并非所有代码路径都返回值

Question

I am having this Linq To SQL query which is taking Customer Category from database .The CustCategory will be defined already.Here is the query.

public IList<string> GetAccountType()
        {
            using (var db = new DataClasses1DataContext())
            {
                var  acctype = db.mem_types.Select(account=>account.CustCategory).Distinct().ToList();
                if (acctype != null)
                {
                    return acctype;
                }
            }

        }

Currently I am getting an error that Not all code paths return a value. If I am always certain that the value is there in the database then do I need to check for null ,If I need to check for null then how do I handle this. Can anyone help me with this. Any suggestions are welcome.

Answer 1

Since Enumerable.ToList never returns null (see the Return Value section of the documentation ), you can safely remove the if .

EDIT: Note that, no matter what your database contains, acctype will never be null:

• If no value is found in the database, the return value will be an empty list (which is different than null ).
• If one record is found and its value is null, the return value will be a valid list with one entry, whose value is null. Still, the list itself is not null .

Answer 2

This is not about LINQ to SQL, the method GetAccountType() must return IList<string> . You should return return acctype; and then check this returned list later using Any() , something like:

if(GetAccountType.Any()){
     //not empty
}

Answer 3

How about something like this for a fairly clean and readable solution?:

( Note, updated: removed the check for null, since it would clearly not have any effect).

public IList<string> GetAccountType()
{
        var acctype = new List<string>();
        using (var db = new DataClasses1DataContext())
        {
            acctype = db.mem_types.Select(
                         account=>account.CustCategory).Distinct().ToList();
        }

        return acctype;
    }

Answer 4

What happens if:

if (acctype != null)

Is null? What is your method supposed to return ?

You need to return something

Answer 5

You need to return a value from your function:

    public IList<string> GetAccountType()
            {
                using (var db = new DataClasses1DataContext())
                {
                    var  acctype = db.mem_types.Select(account=>account.CustCategory).Distinct().ToList();
                    if (acctype != null)
                    {
                        return acctype;
                    }
                }
                return acctype;
            }