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ScyllaDB Java Driver is available under the Apache v2 License. ScyllaDB Java Driver is a fork of DataStax Java Driver. See Copyright here.
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Annotate a DAO method with @Increment to generate a query that updates a counter table that is mapped to an entity:
// CREATE TABLE votes(article_id int PRIMARY KEY, up_votes counter, down_votes counter);
@Entity
public class Votes {
@PartitionKey private int articleId;
private long upVotes;
private long downVotes;
... // constructor(s), getters and setters, etc.
}
@Dao
public interface VotesDao {
@Increment(entityClass = Votes.class)
void incrementUpVotes(int articleId, long upVotes);
@Increment(entityClass = Votes.class)
void incrementDownVotes(int articleId, long downVotes);
@Select
Votes findById(int articleId);
}
The entity class must be specified with entityClass in the annotation.
The method’s parameters must start with the full primary key, in the exact order (as defined by the @PartitionKey and @ClusteringColumn annotations in the entity class). The parameter names don’t necessarily need to match the names of the columns, but the types must match. Unlike other methods like @Select or @Delete, counter updates cannot operate on a whole partition, they need to target exactly one row; so all the partition key and clustering columns must be specified.
Then must follow one or more parameters representing counter increments. Their type must be
long or java.lang.Long. The name of the parameter must match the name of the entity
property that maps to the counter (that is, the name of the getter without “get” and
decapitalized). Alternatively, you may annotate a parameter with @CqlName to specify the
raw column name directly; in that case, the name of the parameter does not matter:
@Increment(entityClass = Votes.class)
void incrementUpVotes(int articleId, @CqlName("up_votes") long foobar);
When you invoke the method, each parameter value is interpreted as a delta that will be applied
to the counter. In other words, if you pass 1, the counter will be incremented by 1. Negative values
are allowed. If you are using Cassandra 2.2 or above, you can use Long and pass null for some of
the parameters, they will be ignored (following NullSavingStrategy#DO_NOT_SET
semantics). If you are using Cassandra 2.1, null values will trigger a runtime error.
A Function<BoundStatementBuilder, BoundStatementBuilder> or UnaryOperator<BoundStatementBuilder>
can be added as the last parameter. It will be applied to the statement before execution. This
allows you to customize certain aspects of the request (page size, timeout, etc) at runtime. See
statement attributes.
The method can return void, a void CompletionStage or CompletableFuture, or a
ReactiveResultSet.
If a keyspace was specified when creating the DAO, then the generated query targets that keyspace. Otherwise, it doesn’t specify a keyspace, and will only work if the mapper was built from a session that has a default keyspace set.
If a table was specified when creating the DAO, then the generated query targets that table. Otherwise, it uses the default table name for the entity (which is determined by the name of the entity class and the naming convention).
Was this page helpful?
ScyllaDB Java Driver is available under the Apache v2 License. ScyllaDB Java Driver is a fork of DataStax Java Driver. See Copyright here.