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Start your free trialAntoine Boillot
10,466 PointsActiveRecord : database relationship setup vs foreign keys setup ?
Hi All,
In the ActiveRecord courses, Migration section, Hampton is setting up the following table as below :
class CreateTimeEntries < ActiveRecord::Migration
def change
create_table :time_entries do |t|
t.float :time
t.belongs_to :customer
t.belongs_to :employee
t.timestamps
end
end
end
He then defines in the relevant model their relationship with already existing tables, see below :
class TimeEntry < ActiveRecord::Base
belongs_to :customer
belongs_to :employee
end
Aren't those lines redondant ? Could we avoid typing one or the other ?
#in table setup
t.belongs_to :customer
t.belongs_to :employee
#in the relevant model
belongs_to :customer
belongs_to :employee
Complementary question : If the lines in the table setup are here to defines foreign keys, how come then that we need to define the relationship in the model as well? I thought foreign keys were by themselves defining such relationship.
Hope I'm clear.
Thanks a lot for your help !
1 Answer
Maciej Czuchnowski
36,441 PointsThe belongs_to in the migration is not the same thing as the belongs_to in the model. In the migration it adds the _id column of the associated model (it's the same as writing add_reference :time_entries, :customer
). When used in the model, the belongs_to association lets you streamline some code. This - 1 Why Associations? - explains it nicely:
Antoine Boillot
10,466 PointsAntoine Boillot
10,466 PointsThanks! :)