dgraph-io/dgraph · error

Expected 2 child for not but got

Error message

Expected 2 child for not but got %d.

What it means

The `and` branch of the facet filter arity check requires exactly two children. The message text mistakenly says "for not" (a known copy-paste quirk in the message string), but the failure is an AND node with child count other than 2.

Solutions

1. Limit each AND to two operands and nest the rest: (a AND b) AND c.
2. Recheck the query's boolean tree shape; the confusing message still points to an arity problem on an `and` node.
3. Ensure generated queries produce binary AND nodes.

Example fix

// before
@facets(eq(a,"1") AND eq(b,"2") AND eq(c,"3"))
// after
@facets((eq(a,"1") AND eq(b,"2")) AND eq(c,"3"))

function validateAndArity(tree) {
  if (tree.op === "and" && tree.children.length !== 2)
    throw new Error("and must have exactly 2 children in facet filter");
  (tree.children || []).forEach(validateAndArity);
}

try {
  return await txn.query(query);
} catch (e) {
  if (/Expected 2 child/.test(String(e))) {
    // binarize AND/OR nodes and retry
  }
  throw e;
}

When it happens

Trigger: An AND facet filter with one or three-plus operands, e.g. @facets(eq(a,"1") AND eq(b,"2") AND eq(c,"3")) built as a flat 3-child AND.

Common situations: Writing multi-term AND facet filters expecting n-ary support; query builders emitting n-ary AND nodes.

Related errors

• Expected 1 child for not but got
• Cannot specify order at both args and facets
• Fn not supported in preprocessFilter.
• One argument expected in
• Unsupported operation in facet filtering

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/1187d0b5d628a2bf. Report an issue: GitHub.

Appendix: source

Thrown at worker/task.go:2487

	}

	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)
		}
	case "and":
		if numChild != 2 {
			return nil, errors.Errorf("Expected 2 child for not but got %d.", numChild)
		}
	case "or":
		if numChild != 2 {
			return nil, errors.Errorf("Expected 2 child for not but got %d.", numChild)
		}
	default:
		return nil, errors.Errorf("Unsupported operation in facet filtering: %s.", tree.Op)
	}
	return ftree, nil
}

type countParams struct {
	readTs  uint64
	counts  []int64
	attr    string
	gid     uint32
	reverse bool   // If query is asking for ~pred
	fn      string // function name

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