Introducing Rails console
Rails console is a command line program for interacting with the Rails applications. It has the full power of the Ruby language and Rails environment. We can start the Rails console using the following command:
1bundle exec rails console
1Running via Spring preloader in process 71028 2Loading development environment (Rails 6.1.4) 3irb(main):001:0>
Let's run some commands to see how Rails console can help us get some useful information.
Finding column names of the table
Task.column_names returns the names of all the columns of
1irb(main):001:0> Task.column_names 2=> ["id", "title", "created_at", "updated_at"]
Notice that we have a column named
id present. Rails adds this column by
default and it serves as the primary key of the table. The value of the id auto
increments when a new record is created. We will see it in action shortly.
Finding number of records in the table
Task.count returns the number of records in the table:
1irb(main):002:0> Task.count 2 (0.1ms) SELECT COUNT(*) FROM "tasks" 3=> 0
It means right now we do not have any record in the
Task.create creates and saves a new task in the database:
1irb(main):003:0> Task.create 2 (0.3ms) begin transaction 3 SQL (2.8ms) INSERT INTO "tasks" ("created_at", "updated_at") VALUES (?, ?) [["created_at", "2019-01-28 17:00:26.379031"], ["updated_at", "2019-01-28 17:00:26.379031"]] 4 (11.7ms) commit transaction 5=> #<Task id: 1, title: nil, created_at: "2019-01-28 17:00:26", updated_at: "2019-01-28 17:00:26">
Notice that the id is 1. If we create one more task then the id of the new task will be 2.
We can exit the Rails console by typing
Clearing the console
On Mac we can use Command + K. On Linux we can use Ctrl + l.
Reloading the console
To reload the console we can use the
1>> reload! 2Reloading... 3=> true
Let's say that we have "rails console" open. Now if we make any changes to any
model then that change would not be reflected in the console. One solution is to
exit the console and start console again. The another solution is to execute
Getting value of the last expression
Say we write some query into the console and forget to assign it to a variable.
In the next line we want to refer to the returned value. we can use the special
_), to retrieve the result of the last expression.
12.7.0 :008 > Task.find(1) 2 Task Load (0.3ms) SELECT "tasks".* FROM "tasks" WHERE "tasks"."id" = ? LIMIT ? [["id", 1], ["LIMIT", 1]] 3 => #<Task id: 1, title: "My first task", created_at: "2020-03-30 08:55:09", updated_at: "2020-04-03 09:01:42"> 42.7.0 :009 > _ 5 => #<Task id: 1, title: "My first task", created_at: "2020-03-30 08:55:09", updated_at: "2020-04-03 09:01:42"> 6
We can see in the above example we are using the
_ to access the last
Use c for shortcut
Rails console can be started by either of the following two commands:
1bundle exec rails console
1bundle exec rails c
Switching the environment
Rails console can be started in staging or in production mode like this:
1bundle exec rails console -e production 2bundle exec rails console -e staging
When we do
bundle exec rails console then it is equivalent to the followings:
1bundle exec rails console -e development
If we want to re-execute a previously executed command then we can have two options.
We can use the up and down arrow to get to the previously typed command.
We can also use ctrl+r to search the previously history just like it can be done on bash shell.
Use source location to know the location of the code
If we want to know where a method is defined then we can use source_location to find that.
We know that
Task models have
save method because of Active Record. Let's
find out where this
save method is defined:
1>> Task.first.method(:save).source_location 2==> ["/Users/user.name/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4/lib/active_record/suppressor.rb", 43]
Rails makes helper methods available to console:
1>> helper.number_to_currency(10) 2==> "$10.00" 3 4>> helper.time_ago_in_words(Time.now) 5=> "less than a minute"
Working in a sandbox
When we open console and if we make any changes to the database then those changes are permanent in the database. However sometimes we want to test something and we want all those changes to rollback when we exit console. This is very often used in debugging in the production environment.
1bundle exec rails console -e production --sandbox 2Loading production environment in sandbox 3Any modifications you make will be rolled back on exit 4>> Task.update_all(name: "new name") 5>> exit
Once we exit then all the task name we had changed would be rolled back.
Use exit to quit console
By default when console starts then prompt like this:
1$ bundle exec rails console 2Running via Spring preloader in process 77597 3Loading development environment (Rails 6.1.4) 4irb(main):001:0> a = 1 5irb(main):002:0> b = 2 6irb(main):003:0> c = 3
We can also ask console to have simple prompt:
1$ bundle exec rails console -- --simple-prompt 2Running via Spring preloader in process 77680 3Loading development environment (Rails 6.1.4) 4>> a = 1 5>> b = 2 6>> c = 3
Have fun with app
In console just type app and scroll through all it prints. You will learn a thing or two:
1>> app.cookies 2>> app.get(app.root_path) 3>> app.get('/books/2')
There is nothing to commit in this chapter since all we had done was work in the Rails console.