Running several EntityFramework database queries in parallel

Question

I am trying to run 3 database queries in parallel but I\'m not sure that I am doing it correctly.

I have made 3 functions which each make a query to the database.

Answer 1

You will have to change the last part of the code to make it run in parallel:

var taskAccountCode = getAccountCodeAsync(deviceId);
var taskDeviceType = getDeviceTypeAsync(deviceId);
var taskUsername = getUserNameAsync(userId);
await Task.WhenAll(taskAccountCode, taskDeviceType, taskUsername);
var accountCode = taskAccountCode.Result;
var deviceType = taskDeviceType.Result;
var username  = taskUsername.Result;

Notice that there is only one await. In your original code you await every task one after the other making them run in sequence instead of in parallel.

Also, the methods getAccountCodeAsync etc. are not really async methods (you should get a compiler warning about this). However, Entity Framework 6 has support for async operations and to use that you should replace FirstOrDefault with FirstOrDefaultAsync. For each parallel operation you will have to use a separate context, and that is exactly what you are doing.

Answer 2

No they run one after eachother if you call them like that using await foreach method, it will run first method, then the second one...etc. And the last part await Task.WhenAll(), you did not supplied the tasks to wait for completion.

To run them in parallel you have to do it like this:

var TaskAccountCode = getAccountCodeAsync(deviceId);
var TaskDeviceType = getDeviceTypeAsync(deviceId);
var TaskUsername = getUserNameAsync(userId);
await Task.WhenAll(TaskAccountCode, TaskDeviceType,TaskUsername);