javax.jdo.Query - JDO interface
javax.jdo
Interface Query
- Superinterfaces:
Serializable
Query interface allows applications to obtain persistent
instances, values, and aggregate data
from the data store.
The PersistenceManager is the factory for Query
instances. There may be many Query instances associated with a
PersistenceManager. Multiple queries might be executed
simultaneously by different threads, but the implementation might choose to
execute them serially. In either case, the implementation must be thread
safe.
There are three required elements in a Query: the class of
the results, the candidate collection of instances, and the filter.
There are optional elements: parameter declarations, variable declarations, import statements, ordering and grouping specifications, result and result class, the range of results, and flags indicating whether the query result is unique and whether the query can be modified.
The query namespace is modeled after methods in Java:
setClasscorresponds to the class definitiondeclareParameterscorresponds to formal parameters of a methoddeclareVariablescorresponds to local variables of a methodsetFilterandsetOrderingcorrespond to the method body
There are two namespaces in queries. Type names have their own namespace that is separate from the namespace for fields, variables and parameters.
The method setClass introduces the name of the candidate
class in the type namespace. The method declareImports
introduces the names of the imported class or interface types in the type
namespace. Imported type names must be unique. When used (e.g. in a parameter
declaration, cast expression, etc.) a type name must be the name of the
candidate class, the name of a class or interface imported by method
declareImports, or denote a class or interface from the same
package as the candidate class.
The method setClass introduces the names of the candidate
class fields.
The method declareParameters introduces the names of the
parameters. A name introduced by declareParameters hides the
name of a candidate class field of the same name. Parameter names must be
unique.
The method declareVariables introduces the names of the
variables. A name introduced by declareVariables hides the name
of a candidate class field if equal. Variable names must be unique and must
not conflict with parameter names.
The result of the query by default is a list of result class instances,
but might be specified via setResult. The class of the result
by default is the candidate class, but might be specified via
setResultClass.
A hidden field may be accessed using the 'this' qualifier:
this.fieldName.
The Query interface provides methods which execute the query
based on the parameters given. They return a single instance or a
List of result class instances which the
user can iterate to get results. The signature
of the execute methods specifies that they return an
Object which must be cast to the appropriate result by the user.
Any parameters passed to the execute methods are used only
for this execution, and are not remembered for future execution.
- Since:
- JDO 1.0
PersistenceManager.newQuery(String,Object) to identify that the
created query should obey the JDOQL syntax and semantic rules.
This is the default query language used when creating a query with any
of the other PersistenceManager.newQuery methods, except
PersistenceManager.newQuery(Object), which uses the query
language of the compiled query template object passed to that method.
- Since:
- JDO 2.0
PersistenceManager.newQuery(String,Object) to identify that
the created query should use SQL semantics. This is only
meaningful for relational JDO implementations.
If this is used, the Object argument to the
PersistenceManager.newQuery(String,Object) method
should be a String containing a SQL
SELECT statement.
- Since:
- JDO 2.0
- Parameters:
key- the key of the extensionvalue- the value of the extension
- Since:
- JDO 2.0
- Parameters:
sub- the subquery to add to this QueryvariableDeclaration- the name of the variable in the outer query to bind the results of the subquerycandidateCollectionExpression- the candidate collection of the subquery as an expression using terms of the outer query
- Since:
- JDO 2.1
- Parameters:
sub- the subquery to add to this QueryvariableDeclaration- the name of the variable to be used in this QuerycandidateCollectionExpression- the candidate collection to apply to the subqueryparameters- the expressions from the outer query to bind the parameter in the subquery
- Since:
- JDO 2.1
- Parameters:
sub- the subquery to add to this QueryvariableDeclaration- the name of the variable to be used in this QuerycandidateCollectionExpression- the candidate collection to apply to the subqueryparameter- the expression from the outer query to bind the parameter in the subquery
- Since:
- JDO 2.1
- Parameters:
sub- the subquery to add to this QueryvariableDeclaration- the name of the variable in the outer query to bind the results of the subquerycandidateCollectionExpression- the candidate collection of the subquery as an expression using terms of the outer queryparameters- the expressions from the outer query to bind the parameters in the subquery
- Since:
- JDO 2.1
execute(...) and might have
iterators open on it. Iterators associated with the query result are
invalidated: they return false to hasNext()
and throw NoSuchElementException to next().- Parameters:
queryResult- the result ofexecute(...)on thisQueryinstance.
- Since:
- JDO 1.0
Query
instance, and release all resources associated with them. The query
results might have iterators open on them. Iterators associated with the
query results are invalidated:
they return false to hasNext() and throw
NoSuchElementException to next().- Since:
- JDO 1.0
- Since:
- JDO 1.0
String with
semicolon-separated statements.
The String parameter to this method follows the syntax of
the import statement of the Java language.
- Parameters:
imports- import statements separated by semicolons.
- Since:
- JDO 1.0
String containing one or more
query parameter declarations separated with commas. Each parameter named
in the parameter declaration must be bound to a value when
the query is executed.
The String parameter to this method follows the syntax
for formal parameters in the Java language.
- Parameters:
parameters- the list of parameters separated by commas.
- Since:
- JDO 1.0
String containing one or more unbound variable declarations
separated with semicolons. It follows the syntax for local variables in
the Java language.- Parameters:
variables- the variables separated by semicolons.
- Since:
- JDO 1.0
Dirty instances of affected classes in the cache are first
flushed to the datastore. Instances in the cache or brought into
the cache as a result of executing one of the
deletePersistentAll
methods undergo life cycle changes as if deletePersistent
were called on them.
Specifically, if the class of deleted instances implements the delete callback interface, the corresponding callback methods are called on the deleted instances. Similarly, if there are lifecycle listeners registered for delete events on affected classes, the listener is called for each appropriate deleted instance.
Before returning control to the application, instances of affected classes in the cache are refreshed to reflect whether they were deleted from the datastore.
- Returns:
- the number of instances of the candidate class that were deleted
- Since:
- JDO 2.0
- Parameters:
parameters- for the query
- Returns:
- the number of instances of the candidate class that were deleted
- Since:
- JDO 2.0
- See Also:
deletePersistentAll()
- Parameters:
parameters- for the query
- Returns:
- the number of instances of the candidate class that were deleted
- Since:
- JDO 2.0
- See Also:
deletePersistentAll()
- Returns:
- the filtered
Collection.
- Since:
- JDO 1.0
Collection.- Parameters:
p1- the value of the first parameter declared.
- Returns:
- the filtered
Collection.
- Since:
- JDO 1.0
Collection.- Parameters:
p1- the value of the first parameter declared.p2- the value of the second parameter declared.
- Returns:
- the filtered
Collection.
- Since:
- JDO 1.0
Collection.- Parameters:
p1- the value of the first parameter declared.p2- the value of the second parameter declared.p3- the value of the third parameter declared.
- Returns:
- the filtered
Collection.
- Since:
- JDO 1.0
Collection.
The execution of the query obtains the values of the parameters and matches them against the declared parameters in order. The names of the declared parameters are ignored. The type of the declared parameters must match the type of the passed parameters, except that the passed parameters might need to be unwrapped to get their primitive values.
The filter, import, declared parameters, declared variables, and ordering statements are verified for consistency.
Each element in the candidate Collection is examined to
see that it is assignment compatible to the Class of the
query. It is then evaluated by the Boolean expression of the filter.
The element passes the filter if there exist unique values for all
variables for which the filter expression evaluates to true.
- Parameters:
parameters- theObjectarray with all of the parameters.
- Returns:
- the filtered
Collection.
- Since:
- JDO 1.0
Collection. The
query is executed with the parameters set by the Map values.
Each Map entry consists of a key which is the name of the
parameter in the declareParameters method, and a value which
is the value used in the execute method. The keys in the
Map and the declared parameters must exactly match or a
JDOUserException is thrown.- Parameters:
parameters- theMapcontaining all of the parameters.
- Returns:
- the filtered
Collection.
- Since:
- JDO 1.0
FetchPlan used by this
Query. Modifications of the returned fetch plan will not
cause this query's owning PersistenceManager's
FetchPlan to be modified.- Returns:
- the fetch plan used by this query
- Since:
- JDO 2.0
- Returns:
- the ignoreCache option setting.
- Since:
- JDO 1.0
- See Also:
setIgnoreCache
PersistenceManager associated with this
Query.
If this Query was restored from a serialized form, it has
no PersistenceManager, and this method returns
null.
- Returns:
- the
PersistenceManagerassociated with thisQuery.
- Since:
- JDO 1.0
- Returns:
- the current setting of the flag
- Since:
- JDO 2.0
Extent to query.- Parameters:
pcs- the candidateExtent.
- Since:
- JDO 1.0
Collection to query.- Parameters:
pcs- the candidateCollection.
- Since:
- JDO 1.0
The class specifies the class
of the candidates of the query. Elements of the candidate collection
that are of the specified class are filtered before being
put into the result Collection.
- Parameters:
cls- theClassof the candidate instances.
- Since:
- JDO 1.0
- Parameters:
extensions- the map of extensions
- Since:
- JDO 2.0
- See Also:
addExtension
The filter specification is a String containing a Boolean
expression that is to be evaluated for each of the instances
in the candidate collection. If the filter is not specified,
then it defaults to "true", which has the effect of filtering
the input Collection only for class type.
An element of the candidate collection is returned in the result if:
- it is assignment compatible to the candidate
Classof theQuery; and - for all variables there exists a value for which the filter
expression evaluates to
true.
The user may denote uniqueness in the filter expression by
explicitly declaring an expression (for example, e1 != e2).
Rules for constructing valid expressions follow the Java language, except for these differences:
- Equality and ordering comparisons between primitives and instances of wrapper classes are valid.
- Equality and ordering comparisons of
Datefields andDateparameters are valid. - White space (non-printing characters space, tab, carriage return, and line feed) is a separator and is otherwise ignored.
- The assignment operators
=,+=, etc. and pre- and post-increment and -decrement are not supported. Therefore, there are no side effects from evaluation of any expressions. - Methods, including object construction, are not supported, except
for
Collection.contains(Object o),Collection.isEmpty(),String.startsWith(String s), andString.endsWith(String e). Implementations might choose to support non-mutating method calls as non-standard extensions. - Navigation through a
null-valued field, which would throwNullPointerException, is treated as if the filter expression returnedfalsefor the evaluation of the current set of variable values. Other values for variables might still qualify the candidate instance for inclusion in the result set. - Navigation through multi-valued fields (
Collectiontypes) is specified using a variable declaration and theCollection.contains(Object o)method.
Identifiers in the expression are considered to be in the name
space of the specified class, with the addition of declared imports,
parameters and variables. As in the Java language, this is a
reserved word which means the element of the collection being evaluated.
Navigation through single-valued fields is specified by the Java
language syntax of field_name.field_name....field_name.
A JDO implementation is allowed to reorder the filter expression for optimization purposes.
- Parameters:
filter- the query filter.
- Since:
- JDO 1.0
- Parameters:
group- a comma-delimited list of expressions, optionally followed by the "having" keyword and a boolean expression
- Since:
- JDO 2.0
PersistenceManagerFactory or the
PersistenceManager used to create this Query.
The ignoreCache option setting specifies whether the query should execute
entirely in the back end, instead of in the cache. If this flag is set
to true, an implementation might be able to optimize the
query execution by ignoring changed values in the cache. For optimistic
transactions, this can dramatically improve query response times.- Parameters:
ignoreCache- the setting of the ignoreCache option.
- Since:
- JDO 1.0
Collection.
The ordering specification is a String containing one or
more ordering declarations separated by commas.
Each ordering declaration is the name of the field on which
to order the results followed by one of the following words:
"ascending" or "descending".
The field must be declared in the candidate class or must be a navigation expression starting with a field in the candidate class.
Valid field types are primitive types except boolean;
wrapper types except Boolean; BigDecimal;
BigInteger; String; and Date.
- Parameters:
ordering- the ordering specification.
- Since:
- JDO 1.0
setRange("50, 70"); or
setRange(":from, :to"); or
setRange("50, :to");.
The execution of the query is
modified to return only a subset of results. If the filter would
normally return 100 instances, and fromIncl is set to 50, and
toExcl is set to 70, then the first 50 results that would have
been returned are skipped, the next 20 results are returned and the
remaining 30 results are ignored. An implementation should execute
the query such that the range algorithm is done at the data store.- Parameters:
fromInclToExcl- comma-separated fromIncl and toExcl values
- Since:
- JDO 2.0
- See Also:
setRange(long, long)
- Parameters:
fromIncl- 0-based inclusive start indextoExcl- 0-based exclusive end index, orLong.MAX_VALUEfor no limit.
- Since:
- JDO 2.0
null, this query returns
instances of the query's candidate class. If set, this query
will return expressions, including field values (projections) and
aggregate function results.- Parameters:
data- a comma-delimited list of expressions (fields, functions on fields, or aggregate functions) to return from this query
- Since:
- JDO 2.0
execute or one of its siblings.
If the result is not set or set to null, the result class defaults
to the candidate class of the query. If the result consists of one
expression, the result class defaults to the type of that expression.
If the result consists of more than one expression, the result class
defaults to Object[].
The result class may be specified to be one of the java.lang classes
Character, Boolean, Byte, Short, Integer, Long, Float, Double, String,
or Object[]; or one of the java.math classes BigInteger or BigDecimal;
or the java.util class Date; or one of the java.sql classes Date,
Time, or Timestamp; or a user-defined class.
If there are multiple result expressions, the result class must be able to hold all elements of the result specification or a JDOUserException is thrown.
If there is only one result expression, the result class must be assignable from the type of the result expression or must be able to hold all elements of the result specification. A single value must be able to be coerced into the specified result class (treating wrapper classes as equivalent to their unwrapped primitive types) or by matching. If the result class does not satisfy these conditions, a JDOUserException is thrown.
A constructor of a result class specified in the setResult method will be used if the results specification matches the parameters of the constructor by position and type. If more than one constructor satisfies the requirements, the JDO implementation chooses one of them. If no constructor satisfies the results requirements, or if the result class is specified via the setResultClass method, the following requirements apply:
- A user-defined result class must have a no-args constructor and
one or more public
setorputmethods or fields. - Each result expression must match one of:
- a public field that matches the name of the result expression and is of the type (treating wrapper types equivalent to primitive types) of the result expression;
- or if no public field matches the name and type, a public
setor if neither of the above applies,a public method must be found with the signaturevoid put(Object, Object). During processing of the results, the first argument is the name of the result expression and the second argument is the value from the query result.
set- Parameters:
cls- the result class
- Since:
- JDO 2.0
- Parameters:
unique- if true, only one element is returned
- Since:
- JDO 2.0
- Since:
- JDO 2.0
This documentation page is derived (with some adjustments) from the JDO 2.2 API
and is available under the terms of the Apache License, v. 2.0.