Question

This is how I went about to query for one specific element.

results << read_db.collection("users").find(:created_at => {:$gt => initial_date}).to_a

Now, I am trying to query by more than one.

db.inventory.find({ $and: [ { price: 1.99 }, { qty: { $lt: 20 } }, { sale: true } ] } )

Now how do I build up my query? Essentially I will have have a bunch of if statements, if true, i want to extend my query. I heard there is a .extend command in another langue, is there something similar in ruby?

Essentially i want to do this:

if price
query = "{ price: 1.99 }"
end

if qty
query = query + "{ qty: { $lt: 20 } }"
end

and than just have

 db.inventory.find({ $and: [query]})

This syntax is wrong, what is the best way to go about doing this?

Answer 1

You want to end up with something like this:

db.inventory.find({ :$and => some_array_of_mongodb_queries})

Note that I’ve switched to the hashrocket syntax, you can’t use the JavaScript notation with symbols that aren’t labels. The value for :$and should be an array of individual queries, not an array of strings; so you should build an array:

parts = [ ]
parts.push(:price => 1.99)         if(price)
query.push(:qty => { :$lt => 20 }) if(qty)
#...
db.inventory.find(:$and => parts)

BTW, you might run into some floating point problems with :price => 1.99, you should probably use an integer for that and work in cents instead of dollars. Some sort of check that parts isn’t empty might be a good idea too.