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Scylla Java Driver Manual Mapper Mapper interface

Mapper interface¶

Quick overview¶

Interface annotated with @Mapper, entry point to mapper features.

a corresponding builder gets generated (default: [YourInterfacesName]Builder).
defines @DaoFactory methods that provide DAO instances. They can be parameterized by keyspace and/or table.

The mapper interface is the top-level entry point to mapping features. It wraps a core driver session, and acts as a factory of DAO objects that will be used to execute requests.

It must be annotated with @Mapper:

@Mapper
public interface InventoryMapper {
  @DaoFactory
  ProductDao productDao();
}

Mapper builder¶

For each mapper interface, a builder is generated. By default, it resides in the same package, and is named by appending a “Builder” suffix, for example InventoryMapper => InventoryMapperBuilder.

You can also use the builderName() element to specify a different name. It must be fully-qualified:

@Mapper(builderName = "com.acme.MyCustomBuilder")
public interface InventoryMapper {
  ...
}

The builder allows you to create a mapper instance, by wrapping a core CqlSession (if you need more details on how to create a session, refer to the core driver documentation).

CqlSession session = CqlSession.builder().build();
InventoryMapper inventoryMapper = new InventoryMapperBuilder(session).build();

One nice trick you can use is to create a static factory method on your interface. This hides the name of the generated class from the rest of your application:

@Mapper
public interface InventoryMapper {
  
  static MapperBuilder<InventoryMapper> builder(CqlSession session) {
    return new InventoryMapperBuilder(session);
  }
  ...
}

InventoryMapper inventoryMapper = InventoryMapper.builder(session).build();

Like the session, the mapper is a long-lived object: you should create it once at initialization time, and reuse it for the entire lifetime of your application. It doesn’t need to get closed. It is thread-safe.

DAO factory methods¶

The mapper’s main goal is to provide DAO instances. Your interface should provide one or more methods annotated with @DaoFactory, that return a DAO interface:

@DaoFactory
ProductDao productDao();

These methods can also receive a keyspace and/or table identifier as parameters (how those parameters affect the returned DAO is explained in the next section). They must be annotated with @DaoKeyspace and @DaoTable respectively, and be of type String or CqlIdentifier:

@DaoFactory
ProductDao productDao(@DaoKeyspace String keyspace, @DaoTable String table);

@DaoFactory
ProductDao productDao(@DaoKeyspace String keyspace);

@DaoFactory
ProductDao productDao(@DaoTable CqlIdentifier table);

You can also specify a default keyspace when building the mapper, it will be used for all methods that don’t have a @DaoKeyspace parameter:

InventoryMapper inventoryMapper = new InventoryMapperBuilder(session)
    .withDefaultKeyspace("keyspace1")
    .build();

The mapper maintains an interface cache. Calling a factory method with the same arguments will yield the same DAO instance:

ProductDao dao1 = inventoryMapper.productDao("keyspace1", "product");
ProductDao dao2 = inventoryMapper.productDao("keyspace1", "product");
assert dao1 == dao2;

DAO parameterization¶

Keyspace and table¶

The mapper allows you to reuse the same DAO interface for different tables. For example, given the following definitions:

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

@Mapper
public interface InventoryMapper {
  @DaoFactory
  ProductDao productDao();
  
  @DaoFactory
  ProductDao productDao(@DaoKeyspace String keyspace);
  
  @DaoFactory
  ProductDao productDao(@DaoKeyspace String keyspace, @DaoTable String table);
}

ProductDao dao1 = inventoryMapper.productDao();
ProductDao dao2 = inventoryMapper.productDao("keyspace2");
ProductDao dao3 = inventoryMapper.productDao("keyspace3", "table3");

dao1.findById executes the query SELECT ... FROM product WHERE id = ?. No table name was specified for the DAO, so it uses the default name for the Product entity (which in this case is the entity name converted with the default naming strategy). No keyspace was specified either, so the table is unqualified, and this DAO will only work with a session that was built with a default keyspace:
```
CqlSession session = CqlSession.builder().withKeyspace("keyspace1").build();
InventoryMapper inventoryMapper = new InventoryMapperBuilder(session).build();
ProductDao dao1 = inventoryMapper.productDao();
```
dao2.findById uses the DAO’s keyspace, and the default table name: SELECT ... FROM keyspace2.product WHERE id = ?.
dao3.findById uses the DAO’s keyspace and table name: SELECT ... FROM keyspace3.table3 WHERE id = ?.

The DAO’s keyspace and table can also be injected into custom query strings; see Query methods.

Execution profile¶

Similarly, a DAO can be parameterized to use a particular configuration profile:

@Mapper
public interface InventoryMapper {
  @DaoFactory
  ProductDao productDao(@DaoProfile String profileName);

  @DaoFactory
  ProductDao productDao(@DaoProfile DriverExecutionProfile profile);
}

The mapper will call setExecutionProfileName / setExecutionProfile on every generated statement.

Schema validation¶

The mapper validates entity mappings against the database schema at runtime. This check is performed every time you initialize a new DAO:

// Checks that entity 'Product' can be mapped to table or UDT 'keyspace1.product'
ProductDao dao1 = inventoryMapper.productDao("keyspace1", "product");

// Checks that entity 'Product' can be mapped to table or UDT 'keyspace2.product'
ProductDao dao2 = inventoryMapper.productDao("keyspace2", "product");

For each entity referenced in the DAO, the mapper tries to find a schema element with the corresponding name (according to the naming strategy). It tries tables first, then falls back to UDTs if there is no match. You can speed up this process by providing a hint:

import static com.datastax.oss.driver.api.mapper.annotations.SchemaHint.TargetElement.UDT;
import com.datastax.oss.driver.api.mapper.annotations.SchemaHint;

@Entity
@SchemaHint(targetElement = UDT)
public class Address { ... }

The following checks are then performed:

for each entity field, the database table or UDT must contain a column with the corresponding name (according to the naming strategy).
the types must be compatible, either according to the default type mappings, or via a custom codec registered with the session.
additionally, if the target element is a table, the primary key must be properly annotated in the entity.

If any of those steps fails, an IllegalArgumentException is thrown.

Schema validation adds a small startup overhead, so once your application is stable you may want to disable it:

InventoryMapper inventoryMapper = new InventoryMapperBuilder(session)
    .withSchemaValidationEnabled(false)
    .build();

You can also permanently disable validation of an individual entity by annotating it with @SchemaHint(targetElement = NONE).