LINQ to SQL. Allowing 'get' property to be translated to sql

I have a table of warranties in my SQL database. These are represented by Warranty objects generated via LINQ to SQL. I've extended the partial classes generated to have a new property called Address, which is a combination of each address line field. (There is a bit of logic in there too through).

Code:

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public string Address
        {
            get
            {
                return (!string.IsNullOrEmpty(AddressLine1) ? AddressLine1 + " " : "") +
                      (!string.IsNullOrEmpty(AddressLine2) ? AddressLine2 + " " : "") +
                      (!string.IsNullOrEmpty(AddressLine3) ? AddressLine3 + " " : "") +
                      (!string.IsNullOrEmpty(AddressLine4) ? AddressLine4 + " " : "") +
                      (!string.IsNullOrEmpty(AddressLine5) ? AddressLine5 + " " : "") +
                      (!string.IsNullOrEmpty(Postcode) ? Postcode + " " : "");
            }
        }

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I get the following error if i try and build a LINQ query using the property, which is kind of expected, but also kind of annoying!

Code:

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System.NotSupportedException: The member 'HomeserveSharedClasses.DAL.Warranty.Address' has no supported translation to SQL.

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What do i have to do in order for this property getter to work in a LINQ query?

Make sure that the L2S class and your extended class have the same namespace. I've created custom properties in the same way as you before, so I don't think the problem should be any code there, just the namespaces.