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Oracle® Coherence Java API Reference
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## com.tangosol.util.filter
Class KeyAssociatedFilter

    java.lang.Object
      com.tangosol.util.Base
          com.tangosol.util.BitHelper
              com.tangosol.util.ExternalizableHelper
                  com.tangosol.util.filter.KeyAssociatedFilter

All Implemented Interfaces:
  ExternalizableLite, PortableObject, Filter, java.io.Serializable

    public class KeyAssociatedFilter

extends ExternalizableHelper
implements Filter, ExternalizableLite, PortableObject

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

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 getId method that returns a Long value that uniquely identifies the object. Similarly, the ParentKey and ChildKey classes have a getId method that uniquely identifies the corresponding cached object. Futhermore, the Child and ChildKey classes include a getParentId method 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).

1. Make the ChildKey class implement `KeyAssociation` as follows:

        public Object getAssociatedKey()
            {
            return getParentId();
            }

   and the ParentKey class implement `KeyAssociation` as follows:

        public Object getAssociatedKey()
            {
            return getId();
            }

2. Implement a custom `KeyAssociator` as follows:

        public Object getAssociatedKey(Object oKey)
            {
            if (oKey instanceof ChildKey)
                {
                return ((ChildKey) oKey).getParentId();
                }
            else if (oKey instanceof ParentKey)
                {
                return ((ParentKey) oKey).getId();
                }
            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.getId();

     // this Filter will be applied to all Child objects in order to fetch those
     // for which getParentId() returns the specified Parent identifier
     Filter filterEq = new EqualsFilter("getParentId", parentId);

     // this Filter will direct the query to the cluster node that currently
     // owns the Parent object with the given identifier
     Filter filterAsc = new KeyAssociatedFilter(filterEq, parentId);

     // run the optimized query to get the ChildKey objects
     Set setChildKeys = cacheChildren.keySet(filterAsc);

     // get all the Child objects at once
     Set setChildren = cacheChildren.getAll(setChildKeys);

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

     cacheChildren.keySet().removeAll(setChildKeys);

Author:
  gg 2005.06.09, jh 2005.11.02

Constructor Summary
`KeyAssociatedFilter()` Default constructor (required by ExternalizableLite interface).
`KeyAssociatedFilter(Filter filter, java.lang.Object oHostKey)` Construct a key associated filter.

Method Summary
`boolean` | `equals(java.lang.Object o)` Compare the KeyAssociatedFilter with another object to determine equality.
`boolean` | `evaluate(java.lang.Object o)` Apply the test to the object.
`Filter` | `getFilter()` Obtain the wrapped Filter.
`java.lang.Object` | `getHostKey()` Obtain the host key that serves as an associated key for all keys that the wrapped filter will be applied to.
`int` | `hashCode()` Determine a hash value for the KeyAssociatedFilter object according to the general `Object.hashCode()` contract.
`void` | `readExternal(java.io.DataInput in)` Restore the contents of this object by loading the object's state from the passed DataInput object.
`void` | `readExternal(PofReader in)` Restore the contents of a user type instance by reading its state using the specified PofReader object.
`java.lang.String` | `toString()` Return a human-readable description for this Filter.
`void` | `writeExternal(java.io.DataOutput out)` Save the contents of this object by storing the object's state into the passed DataOutput object.
`void` | `writeExternal(PofWriter out)` Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Methods inherited from class com.tangosol.util.BitHelper
`countBits, countBits, countBits, indexOfLSB, indexOfLSB, indexOfLSB, indexOfMSB, indexOfMSB, indexOfMSB, rotateLeft, rotateLeft, rotateLeft, rotateRight, rotateRight, rotateRight, toBitString, toBitString, toBitString`

Constructor Detail

### KeyAssociatedFilter

    public KeyAssociatedFilter()

  Default constructor (required by ExternalizableLite interface).

### KeyAssociatedFilter

    public KeyAssociatedFilter(Filter filter,
                               java.lang.Object oHostKey)

  Construct a key associated filter.

  Parameters:
    `filter` - the underlying (wrapped) filter
    `oHostKey` - the host key that serves as an associated key for all keys that the wrapped filter will be applied to

Method Detail

### evaluate

    public boolean evaluate(java.lang.Object o)

  Apply the test to the object.

  Specified by:
    `evaluate` in interface `Filter`
  Parameters:
    `o` - the object to test
  Returns:
    true if the test passes, false otherwise

### readExternal

    public void readExternal(java.io.DataInput in)
                      throws java.io.IOException

  Restore the contents of this object by loading the object's state from the passed DataInput object.

  Specified by:
    `readExternal` in interface `ExternalizableLite`
  Parameters:
    `in` - the DataInput stream to read data from in order to restore the state of this object
  Throws:
    `java.io.IOException` - if an I/O exception occurs
    `java.io.NotActiveException` - if the object is not in its initial state, and therefore cannot be deserialized into

### writeExternal

    public void writeExternal(java.io.DataOutput out)
                       throws java.io.IOException

  Save the contents of this object by storing the object's state into the passed DataOutput object.

  Specified by:
    `writeExternal` in interface `ExternalizableLite`
  Parameters:
    `out` - the DataOutput stream to write the state of this object to
  Throws:
    `java.io.IOException` - if an I/O exception occurs

### readExternal

    public void readExternal(PofReader in)
                      throws java.io.IOException

  Restore the contents of a user type instance by reading its state using the specified PofReader object.

  Specified by:
    `readExternal` in interface `PortableObject`
  Parameters:
    `in` - the PofReader from which to read the object's state
  Throws:
    `java.io.IOException` - if an I/O error occurs

### writeExternal

    public void writeExternal(PofWriter out)
                       throws java.io.IOException

  Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

  Specified by:
    `writeExternal` in interface `PortableObject`
  Parameters:
    `out` - the PofWriter to which to write the object's state
  Throws:
    `java.io.IOException` - if an I/O error occurs

### getFilter

    public Filter getFilter()

  Obtain the wrapped Filter.

  Returns:
    the wrapped filter object

### getHostKey

    public java.lang.Object getHostKey()

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

  Returns:
    the host key

### equals

    public boolean equals(java.lang.Object o)

  Compare the KeyAssociatedFilter with another object to determine equality. Two KeyAssociatedFilter objects are considered equal iff the wrapped filters and host keys are equal.

  Returns:
    true iff this KeyAssociatedFilter and the passed object are equivalent KeyAssociatedFilter objects

### hashCode

    public int hashCode()

  Determine a hash value for the KeyAssociatedFilter object according to the general `Object.hashCode()` contract.

  Returns:
    an integer hash value for this KeyAssociatedFilter object

### toString

    public java.lang.String toString()

  Return a human-readable description for this Filter.

  Returns:
    a String description of the Filter

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Oracle® Coherence Java API Reference
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