I want to remove container:references from my table, I have tried:
rails generate migration RemoveContainerfromCreateTasks container:references
followed by rails db:migrate, but it my reference field is still not removed.
Below is my ActiveRecord
class CreateTasks < ActiveRecord::Migration[6.1]
def change
create_table :tasks do |t|
t.string :title
t.text :body
t.references :container, null: false, foreign_key: true
t.text :tag
t.datetime :due
t.integer :priority
t.timestamps
end
end
end
class RemoveContainerfromCreateTasks < ActiveRecod::Migration[6.1]
def change
end
end
The issue here is really a sneaky capitalization error. Running:
rails generate migration RemoveContainerfromCreateTasks container:references
Will generate a migration with an empty change block which will do absolutely nothing when you migrate it except modify the migrations meta table (a table that AR uses to keep track of which migrations have been run). But if you properly capitalize From:
rails generate migration RemoveContainerFromCreateTasks container:references
It will generate:
class RemoveContainerFromCreateTasks < ActiveRecord::Migration[6.0]
def change
remove_reference :create_tasks, :container, null: false, foreign_key: true
end
end
Rails isn't actually intelligent. It just casts the name argument into snake case and compares it to a set of patterns like:
remove_something_from_tablename foo:string bar:integer
create_tablename foo:string bar:integer
create_foo_bar_join_table foo bar
And it then uses a template to generate the according type of migration. If you don't properly pluralize it will be cast into:
remove_containerfrom_create_tasks
Which Rails does not know what to do with as it does not match a known pattern.
Also note despite popular belief migrations are just a DSL to create SQL transformations which is completely unaware about your tables or models. In this case the resulting migration will just blow up when you attempt to run it since you don't have a create_tasks table.
I would roll the missnamed migration back. Delete it then run:
rails g migration RemoveContainerFromTasks container:references
rails db:migrate
Your issue here is that "CreateTasks" is not table in your database. "Tasks" is, however.
rails g migration RemoveContainerFromTasks container:references
will provide you
class RemoveContainerFromTasks < ActiveRecord::Migration[6.1]
def change
remove_reference :tasks, :container, null: false, foreign_key: true
end
end
A migration of this will successfully remove container from your schema.rb file, and subsequently the database system you're using.
Here's some console output, because why not:
unclecid#home:~/Desktop/sample_app$ rails db:migrate
== 20201227150512 CreateTasks: migrating ======================================
-- create_table(:tasks)
-> 0.0022s
== 20201227150512 CreateTasks: migrated (0.0023s) =============================
== 20201227151021 RemoveContainerFromTasks: migrating =========================
-- remove_reference(:tasks, :container, {:null=>false, :foreign_key=>true})
-> 0.0330s
== 20201227151021 RemoveContainerFromTasks: migrated (0.0331s) ================
I am working on a rails app and I keep getting an error saying,
AddIndexToUsersEmail: migrating ===========================================
-- add_index(:users, :email, {:unique=>true})
rake aborted!
An error has occurred, this and all later migrations canceled:
Index name 'index_users_on_email' on table 'users' already exists/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract/schema_statements.rb:576:in `add_index_options'
/app/vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_reco
Here is the migration:
class AddIndexToUsersEmail < ActiveRecord::Migration
def change
add_index :users, :email, unique: true
end
end
This is because one of your earlier migrations setting the index for users table, check your migrations and either remove it from there of remove this migration
I have a HABTM association between Users and Groups in my Rails 3 app. The book I'm following to learn Rails recommends running the following command line to create the join migration:
rails generate migration create_groups_users
However in the documentation it looks like I should've run:
rails generate migration create_groups_users_join_table
So that the following would be in my _create_groups_users.rb migration:
class CreateGroupsUsersJoinTable < ActiveRecord::Migration
Is adding join_table required?
Adding join_table at the end is not explicitly required. Your first command 'create_groups_users' is fine. I've done this in rails 3.0.9 and it works.
You can double check by opening up the migration file and checking that it looks like:
create_table :groups_users, :id => false do |t|
t.integer :group_id
t.integer :user_id
end
The :id => false is needed for a join table as it shouldn't have its own id field.
The last argument in your call to rails generate migration create_groups_users just denotes the class name and a part of the file name of the migration. So it does help to find the migration you have created, the migration file itself is (inside the class body) empty. So both versions are ok.
rails g migration CreateStates
Then add the following code to the migration:
===========================
class CreateStates < ActiveRecord::Migration
def self.up
create_table :states do |t|
t.column :name, :string
t.column :abbreviation, :string
end
State.create :name => 'Alabama', :abbreviation => 'AL'
State.create :name => 'Alaska', :abbreviation => 'AK'
State.create :name => 'Arizona', :abbreviation => 'AZ'
end
def self.down
drop_table :states
end
end
============================
I get an error:
** Invoke db:migrate (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:migrate
== CreateStates: migrating ===================================================
-- create_table(:states)
-> 0.0010s
rake aborted!
An error has occurred, this and all later migrations canceled:
uninitialized constant CreateStates::State
/Users/jondoe/.rvm/rubies/ruby-1.8.7-p330/lib/ruby/gems/1.8/gems/rspec-core-2.5.1/lib/rspec/core/backward_compatibility.rb:20:in `const_missing'
========
It seems like this should be able to do this:
http://api.rubyonrails.org/classes/ActiveRecord/Migration.html
I have also tried to create a model instead of a just a migration file. Still same error. I have also tried creating 2 migrations (one to create table, then one to add data) and that didn't work either. Any ideas?
Try doing:
State.reset_column_information
before your State.create.
documentation
Your code would work perfectly, except that you don't actually have a State class. The only way Rails would know about this class is if you defined it in app/models/state.rb as Class State < ActiveRecord::Base...
Rather than running a custom migration, I'd recommend running this line of code:
rails g model State name:string abbreviation:string
This will:
Create your model (and unit test files)
Create a migration named something like 20110508223913_create_states.rb, which will look nearly identical to your attempted migration above.
Then all you need to do is add your State.create... lines and you should be good to go.
I have a Users model which needs an :email column (I forgot to add that column during the initial scaffold).
I opened the migration file and added t.string :email, did rake db:migrate, and got a NoMethodError. Then I added the line
add_column :users, :email, :string
again rake db:migrate, again NoMethodError. Am I missing a step here?
Edit: here's the migration file.
class CreateUsers < ActiveRecord::Migration
def self.up
add_column :users, :email, :string
create_table :users do |t|
t.string :username
t.string :email
t.string :crypted_password
t.string :password_salt
t.string :persistence_token
t.timestamps
end
end
def self.down
drop_table :users
end
end
If you have already run your original migration (before editing it), then you need to generate a new migration (rails generate migration add_email_to_users email:string will do the trick).
It will create a migration file containing line:
add_column :users, email, string
Then do a rake db:migrate and it'll run the new migration, creating the new column.
If you have not yet run the original migration you can just edit it, like you're trying to do. Your migration code is almost perfect: you just need to remove the add_column line completely (that code is trying to add a column to a table, before the table has been created, and your table creation code has already been updated to include a t.string :email anyway).
Use this command on the terminal:
rails generate migration add_fieldname_to_tablename fieldname:string
and
rake db:migrate
to run this migration
Sometimes rails generate migration add_email_to_users email:string produces a migration like this
class AddEmailToUsers < ActiveRecord::Migration[5.0]
def change
end
end
In that case you have to manually an add_column to change:
class AddEmailToUsers < ActiveRecord::Migration[5.0]
def change
add_column :users, :email, :string
end
end
And then run rake db:migrate
You can also do
rake db:rollback
if you have not added any data to the tables.Then edit the migration file by adding the email column to it and then call
rake db:migrate
This will work if you have rails 3.1 onwards installed in your system.
Much simpler way of doing it is change let the change in migration file be as it is.
use
$rake db:migrate:redo
This will roll back the last migration and migrate it again.
To add a column I just had to follow these steps :
rails generate migration add_fieldname_to_tablename fieldname:string
Alternative
rails generate migration addFieldnameToTablename
Once the migration is generated, then edit the migration and define all the attributes you want that column added to have.
Note: Table names in Rails are always plural (to match DB conventions). Example using one of the steps mentioned previously-
rails generate migration addEmailToUsers
rake db:migrate
Or
You can change the schema in from db/schema.rb, Add the columns you want in the SQL query.
Run this command: rake db:schema:load
Warning/Note
Bear in mind that, running rake db:schema:load automatically wipes all data in your tables.
You can also add column to a specific position using before column or after column like:
rails generate migration add_dob_to_customer dob:date
The migration file will generate the following code except after: :email. you need to add after: :email or before: :email
class AddDobToCustomer < ActiveRecord::Migration[5.2]
def change
add_column :customers, :dob, :date, after: :email
end
end
You also can use special change_table method in the migration for adding new columns:
change_table(:users) do |t|
t.column :email, :string
end
When I've done this, rather than fiddling the original migration, I create a new one with just the add column in the up section and a drop column in the down section.
You can change the original and rerun it if you migrate down between, but in this case I think that's made a migration that won't work properly.
As currently posted, you're adding the column and then creating the table.
If you change the order it might work. Or, as you're modifying an existing migration, just add it to the create table instead of doing a separate add column.
You can also do this ..
rails g migration add_column_to_users email:string
then rake db:migrate
also add :email attribute in your user controller ;
for more detail check out http://guides.rubyonrails.org/active_record_migrations.html
You can also force to table columns in table using force: true, if you table is already exist.
example:
ActiveRecord::Schema.define(version: 20080906171750) do
create_table "authors", force: true do |t|
t.string "name"
t.datetime "created_at"
t.datetime "updated_at"
end
end
You could rollback the last migration by
rake db:rollback STEP=1
or rollback this specific migration by
rake db:migrate:down VERSION=<YYYYMMDDHHMMSS>
and edit the file, then run rake db:mirgate again.