Solved

Linq to Dataset How to handle Null column values?

Posted on 2010-09-16
4
1,130 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
  • 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

Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

Question has a verified solution.

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

This document covers how to connect to SQL Server and browse its contents.  It is meant for those new to Visual Studio and/or working with Microsoft SQL Server.  It is not a guide to building SQL Server database connections in your code.  This is mo…
This article aims to explain the working of CircularLogArchiver. This tool was designed to solve the buildup of log file in cases where systems do not support circular logging or where circular logging is not enabled
Nobody understands Phishing better than an anti-spam company. That’s why we are providing Phishing Awareness Training to our customers. According to a report by Verizon, only 3% of targeted users report malicious emails to management. With compan…
In a recent question (https://www.experts-exchange.com/questions/29004105/Run-AutoHotkey-script-directly-from-Notepad.html) here at Experts Exchange, a member asked how to run an AutoHotkey script (.AHK) directly from Notepad++ (aka NPP). This video…

856 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