I have a registrations model and participants model as follows:
schema "registrations" do
field :conf_number, :string
field :status, :integer, default: 1
belongs_to :event, Event
has_many :participants, Participant
timestamps()
end
schema "participants" do
field :accommodation_choice, :integer, default: 1
field :age, :integer
field :amount_paid, :integer, default: 0
field :arrival_time, :integer, default: 1
field :city, :string
field :conf_number, :integer
...
field :primary, :boolean, default: false
...
field :admin_comment, :string
belongs_to :registration, Registration
belongs_to :country, Country
belongs_to :payment, Payment
timestamps()
end
I am using nested resources to save the registration with participants. I want to include a validation in changeset that there should be one participant with primary boolean as true while saving the registration. What is the best way to achieve this?
I have create_changeset and changeset (for update) with some logic running but both of them call the following common_changeset in the end:
defp common_changeset(changeset) do
changeset
|> validate_required([:conf_number, :event, :status])
|> cast_assoc(:participants, required: true)
|> unique_constraint(:conf_number)
end
I want to be able to add something like check_primary method to the common_changeset pipeline as last step. Thanks.
This does not work as it checks only the changeset and not the participants records. It throws error if changeset does not have primary key. Also, there can be possibility that participant records had a primary: true for a specific participant but changeset is carrying primary: false for same participant. Basically, I need to be able to check it over participants records with changeset applied but before persisting the data.
BTW, I changed valid: true to valid?: true in the above code.
Then you might look into :data instead of :changes
@spec check_primary(Ecto.Changeset.t()) :: Ecto.Changeset.t()
defp check_primary(%{valid?: true, data: %{participants: participants}} = changeset) do
if Enum.find(participants, fn participant -> participant.primary end) do
changeset
else
add_error(changeset, :participants, "needs to have a primary participant")
end
end
defp check_primary(changeset), do: changeset
@idi527 changing to data checks for the validation in persisted records but in case the changeset is carrying primary: false, that is not applied and hence, the validation passes even though it should throw an error. How do we apply the changes and then check the records before persisting?
I ran into another situation where I need the changes applied to record - I need to compute fees for the participant but that can happen only after arrival_date and departure_date changes, if any, are applied to the record. Coming from RoR world, Active_record lets you do that in before_save callback. How would that get translated to Ecto?
this will match only if both, arrival_date and departure_date changes. I need to cover the scenarios where either date change will trigger the computation.
Anyway, will use apply_changes for now and complete this as well.