How do you delete an ActiveRecord object?

It's destroy and destroy_all methods, like

user.destroy
User.find(15).destroy
User.destroy(15)
User.where(age: 20).destroy_all
User.destroy_all(age: 20)

Alternatively you can use delete and delete_all which won't enforce :before_destroy and :after_destroy callbacks or any dependent association options.

User.delete_all(condition: 'value') will allow you to delete records without a primary key

Note: from @hammady's comment, user.destroy won't work if User model has no primary key.

Note 2: From @pavel-chuchuva's comment, destroy_all with conditions and delete_all with conditions has been deprecated in Rails 5.1 - see guides.rubyonrails.org/5_1_release_notes.html

There is delete, delete_all, destroy, and destroy_all.

The docs are: older docs and Rails 3.0.0 docs

delete doesn't instantiate the objects, while destroy does. In general, delete is faster than destroy.

User.destroy

User.destroy(1) will delete user with id == 1 and :before_destroy and :after_destroy callbacks occur. For example if you have associated records

has_many :addresses, :dependent => :destroy

After user is destroyed his addresses will be destroyed too. If you use delete action instead, callbacks will not occur.

User.destroy, User.delete User.destroy_all() or User.delete_all()

Notice: User is a class and user is an instance object

If you are using Rails 5 and above, the following solution will work.

#delete based on id
user_id = 50
User.find(id: user_id).delete_all

#delete based on condition
threshold_age = 20
User.where(age: threshold_age).delete_all

https://www.rubydoc.info/docs/rails/ActiveRecord%2FNullRelation:delete_all

Deleting a row from a particular table or a record set from a table is pretty simple, from your console all you need to do is grab the record set by its Id then delete or destroy it.