DAOs

Quick overview

Interface annotated with @Dao.

• interface-level annotations:
  • @DefaultNullSavingStrategy
  • @HierarchyScanStrategy
• method-level annotations: query methods (see child pages).
• instantiated from a @DaoFactory method on the mapper.

A DAO is an interface that defines a set of query methods. In general, those queries will relate to the same entity (although that is not a requirement).

It must be annotated with @Dao:

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

  @Insert
  void save(Product product);

  @Delete
  void delete(Product product);
}

Query methods

To add queries, define methods on your interface and mark them with one of the following annotations:

• @Delete
• @GetEntity
• @Insert
• @Query
• @QueryProvider
• @Select
• @SetEntity
• @Update
• @Increment

The methods can have any name. The allowed parameters and return type are specific to each annotation.

Runtime usage

To obtain a DAO instance, use a factory method on the mapper interface.

InventoryMapper inventoryMapper = new InventoryMapperBuilder(session).build();
ProductDao dao = inventoryMapper.productDao("someKeyspace");

The returned object is thread-safe, and can securely be shared throughout your application.

Inheritance

DAOs can benefit from inheriting methods from other interfaces. This is useful when you have a common set of query methods that could be shared between entities. For example, using the class hierarchy defined in Entity Inheritance, one may define a set of DAO interfaces in the following manner:

interface BaseDao<T> {
  @Insert
  void save(T t);

  @Select
  T findById(UUID id);
  
  @SetEntity
  void bind(T t, BoundStatementBuilder builder);
}

@Dao
interface CircleDao extends BaseDao<Circle> {}

@Dao
interface RectangleDao extends BaseDao<Rectangle> {}

@Dao
interface SphereDao extends BaseDao<Sphere> {}

@Mapper
public interface ShapeMapper {
  @DaoFactory
  CircleDao circleDao(@DaoKeyspace CqlIdentifier keyspace);

  @DaoFactory
  RectangleDao rectangleDao(@DaoKeyspace CqlIdentifier keyspace);

  @DaoFactory
  SphereDao sphereDao(@DaoKeyspace CqlIdentifier keyspace);
}

Note that interfaces that declare generic type variables should not be annotated with @Dao.

In addition to inheriting methods from parent interfaces, interface-level annotations such as @DefaultNullSavingStrategy are also inherited:

import static com.datastax.oss.driver.api.mapper.entity.saving.NullSavingStrategy.SET_TO_NULL;

@DefaultNullSavingStrategy(SET_TO_NULL)
interface BaseDao {
}

@Dao
interface RectangleDao extends BaseDao {}

Annotation priority is driven by proximity to the @Dao-annotated interface. For example:

import static com.datastax.oss.driver.api.mapper.entity.saving.NullSavingStrategy.SET_TO_NULL;
import static com.datastax.oss.driver.api.mapper.entity.saving.NullSavingStrategy.DO_NOT_SET;

@DefaultNullSavingStrategy(SET_TO_NULL)
interface BaseDao {
}

@Dao
@DefaultNullSavingStrategy(DO_NOT_SET)
interface RectangleDao extends BaseDao {}

In this case @DefaultNullSavingStrategy(DO_NOT_SET) on RectangleDao would override the annotation on BaseDao.

If two parent interfaces at the same level declare the same annotation, the priority of annotation chosen is controlled by the order the interfaces are declared, for example:

interface RectangleDao extends Dao1, Dao2 {}

In this case, any annotations declared in Dao1 would be chosen over Dao2.

To control how the hierarchy is scanned, annotate interfaces with @HierarchyScanStrategy.