HABTM > has_many, through

[davidwessman]

@jforberg have been speaking about it, for example in #69 .

We should merge from our HABTM table to an actual model, which gives us the ability to actually validate before the join is created.

How do you move the data from the HABTM-join table to a new one?
@fsek/admins

[jforberg]

The database doesn't change at all, only the models.

Read: http://stackoverflow.com/questions/24559489/rails-4-habtm-custom-validation-on-associations#answer-24559591

Maybe you want to rename the table to something more descriptive but that's it.

[davidwessman]

Makes sense! Do you add id's as well?
(Does the UserRole-table need an own ID column?)

[jforberg]

Yes. All tables have id columns in rails.

[davidwessman]

@jforberg

unless table_exists? :elections_posts
      create_table "elections_posts", id: false do |t|
        t.integer "election_id"
        t.integer "post_id"
      end
    end

This is standard for all the HABTM-tables that we have. So should we add IDs?

[jforberg]

@davidwessman Yes. Also we should ensure that we remove any duplicates (this is the other problem with HABTM, there is zero protection from duplicates).

The reason for this is, we need a primary key on the table. Otherwise, we can't tell different rows apart or delete a row without also maybe deleting other rows. It's madness. (ok well no but it sucks a bit).

In classic SQL you would make a compound primary key of both election_id and post_id (and this would work) but rails wants us to always have a separate ID column so that's that.

Knowledge about database design is one of those things which can really help understanding a lot. In rails, we're told to just sort of forget about the database which is a bit sad.

[davidwessman]

• app/models//album.rb:5: has_and_belongs_to_many :album_categories
• app/models//album.rb:6: has_and_belongs_to_many :subcategories
• app/models//album_category.rb:3: has_and_belongs_to_many :albums
• app/models//election.rb:5: has_and_belongs_to_many :posts
• app/models//post.rb:7: has_and_belongs_to_many :elections
• app/models//subcategory.rb:3: has_and_belongs_to_many :albums

Ready for refactoring 😄

[davidwessman]

Finally not in use anymore! 💃