generate model using user references vs user id integer

Question

I m confused on how to generate a model that belongs to another model  My book uses this syntax to associate Micropost with User   rails generate model Micropost user id integer   but http   guides rubyonrails org  says to do it like this   rails generate model Micropost user references   The migrations generated by these 2 are different  Also  for the former  how does rails know that user id is a foreign key referencing user  Thanks

User · Accepted Answer

Both will generate the same columns when you run the migration. In rails console, you can see that this is the case:

:001 > Micropost
=> Micropost(id: integer, user_id: integer, created_at: datetime, updated_at: datetime)

The second command adds a belongs_to :user relationship in your Micropost model whereas the first does not. When this relationship is specified, ActiveRecord will assume that the foreign key is kept in the user_id column and it will use a model named User to instantiate the specific user.

The second command also adds an index on the new user_id column.

User · Answer

how does rails know that user id is a foreign key referencing user    Rails itself does not know that user id is a foreign key referencing user  In the first command rails generate model Micropost user id integer it only adds a column user id however rails does not know the use of the col  You need to manually put the line in the Micropost model  class Micropost  lt  ActiveRecord  Base   belongs to  user end  class User  lt  ActiveRecord  Base   has many  microposts end   the keywords belongs to and has many determine the relationship between these models and declare user id as a foreign key to User model   The later command rails generate model Micropost user references adds the line belongs to  user in the Micropost model and hereby declares as a foreign key   FYI Declaring the foreign keys using the former method only lets the Rails know about the relationship the models tables have  The database is unknown about the relationship  Therefore when you generate the EER Diagrams using software like MySql Workbench you find that there is no relationship threads drawn between the models  Like in the following pic    However  if you use the later method you find that you migration file looks like   def change     create table  microposts do  t        t references  user  index  true        t timestamps null  false     end     add foreign key  microposts   users   Now the foreign key is set at the database level  and you can generate proper EER diagrams

User · Answer

For the former  convention over configuration  Rails default when you reference another table with    belongs to  something   is to look for something id   references  or belongs to is actually newer way of writing the former with few quirks   Important is to remember that it will not create foreign keys for you  In order to do that  you need to set it up explicitly using either   t references  something  foreign key  true t belongs to  something else  foreign key  true   or  note the plural    add foreign key  table name   somethings add foreign key  table name   something elses

[ruby-on-rails] generate model using user:references vs user_id:integer

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