How to execute asynchronously three separate queries in one method using ADO.NET ExecuteScalarAsync()

Question

So I'm trying to turn my synchronous method to asnych. The set up is - I have a method that check if an user uses any of the company products. I need different query for each product so I decided to try and give a shot to the asnych programming since I've never tried using Task and await before even though, maybe this is not the perfect situation to do it. But however now I've changed my method to this:

    private static async Task<bool> isUsingProducts(int clientId)
    {
      bool hasProduct = false;

        using (SqlConnection connection1 = new SqlConnection(connString))
        {
            SqlCommand firstProduct = new SqlCommand(firstQuery, connection1);

            firstProduct.CommandTimeout = 300;
            firstProduct.Open();
            Task numberOfUsedProducts1 = firstProduct.ExecuteScalarAsync();
            //int numberOfUsedProducts = (int)firstProduct.ExecuteScalar();
            //if (0 < numberOfUsedProducts)
            //{
            //    hasProduct = true;
            //}
        }
        using (SqlConnection connection2 = new SqlConnection(connString))
        {
            SqlCommand secondProduct= new SqlCommand(secondQuery, connection2);
            secondProduct.CommandTimeout = 300;
            connection2.Open();
            Task numberOfUsedProducts2 = secondProduct.ExecuteScalarAsync();
            //int numberOfUsedProducts = (int)secondProduct.ExecuteScalar();
            //if (0 < numberOfUsedProducts)
            //{
            //    hasProduct = true;
            //}
        }

        return hasProduct;
    }

Basically this is some mix from what I've tried and what has left from the previous method which was synchronous. In this case I only care if the user is using ANY of the products or not so I was checking after the end of each query. However sometimes I'm gonna need the actual count so at the end I want to be able to execute the queries in asnych mode and later decied how exactly i'm gonna deal with the results.

Right now this:

 Task numberOfUsedProducts2 = secondProduct.ExecuteScalarAsync();

is not giving me an error, but I don't know how to proceed. What I don't know how to do is how to add the logic for checking the result of each query (the queries are synch so how shall I know that there's a result already) and how to convert those result to the actual type (int)?

Yuval Itzchakov · Accepted Answer · 2014-10-13 09:26:23Z

2

ExecuteScalarAsync return a Task<object>. You can use a cast on the return type in combination with await:

int numberOfUsedProducts1 = (int) await firstProduct.ExecuteScalarAsync()

if (numberOfUsedProducts > 0)
{
     hasProduct = true;
}

Same goes for the second method as well.

Right now this:

 Task numberOfUsedProducts2 = secondProduct.ExecuteScalarAsync();

is not giving me an error

That's because a Task<T> inherits from Task, so you may use it as the more abstracted base class, but then you lose the Result property containing the returned T

edited Oct 13, 2014 at 9:26

answered Oct 10, 2014 at 14:32

Yuval Itzchakov

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2 Comments

Leron Over a year ago

I ahve problems - the process never ends. But I have to go now. Gonna get in later.

Leron Over a year ago

For some reasons I have problems with this code on my real project but I test it right now and it works.Thanks

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