Oracle Coherence for C++ API: KeyExtractor Class Reference

Detailed Description

The KeyExtractor is a special purpose ValueExtractor implementation that serves as an indicator that a query should be run against the key objects rather than the values.

The major difference between the KeyExtractor and a standard ReflectionExtractor is that when used in various EntryFilter implementations it forces the evaluation of entry keys rather than entry values.

For example, consider a key object that consists of two properties: "FirstName" and "LastName". To retrieve all keys that have a value of the "LastName" property equal to "Smith", the following query could be used:

ValueExtractor::View extractor = KeyExtractor::create("getLastName"); Set::View setKeys = cache->keySet(EqualsFilter::create(extractor, "Smith"));

As of Coherence 3.5, the same effect can be achieved for subclasses of the AbstractExtractor, for example:

ValueExtractor::View vExtractor = ReflectionExtractor::create("getLastName", NULL, AbstractExtractor::KEY); Set::View setKeys = cache->keySet(EqualsFilter::create(vExtractor, "Smith"));

Author:

djl 2008.03.24

Public Types

typedef spec::Handle

Handle

KeyExtractor Handle definition.

typedef spec::View

View

KeyExtractor View definition.

typedef spec::Holder

Holder

KeyExtractor Holder definition.

Public Member Functions

virtual Object::Holder

extract (Object::Holder ohTarget) const

Extract the value from the passed object.

The returned value may be NULL.

Parameters:

ohTarget

an Object to retrieve the value from

Returns:: the extracted value; NULL is an acceptable value

Exceptions:

	ClassCastException	if this ValueExtractor is incompatible with the passed object to extract a value from and the implementation requires the passed object to be of a certain type
	Exception	if this ValueExtractor encounters an exception in the course of extracting the value
	IllegalArgumentException	if this ValueExtractor cannot handle the passed object for any other reason; an implementor should include a descriptive message

virtual void

readExternal (PofReader::Handle hIn)

virtual void

writeExternal (PofWriter::Handle hOut) const

virtual bool

equals (Object::View v) const

virtual size32_t

hashCode () const

Return a hash code value for the Object.

This method is supported for the benefit of hash-based containers.

The general contract of hashCode is:

Whenever it is invoked on the same Object more than once during an execution of an application, the hashCode method must consistently return the same value, provided no information used in equals comparisons on the object is modified. This value need not remain consistent from one execution of an application to another execution of the same application.
If two Objects are equal according to the equals method, then calling the hashCode method on each of the two Objects must produce the same value.
It is not required that if two Objects are unequal according to the equals method, then calling the hashCode method on each of the two objects must produce distinct results. However, the programmer should be aware that producing distinct results for unequal objects may improve the performance of hash-based containers.

The default implementation is identity based.

Returns:: a hash code value for this Object

virtual void

toStream (std::ostream &out) const

Output a human-readable description of this Object to the given stream.

coherence::lang::operator<<(std::ostream, Object::View) is defined and will call into the toStream method, to output Objects. If a managed String object is desired, the COH_TO_STRING macro can be used to build up a String from streamable contents.

 Object::View vKey   = ...
 Object::View vValue = ...
 std::cout << vKey << " = " << vValue << std::endl;

 String::Handle hs = COH_TO_STRING(vKey << " = " << vValue);

Parameters:

out

the stream used to output the description

virtual
ValueExtractor::View

getExtractor () const

Obtain the underlying ValueExtractor.