Class KeyAssociatedFilter

IFilter which limits the scope of another filter according to the key association information.

Inheritance

object

KeyAssociatedFilter

Implements

IFilter

IPortableObject

Inherited Members

object.Equals(object, object)

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

Namespace: Tangosol.Util.Filter

Assembly: Coherence.dll

Syntax

public class KeyAssociatedFilter : IFilter, IPortableObject

Remarks

This filter is intended to be used to optimize queries for partitioned caches that utilize any of the key association algorithms (by implementing either KeyAssociator or KeyAssociation) to ensure placement of all associated entries in the same distributed cache partition (and therefore in the same storage-enabled cluster node). Using the KeyAssociatedFilter will instruct the distributed cache to apply the wrapped filter only to the entries stored at the cache service node that owns the specified host key.

Note 1: This filter must be the outermost filter and cannot be used as a part of any composite filter (AndFilter, OrFilter, etc.)

Note 2: This filter is intended to be processed only on the client side of the partitioned cache service.

For example, consider two classes called Parent and Child that are stored in separate caches using ParentKey and ChildKey objects respectively. The Parent and Child classes have a Id property that returns a Long value that uniquely identifies the object. Similarly, the ParentKey and ChildKey classes have a Id property that uniquely identifies the corresponding cached object. Futhermore, the Child and ChildKey classes include a ParentId property that returns the Long identifier of the Parent object.

There are two ways to ensure that Child objects are collocated with their Parent objects (in the same storage-enabled cluster node).

Make the ChildKey class implement KeyAssociation as follows:

public Object AssociatedKey
 {
     get { return ParentId; }
 }

and the ParentKey class implement KeyAssociation as follows:

public Object AssociatedKey
 {
     get { return Id; }
 }

Implement a custom KeyAssociator as follows:

public object GetAssociatedKey(object key)
 {
     if (key is ChildKey)
     {
         return ((ChildKey) key).ParentId;
     }
     else if (key is ParentKey)
     {
         return ((ParentKey) key).Id;
     }
     else
     {
     return null;
     }
 }

The first approach requires a trivial change to the ChildKey and ParentKey classes, whereas the second requires a new class and a configuration change, but no changes to existing classes.

Now, to retrieve all the Child objects of a given Parent using an optimized query you would do the following:

ParentKey parentKey = new ParentKey(...);
 Long      parentId  = parentKey.Id;
// this Filter will be applied to all Child objects in order to fetch
// those for which ParentId returns the specified Parent identifier
IFilter filterEq = new EqualsFilter("ParentId", parentId);
// this Filter will direct the query to the cluster node that
// currently owns the Parent object with the given identifier
IFilter filterAsc = new KeyAssociatedFilter(filterEq, parentId);
// run the optimized query to get the ChildKey objects
ICollection colChildKeys = cacheChildren.Keys(filterAsc);
// get all the Child objects at once
ICollection colChildren = cacheChildren.GetAll(colChildKeys);

To remove the Child objects you would then do the following:

cacheChildren.Keys.RemoveAll(colChildKeys);

Constructors

KeyAssociatedFilter()

Default constructor.

Declaration

public KeyAssociatedFilter()

KeyAssociatedFilter(IFilter, object)

Construct a key associated filter.

Declaration

public KeyAssociatedFilter(IFilter filter, object hostKey)

Parameters

Type	Name	Description
IFilter	filter	The underlying (wrapped) filter.
object	hostKey	The host key that serves as an associated key for all keys that the wrapped filter will be applied to.

Properties

Filter

Obtain the wrapped IFilter.

Declaration

public virtual IFilter Filter { get; }

Property Value

Type	Description
IFilter	The wrapped filter object.

HostKey

Obtain the host key that serves as an associated key for all keys that the wrapped filter will be applied to.

Declaration

public virtual object HostKey { get; }

Property Value

Type	Description
object	The host key.

Methods

Equals(object)

Compare the KeyAssociatedFilter with another object to determine equality.

Declaration

public override bool Equals(object obj)

Parameters

Type	Name	Description
object	obj	The KeyAssociatedFilter to compare to.

Returns

Type	Description
bool	true if this KeyAssociatedFilter and the passed object are equivalent KeyAssociatedFilter objects.

Overrides

object.Equals(object)

Remarks

Two KeyAssociatedFilter objects are considered equal if the wrapped filters and host keys are equal.

Evaluate(object)

Apply the test to the object.

Declaration

public virtual bool Evaluate(object o)

Parameters

Type	Name	Description
object	o	An object to which the test is applied.

Returns

Type	Description
bool	true if the test passes, false otherwise.

GetHashCode()

Determine a hash value for the KeyAssociatedFilter object according to the general object.GetHashCode() contract.

Declaration

public override int GetHashCode()

Returns

Type	Description
int	An integer hash value for this KeyAssociatedFilter object.

Overrides

object.GetHashCode()

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()

Return a human-readable description for this KeyAssociatedFilter.

Declaration

public override string ToString()

Returns

Type	Description
string	A string description of the KeyAssociatedFilter.

Overrides

object.ToString()

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.

Implements

IFilter

IPortableObject