Support for priming based on variables in Batch queries

[razvanth]

We are currently facing an issue trying to prime a batch query using Scassandra based on specific variables. This is similar to the MultiPrime API that was added recently but this currently does not support batch queries.

We've come up with a proposed api for priming batch queries based on variables (you can find it below).

It's worth noting that at the moment in order to prime a batch which uses prepared statements, you need to prime the prepared statement and the batch separately (see http://scassandra-docs.readthedocs.io/en/latest/java/batches/http://scassandra-docs.readthedocs.io/en/latest/java/batches/ ).

The proposed API would only require priming once, although we're not sure whether this adds additional complexity.

Happy to take feedback based on this and/or if you have any ideas on how else to deliver this functionality.

String query = "INSERT INTO table_name(column_1, column_2,column_3) VALUES (?,?,?);";

        MultiPrimeBatchRequest prime = MultiPrimeBatchRequest.request()
                .withWhen(when().withQuery(query))
                .withThen(
                        MultiPrimeBatchRequest.then()
                                .withVariableTypes(VARCHAR, VARCHAR, VARCHAR)
                                .withOutcomes(
                                    outcome(
                                        match().withVariableMatchers(exactMatch("StringToMatch"), anyMatch(), anyMatch()),
                                        action().withResult(Result.success)
                                    ),
                                    outcome(
                                        match().withVariableMatchers(exactMatch("DifferentStringToMatch"), anyMatch(), anyMatch()),
                                        action().withResult(Result.config_error)
                                    )
                                )
                ).build();

        scassandra.primingClient().multiPrimeBatch(prime);