Hello I am about to attempt to run a rails migration on a database of skills that has a :title and :description. I need to remove the description field and I assume it will look something like this:
rails migration remove_column :skills, :description
I am running it by you pros before I attempt it and end up breaking something on accident. Please let me know if I have the right idea about removing the description field from the database. Thanks a lot!
If skills is the name of your table and description is the name of the column you want to remove, you can type rails g migration RemoveDescriptionFromSkills in your terminal. This will generate a migration file with the name [timestamp]_remove_description_from_skills.rb, located in db/migrate. Edit this file so that it contains the following:
class RemoveDescriptionFromSkills < ActiveRecord::Migration
def change
remove_column :skills, :description
end
end
Then type rake db:migrate in your terminal, and the column will be removed.
For more information, check out this helpful Stack Overflow post: https://stackoverflow.com/a/1992045/3723769.
Note: this answer is intended to describe how to perform the migration. As a safety measure, you should do what Michael Durrant advises before migrating: https://stackoverflow.com/a/25006727/3723769.
Here's some of the things that some to mind:-
check the existing values to see if there's any data you want
see if any indexes exist that should also be dropped.
search the application for that field name
see if there's an existing rails migration that you can use to DOWN the change
Finally, I would consider creating a change migration as normal, i.e. one that actaully adds the field and then I would run it using the down syntax to remove the field.
Related
self explanatory from the title. I have to generate an ERD diagram reflecting customization for primary keys and timestamps in my app, but nothing i'm typing into terminal seems to work. currently using this resource: http://voormedia.github.io/rails-erd/customise.html
i tried something along the lines of
rails g model Comment attribute=primary_keys,timestamps
but my Comment model remains unchanged when i open the erd pdf. any ideas? any constructive input is appreciated. thank you
You should be able to execute the following within your Rails application root directory to generate the ERD diagram for your models:
$ bundle exec erd --attributes=content,primary_keys,foreign_keys,timestamps
Then you'll find a document called erd.pdf within your Rails application root directory.
To add columns to an existing model from the terminal; run a migration:
rails g migration AddPrimaryKeyToModel,
This will generate a new file in app/db/migrate that you would edit to look as follows:
class AddPrimaryKeyToProducts < ActiveRecord::Migration
def change
add_column :model, :id, :primary_key
add_column :model, :timestamp, :datetime
end
end
From the terminal, then run
rake db:migrate
Be aware that ActiveRecord automagically includes :id of type integer and designated as the primary_key, as well as :created_at and :updated_at of type datetime. ERD does NOT show these attributes in the diagram by default and you need to set the ERD attributes to show them in your output file.
Thank you for all your help. I found I could add the attribute using
rake erd attributes=primary_keys
and
rake erd attributes=timestamps
content is the other whole attributes.
to include primary_key and foreign_key plus attributes, do as follow :
rake erd attributes=primary_key,foreign_key,content
tested working on Rails 3.2
You can also create a config file on your project root directory like this:
.erdconfig
title: Project Model Diagram
orientation: vertical
attributes:
- content
- primary_keys
- foreign_keys
- timestamps
I have a rails 4 app.
I have two tables, one for 'scope' and one for 'data'. Data belongs to scope. I forgot to add a foreign key when I set up data and I'm trying to write a migration to add one now.
I have created a change table, but the migration I've written isn't working.
I can't follow the rails guides example because it isn't consistent with the experience I'm having in my setup (not sure why).
The migration I have is:
class AddFKeyToData < ActiveRecord::Migration
def change
add_foreign_key :data, :scopes
end
end
Please can you help me identify the problem.
Thank you
Rollback this migration by:
rake db:rollback
Then go into your migration and edit add_foreign....
to:
add_column :data, :scope_id, :integer
Should work!
I have already read the documentation of "migrate" on Rails 3 (Rails 3.0 Relese Notes Migrate) but I have some doubts.
e.g. I created two class:
rails generate scaffold User name:string age:integer height:float
rails generate scaffold Hat type:string width:float height:float
This create models, controllers, ... User and Hat and its migrate class: xxx_create_users.rb and xxx_create_hats.rb
Ok, now we guess we want modify User class and we delete height attribute, and we add the relationships between Users and Hats:
User
class User < ActiveRecord::Base
attr_accessible :name, :age
has_many :hats
end
Hat
class Hat < ActiveRecord::Base
attr_accessible :type, :width, height
belongs_to :user
end
Options that I guess:
I remove all files xxx_create_xxx.rb and then I will create again with: rails generate migration CreateUser (and the same for Hat)
I create a new migration file: rails generate migration MyNewMigration where I codify by hand all changes.
Is there another way to automate changes in my classes for passed it to the database? What is the correct way to proceed?
The idea of migrations is that you have a stringent storyline where you can start at any point, forward and backwards. This means that it should not ever be necessary to delete a migration.
Instead, you create a new migration that will change, remove or add database fields.
In your example, you would leave the old migration where it is and then create a new migration like so:
rails g migration change_user_fields
And inside def up you write
remove_column :table_name, :column_name
change_column :table_name, :column_name, :data_type
Add a def down - this will be run whenever the migration is reversed by rake db:rollback. Inside def down put:
add_column :table_name, :column_name # add the field that you removed (s.a.)
change_column :table_name, :column_name, :data_type # change back to old data type
Rails 3 gives you a nice shortcut for adding and removing fields from a table by doing:
rails g migration add_something_to_users name:string
which will automatically create a migration that adds a field called name with a data type of string to the users table. Or
rails g migration remove_something_from_users name
which will automatically create a migration to remove the name field from the users table. These shortcuts and the created migration files do not need a def down - rails will automatically be smart enough to figure that out when reversed.
In both cases, you can replace the word "something" with whatever you like.
However, I know of no way to use a shortcut to change data types, so you need to go in the migration file and do that manually.
Eventually, just run rake db:migrate and you'll be all set!
Scaffold only automate a fixed command, so if you create a model and its attributes with scaffold, your migration will only contain the fields you specify on the command line. There is no way to keep track of changes automatically.
If you add/remove/change something on your database, you have to manually set it. Migrations are useful because you can keep track of these changes on time.
So i recommend you to never delete a migration. In this particular case you described, you just have to create another one to reflect the new change on your database, keeping a total of 3 migrations, instead of deleting and creating another.
The answer to your question should be alternative 2. But you don't have to do it all by hand if you just want to add or remove attributes:
http://guides.rubyonrails.org/migrations.html#creating-a-standalone-migration
I am new to RoR. I used "rails generate model ServiceConfigs" command to generate a table.
so may commands are as below
rails generate model ServiceConfigs configs:string
rake db:migrate
-- can see app/db/service_config.rb created.
Now edited service_config.rb file to add 2 columns and which has a foreign key relation to service table. So here is code
class ServiceConfigs < ActiveRecord::Base
belongs_to :service, :dependent => :destroy
validates_presence_of :configs
end
Now when I login to underline database, and look at the table I don't see foreign key relation in table schema. Whats wrong/more I need to do?
highly appreciate your time and help
Krishna
So a few notes for you as you're getting started here: Firstly, I'd name your model in the singular form, as though you are describing a single instance of it: ServiceConfig and in the case where it belongs to a service, you may want to think of a different name all together.
Secondly validates_presence_of suggests that you have that field, so firstly, I'd remove the validation until you know that your DB has that column and that the migration worked. You can make sure by looking at your migration file and confirming that the column is being created.
You can define the relationship the "rails way" in your migration too:
http://guides.rubyonrails.org/association_basics.html
create_table :service_configs do |t|
t.string :configs
t.references :service
t.timestamps
end
Update
If you want to rerun a particular migration run:
rake db:migrate:redo VERSION=20100421175455
You can take a look in your schema to see what migration you are currently at as well. And you can also take a look at the schema to see what your DB is expected to look like as well.
All,
I need clarification on how model changes need to tracked in ruby on rails. I started off by creating a model with say two fields, name and email. Here is what i have done
Created a model by running
"rails generate model user first_name:string last_name:string"
This created a model file
I then added some validations to the files created in user
Used the annotation gem to annotate the class
used "bundle exec rake db:migrate" to move my model to database which created the tables
I now want to add a couple more fields to the model. What steps do i need to follow?
Do i add columns to the database and run some command so that the model(class) is in sync with the db?
Do i delete and recreate the whole model with the new fields?
what is the recommended approach
Venu
You want to use a migration to update the existing table, you can do the entire process from the command line
Assuming you've done
rails generate model user first_name:string last_name:string
previously you would add fields like so;
rails generate migration AddFieldsToModel new_field:string another_field:string....
Rails does magic on the 'AddFieldsToModel' and works out the table name from the value for you.
Once you've created the migration you can look at it in db/migrations and then if you're happy with it just run
rake db:migrate
this will update your database to add the new fields to it. You don't need to do anything to the actual model.rb file - but you will need to re run the annotate task to have it reannotated to the model.rb file.
I am not sure what version of rails your are using .. but int rails 3.x it can be done as
rails generate migration add_fields_user
this creates a file in db/migrate/[timestamp]/add_fields_user.rb
now you can write in the file and run rake db:migrate
add_column :users , :city, :string
What you want to do is run a migration by typing. rails generate migration description_of_migration. This will create an empty migration which you can define what you want to add to your model. In your case it may be something like this:
class DescriptionOfMigration < ActiveRecord::Migration
self.up
add_column :users, :email, :string
end
self.down
remove_column :users, :email
end
end
This makes it so you can migrate both ways on the model.