You perform queries using an XmlManager object. When you perform a query, you can either:
- Perform a one-off query using Query. This is useful if you are performing queries that you know you will never repeat within the process scope. For example, if you are writing a command line utility to perform a query, display the results, then shut down, you may want to use this method.
- Perform the same query repeatedly by using Prepare to obtain an XQueryExpression object. You can then run the query repeatedly by calling Execute.
Regardless of how you want to run your query, you must restrict the scope of your query to a container, document, or node. Usually you use one of the XQuery navigation functions to do this. See Navigation Functions for more information.
You can indicate that the query is to be performed lazily. If it is performed lazily, then only those portions of the document that are actually required to satisfy the query are returned in the results set immediately. All other portions of the document may then be retrieved by Figaro as you iterate over and use the items in the result set.
If you are using node-level storage, then a lazy query may result in only the document being returned, but not its metadata, or the metadata but not the document itself. In this case, use FetchAllData to ensure you have both the document and its metadata.
Be aware that lazy docs are different from lazy evaluation. Lazy docs determine whether all document data and document metadata is returned as a result of the query. Lazy evaluation determines how much query processing is deferred until the results set is actually examined.
CopyC#static void Main() { //get our manager using (var mgr = new XmlManager(ManagerInitOptions.AllowExternalAccess | ManagerInitOptions.AllowAutoOpen)) { //open a container using (var container = mgr.OpenContainer(baseUri + testdb)) { Console.WriteLine("container has {0} documents.",container.GetNumDocuments()); //add a container alias if your container is not in //the same directory as your application container.AddAlias("testdb"); //get a query context QueryContext queryContext = mgr.CreateQueryContext(); //set an XML namespace value queryContext.SetNamespace("fruits","http://groceryItem.dbxml/fruits"); //set an XQuery variable value queryContext.SetVariableValue("myVar", "Bananas"); //the query string xquery = "collection('testdb')/fruits:item[product=$myVar]"; //prepare the query XQueryExpression expression = mgr.Prepare(xquery, queryContext); //execute query with lazy docs enabled XmlResults results = expression.Execute(queryContext, QueryOptions.LazyDocs); /* * do something with the results here */ //find another fruit queryContext.SetVariableValue("myVar", "Cranberry"); results = expression.Execute(queryContext,QueryOptions.LazyDocs); /* * do something with the results here */ //find another fruit queryContext.SetVariableValue("myVar", "Honey Locust"); results = expression.Execute(queryContext, QueryOptions.LazyDocs); /* * do something with the results here */ //TODO: put this in a finally{} block container.Close(); } } }
Finally, note that when you perform a query, by default Figaro will read and validate the document and any attached schema or DTDs. This can cause performance problems, so to avoid it you can pass the WellFormedOnly flag to Execute. This can improve performance by causing the scanner to examine only the XML document itself, but it can also cause parsing errors if the document references information that might have come from a schema or DTD.
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