Query has_many through association Rails -

i have has_many though association this:

user.rb has_many :memberships, :dependent => :destroy  has_many :groups, :through => :memberships  group.rb has_many :users, :through => :memberships has_many :microposts   membership.rb belongs_to :user belongs_to :group 

first need know query groups of user, after need way show microposts of groups. possible 1 query information?

thanks lot!

to user's groups:

some_user = user.find(some_id) some_user.groups 

to microposts, do:

some_user.groups.each |group|   puts group   puts group.microposts end 

however, cause separate query generated collect microposts of each group. can fixed eager-loading microposts using includes:

some_user.groups.includes(:microposts).each |group|   puts group   puts group.microposts end 

now 2 queries generated - 1 fetch groups, , 1 fetch all microposts associated these groups. behind scenes, activerecord match microposts correct group, , return them accordingly when calling .microposts on group.

to microposts hash, can use each_with_object collect them:

@group_microposts = some_user.groups.includes(:microposts).                               each_with_object({}){|group, h| h[group] = group.microposts} 

this return hash in form { group => microposts }.

to them array, could do:

@microposts = some_user.groups.includes(:microposts).map(&:microposts).flatten 

however, there more efficient way if don't need group information @ all:

@microposts = micropost.joins(:group => :users).where(:users => {id: some_user.id}) 

this second method faster because of 2 reasons - requires single query (no eager loading needed) , db lookup more efficient since can use available indices perform necessary joins rather filter against literal integer list (which can slow list gets larger).