CouchDB boolean filtering

Question

I am trying to work with CouchDB filtering but I can not understand how it works

So lets say, like the example they have:

function(doc, req){
    // we need only `mail` documents
    if (doc.type != 'mail'){
        return false;
    }
    // we're interested only in `new` ones
    if (doc.status != 'new'){
        return false;
    }
    return true; // passed!
}

I am bit confused because if I want to return only

mail documents

I think I should implement something like:

 if (doc.type == 'mail'){
        return true;
    }

At the end we have

return true //passed

but, is that mean that I will return all the documnents I have?

Answer 1

The example doesn't just filter for mail documents, it also requires they be new. Without the "new document check" you could just as well write the code as

function(doc, req){
  // we need only `mail` documents
  if (doc.type == 'mail') {
    return true;
  }

  return false;
}

The whole logic of the original, though, is implementing (in pseudo-code)

if (!mail document or !new document) then false
else true