Realize allow null columns by linq to sql

Question

5.00/5 (2 votes)

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C#

SQL-Server

LINQ

, +

hi experts

1. a sql server 2008 table that contains many columns and some of them are checked "not null"
like this:

SQL

create table Book(
    ID bigint identity(1,1) not null,
    Name nvarchar 50 null,
    ISBN nvarchar 10 not null,
    ......

2. in c#4, visual studio 2010, i use linq to sql. like:

C#

var context = new Model().Books;
var query = from b in context 
    select b;

the question is , how can i get only "allowed null" columns? i want linq to sql realize if the field is "allow null" or not?

Posted 25-May-12 6:37am

Vartan Khachatourian

Updated 25-May-12 6:38am

v2

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Clifford Nelson · Answer 1 · 2012-05-25T10:46:00

This might help: http://weblogs.asp.net/grantbarrington/archive/2009/03/17/using-reflection-to-determine-whether-an-type-is-nullable-and-get-the-underlying-type.aspx[^]

There is some information on getting Nullable on msdn (http://msdn.microsoft.com/en-us/library/ms366789.aspx[^]), but only for types. You cannot use the object.GetType() to determine if something is Nullable because if you do a GetType() on an int? you just get the result of int. This code will work with typeof() (ie typeof(int?)):

C#

public static class Extensions
{
    public static bool IsNullable(this Type type)
    {
        return type.IsGenericType
                     && (type.GetGenericTypeDefinition() == typeof(Nullable<>));
    }
}

This code will work with generics;

XML

public class x<T>
{
    public x()
    {
        var x = typeof(T).IsNullable();
    }
}

El_Codero · Answer 2 · 2012-05-25T10:33:00

Solution 1

Hi,

please read this topic from stackoverflow, I think it's what you want to achieve.

http://stackoverflow.com/questions/413084/equivalent-of-sql-isnull-in-linq[^]

Regards

Posted 25-May-12 10:33am

El_Codero

Comments

Clifford Nelson 25-May-12 18:53pm

He is looking to figure out if fields can have a null value, not if they are null.

Vartan Khachatourian 26-May-12 0:14am

im looking to realize if field can have a null value not if it is null