check whether LINQ query returns rows

Question

I need to check whether a query returns rows and if it does, change it to a string, but if it doesn't, return "In Progress". I thought the below code would work but this is always true:

if (System.Linq.Enumerable.Count(columns) == 0)<--- always true but it shouldn't be

And when there isn't a row returned to columns I get the following error in my jQuery Ajax: "The cast to value type \u0027Int32\u0027 failed because the materialized value is null. Either the result type\u0027s generic parameter or the query must use a nullable type."

Here's my WebMethod:

using (dbPSREntities5 myEntities = new dbPSREntities5())
    {
        var thisId = myEntities.tbBreadCrumbs.Where(x => x.ProjectID == projectID && x.StatusID == statusID).Max(x => x.BreadCrumbID);
        var columns = myEntities.tbBreadCrumbs
            .Where(x => x.BreadCrumbID == thisId)
            .Select(x => x.CreateDateTime)
            .ToList();

        if (System.Linq.Enumerable.Count(columns) == 0)
        {
            var formattedList = columns
                .Select(d => null != d
                    ? d.Value.ToString("MMM dd, yyyy")
                    : string.Empty) // this is just one example to handle null
                .ToList();

            return formattedList;<-- return this if there is a BreadCrumbID (columns would have a row)
        }
        else
        {
            return "In Progress";<--- there was no BreadCrumbID (columns would have 0 rows)
        }

    }

Answer 1

You first check for Count == 0, doesn't sound right, I guess you need the opposite check. You should use Any or Count() > 0 check, Like:

if (columns.Any()) //Or columns.Count() > 0
{
    var formattedList = columns
        .Select(d => null != d
            ? d.Value.ToString("MMM dd, yyyy")
            : string.Empty) // this is just one example to handle null
        .ToList();

    return formattedList;<-- return this if there is a BreadCrumbID (columns would have a row)
}
else
{
    return "In Progress";<--- there was no BreadCrumbID (columns would have 0 rows)
}

You have to convert your List to string, in order for your method to return a string.

Answer 2

You could use Any()

MSDN Enumerable.Any Method

Answer 3

Your condition is wrong. Count must be greater than zero

Answer 4

Use the .Any() method provided by List<T>:

If (columns.Any())
{
    // do your bidding
} else {
    // in progress code
}

Also your method has two different return signatures. That won't compile. You can't return a List or a string, unless the return type is object (not recommended).

I suggest to return a null list and check if it's null in your UI layer and then display the appropriate string or date values, since they end up as strings in the UI anyway.

Answer 5

You only needs to ckeck .Count() > 0

if (columns.Count() > 0)
        {
            var formattedList = columns
                .Select(d => null != d
                    ? d.Value.ToString("MMM dd, yyyy")
                    : string.Empty) // this is just one example to handle null
                .ToList();

            return formattedList;<-- return this if there is a BreadCrumbID (columns would have a row)
        }
        else
        {
            return "In Progress";<--- there was no BreadCrumbID (columns would have 0 rows)
        }