How do I create array of data from Users table in Rails Active Record?

Question

I have a User table with the columns full_name, email, phone, address, city, state, zip

I need to create an array from the User table that contains the fullname and email in this format ["user1.full_name, user1.email", "user2.full_name, user2.email" etc]

I am having trouble writing this query.

This is what I have so far

#create empty arrays
full_names = []
emails = []
#populate the full_names array
user_full_name = User.all
user_full_name.each{|x| full_names<<x.full_name}
#populate the emails array
user_email = User.all
user_email.each{|x| emails<<x.email}

#combine the two arrays
full_names.zip(emails)

But that gives me a multidimensional array of [["full_name, email"], ["full_name, email"] etc]

How do I get it in the format of ["full_name, email", "full_name, email" etc]

builder-7000 · Accepted Answer · 2020-10-04 04:49:59Z

1

Here are two^* possible solutions and their corresponding SQL:

# SELECT "users"."full_name", "users"."email" FROM "users"
User.pluck('full_name', 'email').map{ |u| u.join(', ')}.flatten

# SELECT "users".* FROM "users"
User.all.map { |u| "#{u.full_name}, #{u.email}" }

So pluck is more efficient than all.map because it only selects the attributes you want.

^* Both of which were mentioned in an earlier answer.

edited Oct 4, 2020 at 4:49

answered Oct 4, 2020 at 4:39

builder-7000

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max pleaner · Accepted Answer · 2020-10-04 01:57:49Z

User.all.map do |user|
  "#{user.full_name}, #{user.email}"
end

See Array#map

To give a little more info on this. When you use an ActiveRecord::QueryMethod (e.g. you make a query through ActiveRecord) the result is not actually an array, however it behaves like an array, and by calling an array method on it, you fetch the results (See ActiveRecord::Relation). That was a mouthful, but hopefully the following examples will be clearer:

# This builds a query but doesn't actually fire it!
users = User.all

# chain onto the query - it still won't be fired yet
users = users.where.not(name: "Rick")

# see the query that will be run
users.to_sql

# check the type of this variable
users.class
# => ActiveRecord::Relation

# evaluates the query
users.count

# evaluates the query
users.to_a

# evaluates the query
users.any? { |user| user.email.nil? }

# evaluates the query
users.map { |user| user.full_name }

# evaluates the query
# does the same thing as the previous line
users.pluck(:first_name)

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