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

changes

An array of field changes on the data object

source

A hash of the original data set