Question

I have a very simple database. It s a name/value store for various configuration items and I’m trying to simply get them all out and into a list of items.

My LINQ query looks like this:

configurationList = (from c in database.Configurations select new ViewConfigurationSettingModel(c.name, c.value){ IsChanged = (c.name == id) } ).ToArray();

The class ViewConfigurationSettingModel looks like this:

public class ViewConfigurationSettingModel
{
    public ViewConfigurationSettingModel(string name, string value)
    {
        this.Name = name;
        this.Value = value;
        this.IsChanged = false;
    }



    public string Name { get; private set; }
    public string Value { get; private set; }

    public bool IsChanged { get; set; }
}

When I execute the LINQ query I get an exception because ‘IsChanged’ is not a nullable type and cannot contain null. I am stumped how (c.name == id) could result in a null. Both values are strings, but even a comparison with a null should result in a simple true of false.

What going on with LINQ that this all of a sudden results in a null?

Answer 1

A comparison with a null results in a simple true/false in C#, but not in SQL. I suspect that’s the problem here. Assuming id is non-null, you could try something like:

IsChanged = c.name != null && (c.name == id)

If you can make the name column non-nullable in the database, that may help too…