How can I get a nested attribute of each element to an array in Ruby on Rails?

Question

A rails object has following style of info. Say for example, if I do res.students[0].student_id it prints 1

The rails object is the response from other service and it is a proto.

"Students": [
    {
      "student_id": "1",
      "marks": 66,
      "address": 1,234 street,
      "name" : "",
    },
    {
      "student_id": "2",
      "marks": 97,
      "address": 4, 567 street,
      "name" : "",
    },
]

//Name will be empty in this structure

But, How can I get all student_id to an array in Ruby on Rails?
Also, how can I pass an array of student IDs to SQL query and get array of names?

Oh, so is that not an hash?

Ursus
– Ursus

2020-06-05 18:21:22 +00:00
Commented Jun 5, 2020 at 18:21 — Ursus
– Ursus, Commented Jun 5, 2020 at 18:21
@Ursus Its not an hash.

sofs1
– sofs1

2020-06-05 18:21:48 +00:00
Commented Jun 5, 2020 at 18:21 — sofs1
– sofs1, Commented Jun 5, 2020 at 18:21
then what data type is it?

lacostenycoder
– lacostenycoder

2020-06-05 18:25:29 +00:00
Commented Jun 5, 2020 at 18:25 — lacostenycoder
– lacostenycoder, Commented Jun 5, 2020 at 18:25
@lacostenycoder - updated.

sofs1
– sofs1

2020-06-05 18:27:46 +00:00
Commented Jun 5, 2020 at 18:27 — sofs1
– sofs1, Commented Jun 5, 2020 at 18:27
can you be more specific about part 2 of your question?

lacostenycoder
– lacostenycoder

2020-06-05 18:28:31 +00:00
Commented Jun 5, 2020 at 18:28 — lacostenycoder
– lacostenycoder, Commented Jun 5, 2020 at 18:28

lacostenycoder · Accepted Answer · 2020-06-05 18:34:56Z

3

We can assueme res.students is an Enumerable so why not just .map?

student_ids = res.students.map{|r| r.student_id}

For sql perhaps you're looking for this?

Student.where(id: student_ids ).pluck(:name)

answered Jun 5, 2020 at 18:34

lacostenycoder

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4 Comments

3limin4t0r Over a year ago

pluck also works on Enumerable objects if the objects within respond to []. So res.students.pluck(:student_id) would return a list of student ids.

sofs1 Over a year ago

@lacostenycoder - I have a follow up question. After getting names with sql queries I will be assigning it to each student element. If I use an array and say for 3rd element there is no name returned the array would look like ["Mark" , "Tom", "", "Dick", "harry"] and when I assign it back , I have to exactly map it to corresponding studentId. Is map the only way? Ruby seems to have lots of shortcut one-line magic. Is there anything of that sort for this ?

lacostenycoder Over a year ago

@3limin4t0r I guess that was added in newer versions of Rails, do you know when?

lacostenycoder Over a year ago

@sofs1 I'm not sure I understand exactly what you want to do in your comment above. Please post a new question if you need more help on that.

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