I’ve started learning Ruby on Rails recently. I did a blogger tutorial. I want to add one more field archive to my database, but not sure is it possible just to write manually and which command to call?
Here is my database where I want to add code:
class CreateArticles < ActiveRecord::Migration[6.1]
def change
create_table :articles do |t|
t.string :title
t.text :body
t.timestamps
end
end
end
And I want to add a new field archive which is boolean and by default false?
Also is it okay to add in this schema new field or is it better in some other?
1.Run the migration from command line to add the new column
$ rails g migration add_column_archive_to_articles archive:boolean
The above command will create a new migration file in your db/migrate folder.
2.As of now there's no option to add default value to a column, which can be defined through terminal. Set the new column value to true/false by editing the new migration file created. Your migration file will look like this.
class AddColumnArchiveToArticles < ActiveRecord::Migration
def change
add_column :articles, :archive, :boolean, default: false
end
end
3.Then do
$ rails db:migrate
Migrations should never be changed afterwords. That is why they are migrations, and not a static schema definitions.
Just generate a new migration using rails g migration AddArchiveToArticles and then check the rails documentation for add_column to see how you can alter a table to add a column. It also supports default values :)
How do I create a new field in an existing table using the Ruby command prompt?
I created the model (and migrated it) but I forgot to add a field - how would I go about this?
Generate a new migration to add a new column to table.
rails g migration add_column_name_to_table_name column_name:type
This will create a migration class like below:
#config/migration/20150304121554_add_column_name_to_table_name.rb
class AddColumnNameToTableName < ActiveRecord::Migration
def change
add_column :table_name, :column_name, :type
end
end
Here, column_name, table_name and type should be your desired name and type. Than run rake db:migrate command.
There are two ways to make changes in your situation:
Roll back the last migration
Add the new field in a new migration
Undoing the last migration should only be done if you have not yet pushed the migration to a public server. Here's how to do it:
Run rake db:rollback
Add the new field to the same migration file you originally used
Run rake db:migrate
Option 2:
To add the field in a new migration:
rails g migration AddFieldNameToTableName
For example, if your field is name and your table is users, you would run:
rails g migration AddNameToUsers
This will create a new migration file whose name starts with today's date and ends with add_name_to_users.rb. Open the file and add the field using the add_column command, like this:
class AddNameToUsers < ActiveRecord::Migration
def change
add_column :users, :name, :string
end
end
Save the file, then run rake db:migrate.
I encourage you to read the Rails migrations guide to learn more.
I know how to add default value in a migration file already created. i.e.,
`rails generate migration AddTestColumnToTesttable test_status:boolean` to create it.
It will generate this migration:
class AddTestColumnToTable < ActiveRecord::Migration
def change
add_column :table, :test_status, :boolean, :default => true
end
end
But, Can we add the default value through rails g migration command itself?
No, it can't be done from the command line, you need to change it in the migration file
add_column :table, :test_status, :boolean, :default => true
Hope that helps!
**Rails 4.X +**
Still now, as there is no option to add new column to a table with default value defined through terminal in rails migration,
The following steps to be followed to add a new column to an existing table with default value true or false.
1. Run the migration from command line to add the new column
$ rails generate migration add_columnname_to_tablename columnname:boolean
The above command will add a new column in your table.
2. Set the new column value to TRUE/FALSE by editing the new migration file created.
class AddColumnnameToTablename < ActiveRecord::Migration
def change
add_column :tablename, :columnname, :boolean, default: false
end
end
**3. To make the changes into your application database table, run the following command in terminal**
$ rake db:migrate
How do you add a column to a table using ActiveRecord through the terminal. I am trying to use add_column method but its not working. Any ideas please?
It is better to write a migration and a must if you are working with a team. When you make db changes, then every developer's environment has to be updated also. Otherwise, you will have some mad developers at you.
rails generate migration AddPartNumberToProducts part_number:string
will generate
class AddPartNumberToProducts < ActiveRecord::Migration
def change
add_column :products, :part_number, :string
end
end
Then you run the migration
rake db:migrate
http://guides.rubyonrails.org/migrations.html
Edit:
For a rails console command line check #tadman's answer or use what Bengala proposed like
ActiveRecord::Migration.add_column :products, :part_number, :string
You can run migrations directly in rails console rails c with ActiveRecord::Migration
For your purpose the next command will do what you ask:
> ActiveRecord::Migration.add_column :table_name, :field_name, :field_type
If you're just hacking around, it's usually easier to manipulate the database using a SQLite client of some sorts than through the Rails DB layer.
If you're doing this for a project, create a proper migration file and run it.
If you're determined to do this, the add_column method is available through the ActiveRecord::Base.connection driver object.
What's the syntax for dropping a database table column through a Rails migration?
remove_column :table_name, :column_name
For instance:
remove_column :users, :hobby
would remove the hobby Column from the users table.
For older versions of Rails
ruby script/generate migration RemoveFieldNameFromTableName field_name:datatype
For Rails 3 and up
rails generate migration RemoveFieldNameFromTableName field_name:datatype
Rails 4 has been updated, so the change method can be used in the migration to drop a column and the migration will successfully rollback. Please read the following warning for Rails 3 applications:
Rails 3 Warning
Please note that when you use this command:
rails generate migration RemoveFieldNameFromTableName field_name:datatype
The generated migration will look something like this:
def up
remove_column :table_name, :field_name
end
def down
add_column :table_name, :field_name, :datatype
end
Make sure to not use the change method when removing columns from a database table (example of what you don't want in the migration file in Rails 3 apps):
def change
remove_column :table_name, :field_name
end
The change method in Rails 3 is not smart when it comes to remove_column, so you will not be able to rollback this migration.
In a rails4 app it is possible to use the change method also for removing columns. The third param is the data_type and in the optional forth you can give options. It is a bit hidden in the section 'Available transformations' on the documentation .
class RemoveFieldFromTableName < ActiveRecord::Migration
def change
remove_column :table_name, :field_name, :data_type, {}
end
end
There are two good ways to do this:
remove_column
You can simply use remove_column, like so:
remove_column :users, :first_name
This is fine if you only need to make a single change to your schema.
change_table block
You can also do this using a change_table block, like so:
change_table :users do |t|
t.remove :first_name
end
I prefer this as I find it more legible, and you can make several changes at once.
Here's the full list of supported change_table methods:
http://apidock.com/rails/ActiveRecord/ConnectionAdapters/SchemaStatements/change_table
Clear & Simple Instructions for Rails 5 & 6
WARNING: You will lose data.
Warning: the below instructions are for trivial migrations. For complex migrations with e.g. millions of rows, read/write dbs, clusters, this advice is not for you:
1. Create a migration
Run the following command in your terminal:
rails generate migration remove_fieldname_from_tablename fieldname:fieldtype (Table name in plural, as per convention. See the documentation here. )
Example: rails g migration RemoveAcceptedFromQuotes accepted:boolean
2. Check the migration
# db/migrate/20190122035000_remove_accepted_from_quotes.rb
class RemoveAcceptedFromQuotes < ActiveRecord::Migration[5.2]
# with rails 5.2 you don't need to add a separate "up" and "down" method.
def change
remove_column :quotes, :accepted, :boolean
end
end
3. Run the migration
rake db:migrate or rails db:migrate (they're both the same)
....And then you're off to the races!
Generate a migration to remove a column such that if it is migrated (rake db:migrate), it should drop the column. And it should add column back if this migration is rollbacked (rake db:rollback).
The syntax:
remove_column :table_name, :column_name, :type
Removes column, also adds column back if migration is rollbacked.
Example:
remove_column :users, :last_name, :string
Note: If you skip the data_type, the migration will remove the column successfully but if you rollback the migration it will throw an error.
in rails 5 you can use this command in the terminal:
rails generate migration remove_COLUMNNAME_from_TABLENAME COLUMNNAME:DATATYPE
for example to remove the column access_level(string) from table users:
rails generate migration remove_access_level_from_users access_level:string
and then run:
rake db:migrate
Remove Columns For RAILS 5 App
rails g migration Remove<Anything>From<TableName> [columnName:type]
Command above generate a migration file inside db/migrate directory. Snippet blow is one of remove column from table example generated by Rails generator,
class RemoveAgeFromUsers < ActiveRecord::Migration
def up
remove_column :users, :age
end
def down
add_column :users, :age, :integer
end
end
I also made a quick reference guide for Rails which can be found at here.
You can try the following:
remove_column :table_name, :column_name
(Official documentation)
rails g migration RemoveXColumnFromY column_name:data_type
X = column name
Y = table name
EDIT
Changed RemoveXColumnToY to RemoveXColumnFromY as per comments - provides more clarity for what the migration is actually doing.
To remove the column from table you have to run following migration:
rails g migration remove_column_name_from_table_name column_name:data_type
Then run command:
rake db:migrate
remove_column in change method will help you to delete the column from the table.
class RemoveColumn < ActiveRecord::Migration
def change
remove_column :table_name, :column_name, :data_type
end
end
Go on this link for complete reference : http://guides.rubyonrails.org/active_record_migrations.html
For removing column from table in just easy 3 steps as follows:
write this command
rails g migration remove_column_from_table_name
after running this command in terminal one file created by this name and time stamp (remove_column from_table_name).
Then go to this file.
inside file you have to write
remove_column :table_name, :column_name
Finally go to the console and then do
rake db:migrate
Give below command it will add in migration file on its own
rails g migration RemoveColumnFromModel
After running above command you can check migration file remove_column code must be added there on its own
Then migrate the db
rake db:migrate
Heres one more from rails console
ActiveRecord::Migration.remove_column(:table_name, :column_name)
Step 1: Create a migration
rails g migration remove_column_name_from_table
Step 2: Change code in file migration just created
rails version < 3
def change
remove_column :table_name, :column_name, :datatype
end
rails version >= 3
def change
remove_column :table_name, :column_name
end
Step 3: Migrate
rake db:migrate
Simply, You can remove column
remove_column :table_name, :column_name
For Example,
remove_column :posts, :comment
first try to create a migration file running the command:
rails g migration RemoveAgeFromUsers age:string
and then on the root directory of the project run the migration running the command:
rails db:migrate
Through
remove_column :table_name, :column_name
in a migration file
You can remove a column directly in a rails console by typing:
ActiveRecord::Base.remove_column :table_name, :column_name
Do like this;
rails g migration RemoveColumnNameFromTables column_name:type
I.e. rails g migration RemoveTitleFromPosts title:string
Anyway, Would be better to consider about downtime as well since the ActiveRecord caches database columns at runtime so if you drop a column, it might cause exceptions until your app reboots.
Ref: Strong migration
Mark the column as ignored in the model
class MyModel < ApplicationRecord
self.ignored_columns = ["my_field"]
end
Generate a migration
$ bin/rails g migration DropMyFieldFromMyModel
Edit the migration
class DropMyFieldFromMyModel < ActiveRecord::Migration[6.1]
def change
safety_assured { remove_column :my_table, :my_field }
end
end
Run the migration
$ bin/rails db:migrate
you can use rails migration command
rails generate migration RemoveColumnNameFromTableName column_name:column_type
than you can migrate the database:
rails db:migrate
Just run this in the rails console
ActiveRecord::Base.connection.remove_column("table_name", :column_name, :its_data_type)
or
TableName.find_by_sql(“ALTER TABLE table_name DROP column_name”)