quickwit-oss/quickwit · error

subfield ` ` not supported inside a concatenate field

Error message

subfield `{}` not supported inside a concatenate field

What it means

A `concatenate` field listed a sub-field whose mapped type does not support concatenation (supported_for_concat() is false). Only certain leaf types (text-like fields) can feed a concatenate field, and the referenced field's type failed this test.

Solutions

1. Remove the unsupported field from the concatenate field's concatenate_fields list.
2. Index that field additionally as text (via a second field or mapping change) if text search over it is required.
3. Check which types implement supported_for_concat and only list those (text-ish) fields.

Example fix

// before
concatenate:
  all: [title, timestamp]
// after
concatenate:
  all: [title, description]

for sub in &concatenate_options.concatenate_fields {
    if let Some(entry) = mapping.get(sub) {
        if !entry.mapping_type.supported_for_concat() {
            return Err(format!("field `{sub}` type not supported for concatenate"));
        }
    }
}

When it happens

Trigger: build_mapping_tree with a concatenate field whose concatenate_fields list references, e.g., a u64/i64/datetime/bool field, or a json field that is not supported for concat.

Common situations: Adding numeric or date fields to a concatenate list expecting full-text search over them; copy-pasting an Elasticsearch copy_to config onto numeric fields; typos leading to the wrong field being matched.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• duplicated field definition
• `dynamic_mapping` is only allowed with mode=dynamic.
• expected LargeStringArray for service col page
• expected StringArray for service col page
• field name ` ` contains illegal characters. field names…

AI-assisted analysis of quickwit-oss/quickwit@a39730c5cd (2026-09-08). Data as JSON: /api/errors/903977064ac472a4. Report an issue: GitHub.

Appendix: source

Thrown at quickwit/quickwit-doc-mapper/src/doc_mapper/mapping_tree.rs:1060

            // we only pushed Concatenate fields in `concatenate_fields`
            unreachable!();
        };
        let name = &concatenate_field_entry.name;
        if mapping_node.branches.contains_key(name) {
            bail!("duplicated field definition `{}`", name);
        }
        let text_options: JsonObjectOptions = options.clone().into();
        let field = schema.add_json_field(name, text_options);
        for sub_field in &options.concatenate_fields {
            for matched_field in
                mapping_node
                    .find_field_mapping_leaf(sub_field)
                    .ok_or_else(|| {
                        anyhow::anyhow!("concatenate field uses an unknown field `{sub_field}`")
                    })?
            {
                if !matched_field.typ.supported_for_concat() {
                    bail!(
                        "subfield `{}` not supported inside a concatenate field",
                        sub_field
                    );
                }
                matched_field.concatenate.push(field);
            }
        }
        if options.include_dynamic_fields {
            concatenate_dynamic_fields.push(field);
        }
    }
    Ok(MappingNodeRoot {
        field_mappings: mapping_node,
        concatenate_dynamic_fields,
    })
}

fn get_numeric_options_for_bool_field(

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