Sources Contact Advanced Search Tutorials

An Interest In:

Web News this Week

Search Archive

Some of Our Sources

View All Sources

Help Webnuz

Referal links:

January 12, 2023 02:18 pm GMT

Using CQRS in Phoenix Contexts

Recently I read this article Naming Phoenix context functions. And I think using naming conventions is good and all, but maybe we could make a step futher and apply CQRS inside such modules.

Command Query Responsability Segregation is the notion that you can use a different model to update information than the model you use to read information...
--- Martin Fowler

I made a small system to store gameplays results of dancing machines such a Pump it Up.

For example this is the cards.ex file.

defmodule Rankmode.Cards.Queries do  import Ecto.Query, warn: false  alias Rankmode.Repo  alias Rankmode.Cards.Card  def all() do    Repo.all(Card)    |> Repo.preload([:user, :game, :mix])  end  def for(user: user_id) do    from(c in Card,      where: c.user_id == ^user_id,      order_by: [desc: c.activated_at],      preload: [:user, :game, :mix, :profile])    |> Repo.all()  end  def get!(uid: uid) do    from(c in Card, where: c.uid == ^uid,      preload: [:user, :game, :mix, :profile]    )    |> Repo.one!()  end  def get(uid: uid) do    from(c in Card, where: c.uid == ^uid,      preload: [:user, :game, :mix, :profile]    )    |> Repo.one()  end  def get(id: card_id, user: user_id) do    from(c in Card,      where: c.id == ^card_id and c.user_id == ^user_id,      preload: [:user, :game, :mix, :profile]    )    |> Repo.one()  end  def get(:notactivated, uid: uid) do    from(c in Card,      where: c.uid == ^uid and        is_nil(c.activated_at) and        is_nil(c.user_id),      preload: [:user, :game, :mix]    )    |> Repo.one()  endenddefmodule Rankmode.Cards.Changesets do  alias Rankmode.Cards.Card  def new(attrs) do    %Card{}    |> Card.changeset(attrs)  end  def empty() do    new(%{})  end  def activate(id, attrs) do    %Card{id: id}    |> Card.changeset_activate(attrs)  end  def update(id, attrs) do    %Card{id: id}    |> Card.changeset(attrs)  endenddefmodule Rankmode.Cards.Commands do  import Ecto.Query, warn: false  alias Rankmode.Repo  alias Rankmode.Cards.Changesets  def create(attrs) do    Changesets.new(attrs)    |> Repo.insert()  end  def activate(id, attrs) do    Changesets.activate(id, attrs)    |> Repo.update()  end  def update(id, attrs) do    Changesets.update(id, attrs)    |> Repo.update()  endenddefmodule Rankmode.Cards doend

And the corresponding Schema file card.ex

defmodule Rankmode.Cards.Card do  use Ecto.Schema  import Ecto.Changeset  schema "cards" do    field :uid, :string    field :checksum, :string    field :activated_at, :naive_datetime    belongs_to :mix, Rankmode.Mixes.Mix    belongs_to :game, Rankmode.Games.Game    belongs_to :user, Rankmode.Accounts.User    has_one :profile, Rankmode.Profiles.Profile    timestamps()  end  @optional [:activated_at, :user_id, :mix_id, :game_id]  @required [:uid, :checksum]  def changeset(model, attrs) do    model    |> cast(transform(attrs), @optional ++ @required)    |> validate_required(@required)    |> validate_length(:uid, min: 3, max: 255)    |> unique_constraint(:uid, name: :cards_uid_checksum_index)    |> unique_constraint(:checksum, name: :cards_uid_checksum_index)  end  def changeset_activate(model, attrs) do    changeset(model, activate(attrs))  end  defp checksum(attrs) do    Map.merge(attrs, %{checksum: Base.encode16(:crypto.hash(:sha256, Map.get(attrs, :uid, "")))})  end  defp activate(attrs) do    Map.merge(attrs, %{activated_at: NaiveDateTime.utc_now()})  end  defp transform(attrs) do    checksum(attrs)  endend

My approach is separating the concerns in 4 modules.

Base Module

A base module, that could store helper functions or any other function that does not fit in the other modules.

defmodule Rankmode.Cards doend

Queries Module

A module for mostly SELECT type functions

defmodule Rankmode.Cards.Queries doend

Commands Module

A module for mostly INSERT, UPDATE, DELETE type functions.

defmodule Rankmode.Cards.Commands doend

Changesets Module

A module for storing the changesets used both in Queries and Commands.

defmodule Rankmode.Cards.Changesets doend

File structure

I prefer storing these in a single file. But if it becomes messy overtime, an structure like this can be used.

cards/ card.ex cards.ex changesets.ex commands.ex queries.ex

Original Link: https://dev.to/clsource/using-cqrs-in-phoenix-contexts-51oa

Share this article:

View Full Article

Dev To

An online community for sharing and discovering great ideas, having debates, and making friends

More About this Source Visit Dev To