10 replies

Calculations Using Relationships

I'm writing a simple chat app to try to learn Ash. I have models like below and I'd like to write an

:unread_count

:unread_count

calculation on the

Channel

Channel

. It would take the current user as the actor and find the associated member of the channel, use that

:last_read_at

:last_read_at

time to filter down the messages associated with the channel to ones that has a

:created_at

:created_at

after that time, and count them.

I'm having a hard time figuring out how to do that based on the examples.

What I think I want is something like:

  calculations do
    calculate :unread_count,
              :integer, expr(length(messages.channel_id == ^arg(:channel_id) && messages.created_at > current_member.last_read_at))
  end

  calculations do
    calculate :unread_count,
              :integer, expr(length(messages.channel_id == ^arg(:channel_id) && messages.created_at > current_member.last_read_at))
  end

Assuming

:current_member

:current_member

is another calculation that exists to get the member associated with the current user.

Apologies if I'm thinking about this in the completely wrong way and thanks in advance for the help!

Models

defmodule App.Chat.Channel do
  relationships do
    many_to_many :members, App.Account.User do
      through App.Chat.ChannelMember
      source_attribute_on_join_resource :channel_id
      destination_attribute_on_join_resource :user_id
      writable? true
      filterable? true
    end

    has_many :messages, App.Chat.Message do
      sort created_at: :desc
      filterable? true
    end
  end
end

defmodule App.Chat.Channel do
  relationships do
    many_to_many :members, App.Account.User do
      through App.Chat.ChannelMember
      source_attribute_on_join_resource :channel_id
      destination_attribute_on_join_resource :user_id
      writable? true
      filterable? true
    end

    has_many :messages, App.Chat.Message do
      sort created_at: :desc
      filterable? true
    end
  end
end

defmodule App.Chat.ChannelMember do
  attributes do
    attribute :channel_last_read_at, :utc_datetime_usec
  end

  relationships do
    belongs_to :channel, App.Chat.Channel, primary_key?: true, allow_nil?: false
    belongs_to :user, App.Account.User, primary_key?: true, allow_nil?: false
  end
end

defmodule App.Chat.ChannelMember do
  attributes do
    attribute :channel_last_read_at, :utc_datetime_usec
  end

  relationships do
    belongs_to :channel, App.Chat.Channel, primary_key?: true, allow_nil?: false
    belongs_to :user, App.Account.User, primary_key?: true, allow_nil?: false
  end
end

defmodule App.Chat.Message do
  attributes do
    create_timestamp :created_at
  end

  relationships do
    belongs_to :channel, App.Chat.Channel do
      allow_nil? false
      attribute_writable? true
    end
  end
end

defmodule App.Chat.Message do
  attributes do
    create_timestamp :created_at
  end

  relationships do
    belongs_to :channel, App.Chat.Channel do
      allow_nil? false
      attribute_writable? true
    end
  end
end

Ash Framework•3y ago•

10 replies

bahalperin

Calculations Using Relationships

I'm writing a simple chat app to try to learn Ash. I have models like below and I'd like to write an

:unread_count

:unread_count

calculation on the

Channel

Channel

. It would take the current user as the actor and find the associated member of the channel, use that

:last_read_at

:last_read_at

time to filter down the messages associated with the channel to ones that has a

:created_at

:created_at

after that time, and count them.

I'm having a hard time figuring out how to do that based on the examples.

What I think I want is something like:

  calculations do
    calculate :unread_count,
              :integer, expr(length(messages.channel_id == ^arg(:channel_id) && messages.created_at > current_member.last_read_at))
  end

  calculations do
    calculate :unread_count,
              :integer, expr(length(messages.channel_id == ^arg(:channel_id) && messages.created_at > current_member.last_read_at))
  end

Assuming

:current_member

:current_member

is another calculation that exists to get the member associated with the current user.

Apologies if I'm thinking about this in the completely wrong way and thanks in advance for the help!

Models

defmodule App.Chat.Channel do
  relationships do
    many_to_many :members, App.Account.User do
      through App.Chat.ChannelMember
      source_attribute_on_join_resource :channel_id
      destination_attribute_on_join_resource :user_id
      writable? true
      filterable? true
    end

    has_many :messages, App.Chat.Message do
      sort created_at: :desc
      filterable? true
    end
  end
end

defmodule App.Chat.Channel do
  relationships do
    many_to_many :members, App.Account.User do
      through App.Chat.ChannelMember
      source_attribute_on_join_resource :channel_id
      destination_attribute_on_join_resource :user_id
      writable? true
      filterable? true
    end

    has_many :messages, App.Chat.Message do
      sort created_at: :desc
      filterable? true
    end
  end
end

defmodule App.Chat.ChannelMember do
  attributes do
    attribute :channel_last_read_at, :utc_datetime_usec
  end

  relationships do
    belongs_to :channel, App.Chat.Channel, primary_key?: true, allow_nil?: false
    belongs_to :user, App.Account.User, primary_key?: true, allow_nil?: false
  end
end

defmodule App.Chat.ChannelMember do
  attributes do
    attribute :channel_last_read_at, :utc_datetime_usec
  end

  relationships do
    belongs_to :channel, App.Chat.Channel, primary_key?: true, allow_nil?: false
    belongs_to :user, App.Account.User, primary_key?: true, allow_nil?: false
  end
end

defmodule App.Chat.Message do
  attributes do
    create_timestamp :created_at
  end

  relationships do
    belongs_to :channel, App.Chat.Channel do
      allow_nil? false
      attribute_writable? true
    end
  end
end

defmodule App.Chat.Message do
  attributes do
    create_timestamp :created_at
  end

  relationships do
    belongs_to :channel, App.Chat.Channel do
      allow_nil? false
      attribute_writable? true
    end
  end
end

Calculations Using Relationships

Calculations Using Relationships

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