LATEST VERSION: 8.2.6 - CHANGELOG
Pivotal GemFire® v8.2

Creating and Managing Queries

Creating and Managing Queries

You create queries on the cache server by obtaining a QueryService method and manage them through the resulting Query object. The Region interface has several shortcut query methods.

The newQuery method for the Query interface binds a query string. By invoking the execute method, the query is submitted to the cache server and returns SelectResults, which is either a ResultSet or a StructSet.

The QueryService method is the entry point to the query package. It is retrieved from the Cache instance through Cache::getQueryService. If you are using the Pool API you must obtain the QueryService from the pools and not from the cache.

Query

A Query is obtained from a QueryService method, which is obtained from the cache. The Query interface provides methods for managing the compilation and execution of queries, and for retrieving an existing query string.

You must obtain a Query object for each new query. The following example demonstrates the method used to obtain a new instance of Query:
QueryPtr newQuery(const char * querystr); 

Region Shortcut Query Methods

The Region interface has several shortcut query methods. All take a query predicate which is used in the WHERE clause of a standard query. See WHERE Clause for more information. Each of the following examples also set the query response timeout to 10 seconds to allow sufficient time for the operation to succeed.

  • The query method retrieves a collection of values satisfying the query predicate. This call retrieves active portfolios, which in the sample data are the portfolios with keys 111, 222, and 333:
    SelectResultsPtr
    results = regionPtr->query("status 'active' ");
  • The selectValue method retrieves one value object. In this call, you request the portfolio with ID ABC-1 :
    SerializablePtr
    port = region->selectValue("ID='ABC-1'");
  • The existsValue method returns a boolean indicating if any entry exists that satisfies the predicate. This call returns false because there is no entry with the indicated type:
    bool entryExists
    = region->existsValue("'type' = 'QQQ' ");

For more information about these shortcut query methods, see the Region class description in the native client online API documentation.