com.datastax.oss.driver.api.mapper.annotations

Annotation Type Select

@Target(value=METHOD)
 @Retention(value=CLASS)
public @interface Select

Annotates a Dao method that selects one or more rows, and maps them to instances of an Entity-annotated class.

Example:

 @Dao
 public interface ProductDao {
   @Select
   Product findById(UUID productId);
 }
 

Parameters

If customWhereClause() is empty, the mapper defaults to a selection by primary key (partition key + clustering columns). The method's parameters must match the types of the primary key columns, in the exact order (which is defined by the integer values of the PartitionKey and ClusteringColumn annotations in the entity class). The parameter names don't necessarily need to match the names of the columns.

If customWhereClause() is not empty, it completely replaces the WHERE clause. The provided string can contain named placeholders. In that case, the method must have a corresponding parameter for each, with the same name and a compatible Java type:

 @Select(customWhereClause = "description LIKE :searchString")
 PagingIterable<Product> findByDescription(String searchString);
 

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.

Return type

In all cases, the method can return:

• the entity class itself. If the query returns no rows, the method will return null. If it returns more than one row, subsequent rows will be discarded.

   @Select
   Product findById(UUID productId);
         

• an Optional of the entity class. If the query returns no rows, the method will return Optional.empty(). If it returns more than one row, subsequent rows will be discarded.

   @Select
   Optional<Product> findById(UUID productId);
         

• a PagingIterable of the entity class. It behaves like a result set, except that each element is a mapped entity instead of a row.

   @Select(customWhereClause = "description LIKE :searchString")
   PagingIterable<Product> findByDescription(String searchString);
         

• a CompletionStage or CompletableFuture of any of the above. The method will execute the query asynchronously. Note that for iterables, you need to switch to the asynchronous equivalent MappedAsyncPagingIterable.

   @Select
   CompletionStage<Product> findByIdAsync(UUID productId);
  
   @Select
   CompletionStage<Optional<Product>> findByIdAsync(UUID productId);
  
   @Select(customWhereClause = "description LIKE :searchString")
   CompletionStage<MappedAsyncPagingIterable<Product>> findByDescriptionAsync(String searchString);
         

Target keyspace and table

If a keyspace was specified when creating the DAO (see DaoFactory), 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).

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
String	customWhereClause A custom WHERE clause for the SELECT query.

Element Detail

customWhereClause

public abstract String customWhereClause

A custom WHERE clause for the SELECT query.

If this is not empty, it completely replaces the WHERE clause in the generated query. Note that the provided string must not contain the WHERE keyword.

This clause can contain placeholders that will be bound with the method's parameters; see the top-level javadocs of this class for more explanations.

Default:

""