Retrieving data from composite key via astyanax - cassandra

Question

I am very naive in cassandra & am using astyanax
CREATE TABLE employees (empID int, deptID int, first_name varchar,
last_name varchar, PRIMARY KEY (empID, deptID));
i want to get the values of query:
select * from employees where empID =2 and deptID = 800;
public void read(Integer empID, String deptID) {
OperationResult<ColumnList<String>> result;
try {
columnFamilies = ColumnFamily.newColumnFamily("employees", IntegerSerializer.get(), StringSerializer.get());
result = keyspace.prepareQuery(columnFamilies).getKey(empID).execute();
ColumnList<String> cols = result.getResult();
//Other stuff
}
how should i achieve this

Answer 1

As far as I can find, there isn't a super clean way to do this. You have to do it by executing a cql query and then iterating through the rows. This code is taken from the astynax examples file
public void read(int empId) {
logger.debug("read()");
try {
OperationResult<CqlResult<Integer, String>> result
= keyspace.prepareQuery(EMP_CF)
.withCql(String.format("SELECT * FROM %s WHERE %s=%d;", EMP_CF_NAME, COL_NAME_EMPID, empId))
.execute();
for (Row<Integer, String> row : result.getResult().getRows()) {
logger.debug("row: "+row.getKey()+","+row); // why is rowKey null?
ColumnList<String> cols = row.getColumns();
logger.debug("emp");
logger.debug("- emp id: "+cols.getIntegerValue(COL_NAME_EMPID, null));
logger.debug("- dept: "+cols.getIntegerValue(COL_NAME_DEPTID, null));
logger.debug("- firstName: "+cols.getStringValue(COL_NAME_FIRST_NAME, null));
logger.debug("- lastName: "+cols.getStringValue(COL_NAME_LAST_NAME, null));
}
} catch (ConnectionException e) {
logger.error("failed to read from C*", e);
throw new RuntimeException("failed to read from C*", e);
}
}
You just have to tune the cql query to return what you want. This is a bit frustrating because according to the documentation, you can do
Column<String> result = keyspace.prepareQuery(CF_COUNTER1)
.getKey(rowKey)
.getColumn("Column1")
.execute().getResult();
Long counterValue = result.getLongValue();
However I don't know what rowkey is. I've posted a question about what rowkey can be. Hopefully that will help