dgraph-io/dgraph · error

Fn %s not supported in preprocessFilter.

Error message

Fn %s not supported in preprocessFilter.

What it means

During preprocessing of a filter tree into a facet filter tree, only certain function types (facet comparators) are allowed. If a function name parsed from the query is not in the supported set, preprocessFilter rejects it with this error.

Source

Thrown at worker/task.go:2466

			for _, typeID := range commonTypeIDs {
				// TODO: if conversion is not possible we are not putting anything to map. In
				// applyFacetsTree we check if entry for a type is not present, we try to convert
				// it. This double conversion can be avoided.
				cv, err := types.Convert(ftree.function.val, typeID)
				if err != nil {
					continue
				}
				ftree.function.typesToVal[typeID] = cv
			}
		case standardFn:
			argTokens, aerr := tok.GetTermTokens(tree.Func.Args)
			if aerr != nil { // query error ; stop processing.
				return nil, aerr
			}
			sort.Strings(argTokens)
			ftree.function.tokens = argTokens
		default:
			return nil, errors.Errorf("Fn %s not supported in preprocessFilter.", fname)
		}
		return ftree, nil
	}

	for _, c := range tree.Children {
		ftreec, err := preprocessFilter(c)
		if err != nil {
			return nil, err
		}
		ftree.children = append(ftree.children, ftreec)
	}

	numChild := len(tree.Children)
	switch ftree.op {
	case "not":
		if numChild != 1 {
			return nil, errors.Errorf("Expected 1 child for not but got %d.", numChild)
		}

View on GitHub (pinned to 759e242be6)

Solutions

1. Use only supported facet functions (eq, le, ge, lt, gt) inside @facets.
2. Move non-facet predicates (has, uid_in, type) out of @facets into the edge filter or func().
3. Verify function availability for your Dgraph version.

Example fix

// before
friend @facets(uid_in(0x2))
// after
friend filter uid_in(0x2) { @facets(eq(name, "x")) }

const preprocessableFns = new Set(["eq","le","ge","lt","gt"]);
function checkFacetFns(query) {
  for (const m of query.matchAll(/@facets\((\w+)/g)) {
    if (!preprocessableFns.has(m[1])) throw new Error(`Fn not allowed in preprocessFilter: ${m[1]}`);
  }
}

try {
  return await txn.query(query);
} catch (e) {
  if (/not supported in preprocessFilter/.test(String(e))) {
    // move the offending predicate out of @facets and retry
  }
  throw e;
}

When it happens

Trigger: Using a function like uid_in, has, type(), or an unknown name inside an @facets filter, so the switch on fnType hits its default branch.

Common situations: Putting UID or scalar-predicate functions in facet filters; typos such as @facets(geq(x,1)); version drift where a function exists in newer Dgraph but not in the deployed one.

Related errors

• Cannot specify order at both args and facets
• One argument expected in %s, but got %d.
• Expected 1 child for not but got %d.
• Expected 2 child for not but got %d.
• Unsupported operation in facet filtering: %s.

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/65255be0787ccad6. Report an issue: GitHub.