Deleting Table from Schema - Rails

Deleting table from schema - Rails

If you create an empty migration by running:

rails g migration DropInstalls
or:

rails generate migration DropInstalls

You can then add this into that empty migration:

class DropInstalls < ActiveRecord::Migration
  def change
    drop_table :installs
  end
end

Then run rake db:migrate in the command line which should remove the Installs table

Note: db/schema.rb is an autogenerated file. To alter the db structure, you should use the migrations instead of attempting to edit the schema file.

Removing table from schema.rb

If you want to really really remove it you should prepare a migration to drop the table.

If you just remove the model ActiveRecord will still find the table in db (and that's probably why you're seeing it in schema.rb - if I am right that you mean file and not db schema)

EDIT:

So I tried to reproduce this, and as a result I ended up with following order of commands.

1. first drop the table (make a new migration with drop_table :locations and run it)
2. then run rails destroy model location (you will get an error if you destroy model first)
3. run rails c so Rails picks up the db change and updates schema.rb

Rails DB Migration - How To Drop a Table?

You won't always be able to simply generate the migration to already have the code you want. You can create an empty migration and then populate it with the code you need.

You can find information about how to accomplish different tasks in a migration here:

http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

More specifically, you can see how to drop a table using the following approach:

drop_table :table_name

Unable to delete tables in schema.rb from rails app

Firstly check if the table is present...in rails console...

##to view all tables 
ActiveRecord::Base.connection.tables

i use rails console to delete tables directly...

    ActiveRecord::Base.connection.execute("drop table table_name")
    ###========OR===============
    ActiveRecord::Migration.drop_table(:table_name)
   ###=========OR===============
   ActiveRecord::Migration.drop_table("table_name")     
   ###=========WITH EXAMPLE===============
   ActiveRecord::Base.connection.drop_table :subscriptions

Then,delete the migration file or rename it again by changing timestamp and again run rake db:migrate

Hope it helps :)

How to Delete Table from Database permanently in ROR

If you haven't pushed your code then the solution given by @Cryptex Technologies works fine. But if you have(i.e if you are using version control) then i won't recommend that approach. In that case you should create a new migration something like this:

class RemoveTable < ActiveRecord::Migration[5.2]
  def up
    drop_table :table_name
  end

  def down
    create_table :table_name do |t|
      t.string :field_name_1
      t.text :field_name_2
      t.timestamps
    end

    add_index :table_name, :field_name_1, unique: true
  end
end

Remove Model and Table so can start again in Rails

In order to completely remove all columns &
tables that migration has created you need to run:

rails db:migrate:down VERSION=012345678 (where 012345678 should be the version number of your migration)

.............................

rails destroy model Comments

will delete your Model, pending migration, tests and fixtures

So destroy it's the opposite of generate:

$ bin/rails destroy model Oops
      invoke  active_record
      remove    db/migrate/20120528062523_create_oops.rb
      remove    app/models/oops.rb
      invoke    test_unit
      remove      test/models/oops_test.rb
      remove      test/fixtures/oops.yml

And, you can now create a new Model with the same name, as there's no trace of your previous one :)

How to completely remove a model and its associations in Rails?

About the unusual `schema.rb` behavior

I tried checking out an older commit, but the schema file stubbornly refuses to change.

This is quite unusual. Do verify that you're tracking the db/schema.rb file using git. If it is tracked, there's no reason why checking out an older commit shouldn't return it to the older state. At that point, you should be able to:

$ rails db:drop
$ rails db:create
$ rails db:schema:load

...to load the old schema into the database. Then, you should be able to return to the latest code with git, and run pending migrations after the date at which the older schema was created.

About a cleaner way to implement this

Before writing the below migration, the first step would be to remove any existing relationship written in the Book class. For example:

# app/models/book.rb
class Book < ApplicationRecord
  # The line below should be deleted! Otherwise, it will probably interfere
  # with the `book.update!(author: ...)` line in the migration.
  belongs_to :author
end

I've taken to writing related migrations in a single file, since they're all related. To me, this looks like:

class MoveAuthorToBooks < ActiveRecord::Migration[6.0]
  class Author < ApplicationRecord
  end

  class Book < ApplicationRecord
  end

  def up
    # Start by adding a string column.
    add_column :books, :author, :string

    # Let's preserve existing author names.
    Book.all.each do |book|
      author = Author.find(book.author_id)
      book.update!(author: author.name)
    end

    # Now that the names have been moved to the books table, we don't
    # need the relationship to `authors` table anymore. This should
    # also delete any related foreign keys - manual foreign key deletion
    # should not be required.
    remove_column :books, :author_id

    # Alternative: If you'd created the `authors_id` column using the
    # `add_reference` command, then it's probably best to use the opposite
    # `remove_reference` command.
    #
    #remove_reference :books, :author, index: true, foreign_key: true

    # Finally, remove the `authors` table.
    drop_table :authors 
  end

  def down
    # This can be technically be reversed, but that'll need some more code that
    # reverses the action of the `up` function, and it may not be needed.

    raise ActiveRecord::IrreversibleMigration
  end
end

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