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cassandracqldatastaxdatastax-java-driver
anatolyr
anatolyr

Reputation: 217

Cassandra BoundStatement with Multiple Parameters and Multi-Partition Query

After reading "Asynchronous queries with the Java driver" article in the datastax blog, I was trying to implement a solution similar to the one in the section called - 'Case study: multi-partition query, a.k.a. “client-side SELECT...IN“'.

I currently have code that looks something like this:

public Future<List<ResultSet>> executeMultipleAsync(final BoundStatement statement, final Object... partitionKeys) {
    List<Future<ResultSet>> futures = Lists.newArrayListWithExpectedSize(partitionKeys.length);
    for (Object partitionKey : partitionKeys) {
      Statement bs = statement.bind(partitionKey);
      futures.add(executeWithRetry(bs));
    }
    return Futures.successfulAsList(futures);
}

But, I'd like to improve on that. In the cql query this BoundStatement holds, I'd like to have something that looks like this:

SELECT * FROM <column_family_name> WHERE <param1> = :p1_name AND param2 = :p2_name AND <partiotion_key_name> = ?;

I'd like the clients of this method to give me a BoundStatement with an already bound parameters (two parameters in this case) and a list of partition keys. In this case, all I need to do, is bind the partition keys and execute the queries. Unfortunately, when I bind the key to this statement I fail with an error - com.datastax.driver.core.exceptions.InvalidTypeException: Invalid type for value 0 of CQL type varchar, expecting class java.lang.String but class java.lang.Long provided. The problem is, that I try to bind the key to the first parameter and not the last. Which is a string and not a long.

I can solve this by either giving the partition parameter a name but then I'd have to get the name via method parameters, or by specifying it's index which again will require an additional method parameter. Either way, if I use the name or the index I have to bind it with a specific type. For instance: bs.setLong("<key_name>", partitionKey);. For some reason, I can't leave it to the BoundStatement to interpret the type of the last parameter.

I'd like to avoid passing the parameter name explicitly and bypass the type problem. Is there anything that can be done?

Thanks!

Upvotes: 3

Views: 2008

Answers (1)

anatolyr
anatolyr

Reputation: 217

I've posted the same question in 'DataStax Java Driver for Apache Cassandra User Mailing List' and got an answer saying the functionality that I'm missing may be added in the next version (2.2) of the datastax java driver.

In JAVA-721 (to be introduced in 2.2) we are tentatively planning on adding the following methods with the signature to BoundStatement:

public BoundStatement setObject(int i, V v) public BoundStatement setObject(String name, V v)

and

You can emulate setObject in 2.1:

void setObject(BoundStatement bs, int position, Object object,
               ProtocolVersion protocolVersion) {
     DataType type =  bs.preparedStatement().getVariables().getType(position);
     ByteBuffer buffer = type.serialize(object, protocolVersion);
     bs.setBytesUnsafe(position, buffer);
 }

To avoid passing the parameter name, one thing you could do is look for a position that isn't bound yet:

int findUnsetPosition(BoundStatement bs) {
    int size = bs.preparedStatement().getVariables().size();
    for (int i = 0; i < size; i++)
        if (!bs.isSet(i))
            return i;
    throw new IllegalArgumentException("found no unset position");
}

I don't recommend it though, because it's ugly and unpredictable if the user forgot to bind one of the non-PK variables.

The way I would do it is require the user to pass a callback that sets the PK:

interface PKBinder<T> {
    void bind(BoundStatement bs, T pk);
}
public <T> Future<List<ResultSet>> executeMultipleAsync(final BoundStatement statement, PKBinder<T> pkBinder, final T...

partitionKeys)

As a bonus, this will also work with composite partition keys.

Upvotes: 3

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