CODEWITHSUNDEEP
ruby-on-rails
Trinity76
Trinity76

Reputation: 665

Rails Association about a "helper" table

I'm rewriting an old PHP application and have to migrate the database. It has a join table harddisks_imagecapturing:

id  manuscripts_id   harddisk_id
-------------------------------
1   206              18
2   206              17
3   206              16

Table imagecapturing:

id harddisk_id library signature
-------------------------------
1   16         "foo"    "MS352"
2   17         "bar"    "AB67"
3   18         "baz"    "WQ62"

Table harddisks: 

id   harddisk_name capacity
-------------------------------
16   "Seagate"    2000
17   "Seagate"    2000
18   "Seagate"    4000

The problem is, that I don't have an manuscript_id in the table imagecapturing instead a signature that is unique and could be used as a "helper table" to reference from manuscript table.

Table manuscripts:

id   signature
---------------
206   "MS352"

How can I make the Rails associations right to retrieve the data into a table with the columns:

signature, library, harddisk_name, capacity

? I suppose one had to use the manuscript_id from harddisks_imagecapturing table to get the signature from the manuscript table.

class Imagecapturing < ApplicationRecord
  self.table_name = 'imagecapturing'

  belongs_to :harddisk

end

class HarddisksImagecapturing < ApplicationRecord
  self.table_name = 'harddisks_imagecapturing'

  belongs_to :harddisk
  belongs_to :imagecapturing
end

class Harddisk < ApplicationRecord
  has_many :manuscripts_harddisks
  has_many :manuscripts, through: :manuscripts_harddisks

  default_scope { order(kaufdatum: :desc) }

  # Harddisk.order('id ASC').reorder('kaufdatum DESC')
end

class Manuscript < ApplicationRecord

end

Upvotes: 0

Views: 27

Answers (1)

Daniel Westendorf
Daniel Westendorf

Reputation: 3475

You can specify which column(s) to use as the primary_key and foreign_key for associations. http://guides.rubyonrails.org/association_basics.html#options-for-belongs-to

class Manuscript < ApplicationRecord
  belongs_to :imagecapturing, foreign_key: "signature", primary_key: "signature"
end

Alternatively, like you mentioned, you could navigate through your harddisks_imagecapturing table as well.

Upvotes: 1

Related Questions