refactor: move item_code reactivity to server-side

[ruthra-kumar]

Context

Selecting an Item is the most common action in Sales / Purchase cycle. Whenever an Item is selected, system fetches the basic details like rate, discounts, stock qty, warehouse and sales account as such and auto-fills these details in it's respective fields. These can simply be called as Reactivity.

All of this is achieved by a JS trigger on item_code located in transaction.js

erpnext/erpnext/public/js/controllers/transaction.js

Lines 499 to 678 in 5266f23

	item_code(doc, cdt, cdn) {
	var me = this;
	var item = frappe.get_doc(cdt, cdn);
	var update_stock = 0, show_batch_dialog = 0;
	item.weight_per_unit = 0;
	item.weight_uom = '';
	item.conversion_factor = 0;
	if(['Sales Invoice', 'Purchase Invoice'].includes(this.frm.doc.doctype)) {
	update_stock = cint(me.frm.doc.update_stock);
	show_batch_dialog = update_stock;
	} else if((this.frm.doc.doctype === 'Purchase Receipt') ||
	this.frm.doc.doctype === 'Delivery Note') {
	show_batch_dialog = 1;
	}
	if (show_batch_dialog && item.use_serial_batch_fields === 1) {
	show_batch_dialog = 0;
	}
	item.barcode = null;
	if(item.item_code || item.serial_no) {
	if(!this.validate_company_and_party()) {
	this.frm.fields_dict["items"].grid.grid_rows[item.idx - 1].remove();
	} else {
	item.pricing_rules = ''
	return this.frm.call({
	method: "erpnext.stock.get_item_details.get_item_details",
	child: item,
	args: {
	doc: me.frm.doc,
	ctx: {
	item_code: item.item_code,
	barcode: item.barcode,
	serial_no: item.serial_no,
	batch_no: item.batch_no,
	set_warehouse: me.frm.doc.set_warehouse,
	warehouse: item.warehouse,
	customer: me.frm.doc.customer || me.frm.doc.party_name,
	quotation_to: me.frm.doc.quotation_to,
	supplier: me.frm.doc.supplier,
	currency: me.frm.doc.currency,
	is_internal_supplier: me.frm.doc.is_internal_supplier,
	is_internal_customer: me.frm.doc.is_internal_customer,
	update_stock: update_stock,
	conversion_rate: me.frm.doc.conversion_rate,
	price_list: me.frm.doc.selling_price_list || me.frm.doc.buying_price_list,
	price_list_currency: me.frm.doc.price_list_currency,
	plc_conversion_rate: me.frm.doc.plc_conversion_rate,
	company: me.frm.doc.company,
	order_type: me.frm.doc.order_type,
	is_pos: cint(me.frm.doc.is_pos),
	is_return: cint(me.frm.doc.is_return),
	is_subcontracted: me.frm.doc.is_subcontracted,
	ignore_pricing_rule: me.frm.doc.ignore_pricing_rule,
	doctype: me.frm.doc.doctype,
	name: me.frm.doc.name,
	project: item.project || me.frm.doc.project,
	qty: item.qty || 1,
	net_rate: item.rate,
	base_net_rate: item.base_net_rate,
	stock_qty: item.stock_qty,
	conversion_factor: item.conversion_factor,
	weight_per_unit: item.weight_per_unit,
	uom: item.uom,
	weight_uom: item.weight_uom,
	manufacturer: item.manufacturer,
	stock_uom: item.stock_uom,
	pos_profile: cint(me.frm.doc.is_pos) ? me.frm.doc.pos_profile : '',
	cost_center: item.cost_center,
	tax_category: me.frm.doc.tax_category,
	item_tax_template: item.item_tax_template,
	child_doctype: item.doctype,
	child_docname: item.name,
	is_old_subcontracting_flow: me.frm.doc.is_old_subcontracting_flow,
	}
	},
	callback: function(r) {
	if(!r.exc) {
	frappe.run_serially([
	() => {
	if (item.docstatus === 0
	&& frappe.meta.has_field(item.doctype, "use_serial_batch_fields")
	&& !item.use_serial_batch_fields
	&& cint(frappe.user_defaults?.use_serial_batch_fields) === 1
	) {
	item["use_serial_batch_fields"] = 1;
	}
	},
	() => {
	var d = locals[cdt][cdn];
	me.add_taxes_from_item_tax_template(d.item_tax_rate);
	if (d.free_item_data && d.free_item_data.length > 0) {
	me.apply_product_discount(d);
	}
	},
	() => {
	// for internal customer instead of pricing rule directly apply valuation rate on item
	if ((me.frm.doc.is_internal_customer || me.frm.doc.is_internal_supplier) && me.frm.doc.represents_company === me.frm.doc.company) {
	me.get_incoming_rate(item, me.frm.posting_date, me.frm.posting_time,
	me.frm.doc.doctype, me.frm.doc.company);
	} else {
	me.frm.script_manager.trigger("price_list_rate", cdt, cdn);
	}
	},
	() => {
	if (me.frm.doc.is_internal_customer || me.frm.doc.is_internal_supplier) {
	me.calculate_taxes_and_totals();
	}
	},
	() => me.toggle_conversion_factor(item),
	() => {
	if (show_batch_dialog && !frappe.flags.trigger_from_barcode_scanner)
	return frappe.db.get_value("Item", item.item_code, ["has_batch_no", "has_serial_no"])
	.then((r) => {
	if (r.message &&
	(r.message.has_batch_no || r.message.has_serial_no)) {
	frappe.flags.hide_serial_batch_dialog = false;
	} else {
	show_batch_dialog = false;
	}
	});
	},
	() => {
	// check if batch serial selector is disabled or not
	if (show_batch_dialog && !frappe.flags.hide_serial_batch_dialog)
	return frappe.db.get_single_value('Stock Settings', 'disable_serial_no_and_batch_selector')
	.then((value) => {
	if (value) {
	frappe.flags.hide_serial_batch_dialog = true;
	}
	});
	},
	() => {
	if(show_batch_dialog && !frappe.flags.hide_serial_batch_dialog && !frappe.flags.dialog_set) {
	var d = locals[cdt][cdn];
	$.each(r.message, function(k, v) {
	if(!d[k]) d[k] = v;
	});
	if (d.has_batch_no && d.has_serial_no) {
	d.batch_no = undefined;
	}
	frappe.flags.dialog_set = true;
	erpnext.show_serial_batch_selector(me.frm, d, (item) => {
	me.frm.script_manager.trigger('qty', item.doctype, item.name);
	if (!me.frm.doc.set_warehouse)
	me.frm.script_manager.trigger('warehouse', item.doctype, item.name);
	me.apply_price_list(item, true);
	}, undefined, !frappe.flags.hide_serial_batch_dialog);
	} else {
	frappe.flags.dialog_set = false;
	}
	},
	() => me.conversion_factor(doc, cdt, cdn, true),
	() => me.remove_pricing_rule(item),
	() => {
	if (item.apply_rule_on_other_items) {
	let key = item.name;
	me.apply_rule_on_other_items({key: item});
	}
	},
	() => {
	var company_currency = me.get_company_currency();
	me.update_item_grid_labels(company_currency);
	}
	]);
	}
	}
	});
	}
	}
	}

But, due to a lack of UI test cases, this Reactivity is prone to regression, especially the ones related to discounts and free items. Check #42195 for more broken cases on Pricing Rules.

Long-Term Stability and Maintenance

To prevent frequent regression, moving most of the Reactivity to the server-side code makes sense, as it allows for server-side tests and a single source to maintain.

This PR is the first in that direction. It moves all of the UI Reactivity associated with Item selection to service-side.