Select query in Ruby on Rails

Question

I am new to ruby on rails but I am not finding the meaning of this line of code. I saw in the documentation of rails that select will build an array of objects from the database for the scope, converting them into an array and iterating through them using Array#select. Anyway I can’t understand the result of this line of code and on what it consists.

model.legal_storages.select{|storage| storage.send(document_type)==true}.last

There are many differences between the Rails version 3, 4 and 5. Please use the specific tag. — Sebastián Palma
– Sebastián Palma, Commented Oct 21, 2019 at 21:16
This doesn't provide an answer, but the code used seems a bit strange .If model.legal_storages isn't already loaded I would go for a direct query instead. model.legal_storages.where(document_type => true).last If model.legal_storages is loaded I would use the square bracket notation to make sure only attributes can be invoked. model.legal_storages.select{|storage| storage[document_type] }.last — 3limin4t0r
– 3limin4t0r, Commented Oct 21, 2019 at 23:13

Sebastián Palma · Accepted Answer · 2019-10-21 22:06:12Z

4

model.legal_storages.select { |storage| storage.send(document_type) == true }.last - From the result of the last operation, select only the last element.
             |         |                                  |
             |         |                                   --------------------- For each element in model.legal_stores invoke
             |         |                                                         the method that is held by the variable document_type
             |         |                                                         and check if it's equal to true.
             |         |
             |          --------- Over the result of the last method,
             |                    call select to filter those elements where
             |                    condition in the block evaluates to true.
             |
              ------------------- Invoke the method legal_stores in model.

edited Oct 21, 2019 at 22:06

answered Oct 21, 2019 at 21:22

Sebastián Palma

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5 Comments

max Over a year ago

A true masterpiece of ASCII art.

Cary Swoveland Over a year ago

@max, I'll start the bidding at $50,000.

john bowlee Over a year ago

Thank you for your respose but what does storage.send(document_type) do in this case? It stores the records in an array in case the condition is true?

3limin4t0r Over a year ago

@johnbowlee It invokes the method name, stored in the document_type variable on storage. foo.send("bar") is similar to foo.bar but negates private and protected access.

Sebastián Palma Over a year ago

storage.send(document_type) is the same to do method_name = :succ; 1.send(method_name) # => 2. send receives a method name (document_type), and then that method is invoked in the receiver (storage) @johnbowlee.

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