Querying multiple related records in Rails

Question

I have an Account, User and Group model. All User and Group records belong to an Account, so it is possible for both users and groups to be related to various accounts.

Basically, I have some really hacky, pieced together SQL queries that lookup all Account records related to a given User or Group record through various associations.

Even though it's fast and only requires a single query for everything to work, I really hate the way it's written.

I was wondering if there is any way I could do this more programatically with something like arel, or if there was a better approach. I also have some security concerns about the code.

class Account < ActiveRecord::Base

  belongs_to :accountable, touch: true, polymorphic: true

  CLAUSE_FOR_RELATED = '"accounts"."accountable_type" = \'%s\' AND "accounts"."accountable_id" IN (%s)'.freeze

  def self.related_to_user(user)
    groups = user.groups.select('"groups".id')
    friends = user.following_friendships.select('"friendships".following_id')

    queries = []
    queries.push ['Group', groups.to_sql]
    queries.push ['User', friends.to_sql]
    queries.push ['User', user.id]

    self.related_to(queries)
  end

  def self.related_to_group(group)
    queries = [
      ['User', group.members.select('"users".id').to_sql]
    ]

    self.related_to(queries)
  end

  def self.related_to(queries)
    clauses = queries.map do |clause|
      sprintf(CLAUSE_FOR_RELATED, clause[0], clause[1])
    end

    self.where(clauses.join(" OR "))
  end
end

Is the SQL tag properly used here? Was looking for SQL to review in your code but found only tiny snippets. No bad karma just seems a bit misleading. — Phrancis
– Phrancis, Commented May 21, 2014 at 4:31

mabe02 · Accepted Answer · 2017-09-27 21:16:22Z

I would try to use as much as possible what is provided by ActiveRecord. I was thinking to something like:

class Account < ActiveRecord::Base
  belongs_to :accountable, touch: true, polymorphic: true
  CLAUSE_FOR_RELATED = '"accounts"."accountable_type" = \'%s\' AND "accounts"."accountable_id" IN (%s)'.freeze

  class << self
    def related_to_user(user)
      group_ids = user.groups.pluck('groups.id')
      friend_ids = user.following_friendships.pluck('friendships.following_id') 

      query = [
        compose_clause('Group', group_ids.join(', ')),
        compose_clause('User', [user.id, *friend_ids].join(', '))
      ].join(' or ')

      where(query)
    end

    def related_to_group(group)
      member_ids = group.members.pluck('users.id')
      where(compose_clause('User', member_ids.join(', ')))
    end

    private
    def compose_clause(accountable_type, ids)
      sprintf(CLAUSE_FOR_RELATED, accountable_type, ids)
    end
  end
end

Now in Rails 5 you could even write it like:

class Account < ActiveRecord::Base
  belongs_to :accountable, touch: true, polymorphic: true

  class << self
    def related_to_user(user)
      group_ids = user.groups.pluck('groups.id')
      friend_ids = user.following_friendships.pluck('friendships.following_id') 

      where(accountable_type: 'Group', accountable_id: group_ids).or(
         Account.where(accountable_type: 'User', accountable_id: [user.id, *friend_ids])
      )
    end

    def related_to_group(group)
      member_ids = group.members.pluck('users.id')
      where(accountable_type: 'User', accountable_id: member_ids)
    end
  end
end

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