org.apache.ignite.cache.query

## Class ContinuousQuery<K,V>

- java.lang.Object
- - org.apache.ignite.cache.query.Query<javax.cache.Cache.Entry<K,V>>
  - - org.apache.ignite.cache.query.AbstractContinuousQuery<K,V>
    - - org.apache.ignite.cache.query.ContinuousQuery<K,V>

- All Implemented Interfaces:
    Serializable

      public final class ContinuousQuery<K,V>
      extends AbstractContinuousQuery<K,V>

  API for configuring continuous cache queries.

  Continuous queries allow registering a remote filter and a local listener for cache updates. If an update event passes the filter, it will be sent to the node that executed the query, and local listener will be notified.

  Additionally, you can execute an initial query to get currently existing data. Query can be of any type (SQL, TEXT or SCAN) and can be set via `setInitialQuery(Query)` method.

  Query can be executed either on all nodes in topology using `IgniteCache.query(Query)` method, or only on the local node, if `Query.setLocal(boolean)` parameter is set to `true`. Note that if the query is distributed and a new node joins, it will get the remote filter for the query during discovery process before it actually joins a topology, so no updates will be missed.

  # Example

  As an example, suppose we have a cache with `'Person'` objects and we need to query for all people with salary above 1000.

  Here is the `Person` class:

       public class Person {
           // Name.
           private String name;

           // Salary.
           private double salary;

           ...
       }

  You can create and execute a continuous query like so:

       // Create a new continuous query.
       ContinuousQuery<Long, Person> qry = new ContinuousQuery<>();

       // Initial iteration query will return all people with salary above 1000.
       qry.setInitialQuery(new ScanQuery<>((id, p) -> p.getSalary() > 1000));

       // Callback that is called locally when update notifications are received.
       // It simply prints out information about all created or modified records.
       qry.setLocalListener((evts) -> {
           for (CacheEntryEvent<? extends Long, ? extends Person> e : evts) {
               Person p = e.getValue();

               System.out.println(p.getFirstName() + " " + p.getLastName() + "'s salary is " + p.getSalary());
           }
       });

       // The continuous listener will be notified for people with salary above 1000.
       qry.setRemoteFilter(evt -> evt.getValue().getSalary() > 1000);

       // Execute the query and get a cursor that iterates through the initial data.
       QueryCursor<Cache.Entry<Long, Person>> cur = cache.query(qry);

  This will execute query on all nodes that have the cache you are working with and listener will start receiving notifications for cache updates.

  To stop receiving updates call `QueryCursor.close()` method:

       cur.close();

  Note that this works even if you didn't provide the initial query. Cursor will be empty in this case, but it will still unregister listeners when `QueryCursor.close()` is called.

  `IgniteAsyncCallback` annotation is supported for `CacheEntryEventFilter` (see `AbstractContinuousQuery.setRemoteFilterFactory(Factory)`) and `CacheEntryUpdatedListener` (see `setLocalListener(CacheEntryUpdatedListener)`). If a filter and/or listener are annotated with `IgniteAsyncCallback` then the annotated callback is executed in an async callback pool (see `IgniteConfiguration.getAsyncCallbackPoolSize()`) and a notification order is kept the same as an update order for a given cache key.

  See Also:
    `ContinuousQueryWithTransformer`, `IgniteAsyncCallback`, `IgniteConfiguration.getAsyncCallbackPoolSize()`, Serialized Form

- - ### Field Summary

    - ### Fields inherited from class org.apache.ignite.cache.query.AbstractContinuousQuery

      `DFLT_AUTO_UNSUBSCRIBE, DFLT_PAGE_SIZE, DFLT_TIME_INTERVAL`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ContinuousQuery()` Creates new continuous query.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods Deprecated Methods
    Modifier and Type | Method and Description
    --- | ---
    `javax.cache.event.CacheEntryUpdatedListener<K,V>` | `getLocalListener()`
    `CacheEntryEventSerializableFilter<K,V>` | `getRemoteFilter()` Gets remote filter.
    `ContinuousQuery<K,V>` | `setAutoUnsubscribe(boolean autoUnsubscribe)` Sets automatic unsubscribe flag.
    `ContinuousQuery<K,V>` | `setInitialQuery(Query<javax.cache.Cache.Entry<K,V>> initQry)` Sets initial query.
    `ContinuousQuery<K,V>` | `setLocal(boolean loc)` Sets whether this query should be executed on a local node only.
    `ContinuousQuery<K,V>` | `setLocalListener(javax.cache.event.CacheEntryUpdatedListener<K,V> locLsnr)` Sets a local callback.
    `ContinuousQuery<K,V>` | `setPageSize(int pageSize)` Sets optional page size, if `0`, then default is used.
    `ContinuousQuery<K,V>` | `setRemoteFilter(CacheEntryEventSerializableFilter<K,V> rmtFilter)` Deprecated. Use `AbstractContinuousQuery.setRemoteFilterFactory(Factory)` instead.
    `ContinuousQuery<K,V>` | `setTimeInterval(long timeInterval)` Sets time interval.

    - ### Methods inherited from class org.apache.ignite.cache.query.AbstractContinuousQuery

      `getInitialQuery, getRemoteFilterFactory, getTimeInterval, isAutoUnsubscribe, isIncludeExpired, setIncludeExpired, setRemoteFilterFactory`

    - ### Methods inherited from class org.apache.ignite.cache.query.Query

      `getPageSize, isLocal, prepare, toString`

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### ContinuousQuery

          public ContinuousQuery()

      Creates new continuous query.

  - ### Method Detail

    - #### setInitialQuery

          public ContinuousQuery<K,V> setInitialQuery(Query<javax.cache.Cache.Entry<K,V>> initQry)

      Sets initial query.

      This query will be executed before continuous listener is registered which allows to iterate through entries which already existed at the time continuous query is executed.

      Overrides:
        `setInitialQuery` in class `AbstractContinuousQuery<K,V>`
      Parameters:
        `initQry` - Initial query.
      Returns:
        `this` for chaining.

    - #### setLocalListener

          public ContinuousQuery<K,V> setLocalListener(javax.cache.event.CacheEntryUpdatedListener<K,V> locLsnr)

      Sets a local callback. This callback is called only on local node when new updates are received.

      The callback predicate accepts ID of the node from where updates are received and a collection of the received entries. Note that for removed entries values will be `null`.

      If the predicate returns `false`, query execution will be cancelled.

      WARNING: all operations that involve any kind of JVM-local or distributed locking (e.g., synchronization or transactional cache operations), should be executed asynchronously without blocking the thread that called the callback. Otherwise, you can get deadlocks.

      If local listener are annotated with `IgniteAsyncCallback` then it is executed in an async callback pool (see `IgniteConfiguration.getAsyncCallbackPoolSize()`) that allow to perform a cache operations.

      Parameters:
        `locLsnr` - Local callback.
      Returns:
        `this` for chaining.
      See Also:
        `IgniteAsyncCallback`, `IgniteConfiguration.getAsyncCallbackPoolSize()`, `ContinuousQueryWithTransformer.setLocalListener(EventListener)`

    - #### getLocalListener

          public javax.cache.event.CacheEntryUpdatedListener<K,V> getLocalListener()

      Returns:
        Local listener.

    - #### setRemoteFilter

          @Deprecated
          public ContinuousQuery<K,V> setRemoteFilter(CacheEntryEventSerializableFilter<K,V> rmtFilter)

      Deprecated. Use `AbstractContinuousQuery.setRemoteFilterFactory(Factory)` instead.
      Sets optional key-value filter. This filter is called before entry is sent to the master node.

      WARNING: all operations that involve any kind of JVM-local or distributed locking (e.g., synchronization or transactional cache operations), should be executed asynchronously without blocking the thread that called the filter. Otherwise, you can get deadlocks.

      If remote filter are annotated with `IgniteAsyncCallback` then it is executed in async callback pool (see `IgniteConfiguration.getAsyncCallbackPoolSize()`) that allow to perform a cache operations.

      Parameters:
        `rmtFilter` - Key-value filter.
      Returns:
        `this` for chaining.
      See Also:
        `IgniteAsyncCallback`, `IgniteConfiguration.getAsyncCallbackPoolSize()`

    - #### getRemoteFilter

          public CacheEntryEventSerializableFilter<K,V> getRemoteFilter()

      Gets remote filter.
      Returns:
        Remote filter.

    - #### setTimeInterval

          public ContinuousQuery<K,V> setTimeInterval(long timeInterval)

      Sets time interval.

      When a cache update happens, entry is first put into a buffer. Entries from buffer will be sent to the master node only if the buffer is full (its size can be provided via `Query.setPageSize(int)` method) or time provided via this method is exceeded.

      Default time interval is `0` which means that time check is disabled and entries will be sent only when buffer is full.

      Overrides:
        `setTimeInterval` in class `AbstractContinuousQuery<K,V>`
      Parameters:
        `timeInterval` - Time interval.
      Returns:
        `this` for chaining.

    - #### setAutoUnsubscribe

          public ContinuousQuery<K,V> setAutoUnsubscribe(boolean autoUnsubscribe)

      Sets automatic unsubscribe flag.

      This flag indicates that query filters on remote nodes should be automatically unregistered if master node (node that initiated the query) leaves topology. If this flag is `false`, filters will be unregistered only when the query is cancelled from master node, and won't ever be unregistered if master node leaves grid.

      Default value for this flag is `true`.

      Overrides:
        `setAutoUnsubscribe` in class `AbstractContinuousQuery<K,V>`
      Parameters:
        `autoUnsubscribe` - Automatic unsubscription flag.
      Returns:
        `this` for chaining.

    - #### setPageSize

          public ContinuousQuery<K,V> setPageSize(int pageSize)

      Sets optional page size, if `0`, then default is used.
      Overrides:
        `setPageSize` in class `Query<javax.cache.Cache.Entry<K,V>>`
      Parameters:
        `pageSize` - Optional page size.
      Returns:
        `this` for chaining.

    - #### setLocal

          public ContinuousQuery<K,V> setLocal(boolean loc)

      Sets whether this query should be executed on a local node only. Note: backup event queues are not kept for local continuous queries. It may lead to loss of notifications in case of node failures. Use `AbstractContinuousQuery.setRemoteFilterFactory(Factory)` to register cache event listeners on all cache nodes, if delivery guarantee is required.
      Overrides:
        `setLocal` in class `Query<javax.cache.Cache.Entry<K,V>>`
      Parameters:
        `loc` - Local flag.
      Returns:
        `this` for chaining.

2021 Copyright © Apache Software Foundation
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Ignite Database and Caching Platform | : ver. 2.11.0
Release Date | : September 11 2021