Class ColumnSelect<T>
- All Implemented Interfaces:
Serializable
,Query
,Select<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, PropertyFactory.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:
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Field Summary
FieldsFields inherited from class org.apache.cayenne.query.FluentSelect
dbEntityName, distinct, entityName, entityType, having, havingExpressionIsActive, metaData, orderings, where
Fields inherited from class org.apache.cayenne.query.AbstractQuery
root
Fields inherited from class org.apache.cayenne.query.CacheableQuery
logger
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Constructor Summary
ConstructorsModifierConstructorDescriptionprotected
protected
ColumnSelect
(ObjectSelect<T> select) Copy constructor to convert ObjectSelect to ColumnSelect -
Method Summary
Modifier and TypeMethodDescription<E> ColumnSelect
<Object[]> aggregate
(BaseProperty<E> property, String function, Class<E> type) Select result of some function, that aggregates values.avg
(NumericProperty<?> property) Select average value of propertyprotected <E> ColumnSelect
<E> columns
(Collection<Property<?>> properties) Add properties to select.Add properties to select.count()
Shortcut forcolumns(Property[])
columns}(Property.COUNT)count
(BaseProperty<?> property) Select COUNT(property)protected org.apache.cayenne.query.ColumnSelectMetadata
distinct()
Explicitly request distinct in query.protected org.apache.cayenne.query.ColumnSelectMetadata
Collection
<Property<?>> getMetaData
(EntityResolver resolver) Returns default select parameters.Appends a having qualifier expression of this query, using provided expression String and an array of position parameters.having
(Expression expression) Appends a having qualifier expression of this query.<E> ColumnSelect
<E> Maps result of this query by processing with a given function.max
(ComparableProperty<?> property) Select maximum value of propertymin
(ComparableProperty<?> property) Select minimum value of propertyselectFirst
(ObjectContext context) Selects a single object using provided context.<E extends Number>
ColumnSelect<Object[]> sum
(NumericProperty<E> property) Select sum of valuesExplicitly suppress distinct in query.Methods inherited from class org.apache.cayenne.query.FluentSelect
and, and, batchIterator, cacheGroup, cacheStrategy, cacheStrategy, castSelf, createSQLAction, dbEntityName, entityName, entityType, getActiveExpression, getDbEntityName, getEntityName, getEntityType, getHaving, getLimit, getOffset, getOrderings, getPageSize, getPrefetches, getQueryTimeout, getStatementFetchSize, getWhere, initWithProperties, isDistinct, isFetchingDataRows, iterate, iterator, joinExpression, limit, localCache, localCache, offset, or, or, orderBy, orderBy, orderBy, orderBy, pageSize, prefetch, prefetch, queryTimeout, resolveRoot, route, routePrefetches, select, selectOne, setActiveExpression, sharedCache, sharedCache, statementFetchSize, where, where
Methods inherited from class org.apache.cayenne.query.AbstractQuery
getRoot, setRoot, toString
Methods inherited from class org.apache.cayenne.query.CacheableQuery
getCacheGroup, getCacheStrategy, setCacheGroup, setCacheStrategy, useLocalCache, useLocalCache, useSharedCache, useSharedCache
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Field Details
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columns
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singleColumn
protected boolean singleColumn
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Constructor Details
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ColumnSelect
protected ColumnSelect() -
ColumnSelect
Copy constructor to convert ObjectSelect to ColumnSelect
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Method Details
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createMetadata
protected org.apache.cayenne.query.ColumnSelectMetadata createMetadata()- Specified by:
createMetadata
in classFluentSelect<T,
ColumnSelect<T>>
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columns
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:
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columns
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:
-
column
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count
Shortcut for
columns(Property[])
columns}(Property.COUNT) -
count
Select COUNT(property)
Can return different result than COUNT(*) as it will count only non null values
- See Also:
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min
Select minimum value of property
- See Also:
-
max
Select maximum value of property
- See Also:
-
avg
Select average value of property
- See Also:
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sum
Select sum of values
- See Also:
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aggregate
public <E> ColumnSelect<Object[]> aggregate(BaseProperty<E> property, String function, Class<E> type) Select result of some function, that aggregates values.
- Since:
- 5.0
- See Also:
-
having
Appends a having qualifier expression of this query. An equivalent toFluentSelect.and(Expression...)
that can be used a syntactic sugar.- Returns:
- this object
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having
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
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distinct
Explicitly request distinct in query. -
suppressDistinct
Explicitly suppress distinct in query. -
getColumns
- Overrides:
getColumns
in classFluentSelect<T,
ColumnSelect<T>>
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selectFirst
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.
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getMetaData
Description copied from class:AbstractQuery
Returns default select parameters.- Specified by:
getMetaData
in interfaceQuery
- Overrides:
getMetaData
in classAbstractQuery
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getBaseMetaData
protected org.apache.cayenne.query.ColumnSelectMetadata getBaseMetaData()- Specified by:
getBaseMetaData
in classCacheableQuery
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map
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
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