List and Set

When reading columns with CQL list or set data types, the driver exposes them as native Arrays. When writing values to a list or set column, you can pass in a Array.

client.execute('SELECT list_val, set_val, double_val FROM tbl')
  .then(function (result) {
    console.log(Array.isArray(result.rows[0]['list_val'])); // true
    console.log(Array.isArray(result.rows[0]['set_val']));  // true


JavaScript objects are used to represent the CQL map data type in the driver, because JavaScript objects are associative arrays.

client.execute('SELECT map_val FROM tbl')
  .then(function (result) {
    console.log(JSON.stringify(result.rows[0]['map_val'])); // {"key1":1,"key2":2}

When using CQL maps, the driver needs a way to determine that the object instance passed as a parameter must be encoded as a map. Inserting a map as an object will fail:

const query = 'INSERT INTO tbl (id, map_val) VALUES (?, ?)';
const params = [id, {key1: 1, key2: 2}];
client.execute(query, params)
  .catch(function (err) {
    console.log(err) // TypeError: The target data type could not be guessed

To overcome this limitation, you should prepare your queries. Preparing and executing statements in the driver does not require chaining two asynchronous calls, you can set the prepare flag in the query options and the driver will handle the rest. The previous query, using the prepare flag, will succeed:

client.execute(query, params, { prepare: true });

ECMAScript Map and Set support

The new built-in types in ECMAScript 6, Map and Set, can be used to represent CQL map and set values. To enable this option, you should specify the constructors in the client options.

const options = {
  encoding: { 
    map: Map,
    set: Set

const client = new Client(options);

This way, when encoding or decoding map or set values, the driver uses those constructors:

client.execute('SELECT map_val FROM tbl')
  .then(function (result) {
    console.log(result.rows[0]['map_val'] instanceof Map); // true