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The Query interface allows applications to obtain persistent instances
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, and an ordering specification.
The query namespace is modeled after methods in Java:
setClass corresponds to the class definition
declareParameters corresponds to formal parameters of a method
declareVariables corresponds to local variables of a method
setFilter and setOrdering correspond 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 if equal. 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.
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 Collection which the
user can iterate to get results. For future extension, the signature
of the execute methods specifies that they return an Object which
must be cast to Collection by the user.
Any parameters passed to the execute methods are used only for
this execution, and are not remembered for future execution.
| Method Summary | |
void |
close(java.lang.Object queryResult)
Close a query result and release any resources associated with it. |
void |
closeAll()
Close all query results associated with this Query instance, and release all
resources associated with them. |
void |
compile()
Verify the elements of the query and provide a hint to the query to prepare and optimize an execution plan. |
void |
declareImports(java.lang.String imports)
Set the import statements to be used to identify the fully qualified name of variables or parameters. |
void |
declareParameters(java.lang.String parameters)
Declare the list of parameters query execution. |
void |
declareVariables(java.lang.String variables)
Declare the unbound variables to be used in the query. |
java.lang.Object |
execute()
Execute the query and return the filtered Collection. |
java.lang.Object |
execute(java.lang.Object p1)
Execute the query and return the filtered Collection. |
java.lang.Object |
execute(java.lang.Object p1,
java.lang.Object p2)
Execute the query and return the filtered Collection. |
java.lang.Object |
execute(java.lang.Object p1,
java.lang.Object p2,
java.lang.Object p3)
Execute the query and return the filtered Collection. |
java.lang.Object |
executeWithArray(java.lang.Object[] parameters)
Execute the query and return the filtered Collection. |
java.lang.Object |
executeWithMap(java.util.Map parameters)
Execute the query and return the filtered Collection. |
boolean |
getIgnoreCache()
Get the ignoreCache option setting. |
PersistenceManager |
getPersistenceManager()
Get the PersistenceManager associated with this Query. |
void |
setCandidates(java.util.Collection pcs)
Set the candidate Collection to query. |
void |
setCandidates(Extent pcs)
Set the candidate Extent to query. |
void |
setClass(java.lang.Class cls)
Set the class of the candidate instances of the query. |
void |
setFilter(java.lang.String filter)
Set the filter for the query. |
void |
setIgnoreCache(boolean ignoreCache)
Set the ignoreCache option. |
void |
setOrdering(java.lang.String ordering)
Set the ordering specification for the result Collection. |
| Method Detail |
public void setClass(java.lang.Class cls)
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.
cls - the Class of the candidate instances.public void setCandidates(Extent pcs)
Extent to query.
pcs - the candidate Extent.public void setCandidates(java.util.Collection pcs)
Collection to query.
pcs - the candidate Collection.public void setFilter(java.lang.String filter)
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:
Class of the Query; and
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:
Date fields and Date
parameters are valid.
=, +=, etc. and pre- and post-increment
and -decrement are not supported. Therefore, there are no side
effects from evaluation of any expressions.
Collection.contains(Object o), Collection.isEmpty(),
String.startsWith(String s), and String.endsWith(String e).
Implementations might choose to support non-mutating method
calls as non-standard extensions.
null-valued field, which would throw
NullPointerException, is treated as if the filter expression
returned false for 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.
Collection types) is
specified using a variable declaration and the
Collection.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.
filter - the query filter.public void declareImports(java.lang.String imports)
String with semicolon-separated
statements.
The String parameter to this method follows the syntax of the
import statement of the Java language.
imports - import statements separated by semicolons.public void declareParameters(java.lang.String parameters)
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 - the list of parameters separated by commas.public void declareVariables(java.lang.String variables)
String
containing one or more unbound variable declarations separated
with semicolons. It follows the syntax for local variables in
the Java language.
variables - the variables separated by semicolons.public void setOrdering(java.lang.String ordering)
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.
ordering - the ordering specification.public void setIgnoreCache(boolean ignoreCache)
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.
ignoreCache - the setting of the ignoreCache option.public boolean getIgnoreCache()
setIgnoreCache(boolean)public void compile()
public java.lang.Object execute()
Collection.executeWithArray(Object[] parameters)public java.lang.Object execute(java.lang.Object p1)
Collection.
p1 - the value of the first parameter declared.
Collection.executeWithArray(Object[] parameters)public java.lang.Object execute(java.lang.Object p1,
java.lang.Object p2)
Collection.
p1 - the value of the first parameter declared.p2 - the value of the second parameter declared.
Collection.executeWithArray(Object[] parameters)public java.lang.Object execute(java.lang.Object p1,
java.lang.Object p2,
java.lang.Object p3)
Collection.
p1 - the value of the first parameter declared.p2 - the value of the second parameter declared.p3 - the value of the third parameter declared.
Collection.executeWithArray(Object[] parameters)public java.lang.Object executeWithMap(java.util.Map parameters)
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 - the Map containing all of the parameters.
Collection.executeWithArray(Object[] parameters)public java.lang.Object executeWithArray(java.lang.Object[] parameters)
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 - the Object array with all of the parameters.
Collection.public PersistenceManager getPersistenceManager()
PersistenceManager associated with this Query.
If this Query was restored from a serialized form, it has no
PersistenceManager, and this method returns null.
PersistenceManager associated with this Query.public void close(java.lang.Object queryResult)
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().
queryResult - the result of execute(...) on this Query instance.public void closeAll()
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().
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