How to restructure results from database

Question

I've got a model User which has id, name, surname, role_id, permission_id

Here is few user entries :

User => {:name => 'Bob', :surname => 'surnmae', :role_id => 1, :permission_id = 2}
User => {:name => 'Alice', :surname => 'strange', :role_id => 1, :permission_id = 3}
User => {:name => 'Ted', :surname => 'Teddy', :role_id => 2, :permission_id = 3}

Now I need to group them first by role_id and then by permission_id , here is what I mean :

Category.select([:name, :role_id, :permission_id]).group_by(&:role_id)

Produces :

{1 => 
[#<User name: "Bob", role_id: 1, permission_id: 2>,
#<User name: "Alice", role_id: 1, permission_id: 3>]
2 => [#<User name: "Ted", role_id: 2, permission_id: 3>]
}

Which is close enough but I need them grouped with permission_id as well so it would look like this :

{:role_id => {:permision_id => [Array of users grouped by this criteria]}

}

Answer 1

maybe something like

Category.select([:name, :role_id, :permission_id]).group_by(&:role_id).map{|role| role.group_by(&:permission_id)}

Answer 2

It is bit more tricky than it seems. It is better to write it into multiple steps. However, the following one-liner will work:

Hash[ User.all.group_by(&:role_id).collect{|role, grp| [role, grp.group_by(&:permission_id)]} ]

Output will be the following (which is probably what you are looking for):

{1=>
  {2=>[{:name=>"Bob", :surname=>"surnmae", :role_id=>1, :permission_id=>2}],
   3=>[{:name=>"Alice", :surname=>"strange", :role_id=>1, :permission_id=>3}]},
 2=>{3=>[{:name=>"Ted", :surname=>"Teddy", :role_id=>2, :permission_id=>3}]}}

Same logic, but simpler to comprehend:

output={}
User.all.group_by(&:role_id).each{|role, grp| output[role]= grp.group_by(&:permission_id)}
# output has required goruping

Answer 3

Category.select([:name, :role_id, :permission_id]).group_by { |category| [category.role_id, category.permission_id] }

编辑：没关系，这并不能提供您正在寻找的格式。