pos_session_id'], [['state','=','open'],['pos_session_id', '=', self.get('pos_session').id]] ); }).then(function(bank_statements){ var journals = new Array(); _.each(bank_statements,function(statement) { journals.push(statement.journal_id[0]) }); self.set('bank_statements', bank_statements); return self.fetch('account.journal', undefined, [['id','in', journals]]); }).then(function(journals){ self.set('journals',journals); // associate the bank statements with their journals. var bank_statements = self.get('bank_statements'); for(var i = 0, ilen = bank_statements.length; i < ilen; i++){ for(var j = 0, jlen = journals.length; j < jlen; j++){ if(bank_statements[i].journal_id[0] === journals[j].id){ bank_statements[i].journal = journals[j]; bank_statements[i].self_checkout_payment_method = journals[j].self_checkout_payment_method; } } } self.set({'cashRegisters' : new module.CashRegisterCollection(self.get('bank_statements'))}); }); return loaded; }, // logs the usefull posmodel data to the console for debug purposes log_loaded_data: function(){ console.log('PosModel data has been loaded:'); console.log('PosModel: units:',this.get('units')); console.log('PosModel: bank_statements:',this.get('bank_statements')); console.log('PosModel: journals:',this.get('journals')); console.log('PosModel: taxes:',this.get('taxes')); console.log('PosModel: pos_session:',this.get('pos_session')); console.log('PosModel: pos_config:',this.get('pos_config')); console.log('PosModel: cashRegisters:',this.get('cashRegisters')); console.log('PosModel: shop:',this.get('shop')); console.log('PosModel: company:',this.get('company')); console.log('PosModel: currency:',this.get('currency')); console.log('PosModel: user_list:',this.get('user_list')); console.log('PosModel: user:',this.get('user')); console.log('PosModel.session:',this.session); console.log('PosModel end of data log.'); }, // this is called when an order is removed from the order collection. It ensures that there is always an existing // order and a valid selected order on_removed_order: function(removed_order){ if( this.get('orders').isEmpty()){ this.add_new_order(); }else{ this.set({ selectedOrder: this.get('orders').last() }); } }, // saves the order locally and try to send it to the backend. 'record' is a bizzarely defined JSON version of the Order push_order: function(record) { this.db.add_order(record); this.flush(); }, //creates a new empty order and sets it as the current order add_new_order: function(){ var order = new module.Order({pos:this}); this.get('orders').add(order); this.set('selectedOrder', order); }, // attemps to send all pending orders ( stored in the pos_db ) to the server, // and remove the successfully sent ones from the db once // it has been confirmed that they have been sent correctly. flush: function() { //TODO make the mutex work //this makes sure only one _int_flush is called at the same time /* return this.flush_mutex.exec(_.bind(function() { return this._flush(0); }, this)); */ this._flush(0); }, // attempts to send an order of index 'index' in the list of order to send. The index // is used to skip orders that failed. do not call this method outside the mutex provided // by flush() _flush: function(index){ var self = this; var orders = this.db.get_orders(); self.set('nbr_pending_operations',orders.length); var order = orders[index]; if(!order){ return; } //try to push an order to the server // shadow : true is to prevent a spinner to appear in case of timeout (new instance.web.Model('pos.order')).call('create_from_ui',[[order]],undefined,{ shadow:true }) .fail(function(unused, event){ //don't show error popup if it fails event.preventDefault(); console.error('Failed to send order:',order); self._flush(index+1); }) .done(function(){ //remove from db if success self.db.remove_order(order.id); self._flush(index); }); }, scan_product: function(parsed_ean){ var self = this; var product = this.db.get_product_by_ean13(parsed_ean.base_ean); var selectedOrder = this.get('selectedOrder'); if(!product){ return false; } if(parsed_ean.type === 'price'){ selectedOrder.addProduct(new module.Product(product), {price:parsed_ean.value}); }else if(parsed_ean.type === 'weight'){ selectedOrder.addProduct(new module.Product(product), {quantity:parsed_ean.value, merge:false}); }else{ selectedOrder.addProduct(new module.Product(product)); } return true; }, }); }

thanks!