Solved

Linq to Dataset How to handle Null column values?

Posted on 2010-09-16
4
1,139 Views
Last Modified: 2013-11-11
How do you handle null column values in Linq to Dataset?  If the column in the customers table below has any null values, the statement stops and the query is empty.  

Thanks.

//find all of the rows that have values that start with the provided prefix
                EnumerableRowCollection<DataRow> query =
                    from customer in customerData.Tables["customer"].AsEnumerable()
                    where customer.Field<string>(columnName).ToLower().StartsWith(prefix.ToLower())
                    select customer;

Open in new window

0
Comment
Question by:kruegerste
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
4 Comments
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 500 total points
ID: 33694390
What about this?
//find all of the rows that have values that start with the provided prefix
EnumerableRowCollection<DataRow> query =
    from customer in customerData.Tables["customer"].AsEnumerable()
    where customer != null && !Convert.IsDBNull(customer) && customer.Field<string>(columnName).ToLower().StartsWith(prefix.ToLower())
    select customer;

Open in new window

0
 
LVL 4

Author Comment

by:kruegerste
ID: 33694552
No, I'm talking about the column in the customer table, not the customer table itself.  

It basically loops through each row of the datatable and everything is good until the column its checking is null, then the whole statement ends and the query enumerator is nothing.  
0
 
LVL 4

Author Comment

by:kruegerste
ID: 33695088
Below is the full statement.  In the GetDistinctItems as it loops through each datarow, it executes this line in the Linq and returns a boolean value:

where customer.Field<string>(columnName).ToLower().StartsWith(prefix.ToLower())

and everything is fine, items are added to string array until  customer.Field<string>(columnName)  is null value, then it errors out and throws exception below:

'customer.Field<string>(columnName)' is null      

How do we execute this Linq query on a column in a table that may have null values?  Obviously these are matches so I would like them to be ignored instead of throwing exception.

 try
            {
                UtilityBF utilityBF = new UtilityBF();
                CustomerData customerData = new CustomerData();
                customerData = GetCustomersAll();

                //find all of the rows that have values that start with the provided prefix
                EnumerableRowCollection<DataRow> query =
                    from customer in customerData.Tables["customer"].AsEnumerable()
                    where customer.Field<string>(columnName).ToLower().StartsWith(prefix.ToLower())
                    select customer;

                return utilityBF.GetDistinctQueryItems(query, columnName, count);
            }
            catch (HandledException ex)
            {
                throw ex;
            }

===================================================

public string[] GetDistinctQueryItems(EnumerableRowCollection<DataRow> query, string columnName, int count)
        {
                List<string> items = new List<string>();

                foreach (DataRow dataRow in query)
                {
                    string value = dataRow[columnName].ToString();
                    if (!items.Contains(value))
                    {
                        items.Add(value);
                    }
                }
                if (items.Count == 0)
                {
                    items.Add("no match");
                }

                return items.ToArray();
        }

Open in new window

0
 
LVL 4

Author Closing Comment

by:kruegerste
ID: 33695592
You were close, thanks.  Right idea, just changed to look for column value not null. Works
0

Featured Post

Salesforce Made Easy to Use

On-screen guidance at the moment of need enables you & your employees to focus on the core, you can now boost your adoption rates swiftly and simply with one easy tool.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

For those of you who don't follow the news, or just happen to live under rocks, Microsoft Research released a beta SDK (http://www.microsoft.com/en-us/download/details.aspx?id=27876) for the Xbox 360 Kinect. If you don't know what a Kinect is (http:…
This article is for Object-Oriented Programming (OOP) beginners. An Interface contains declarations of events, indexers, methods and/or properties. Any class which implements the Interface should provide the concrete implementation for each Inter…
There are cases when e.g. an IT administrator wants to have full access and view into selected mailboxes on Exchange server, directly from his own email account in Outlook or Outlook Web Access. This proves useful when for example administrator want…
This is my first video review of Microsoft Bookings, I will be doing a part two with a bit more information, but wanted to get this out to you folks.

726 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question