CODEWITHSUNDEEP
c#linq-to-sql
Giraffe
Giraffe

Reputation: 23

LINQ and check for !=null

Never used LINQ within C# before until 30 mins ago and am struggling to find an answer to my query online (probably due to my lack of understanding).

I have a simple query

var variableName = from a in tableName.AsEnumerable()
    where a.column1 == item1
        && a.column2 == item2
        && a.column3 != null
    select a;

The SQL column is defined as an int, null.

When the code encounters a record that is null on the database for column3, the following error is generated "the value for column3 in table <tableName> is DBNull".

Instead of checking for != null, i guess i should be using something else, but have attempted checking for DBNull.Value but the compiler states "Operation != cannot be applied to operands of type int and system.DBNull".

Any ideas?

Upvotes: 2

Views: 2730

Answers (4)

gudatcomputers
gudatcomputers

Reputation: 2882

try

var variableName = from a in tableName.AsEnumerable()
    where a.column1 == item1
        && a.column2 == item2
        && !DBNull.Value.Equals(a.column3)
    select a;

edit apparently I need to read up on typed data sets :) and why I should never use them

Upvotes: 0

Marc Gravell
Marc Gravell

Reputation: 1062502

This looks like a typed dataset, which : yeuch - stop using those, but I digress.

As such, accessing a.column3 will always raise an exception if that value is DBNull. You would need to use the typed-dataset pattern:

&& !c.Iscolumn3Null()

Upvotes: 6

user1812171
user1812171

Reputation: 5

Try this..

var variableName = from a in tableName.AsEnumerable()
    where a.column1 == item1
        && a.column2 == item2
        && a.column3 != dbnull.value
    select a;

Upvotes: 0

MarcinJuraszek
MarcinJuraszek

Reputation: 125610

tableName.AsEnumerable() makes the query in-memory, so all table rows are downloaded from DB and the conditions are checked on application.

Try that:

var variableName = from a in tableName
                   where a.column1 == item1
                       && a.column2 == item2
                       && a.column3 != null
                   select a;

It should be translated into an SQL query and download only necessary rows.

Upvotes: 0

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