your objects are wrong
the model is person and the table is people
Model Person.rb
has_and_belongs_to_many :segments
Model Segment.rb
has_and_belongs_to_many :people
The migration looks like this
class CreatePeopleAndSegments < ActiveRecord::Migration[5.0]
def change
create_table :people do |t|
t.string :name
t.timestamps
end
create_table :segments do |t|
t.string :part_number
t.timestamps
end
create_table :people_segments, id: false do |t|
t.belongs_to :person, index: true
t.belongs_to :segment, index: true
end
end
end
So when you do @person.segments you get an array including all the segments viceversa @segment.people
Here I want to get the people who not associated with particular segment. I tried using join but could not get result. Now I am using "not in" query and it took more time. Is there any other way without using "not in"?
Between the two tables there is already a Join, maybe your best choice is making sure you can use that join as Model in the application side.
There is a specific chapter in the association_basics guide from rails discussing about this, it is called choosing-between-has-many-through-and-has-and-belongs-to-many
I quote them
The simplest rule of thumb is that you should set up a has_many :through relationship if you need to work with the relationship model as an independent entity. If you don't need to do anything with the relationship model, it may be simpler to set up a has_and_belongs_to_many relationship (though you'll need to remember to create the joining table in the database).
I believe that if you read that chapter you will understand the best choice for you is using has_many :through and having an object in your Application that represents the table people_segments.
Think with creativity what is this relationship, is this relationship between people and segments a role or a position...
To implement has_many :through you can follow the guide
Once you have done that, you can use the Position object to do the query.
Position.where.not(segment_id: 1)
If this is not what you need, the rails query documentation includes many more info and StackOverflow does not substitute the official documentation
