Repository.GetById using LINQ Expression Syntax

A while ago I talked about using the IRepository<T> pattern with LINQ to SQL. One of the methods of my repository is GetById. The slight difficulty here is that we need to discover the primary key property of the (generated) type at runtime so we can't use a vanilla lambda expression in the Where clause. Before I used the DynamicQueriable helper library, but I've just re-written the function using an explicit expression tree which removes the need to reference the helper library.

public T GetById(int id)
{
    var itemParameter = Expression.Parameter(typeof(T), "item");

    var whereExpression = Expression.Lambda<Func<T, bool>>
        (
            Expression.Equal(
                Expression.Property(
                    itemParameter,
                    typeof(T).GetPrimaryKey().Name
                ),
                Expression.Constant(id)
            ),
            new ParameterExpression[] { itemParameter }
        );

    return dataContext.GetTable<T>().Where(whereExpression).Single();
}

Here is the extension method that finds the primary key:

public static PropertyInfo GetPrimaryKey(this Type entityType)
{
    foreach (PropertyInfo property in entityType.GetProperties())
    {
        ColumnAttribute[] attributes = (ColumnAttribute[])property.GetCustomAttributes(typeof(ColumnAttribute), true);
        if (attributes.Length == 1)
        {
            ColumnAttribute columnAttribute = attributes[0];
            if (columnAttribute.IsPrimaryKey)
            {
                if (property.PropertyType != typeof(int))
                {
                    throw new ApplicationException(string.Format("Primary key, '{0}', of type '{1}' is not int",
                        property.Name, entityType));
                }
                return property;
            }
        }
    }
    throw new ApplicationException(string.Format("No primary key defined for type {0}", entityType.Name));
}