Return array of values instead of array of objects from SQL query in Rails

Question

I have a SQL query in a Rails model that responds with an array of objects. And each object has an attribute called points with a value.

But its preferable for query to just return an array of points like [10,15,5] instead of [object,object,object] which requires then extracting the points out into another array to be useful.

Model file

LAST_3_SELECT = "
  SELECT
    (
      (data.ap / (data.apa * 1.0))
      +
      (data.vp / (data.vpa * 1.0))
    )
    / 2 * 1.5 * data.level
    AS points
  FROM data
  WHERE data.user_id = ?
  GROUP BY data.id
  ORDER BY data.created_at DESC
  LIMIT 3
"

def self.last_3(user_id)
  connection.select_all(sanitize_sql_array( [LAST_3_SELECT, user_id]), "last-3")
end

Is this possible to do in a query itself, or necessary to do in a method outside it?

I don't have much experience writing raw SQL queries into Rails methods so any guidance would be very appreciated.

For .map(&:points), it returned NoMethodError (undefined method 'points' for {"points"=>2.4000000000000004}:Hash): — tim_xyz
– tim_xyz, Commented May 8, 2016 at 6:56

coderVishal · Accepted Answer · 2016-05-08 05:34:57Z

4

You can use pluck to get the points into an array

def self.last_3(user_id)
  connection.select_all(sanitize_sql_array( [LAST_3_SELECT, user_id]), "last-3").pluck(:points)
end

Here points is the column name to be plucked

answered May 8, 2016 at 5:34

coderVishal

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4 Comments

tim_xyz Over a year ago

NoMethodError (undefined method 'pluck' for #<ActiveRecord::Result:...>)

Meer Over a year ago

Instead of .pluck(:points) use .collect(&:points). This will get you the list of pints in array.

coderVishal Over a year ago

@pandaman, for the active record result, is this working, result.first.points

tim_xyz Over a year ago

Rails4. Tried .collect() and ran into something like NoMethodError (undefined method 'points' for {"points"=>...}:Hash). But was able to get it working using .map.

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