Future Queries

Future queries are created with the following extension methods...

• Future()
• FutureFirstOrDefault()
• FutureCount()

Sample

// build up queries
var q1 = db.Users
    .Where(t => t.EmailAddress == "[email protected]")
    .Future();

var q2 = db.Tasks
    .Where(t => t.Summary == "Test")
    .Future();

// this triggers the loading of all the future queries
var users = q1.ToList();

In the example above, there are 2 queries built up, as soon as one of the queries is enumerated, it triggers the batch load of both queries.

// base query
var q = db.Tasks.Where(t => t.Priority == 2);
// get total count
var q1 = q.FutureCount();
// get page
var q2 = q.Skip(pageIndex).Take(pageSize).Future();

// triggers execute as a batch
int total = q1.Value;
var tasks = q2.ToList();

In this example, we have a common senerio where you want to page a list of tasks. In order for the GUI to setup the paging control, you need a total count. With Future, we can batch together the queries to get all the data in one database call.

Future queries work by creating the appropriate IFutureQuery object that keeps the IQuerable. The IFutureQuery object is then stored in IFutureContext.FutureQueries list. Then, when one of the IFutureQuery objects is enumerated, it calls back to IFutureContext.ExecuteFutureQueries() via the LoadAction delegate. ExecuteFutureQueries builds a batch query from all the stored IFutureQuery objects. Finally, all the IFutureQuery objects are updated with the results from the query.