Configuring the proper join column in Rails Admin - ruby

Question

I have two models, which associate with each other through a has_and_belongs_to_many relationship.
class Band < ActiveRecord::Base
has_and_belongs_to_many :stages, association_foreign_key: :stage_number
end
class Stage < ActiveRecord::Base
has_and_belongs_to_many :bands
end
Assume both tables have an id field, and that stage has a stage_name field.
They're related to each other through a table called bands_stages, with a schema that looks similar to this:
create_table :bands_stages, id: false do |t|
t.integer :band_id
t.integer :stage_number
end
My intention is to use Rails Admin to allow us to modify certain fields on the Stage, but every time that runs, I get an SQL error doing so:
column stages.id does not exist
It seems that Rails Admin is picking the wrong column by default to join on. How would I inform Rails Admin that I want it to join on a column that actually exists in my join table?
Note that I can't actually make use of the ID in the stages table. The intention is that only ten stages exist at any given time, denoted by their stage number, but every band can visit each stage. Since an ID would automatically increment, it seems to be safer and more explicit to its intent to leverage the more concrete :stage_number field instead.

Answer 1

I'm sure that it's not a problem of rails admin but habtm association.
To make habtm use the right column in sql primary key must be specified for stage model and foreign key for association.
And it is the only way to make it works right.
class Stage < ActiveRecord::Base
self.primary_key = "stage_number"
has_and_belongs_to_many :bands, foreign_key: :stage_number
end
But I think the best way is to use joint model and has_many/belongs_to because for has_many/belongs_to it's possible to set any column to be used as primary key via :primary_key option.
class BandStageLink < ActiveRecord::Base
self.table_name = "bands_stages"
belongs_to :band
belongs_to :stage, foreign_key: :stage_number, primary_key: :stage_number
end
class Band < ActiveRecord::Base
has_many :band_stage_links
has_many :stages, through: :band_stage_links, foreign_key: :stage_number
end
class Stage < ActiveRecord::Base
has_many :band_stage_links, primary_key: :stage_number, foreign_key: :stage_number
has_many :bands, through: :band_stage_links
end
Update: Note that in this case there is still no need to specify any primary keys for stage table. For instance my migration is:
class CreateStageBandTables < ActiveRecord::Migration
def change
create_table :bands_stages, id: false do |t|
t.integer :band_id
t.integer :stage_number
end
create_table :bands do |t|
t.string :name
end
create_table :stages, id: false do |t|
t.integer :stage_number
t.string :name
end
end
end
I tested both cases for rails 4.2.5 and everything works just fine.

Answer 2

Edit - I did mis-understand the primary key bit, I think the desire was to tell Rails to use different attribute as PK, which should be less problematic than re-purposing the auto-increment-by-default PK ID. In that case, the Stage model should include self.primary_key = "stage_number", and the rest of the details at the bottom of this answer relating to HABTM alongside that. Of course has-many-through would still be my preferred solution here.
I think there's a bigger problem with the models and approach, than Rails Admin.
If I understand what you're trying to do, then you'd also need to turn off auto-increment for the primary key in stages table, to hold arbitrary numbers (representing stage numbers) as primary key IDs. It could end badly very quickly, so I'd advise against it.
If the data is genuinely static (10 stages ever), you could even keep it as a constant in the Band model and scrap Stage completely (unless there's more there), e.g.
class Band < ActiveRecord::Base
POSSIBLE_STAGES = [1, 2, ...]
validates :stage, inclusion: { in: POSSIBLE_STAGES, message: "%{value} is not a stage we know of!" }
end
For a table-based approach, I would suggest has-many-through, it'll save you a lot of pain in the future (even if you don't need additional attributes on the join table, things like nested forms are a little easier to work with than in HABTM). Something like this:
class Band < ActiveRecord::Base
has_many :events
has_many :stages, through :events
# band details go into this model
end
class Event < ActiveRecord::Base
belongs_to :band
belongs_to :stage
# you could later add attributes here, such as date/time of event, used_capacity, attendee rating, and
# even validations such as no more than X bands on any given stage at the same time etc.
end
class Stage < ActiveRecord::Base
has_many :events
has_many :bands, through :events
# stage number/details go into this model
end
The migration for that could look something like this:
create_table :bands do |t|
t.string :bandname
# whatever else
end
create_table :events do |t|
t.belongs_to :band
t.belongs_to :stage
# you could add attributes here as well, e.g. t.integer :used_capacity
end
create_table :stages do |t|
t.integer :number
t.integer :total_capacity
# whatever else
end
As you can see primary key IDs are not touched here at all, and I would always avoid storing business data in Rails' and databases' plumbing of any sort (which is what I consider IDs to be, they're there to ensure relation/integrity of the data in a relational database, as well as nice and consistent mapping to ActiveRecord - all business data should be beside that, in actual attributes, not plumbing used to connect models).
If you still want HABTM and re-purposing of primary ID, then I think Stage should include a foreign_key statement to "advertise" itself to the bands_stages join table as having a custom key name (in bands_stages only), while keeping the association_foreign_key on the Band end to show what you want to query in the join table to reach the other side. The stages table would still utilise id though as its primary key, you'd just want to turn off auto-increment with something like t.integer :id, :options => 'PRIMARY KEY' (might be dependent on the database flavour - and again, I would advise against this).
Your models would look like this:
class Band < ActiveRecord::Base
has_and_belongs_to_many :stages, association_foreign_key: "stage_number"
end
class Stage < ActiveRecord::Base
has_and_belongs_to_many :bands, foreign_key: "stage_number"
end
The connection between bands and bands_stages would be bands.id = bands_stages.band_id, for which many bands_stages.stage_number would be found, and each would be connected to stage via bands_stages.stage_number = stages.id (where stages.id has been re-purposed to represent business data at a likely future peril).

Answer 3

Change the association_foreign_key value to be a string instead of symbol.
class Band < ActiveRecord::Base
has_and_belongs_to_many :stages, association_foreign_key: 'stage_number'
end
class Stage < ActiveRecord::Base
has_and_belongs_to_many :bands, foreign_key: 'stage_number'
end