fetch_from & depends_on¶

fetch_from — Auto-Populate from Linked Documents¶

When a document has a Link field, you can auto-fetch values from the linked document.

Example¶

An Employee DocType has a department Link field. You want department_name to auto-fill:

{
  "fieldname": "department",
  "label": "Department",
  "fieldtype": "Link",
  "options": "Department"
},
{
  "fieldname": "department_name",
  "label": "Department Name",
  "fieldtype": "Data",
  "read_only": true,
  "fetch_from": "department.department_name"
}

Format: link_fieldname.source_fieldname

When the user saves with department = "DEP-001", the server fetches department_name from the Department document and sets it on the Employee.

How It Works¶

Runs before hooks (validate, before_save) on both insert and update
Groups fetches by link field — multiple fetch_from fields pointing to the same link = one DB query
Clears fetched fields when the link is emptied

Frontend¶

The Form page also fetches on the client side when the Link field changes (for instant UI feedback). The server-side fetch is the authoritative one.

mandatory_depends_on — Conditional Required Fields¶

Make a field required only when a condition is met.

{
  "fieldname": "rejection_reason",
  "label": "Rejection Reason",
  "fieldtype": "Text",
  "mandatory_depends_on": "eval:doc.status == \"Rejected\""
}

If status is "Rejected" and rejection_reason is empty, save will fail with a validation error.

Supported Expressions¶

Expression	Meaning
`fieldname`	Truthy check (non-empty, non-zero, non-null)
`eval:doc.fieldname`	Same, with Frappe-style prefix
`eval:doc.status == "Active"`	Equality check
`eval:doc.type != "Draft"`	Inequality check

depends_on — Conditional Field Visibility¶

Controls whether a field is shown in the form (client-side only):

{
  "fieldname": "shipping_address",
  "label": "Shipping Address",
  "fieldtype": "Text",
  "depends_on": "eval:doc.requires_shipping"
}

When requires_shipping is falsy, the field is hidden.

read_only_depends_on — Conditional Read-Only¶

{
  "fieldname": "amount",
  "label": "Amount",
  "fieldtype": "Currency",
  "read_only_depends_on": "eval:doc.is_locked"
}