Trouble understanding LINQ return value

Question

I am trying to return the Actual Value in this query but I only get the Expression. Can someone point me in the right direction please.

    public static String NurseName(Guid? userID)
    {
        var nurseName = from demographic in context.tblDemographics
                        where demographic.UserID == userID
                        select new {FullName = demographic.FirstName +" " + demographic.LastName};

        String nurseFullName = nurseName.ToString();

        return nurseFullName;
    }

nurseFullName ends up as --> SELECT ([t0].[FirstName] + @p1) + [t0].[LastName] AS [FullName] FROM [dbo].[tblDemographics] AS [t0] WHERE ([t0].[UserID]) = @p0

Answer 1

Try this:

var nurseName = (from demographic in context.tblDemographics
                where demographic.UserID == userID
                select new {FullName = demographic.FirstName +" " + demographic.LastName}).First().FullName;

Your code was grabbing a collection, but not a specific item. This modification takes the first item in the list and returns the FullName property.

Answer 2

public static String NurseName(Guid? userID)
    {
        var nurseName = from demographic in context.tblDemographics
                        where demographic.UserID == userID
                        select demographic.FirstName +" " + demographic.LastName;

        return nurseName.SingleOrDefault();
    }

In the above nurseName has the IQueryable expression, so it hasn't executed anything. Its when you enumerate on it, that the query is called. That's also the case when you call methods like SingleOrDefault.

---

If you were to use your original query expression instead, you can:

public static String NurseName(Guid? userID)
    {
        var query= from demographic in context.tblDemographics
                        where demographic.UserID == userID
                        select new {FullName = demographic.FirstName +" " + demographic.LastName; }
        var nurseName = query.SingleOrDefault();
        return nurseName != null ? nurseName.FullName : "";
    }

---

Difference between Single vs. SingleOrDefault is that the later allows an empty result. Difference between First vs. Single is that the later prevents more than 1 row.

Answer 3

public static String NurseName(Guid? userID)
{
    var nurseName = (from demographic in context.tblDemographics
                    where demographic.UserID == userID
                    select new {FullName = demographic.FirstName +" " + demographic.LastName}).SingleOrDefault();

    if(null == nurseName)
    {
        //TODO: Uh-Oh ID not found...
    }

    string nurseFullName = nurseName.FullName;

    return nurseFullName;
}