如何执行ASK查询？

Question

如果我想通过Netbeans在Sesame存储库中进行SPARQL SELECT查询，我使用以下代码（我在绑定集中得到三个值）。如何进行只返回一个布尔值的ASK查询？

TupleQuery tupleQuery = con.prepareTupleQuery(QueryLanguage.SPARQL, queryString);
TupleQueryResult result = tupleQuery.evaluate();
List<String> bindingNames = result.getBindingNames();

try {
    while (result.hasNext()) {    
        BindingSet bindingSet = result.next();
        Value firstValue1 = bindingSet.getValue(bindingNames.get(0));
        Value firstValue2 = bindingSet.getValue(bindingNames.get(1));
        Value firstValue3 = bindingSet.getValue(bindingNames.get(2));
    }
}

Answer 1

假设您的con是RepositoryConnection，您可以使用prepareBooleanQuery(…)的某个版本。这将返回BooleanQuery，其evaluate()方法返回一个布尔值。修改您提供的代码将为您提供

BooleanQuery booleanQuery = con.prepareBoleanQuery(QueryLanguage.SPARQL, queryString);
boolean result = booleanQuery.evaluate();