Overriding Link Query By Custom Script

You can override the standard link query by using set_query via the Client Script DocType from the desk.

The set_query method takes one of two formats: set_query(field_name, options_function()) for regular fields, or set_query(field_name, child_table_name, options_function()) for fields in child tables.

No1. RevisionsAdding Filters

You can add filters to the query:

frappe.ui.form.on("Bank Reconciliation", "onload", function(frm) {
 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){
 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
@frappe.whitelist()
@frappe.validate_and_sanitize_search_inputs
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': "%{}%".format(txt),
 '_txt': txt.replace("%", ""),
 'start': start,
 'page_len': page_len
 })

Note: @frappe.whitelist() is used to expose lead_query to the client-side and @frappe.validate_and_sanitize_search_inputs decorator is used to validate and sanitize user inputs sent through API or client-side request to avoid possible SQLi.

For more examples see:

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