Have model contain field without adding it to the database?

In my Asp.NET MVC4 application I want to add a field to my model without adding it to the database.

Sort of a field that only lives in c# instances of the model but not in the database itself.

Is there any annotation or other way to exclude the field from the database itself?

I mean an object I can read and write in runtime which the database has no knowledge of.

Answers:

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Method 1

Just decorate your field/property with [NotMapped].

For example:

public class MyModel
{
    public int Id { get; set; }
    public string Name { get; set; }

    [NotMapped]
    public string Type { get; set; }
}

See http://msdn.microsoft.com/en-us/library/system.componentmodel.dataannotations.schema.notmappedattribute.aspx

Method 2

That depends what framework you are using to access your data. I assume it’s Entity Framework. Well, you can create partial class with the property that you wanty to not be mapped to your database.

something like

public class Class1
{
    string Text { get; set; }

    int Number { get; set; }
}

public partial class Class1
{
    bool IsSomething { get; set; }
}

but that is not advised.
More:
Entity Framework: add property that don’t map to database

Or if you’re using Code First:
Ignoring a class property in Entity Framework 4.1 Code First

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