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KeyExtractor Class

Oracle® Fusion Middleware .NET API Reference for Oracle Coherence
14c (14.1.1.0)
F23534-02
The KeyExtractor is a special purpose IValueExtractor implementation that serves as an indicator that a query should be run against the key objects rather than the values.
Inheritance Hierarchy

Namespace:  Tangosol.Util.Extractor
Assembly:  Coherence (in Coherence.dll) Version: 14.1.1.14 (14.1.1.14)
Syntax
C#
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public class KeyExtractor : AbstractExtractor, 
	IPortableObject

The KeyExtractor type exposes the following members.

Constructors
  NameDescription
Public methodKeyExtractor
Default constructor.
Public methodKeyExtractor(String)
Construct a KeyExtractor for a specified member name.
Public methodKeyExtractor(IValueExtractor)
Construct a KeyExtractor based on a specified IValueExtractor.
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Properties
  NameDescription
Public propertyExtractor
The underlying IValueExtractor.
Public propertyTarget
The target of the extractor.
(Inherited from AbstractExtractor.)
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Methods
  NameDescription
Public methodCompare
Compares its two arguments for order.
(Inherited from AbstractExtractor.)
Public methodCompareEntries
Compare two entries.
(Inherited from AbstractExtractor.)
Public methodEquals
Compare the KeyExtractor with another object to determine equality.
(Overrides ObjectEquals(Object).)
Public methodExtract
Extract the value from the passed object.
(Overrides AbstractExtractorExtract(Object).)
Public methodExtractFromEntry
Extract the value from the passed Entry object. The returned value should follow the conventions outlined in the Extract(Object) method.
(Inherited from AbstractExtractor.)
Public methodExtractOriginalFromEntry
Extract the value from the "original value" of the passed CacheEntry object or the key (if targeted). This method's conventions are exactly the same as the ExtractFromEntry(ICacheEntry) method.
(Inherited from AbstractExtractor.)
Protected methodFinalize
Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.
(Inherited from Object.)
Public methodGetHashCode
Determine a hash value for the KeyExtractor object according to the general Object.GetHashCode contract.
(Overrides ObjectGetHashCode.)
Public methodGetType
Gets the Type of the current instance.
(Inherited from Object.)
Protected methodMemberwiseClone
Creates a shallow copy of the current Object.
(Inherited from Object.)
Public methodReadExternal
Restore the contents of a user type instance by reading its state using the specified IPofReader object.
Public methodToString
Provide a human-readable description of this KeyExtractor object.
(Overrides ObjectToString.)
Public methodWriteExternal
Save the contents of a POF user type instance by writing its state using the specified IPofWriter object.
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Fields
  NameDescription
Protected fieldm_extractor
The underlying IValueExtractor.
Protected fieldm_target
Specifies which part of the entry should be used by the ExtractFromEntry(ICacheEntry) operation. Legal values are VALUE (default) or KEY.
(Inherited from AbstractExtractor.)
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Remarks

The major difference between the KeyExtractor and a standard ReflectionExtractor is that when used in various IFilter 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:

            IValueExtractor extractor = new KeyExtractor("LastName");
            ICollection keys = cache.GetKeys(new EqualsFilter(extractor, "Smith"));
As of Coherence 3.5, the same effect can be achieved for subclasses of the AbstractExtractor, for example: 
            IValueExtractor extractor = new ReflectionExtractor("LastName", 
            null,AbstractExtractor.KEY);
            ICollection keys = cache.GetKeys(new EqualsFilter(extractor, "Smith"));
See Also