Package org.apache.cayenne.query

Class ColumnSelect<T>

  • All Implemented Interfaces:
    Serializable, Query, Select<T>
    public class ColumnSelect<T>
extends FluentSelect<T>

    A helper builder for queries selecting individual properties based on the root object.

    It can be used to select properties of the object itself, properties of related entities or some function calls (including aggregate functions).

    Usage examples: 

     
      // select list of names:
      List<String> names = ObjectSelect.columnQuery(Artist.class, Artist.ARTIST_NAME).select(context);

      // select count:
      long count = ObjectSelect.columnQuery(Artist.class, Property.COUNT).selectOne();

      // select only required properties of an entity:
      List<Object[]> data = ObjectSelect.columnQuery(Artist.class, Artist.ARTIST_NAME, Artist.DATE_OF_BIRTH)
                                  .where(Artist.ARTIST_NAME.like("Picasso%))
                                  .select(context);

    Note: this class can't be instantiated directly. Use ObjectSelect.

    Since:
    4.0
    See Also:
    ObjectSelect.columnQuery(Class, Property), Serialized Form

    • Constructor Detail

      • ColumnSelect

        protected ColumnSelect()

      • ColumnSelect

        protected ColumnSelect​(ObjectSelect<T> select)
        Copy constructor to convert ObjectSelect to ColumnSelect

    • Method Detail

      • entityType

        public ColumnSelect<T> entityType​(Class<?> entityType)
        Sets the type of the entity to fetch without changing the return type of the query.
        Returns:
        this object

      • entityName

        public ColumnSelect<T> entityName​(String entityName)
        Sets the ObjEntity name to fetch without changing the return type of the query. This form is most often used for generic entities that don't map to a distinct class.
        Returns:
        this object

      • dbEntityName

        public ColumnSelect<T> dbEntityName​(String dbEntityName)
        Sets the DbEntity name to fetch without changing the return type of the query. This form is most often used for generic entities that don't map to a distinct class.
        Returns:
        this object

      • where

        public ColumnSelect<T> where​(String expressionString,
                             Object... parameters)
        Appends a qualifier expression of this query, using provided expression String and an array of position parameters. This is an equivalent to calling "and".
        Returns:
        this object

      • and

        public ColumnSelect<T> and​(Expression... expressions)
        AND's provided expressions to the existing WHERE clause expression.
        Returns:
        this object

      • or

        public ColumnSelect<T> or​(Expression... expressions)
        OR's provided expressions to the existing WHERE clause expression.
        Returns:
        this object

      • orderBy

        public ColumnSelect<T> orderBy​(String property)
        Add an ascending ordering on the given property. If there is already an ordering on this query then add this ordering with a lower priority.
        Parameters:
        property - the property to sort on
        Returns:
        this object

      • orderBy

        public ColumnSelect<T> orderBy​(String property,
                               SortOrder sortOrder)
        Add an ordering on the given property. If there is already an ordering on this query then add this ordering with a lower priority.
        Parameters:
        property - the property to sort on
        sortOrder - the direction of the ordering
        Returns:
        this object

      • orderBy

        public ColumnSelect<T> orderBy​(Ordering... orderings)
        Add one or more orderings to this query.
        Returns:
        this object

      • prefetch

        public ColumnSelect<T> prefetch​(String path,
                                int semantics)
        Merges a prefetch path with specified semantics into the query prefetch tree.
        Returns:
        this object

      • limit

        public ColumnSelect<T> limit​(int fetchLimit)
        Resets query fetch limit - a parameter that defines max number of objects that should be ever be fetched from the database.

      • offset

        public ColumnSelect<T> offset​(int fetchOffset)
        Resets query fetch offset - a parameter that defines how many objects should be skipped when reading data from the database.

      • pageSize

        public ColumnSelect<T> pageSize​(int pageSize)
        Resets query page size. A non-negative page size enables query result pagination that saves memory and processing time for large lists if only parts of the result are ever going to be accessed.

      • statementFetchSize

        public ColumnSelect<T> statementFetchSize​(int size)
        Sets fetch size of the PreparedStatement generated for this query. Only non-negative values would change the default size.
        See Also:
        Statement.setFetchSize(int)

      • localCache

        public ColumnSelect<T> localCache​(String cacheGroup)
        Instructs Cayenne to look for query results in the "local" cache when running the query. This is a short-hand notation for: 

         query.cacheStrategy(QueryCacheStrategy.LOCAL_CACHE, cacheGroup);

      • localCache

        public ColumnSelect<T> localCache()
        Instructs Cayenne to look for query results in the "local" cache when running the query. This is a short-hand notation for: 

         query.cacheStrategy(QueryCacheStrategy.LOCAL_CACHE);

      • sharedCache

        public ColumnSelect<T> sharedCache​(String cacheGroup)
        Instructs Cayenne to look for query results in the "shared" cache when running the query. This is a short-hand notation for: 

         query.cacheStrategy(QueryCacheStrategy.SHARED_CACHE, cacheGroup);

      • sharedCache

        public ColumnSelect<T> sharedCache()
        Instructs Cayenne to look for query results in the "shared" cache when running the query. This is a short-hand notation for: 

         query.cacheStrategy(QueryCacheStrategy.SHARED_CACHE);

      • columns

        public ColumnSelect<Object[]> columns​(Property<?>... properties)

        Add properties to select.

        Can be any properties that can be resolved against root entity type (root entity properties, function call expressions, properties of relationships, etc).

         
 List<Object[]> columns = ObjectSelect.columnQuery(Artist.class, Artist.ARTIST_NAME)
                                    .columns(Artist.ARTIST_SALARY, Artist.DATE_OF_BIRTH)
                                    .select(context);
        Parameters:
        properties - array of properties to select
        See Also:
        column(Property), columns(Collection)

      • columns

        public ColumnSelect<Object[]> columns​(Collection<Property<?>> properties)

        Add properties to select.

        Can be any properties that can be resolved against root entity type (root entity properties, function call expressions, properties of relationships, etc).

        Parameters:
        properties - collection of properties, must contain at least one element
        See Also:
        columns(Property[])

      • count

        public ColumnSelect<Object[]> count​(BaseProperty<?> property)

        Select COUNT(property)

        Can return different result than COUNT(*) as it will count only non null values

        See Also:
        count()

      • having

        public ColumnSelect<T> having​(Expression expression)
        Appends a having qualifier expression of this query. An equivalent to and(Expression...) that can be used a syntactic sugar.
        Returns:
        this object

      • having

        public ColumnSelect<T> having​(String expressionString,
                              Object... parameters)
        Appends a having qualifier expression of this query, using provided expression String and an array of position parameters. This is an equivalent to calling "and".
        Returns:
        this object

      • and

        public ColumnSelect<T> and​(Collection<Expression> expressions)
        AND's provided expressions to the existing WHERE or HAVING clause expression.
        Returns:
        this object

      • or

        public ColumnSelect<T> or​(Collection<Expression> expressions)
        OR's provided expressions to the existing WHERE or HAVING clause expression.
        Returns:
        this object

      • distinct

        public ColumnSelect<T> distinct()
        Explicitly request distinct in query.

      • suppressDistinct

        public ColumnSelect<T> suppressDistinct()
        Explicitly suppress distinct in query.

      • selectFirst

        public T selectFirst​(ObjectContext context)
        Description copied from interface: Select
        Selects a single object using provided context. The query itself can match any number of objects, but will return only the first one. It returns null if no objects were matched.

        If it matched more than one object, the first object from the list is returned. This makes 'selectFirst' different from Select.selectOne(ObjectContext), which would throw in this situation. 'selectFirst' is useful e.g. when the query is ordered and we only want to see the first object (e.g. "most recent news article"), etc.

        Selecting the first object via "Select.selectFirst(ObjectContext)" is more comprehensible than selecting via "ObjectContext.selectFirst(Select)", because implementations of "Select" set fetch size limit to one.

      • getBaseMetaData

        protected org.apache.cayenne.query.BaseQueryMetadata getBaseMetaData()
        Specified by:
        getBaseMetaData in class CacheableQuery

      • map

        public <E> ColumnSelect<E> map​(Function<T,​E> mapper)
        Maps result of this query by processing with a given function.
        Could be used to map plain Object[] to some domain-specific object.
        Note: this method could be called multiple time, result will be mapped by all functions in the call order.
        Type Parameters:
        E - new result type
        Parameters:
        mapper - function that maps result to the required type.
        Returns:
        this query with changed result type
        Since:
        4.2