seitime-frappe/frappe/docs/user/en/guides/app-development/overriding-link-query-by-custom-script.md

Overriding Link Query By Custom Script

You can override the standard link query by using set_query

1. Adding Fitlers

You can add filters to the query:

frappe.ui.form.on("Bank Reconciliation", "onload", function(frm) {
	cur_frm.set_query("bank_account", function() {
		return {
			"filters": {
				"account_type": "Bank",
				"group_or_ledger": "Ledger"
			}
		};
	});
});

A more complex query:

frappe.ui.form.on("Bank Reconciliation", "onload", function(frm){
	cur_frm.set_query("bank_account", function(){
		return {
			"filters": [
				["Bank Account": "account_type", "=", "Bank"],
                            ["Bank Account": "group_or_ledger", "!=", "Group"]
			]
		}
	});
});

---

2. Calling a Different Method to Generate Results

You can also set a server side method to be called on the query:

frm.set_query("item_code", "items", function() {
	return {
		query: "erpnext.controllers.queries.item_query",
		filters: frm.doc.enquiry_type === "Maintenance" ?
			{"is_service_item": "Yes"} : {"is_sales_item": "Yes"}
	};
});

Custom Method

The custom method should return a list of items for auto select. If you want to send additional data, you can send multiple columns in the list.

Parameters to the custom method are:

def custom_query(doctype, txt, searchfield, start, page_len, filters)

Example:

# searches for leads which are not converted
def lead_query(doctype, txt, searchfield, start, page_len, filters):
	return frappe.db.sql("""select name, lead_name, company_name from `tabLead`
		where docstatus < 2
			and ifnull(status, '') != 'Converted'
			and ({key} like %(txt)s
				or lead_name like %(txt)s
				or company_name like %(txt)s)
			{mcond}
		order by
			if(locate(%(_txt)s, name), locate(%(_txt)s, name), 99999),
			if(locate(%(_txt)s, lead_name), locate(%(_txt)s, lead_name), 99999),
			if(locate(%(_txt)s, company_name), locate(%(_txt)s, company_name), 99999),
			name, lead_name
		limit %(start)s, %(page_len)s""".format(**{
			'key': searchfield,
			'mcond':get_match_cond(doctype)
		}), {
			'txt': "%%%s%%" % txt,
			'_txt': txt.replace("%", ""),
			'start': start,
			'page_len': page_len
		})

For more examples see:

https://github.com/frappe/erpnext/blob/develop/erpnext/controllers/queries.py