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

Annotation Type Select

@Target(value=METHOD)
 @Retention(value=RUNTIME)
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. It is also possible for the method to only take a partial primary key (the first n columns), in which case it will return multiple entities.

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);
 

The generated SELECT query can be further customized with limit(), perPartitionLimit(), orderBy(), groupBy() and allowFiltering(). Some of these clauses can also contain placeholders whose values will be provided through additional method parameters. Note that it is sometimes not possible to determine if a parameter is a primary key component or a placeholder value; therefore the rule is that if your method takes a partial primary key, the first parameter that is not a primary key component must be explicitly annotated with CqlName. For example if the primary key is ((day int, hour int, minute int), ts timestamp):

 // Annotate 'l' so that it's not mistaken for the second PK component
 @Select(limit = ":l")
 PagingIterable<Sale> findDailySales(int day, @CqlName("l") int l);
 

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
boolean	allowFiltering Whether to add an ALLOW FILTERING clause to the SELECT query.
String	customWhereClause A custom WHERE clause for the SELECT query.
String[]	groupBy A list of column names to be added to a GROUP BY clause in the SELECT query.
String	limit The LIMIT to use in the SELECT query.
String[]	orderBy A list of orderings to add to an ORDER BY clause in the SELECT query.
String	perPartitionLimit The PER PARTITION LIMIT to use in 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:

""

limit

public abstract String limit

The LIMIT to use in the SELECT query.

If this starts with ":", it is interpreted as a named placeholder (that must have a corresponding parameter in the method signature). Otherwise, it must be a literal integer value.

If the placeholder name is invalid or the literal can't be parsed as an integer (according to the rules of Integer.parseInt(String)), the mapper will issue a compile-time warning.

Default:

""

perPartitionLimit

public abstract String perPartitionLimit

The PER PARTITION LIMIT to use in the SELECT query.

If this starts with ":", it is interpreted as a named placeholder (that must have a corresponding parameter in the method signature). Otherwise, it must be a literal integer value.

If the placeholder name is invalid or the literal can't be parsed as an integer (according to the rules of Integer.parseInt(String)), the mapper will issue a compile-time warning.

Default:

""

orderBy

public abstract String[] orderBy

A list of orderings to add to an ORDER BY clause in the SELECT query.

Each element must be a column name followed by a space and the word "ASC" or "DESC". If there are multiple columns, pass an array:

 @Select(orderBy = {"hour DESC", "minute DESC"})
 

If an element can't be parsed, the mapper will issue a compile-time error.

Default:

{}

groupBy

public abstract String[] groupBy

A list of column names to be added to a GROUP BY clause in the SELECT query.

Default:

{}

allowFiltering

public abstract boolean allowFiltering

Whether to add an ALLOW FILTERING clause to the SELECT query.

Default:

false