javax.jdo
Interface Query

All Superinterfaces:

java.io.Serializable

public interface Query

extends java.io.Serializable

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.

Version:

1.0

Author:

Craig Russell

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

setClass

public void setClass(java.lang.Class cls)

Set the class of the candidate instances of the query.

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 - the Class of the candidate instances.

setCandidates

public void setCandidates(Extent pcs)

Set the candidate Extent to query.

Parameters:

pcs - the candidate Extent.

setCandidates

public void setCandidates(java.util.Collection pcs)

Set the candidate Collection to query.

Parameters:

pcs - the candidate Collection.

setFilter

public void setFilter(java.lang.String filter)

Set the filter for the query.

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 Class of the Query; 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 Date fields and Date parameters 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), and String.endsWith(String e). Implementations might choose to support non-mutating method calls as non-standard extensions.
• Navigation through a 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.
• Navigation through multi-valued fields (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.

Parameters:

filter - the query filter.

declareImports

public void declareImports(java.lang.String imports)

Set the import statements to be used to identify the fully qualified name of variables or parameters. Parameters and unbound variables might come from a different class from the candidate class, and the names need to be declared in an import statement to eliminate ambiguity. Import statements are specified as a 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.

declareParameters

public void declareParameters(java.lang.String parameters)

Declare the list of parameters query execution. The parameter declaration is a 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.

declareVariables

public void declareVariables(java.lang.String variables)

Declare the unbound variables to be used in the query. Variables might be used in the filter, and these variables must be declared with their type. The unbound variable declaration is a 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.

setOrdering

public void setOrdering(java.lang.String ordering)

Set the ordering specification for the result 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.

setIgnoreCache

public void setIgnoreCache(boolean ignoreCache)

Set the ignoreCache option. The default value for this option was set by the 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.

getIgnoreCache

public boolean getIgnoreCache()

Get the ignoreCache option setting.

Returns:

the ignoreCache option setting.

See Also:

setIgnoreCache(boolean)

compile

public void compile()

Verify the elements of the query and provide a hint to the query to prepare and optimize an execution plan.

execute

public java.lang.Object execute()

Execute the query and return the filtered Collection.

Returns:

the filtered Collection.

See Also:

executeWithArray(Object[] parameters)

execute

public java.lang.Object execute(java.lang.Object p1)

Execute the query and return the filtered Collection.

Parameters:

p1 - the value of the first parameter declared.

Returns:

the filtered Collection.

See Also:

executeWithArray(Object[] parameters)

execute

public java.lang.Object execute(java.lang.Object p1,
                                java.lang.Object p2)

Execute the query and return the filtered Collection.

Parameters:

p1 - the value of the first parameter declared.

p2 - the value of the second parameter declared.

Returns:

the filtered Collection.

See Also:

executeWithArray(Object[] parameters)

execute

public java.lang.Object execute(java.lang.Object p1,
                                java.lang.Object p2,
                                java.lang.Object p3)

Execute the query and return the filtered 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.

See Also:

executeWithArray(Object[] parameters)

executeWithMap

public java.lang.Object executeWithMap(java.util.Map parameters)

Execute the query and return the filtered 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 - the Map containing all of the parameters.

Returns:

the filtered Collection.

See Also:

executeWithArray(Object[] parameters)

executeWithArray

public java.lang.Object executeWithArray(java.lang.Object[] parameters)

Execute the query and return the filtered 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 - the Object array with all of the parameters.

Returns:

the filtered Collection.

getPersistenceManager

public PersistenceManager getPersistenceManager()

Get the 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 PersistenceManager associated with this Query.

close

public void close(java.lang.Object queryResult)

Close a query result and release any resources associated with it. The parameter is the return from 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 of execute(...) on this Query instance.

closeAll

public void closeAll()

Close all query results associated with this 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().