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Oracle® Coherence Java API Reference Release 3.7.1.0 E22843-01 |
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java.lang.Object
com.tangosol.util.Base
com.tangosol.util.BitHelper
com.tangosol.util.ExternalizableHelper
com.tangosol.util.filter.KeyAssociatedFilter
public class KeyAssociatedFilter
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).
KeyAssociation
as follows:
public Object getAssociatedKey() { return getParentId(); }and the ParentKey class implement
KeyAssociation
as follows:
public Object getAssociatedKey() { return getId(); }
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);
Constructor Summary | |
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KeyAssociatedFilter() Default constructor (required by ExternalizableLite interface). |
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KeyAssociatedFilter(Filter filter, java.lang.Object oHostKey) Construct a key associated filter. |
Method Summary | |
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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 |
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countBits, countBits, countBits, indexOfLSB, indexOfLSB, indexOfLSB, indexOfMSB, indexOfMSB, indexOfMSB, rotateLeft, rotateLeft, rotateLeft, rotateRight, rotateRight, rotateRight, toBitString, toBitString, toBitString |
Constructor Detail |
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public KeyAssociatedFilter()
public KeyAssociatedFilter(Filter filter, java.lang.Object oHostKey)
filter
- the underlying (wrapped) filteroHostKey
- the host key that serves as an associated key for all keys that the wrapped filter will be applied toMethod Detail |
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public boolean evaluate(java.lang.Object o)
evaluate
in interface Filter
o
- the object to testpublic void readExternal(java.io.DataInput in) throws java.io.IOException
readExternal
in interface ExternalizableLite
in
- the DataInput stream to read data from in order to restore the state of this objectjava.io.IOException
- if an I/O exception occursjava.io.NotActiveException
- if the object is not in its initial state, and therefore cannot be deserialized intopublic void writeExternal(java.io.DataOutput out) throws java.io.IOException
writeExternal
in interface ExternalizableLite
out
- the DataOutput stream to write the state of this object tojava.io.IOException
- if an I/O exception occurspublic void readExternal(PofReader in) throws java.io.IOException
readExternal
in interface PortableObject
in
- the PofReader from which to read the object's statejava.io.IOException
- if an I/O error occurspublic void writeExternal(PofWriter out) throws java.io.IOException
writeExternal
in interface PortableObject
out
- the PofWriter to which to write the object's statejava.io.IOException
- if an I/O error occurspublic Filter getFilter()
public java.lang.Object getHostKey()
public boolean equals(java.lang.Object o)
public int hashCode()
Object.hashCode()
contract.public java.lang.String toString()
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Oracle® Coherence Java API Reference Release 3.7.1.0 E22843-01 |
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