cube-js/cube · error

Unsupported data type for List: {}

Error message

Unsupported data type for List: {}

What it means

When mapping Cube's internal DataType to a PostgreSQL wire type for list/array columns, only a fixed set of element types is translated. Any other element type falls into a catch-all unimplemented! panic, since no corresponding PgTypeId ARRAY OID exists in the mapping.

Source

Thrown at rust/cubesql/cubesql/src/sql/types.rs:70

            ColumnType::Int8 => PgTypeId::INT2,
            ColumnType::Int32 => PgTypeId::INT4,
            ColumnType::String | ColumnType::VarStr => PgTypeId::TEXT,
            ColumnType::Interval(_) => PgTypeId::INTERVAL,
            ColumnType::Date(_) => PgTypeId::DATE,
            ColumnType::Timestamp => PgTypeId::TIMESTAMP,
            ColumnType::Double => PgTypeId::NUMERIC,
            ColumnType::Decimal(_, _) => PgTypeId::NUMERIC,
            ColumnType::List(field) => match field.data_type() {
                DataType::Binary => PgTypeId::ARRAYBYTEA,
                DataType::Boolean => PgTypeId::ARRAYBOOL,
                DataType::Utf8 => PgTypeId::ARRAYTEXT,
                DataType::Int16 => PgTypeId::ARRAYINT2,
                DataType::Int32 => PgTypeId::ARRAYINT4,
                DataType::Int64 => PgTypeId::ARRAYINT8,
                DataType::UInt16 => PgTypeId::ARRAYINT2,
                DataType::UInt32 => PgTypeId::ARRAYINT4,
                DataType::UInt64 => PgTypeId::ARRAYINT8,
                dt => unimplemented!("Unsupported data type for List: {}", dt),
            },
        }
    }

    pub fn avg_size(&self) -> usize {
        match self {
            ColumnType::Boolean | ColumnType::Int8 => 1,
            ColumnType::Int32
            | ColumnType::Date(true)
            | ColumnType::Interval(IntervalUnit::YearMonth) => 4,
            ColumnType::Double
            | ColumnType::Int64
            | ColumnType::Date(false)
            | ColumnType::Interval(IntervalUnit::DayTime)
            | ColumnType::Timestamp => 8,
            ColumnType::Interval(IntervalUnit::MonthDayNano) | ColumnType::Decimal(_, _) => 16,
            ColumnType::String | ColumnType::VarStr => 64,
            ColumnType::Blob | ColumnType::List(_) => 128,

View on GitHub (pinned to 7d981676b3)

Solutions

1. Cast the array elements to a supported type (int) in the data model or query before returning
2. Avoid exposing array columns of unhandled element types over the Postgres protocol
3. Add the missing mapping (e.g. Utf8 -> a text array PgTypeId) in types.rs:70
4. Unnest the array into scalar rows in the query

Example fix

// before
dt => unimplemented!("Unsupported data type for List: {}", dt),
// after
DataType::Utf8 => PgTypeId::ARRAYTEXT,
dt => PgTypeId::ARRAYTEXT, // fallback with a warning log

fn list_element_supported(dt: &DataType) -> bool {
    matches!(dt, DataType::List(f) if matches!(f.data_type(), DataType::Int16|DataType::Int32|DataType::Int64|DataType::UInt16|DataType::UInt32|DataType::UInt64))
}

fn to_pg_array_type(dt: &DataType) -> Option<PgTypeId> {
    match dt { DataType::Int64 => Some(PgTypeId::ARRAYINT8), DataType::Utf8 => Some(PgTypeId::ARRAYTEXT), _ => None }
}

match to_pg_type(dt) {
    Some(t) => t,
    None => { log::warn!("falling back to text for {}", dt); PgTypeId::ARRAYTEXT }
}

When it happens

Trigger: add_attribute serializing a result column that is a List whose element DataType is not one of the handled numeric types — e.g. list of strings, booleans, decimals, or dates.

Common situations: Queries returning arrays of non-integer elements through the Postgres protocol; data models that expose array fields whose element types weren't anticipated by the type mapping table.

Related errors

• Unsupported data type: {:?}
• Unimplemented support for {:?}
• Unable to convert List of {} to string
• Unable to detect type for field "${f.name}" with dataTypeID:
• PostgreSQL can not work with table names longer than 63 symb

AI-assisted analysis of cube-js/cube@7d981676b3 (2026-09-02). Data as JSON: /api/errors/33d021443179fa6c. Report an issue: GitHub.