Using Tuples with the Java driver
Cassandra allows to use tuple
data types in tables and user-defined types:
CREATE TABLE ks.collect_things (
pk int,
ck1 text,
ck2 text,
v tuple<int, text, float>,
PRIMARY KEY (pk, ck1, ck2)
);
Fetching Tuples from Rows results
The DataStax Java driver exposes a special TupleValue
class to handle such columns.
TupleValue
exposes getters allowing to extract from the tuple all the data types
supported by Cassandra:
Row row = session.execute("SELECT v FROM ks.collect_things WHERE pk = 1").one();
TupleValue tupleValue = row.getTupleValue("v");
int firstValueInTuple = tupleValue.getInt(0);
String secondValueInTuple = tupleValue.getString(1);
Float thirdValueInTuple = tupleValue.getFloat(2);
Using tuples as statement parameters
A prepared statement may contain a Tuple as a query parameter. In such cases, users
will need to create or gather a TupleType
first, in order to be able to create a TupleValue
to bind:
PreparedStatement ps = session.prepare("INSERT INTO ks.collect_things (pk, ck1, ck2, v) VALUES (:pk, :ck1, :ck2, :v)");
TupleType tupleType = cluster.getMetadata().newTupleType(DataType.cint(), DataType.text(), DataType.cfloat());
BoundStatement bs = ps.bind();
bs.setInt("pk", 1);
bs.setString("ck1", "1");
bs.setString("ck2", "1");
bs.setTupleValue("v", tupleType.newValue(1, "hello", 2.3f));
session.execute(bs);
The method newValue(Object...)
follows the same rules as new SimpleStatement(String, Object...)
;
there can be ambiguities due to the fact that the driver will infer the data types from the values
given in parameters of the method, whereas the data types required may differ (numeric
literals are always interpreted as int
).
To avoid such ambiguities, a TupleValue
returned by newValue()
also exposes specific
setters for all the existing Cassandra data types:
TupleType tupleType = cluster.getMetadata().newTupleType(DataType.bigint(), DataType.text(), DataType.cfloat());
TupleValue value = tupleType.newValue().setLong(0, 2).setString(1, "hello").setDouble(2, 2.3f);
More use cases
Users can also define single-usage tuples in SELECT queries with the IN
keyword
(called a “multi-column IN restriction”), usually for tables with composite clustering
keys. In this case, a tuple will be usable the same way it was for prepared statements’ parameters:
TupleType oneTimeUsageTuple = cluster.getMetadata().newTupleType(DataType.text(), DataType.text());
PreparedStatement ps = session.prepare("SELECT * FROM ks.collect_things WHERE pk = 1 and (ck1, ck2) IN (:t)");
BoundStatement bs = ps.bind();
bs.setTupleValue("t", oneTimeUsageTuple.newValue("1", "1"));
session.execute(bs);
More generally, the IN
keyword in a SELECT
query will be used to define a list of
desired values of the filtered clustering keys, those would simply be bound as a list of
TupleValue
with the Java driver:
TupleType oneTimeUsageTuple = cluster.getMetadata().newTupleType(DataType.text(), DataType.text());
PreparedStatement ps = session.prepare("SELECT * FROM ks.collect_things WHERE pk = 1 AND (ck1, ck2) IN :l");
BoundStatement bs = ps.bind();
bs.setList("l", Arrays.asList(oneTimeUsageTuple.newValue("1", "1"), oneTimeUsageTuple.newValue("1", "2"), oneTimeUsageTuple.newValue("2", "1")));
session.execute(bs);