Class KeyExtractor
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.
Inherited Members
Namespace: Tangosol.Util.Extractor
Assembly: Coherence.dll
Syntax
public class KeyExtractor : AbstractExtractor, IValueExtractor, IQueryCacheComparer, IComparer, IPortableObjectRemarks
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"));
Constructors
KeyExtractor()
Default constructor.
Declaration
public KeyExtractor()KeyExtractor(string)
Construct a KeyExtractor for a specified member name.
Declaration
public KeyExtractor(string member)Parameters
| Type | Name | Description |
|---|---|---|
| string | member | A member name to construct an underlying ReflectionExtractor for; this parameter can also be a dot-delimited sequence of member names which would result in a KeyExtractor based on the ChainedExtractor that is based on an array of corresponding ReflectionExtractor objects. |
KeyExtractor(IValueExtractor)
Construct a KeyExtractor based on a specified IValueExtractor.
Declaration
public KeyExtractor(IValueExtractor extractor)Parameters
| Type | Name | Description |
|---|---|---|
| IValueExtractor | extractor | The underlying IValueExtractor. |
Fields
m_extractor
The underlying IValueExtractor.
Declaration
protected IValueExtractor m_extractorField Value
| Type | Description |
|---|---|
| IValueExtractor |
Properties
Extractor
The underlying IValueExtractor.
Declaration
public virtual IValueExtractor Extractor { get; }Property Value
| Type | Description |
|---|---|
| IValueExtractor | The underlying IValueExtractor. |
Methods
Equals(object)
Compare the KeyExtractor with another object to determine equality.
Declaration
public override bool Equals(object o)Parameters
| Type | Name | Description |
|---|---|---|
| object | o | The reference object with which to compare. |
Returns
| Type | Description |
|---|---|
| bool | true if this KeyExtractor and the passed object are equivalent. |
Overrides
Remarks
Two KeyExtractor objects are considered equal if their underlying IValueExtractors are equal.
Extract(object)
Extract the value from the passed object.
Declaration
public override object Extract(object obj)Parameters
| Type | Name | Description |
|---|---|---|
| object | obj | An object to retrieve the value from. |
Returns
| Type | Description |
|---|---|
| object | The extracted value as an object; |
Overrides
Remarks
The returned value may be null.
Exceptions
| Type | Condition |
|---|---|
| InvalidCastException | If this IValueExtractor is incompatible with the passed object to extract a value from and the implementation requires the passed object to be of a certain type. |
| ArgumentException | If this AbstractExtractor cannot handle the passed object for any other reason; an implementor should include a descriptive message. |
GetHashCode()
Determine a hash value for the KeyExtractor object according to the general Object.GetHashCode contract.
Declaration
public override int GetHashCode()Returns
| Type | Description |
|---|---|
| int | An integer hash value for this IValueExtractor object. |
Overrides
ReadExternal(IPofReader)
Restore the contents of a user type instance by reading its state using the specified IPofReader object.
Declaration
public virtual void ReadExternal(IPofReader reader)Parameters
| Type | Name | Description |
|---|---|---|
| IPofReader | reader | The IPofReader from which to read the object's state. |
Exceptions
| Type | Condition |
|---|---|
| IOException | If an I/O error occurs. |
ToString()
Provide a human-readable description of this KeyExtractor object.
Declaration
public override string ToString()Returns
| Type | Description |
|---|---|
| string | A human-readable description of this KeyExtractor object. |
Overrides
WriteExternal(IPofWriter)
Save the contents of a POF user type instance by writing its state using the specified IPofWriter object.
Declaration
public virtual void WriteExternal(IPofWriter writer)Parameters
| Type | Name | Description |
|---|---|---|
| IPofWriter | writer | The IPofWriter to which to write the object's state. |
Exceptions
| Type | Condition |
|---|---|
| IOException | If an I/O error occurs. |