Question

When I want to do OR-queries with DataMapper I use

result = MyModel.all(:first_name.like => '%john%') + MyModel.all(:last_name.like => '%john%')

This works fine and generates only one SQL query.
How can I create the same result with properties given in an array?

result = [ :first_name, :last_name ].reduce([]) do |sum, prop|
  sum + MyModel.all(prop.like => '%john%')
end

Although this works, it uses two separate SQL queries which is not what I want. Is there a way to create such a “lazy” query in a loop?

Answer 1

I figured it out myself. The problem is that you cannot use an empty regular array ([]) as the initial value of the result variable. I did not want to dig into the DataMapper internals too deeply, so I just used additional checking for the first assignment of result, like this:

result = nil
[ :first_name, :last_name ].each do |prop|
  cur = MyModel.all(prop.like => '%john%')
  next unless cur
  result ? result.nil? cur : result + cur
end