Write a LINQ query to select all rows from the first table in the dataset where the ContactName field is not null.

Question

You are using Visual Studio 2010 and the .NET Framework 4 to create an application. The application connects to a SQL Server database. You use the following SQL statement to retrieve an instance of a DataSet called ds: SELECT CustomerID, CompanyName, ContactName, Address, City FROM dbo.Customers.

You need to query the DataSet to retrieve only the rows that have the ContactName field not null. What code segment should you use?

Accepted Answer

from row in ds.Tables[0].AsEnumerable()
where row.Field <string>("ContactName") != null
select row;

Answer

from row in ds.Tables[0].AsEnumerable()
where (string)row["ContactName"] != null 
select row;

Answer

from row in ds.Tables[0].AsEnumerable()
where !row.IsNull((string)row["ContactName"]) 
select row;

Answer

from row in ds.Tables[0].AsEnumerable() 
where !Convert.IsDBNull(row.Field <string>("Region")) 
select row;

Question from the Entity Framework test

Write a LINQ query to select all rows from the first table in the dataset where the ContactName field is not null.