The changeset performs validations on data objects. If any changeset is not valid, then the database operation will not happen.
user =User.new
changeset = User.changeset(user)
changeset.valid?
Repo operations on single instances will also return a changeset, where you can check is validity and also check for error messages and constraint error messages.
user =User.new
changeset = Repo.insert(user)
changeset.errors.any?
Changeset methods
errors
An array of validation and constraint errors
valid?
Returns whether the changeset is valid not
instance
The new object instance after the database operation
user =User.new
changeset = Repo.insert(user)
changeset.instance.id # new database id
action
Action performed on the changeset afer the database operation :insert, :update, etc