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| <h1 class="title-container" > |
| Continuous Queries |
| </h1> |
| |
| <div id="js-quick-links" > |
| <div class="quick-links"><ul> |
| <li><a href="#cq_main_features">Continuous Query Basics</a></li> |
| <li><a href="#cq_api">Typical Continuous Query Lifecycle</a></li> |
| <li> |
| <a href="#ExecutingACQ">Executing a Continuous Query from the Client</a><ul><li><a href="#DotNetCQExample">.NET Continuous Query Example</a></li></ul> |
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| |
| <p>The C++ and .NET clients can initiate queries that run on the Geode cache server |
| and notify the client when the query results have changed. For details on the server-side setup for |
| continuous queries, see <a href="serverman/developing/continuous_querying/how_continuous_querying_works.html">How Continuous Querying Works</a> |
| in the <em>Geode User Guide</em>.</p> |
| |
| <h2 id="continuous-query-basics"><a id="cq_main_features" ></a>Continuous Query Basics</h2> |
| |
| <p>Continuous querying provides the following features:</p> |
| |
| <ul> |
| <li><p><strong>Standard Geode native client query syntax and semantics</strong>. Continuous queries are expressed in the same language used for other native client queries. See <a href="/docs/geode-native/dotnet/113/remote-queries.html">Remote Queries</a>.</p></li> |
| <li><p><strong>Standard Geode events-based management of CQ events</strong>. The event handling used |
| to process CQ events is based on the standard Geode event handling framework. </p></li> |
| <li><p><strong>Complete integration with the client/server architecture</strong>. CQ functionality uses existing |
| server-to-client messaging mechanisms to send events. All tuning of your server-to-client |
| messaging also tunes the messaging of your CQ events. If your system is configured for high |
| availability then your CQs are highly available, with seamless failover provided in case of |
| server failure (see <a href="/docs/geode-native/dotnet/113/preserving-data/high-availability-client-server.html">High Availability for Client-to-Server Communication</a>). |
| If your clients are durable, you can also define any of your CQs as durable (see <a href="/docs/geode-native/dotnet/113/preserving-data/durable-client-messaging.html">Durable Client Messaging</a>).</p></li> |
| <li><p><strong>Interest criteria based on data values</strong>. Continuous queries are run against the region’s entry values. |
| Compare this to register interest by reviewing <a href="/docs/geode-native/dotnet/113/regions/registering-interest-for-entries.html">Registering Interest for Entries</a>.</p></li> |
| <li><p><strong>Active query execution</strong>. Once initialized, the queries operate on new events. Events that change the query result are sent to the client immediately.</p></li> |
| </ul> |
| |
| <h2 id="typical-continuous-query-lifecycle"><a id="cq_api"></a>Typical Continuous Query Lifecycle</h2> |
| |
| <ol> |
| <li> The client creates the CQ. This sets up everything for running the query and provides the client with a <code>CqQuery</code> object, but does not execute the CQ. At this point, the query is in a <code>STOPPED</code>state, ready to be closed or run.</li> |
| <li><p>The client initiates the CQ with an API call to one of the <code>CqQuery execute*</code> methods. This puts the query into a <code>RUNNING</code> state on the client and on the server. The server remotely evaluates the query string, and optionally returns the results to the client. <code>CqQuery execute*</code> methods include:</p> |
| |
| <ul> |
| <li><code>CqQuery.Execute()</code></li> |
| <li><code>CqQuery.ExecuteWithInitialResults()</code></li> |
| </ul></li> |
| <li><p>A CQ Listener waits for events. When it receives events, it takes action accordingly with the data in the CqEvent.</p></li> |
| <li><p>The CQ is closed by a client call to <code>CqQuery.close</code>. This de-allocates all resources in use for the CQ on the client and server. At this point, the cycle could begin again with the creation of a new <code>CqQuery</code> instance.</p></li> |
| </ol> |
| |
| <h2 id="executing-a-continuous-query-from-the-client"><a id="ExecutingACQ"></a>Executing a Continuous Query from the Client</h2> |
| |
| <p>The essential steps to create and execute a continuous query are:</p> |
| |
| <ol> |
| <li> Create an instance of the <code>QueryService</code> class. If you are using the pool API (recommended), you should obtain the <code>QueryService</code> from the pool.</li> |
| <li> Define a CQ Listener (an <code>ICqListener</code>) to field events sent from the server.</li> |
| <li> Use one of the <code>CqQuery execute*</code> methods to submit the query string to the cache server.</li> |
| <li> The server remotely evaluates the query string, then monitors those results and notifies the client if they change.</li> |
| <li> The client listens for changes that match the query predicate.</li> |
| <li> Iterate through the returned objects.</li> |
| <li> When finished, close down the continuous query.</li> |
| </ol> |
| |
| <h3 id=".net-continuous-query-example"><a id="DotNetCQExample"></a>.NET Continuous Query Example</h3> |
| |
| <p>These C# code excerpts are from the <code>examples\dotnet\continuousquery</code> example included in your client |
| distribution. See the example for full context.</p> |
| |
| <p>Following the steps listed above,</p> |
| |
| <ol> |
| <li><p>Create a query service:</p> |
| <pre class="highlight plaintext"><code>var queryService = pool.GetQueryService(); |
| </code></pre></li> |
| <li><p>Define an ICqListener:</p> |
| <pre class="highlight plaintext"><code>public class MyCqListener<TKey, TResult> : ICqListener<TKey, TResult> |
| { |
| </code></pre></li> |
| <li><p>Create an instance of your ICqListener and insert it into a CQ attributes object:</p> |
| <pre class="highlight plaintext"><code>var cqListener = new MyCqListener<string, Order>(); |
| var cqAttributesFactory = new CqAttributesFactory<string, Order>(); |
| cqAttributesFactory.AddCqListener(cqListener); |
| var cqAttributes = cqAttributesFactory.Create(); |
| </code></pre></li> |
| <li><p>Create a Continuous Query using the query service and the CQ attributes:</p> |
| <pre class="highlight plaintext"><code>var query = queryService.NewCq("MyCq", "SELECT * FROM /example_orderobject WHERE quantity > 30", cqAttributes, false); |
| </code></pre></li> |
| <li><p>Execute the query:</p> |
| <pre class="highlight plaintext"><code>query.Execute(); |
| </code></pre></li> |
| <li><p>Wait for events and do something with them.</p> |
| <pre class="highlight plaintext"><code>/* Excerpt from the CqListener */ |
| |
| /* Determine Operation Type */ |
| switch (ev.getQueryOperation()) |
| { |
| case CqOperation.OP_TYPE_CREATE: |
| operationType = "CREATE"; |
| break; |
| case CqOperation.OP_TYPE_UPDATE: |
| operationType = "UPDATE"; |
| break; |
| case CqOperation.OP_TYPE_DESTROY: |
| operationType = "DESTROY"; |
| break; |
| default: |
| break; |
| } |
| |
| ... |
| |
| /* Take action based on OP Type */ |
| |
| </code></pre></li> |
| <li><p>When finished, close up shop.</p> |
| <pre class="highlight plaintext"><code>query.Execute(); |
| ... (respond to events as they arrive) |
| |
| query.Stop(); |
| query.Close(); |
| |
| cache.Close(); |
| </code></pre></li> |
| </ol> |
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