# Class NestedQueryCache

java.lang.Object
org.apache.cayenne.cache.NestedQueryCache

All Implemented Interfaces:
  `QueryCache`

public class NestedQueryCache extends Object implements QueryCache
A `QueryCache` wrapper that introduces a key namespace on top of a delegate shared cache. This way multiple cache users can share the same underlying cache without a possibility of key conflicts, yet refresh the cache groups in a coordinated fashion.

Since:
  3.0

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected QueryCache`
  `delegate`
  `protected String`
  `namespace`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `NestedQueryCache(QueryCache delegate)`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `clear()`
  Deprecated.
  `List`
  `get(QueryMetadata metadata)`
  Returns a cached query result for the given QueryMetadata or null if the result is not cached or is expired.
  `List`
  `get(QueryMetadata metadata, QueryCacheEntryFactory factory)`
  Returns a cached query result for the given QueryMetadata.
  `QueryCache`
  `getDelegate()`
  Returns the actual implementation of the query cache that is wrapped by this NestedQueryCache.
  `void`
  `put(QueryMetadata metadata, List results)`
  `void`
  `remove(String key)`
  Removes an entry for key in the current namespace.
  `void`
  `removeGroup(String groupKey)`
  Invalidates a shared cache group.
  `void`
  `removeGroup(String groupKey, Class<?> keyType, Class<?> valueType)`
  Removes a group of entries identified by group key.

  ### Methods inherited from class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### delegate

    protected QueryCache delegate

  - ### namespace

    protected String namespace

- ## Constructor Details

  - ### NestedQueryCache

    public NestedQueryCache(QueryCache delegate)

- ## Method Details

  - ### getDelegate

    public QueryCache getDelegate()
    Returns the actual implementation of the query cache that is wrapped by this NestedQueryCache.

  - ### clear

    @Deprecated public void clear()
    Deprecated.
    Clears the underlying shared cache.
    Specified by:
      `clear` in interface `QueryCache`
    See Also:
      - `QueryCache.clear()`

  - ### get

    public List get(QueryMetadata metadata, QueryCacheEntryFactory factory)
    Description copied from interface: `QueryCache`
    Returns a cached query result for the given QueryMetadata. If the result is not cached or is expired, cache will use provided factory to rebuild the value and store it in the cache. A corollary is that this method never returns null.

    Compared to `QueryCache.get(QueryMetadata)`, this method allows the cache to do appropriate synchronization when refreshing the entry, preventing multiple threads from running the same query when a missing entry is requested by multiple threads simultaneously.

    Specified by:
      `get` in interface `QueryCache`

  - ### get

    public List get(QueryMetadata metadata)
    Description copied from interface: `QueryCache`
    Returns a cached query result for the given QueryMetadata or null if the result is not cached or is expired.
    Specified by:
      `get` in interface `QueryCache`

  - ### put

    public void put(QueryMetadata metadata, List results)
    Specified by:
      `put` in interface `QueryCache`

  - ### remove

    public void remove(String key)
    Removes an entry for key in the current namespace.
    Specified by:
      `remove` in interface `QueryCache`

  - ### removeGroup

    public void removeGroup(String groupKey)
    Invalidates a shared cache group.
    Specified by:
      `removeGroup` in interface `QueryCache`

  - ### removeGroup

    public void removeGroup(String groupKey, Class<?> keyType, Class<?> valueType)
    Description copied from interface: `QueryCache`
    Removes a group of entries identified by group key. Can be used if cache provider supports strictly typed caches.
    Specified by:
      `removeGroup` in interface `QueryCache`
    See Also:
      - `QueryCache.removeGroup(String)`