Assume we have two models: User and Image. User has one image and image belongs to a user. The code below:
Now we want to add validation for the image to check if the user is there or not.
So by adding just one line whenever you are trying to save image object, it will fire a query with respect to the user_id to check whether that user exists or not. In case the user doesn’t exit “image.save” with return an error.
Happy Hacking :)