Extending your Ecto model

Last week I used Ecto models to quickly created the database and I was very surprised how all got generated for me. But the model I build was very simplistic, and now I need to extend it. I started working on first serious functionality for the project, and I’ll have to do some changes. For start, I’m just testing by adding one field.

I generated new migrations file in /priv/repo/migrations folder and a bit by trial and error I end up with file like that:

defmodule Flightlog.Repo.Migrations.CreateFlight do
  use Ecto.Migration

  def change do
    alter table(:flights) do
      add :plane_type, :string
    end

  end
end

And after running mix ecto.migrate, I actually got some results:

Michals-MBP:flightlog michal$ mix ecto.migrate
01:01:37.663 [info]  == Running Flightlog.Repo.Migrations.CreateFlight.change/0 forward
01:01:37.663 [info]  alter table flights
01:01:37.666 [info]  == Migrated in 0.0s

This worked for adding fields to the database but didn’t automagically update all the access layers. There’s probably some way to it, but this time I did it manually.

First I updated the views, for example added following into show.html.eex:

https://gist.github.com/mlusiak/0979cb46187ee75cd724190e09aa96c1

This solved the visuals but still didn’t work. The crucial were changes in the model:

  defmodule Flightlog.Flight do
  use Flightlog.Web, :model

  schema "flights" do
    field :date, Ecto.DateTime
    field :flight_number, :string
    field :plane_type, :string
    field :from, :string
    field :to, :string

    timestamps()
  end

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:date, :flight_number, :plane_type, :from, :to])
    |> validate_required([:date, :flight_number, :plane_type, :from, :to])
  end
end

I added new field both in schema part and in changeset. Cast is responsible for things being updated. I didn’t have to add it to be validates as required.

So this was actually a bit tedious, but I’m probably missing something here. Hopefully I’ll figure it out by the time I’ll need to make bigger changes.

I also found this post, that’s deal with similar problem.

That’s all for today. Tune in next week for another part. Also, check previous episodes. And if you’re interested in machine learning, look into my weekly link drop.