User-defined types

CQL user-defined types are ordered sets of named, typed fields. They must be defined in a keyspace:

CREATE TYPE ks.type1 (
  a int,
  b text,
  c float);

And can then be used as a column type in tables, or a field type in other user-defined types in that keyspace:

CREATE TABLE ks.collect_things (
  pk int,
  ck1 text,
  ck2 text,
  v frozen<type1>,
  PRIMARY KEY (pk, ck1, ck2)

CREATE TYPE ks.type2 (v frozen<type1>);

Fetching UDTs from results

The driver maps UDT columns to the UDTValue class, which exposes getters and setters to access individual fields by index or name:

Row row = session.execute("SELECT v FROM ks.collect_things WHERE pk = 1").one();

UDTValue udtValue = row.getUDTValue("v");
int a = udtValue.getInt(0);
String b = udtValue.getString("b");
Float c = udtValue.getFloat(2);

Using UDTs as parameters

Statements may contain UDTs as bound values:

PreparedStatement ps =
      "INSERT INTO ks.collect_things (pk, ck1, ck2, v) VALUES (:pk, :ck1, :ck2, :v)");

To create a new UDT value, you must first have a reference to its UserType. There are various ways to get it:

  • from the statement’s metadata

    UserType udt = (UserType) ps.getVariables().getType("v");
  • from the driver’s schema metadata:

    UserType udt = session.getCluster().getMetadata().getKeyspace("ks").getUserType("type1");
  • from another UDT value:

    UserType udt = udtValue.getType();

Note that the driver’s official API does not expose a way to build UserType instances manually. This is because the type’s internal definition must precisely match the database schema; if it doesn’t (for example if the fields are not in the same order), you run the risk of inserting corrupt data, that you won’t be able to read back.

Once you have the type, call newValue() and set the fields:

UDTValue udtValue = udt.newValue().setInt(0, 1).setString(1, "hello").setFloat(2, 2.3f);

And bind your UDT value like any other type:

BoundStatement bs =
        .setInt("pk", 1)
        .setString("ck1", "1")
        .setString("ck2", "1")
        .setUDTValue("v", udtValue);