5 replies

Loading data from an external API for a calculation

Hello! I have a resource that I would like to enhance in certain reads with a calculation that needs to be based off data from an external API.
I'm mindful of not wanting to make the API request from within a transaction if possible.

I thought of adding a preparation to the read action that will fetch the API data and put it into the context, which the calculation can use.

 # preparation module
  Ash.Query.before_transaction(query, fn query ->
    api_data = make_external_api_call()
    Ash.Query.put_context(query, :external_api_data, api_data)
  end)
 
  # calculation module
  def calculate(records, _opts, context) do
    api_data = context.source_context[:external_api_data]
    Enum.map(records, fn record -> 
       # get apppropriate field from api_data
       ... 
    end)
  end

 # preparation module
  Ash.Query.before_transaction(query, fn query ->
    api_data = make_external_api_call()
    Ash.Query.put_context(query, :external_api_data, api_data)
  end)
 
  # calculation module
  def calculate(records, _opts, context) do
    api_data = context.source_context[:external_api_data]
    Enum.map(records, fn record -> 
       # get apppropriate field from api_data
       ... 
    end)
  end

 # preparation module
  Ash.Query.before_transaction(query, fn query ->
    api_data = make_external_api_call()
    Ash.Query.put_context(query, :external_api_data, api_data)
  end)
 
  # calculation module
  def calculate(records, _opts, context) do
    api_data = context.source_context[:external_api_data]
    Enum.map(records, fn record -> 
       # get apppropriate field from api_data
       ... 
    end)
  end

 # preparation module
  Ash.Query.before_transaction(query, fn query ->
    api_data = make_external_api_call()
    Ash.Query.put_context(query, :external_api_data, api_data)
  end)
 
  # calculation module
  def calculate(records, _opts, context) do
    api_data = context.source_context[:external_api_data]
    Enum.map(records, fn record -> 
       # get apppropriate field from api_data
       ... 
    end)
  end

Is this a reasonable approach? Are there any escape hatches to be able to avoid decoupling the API request from the calculation module while still ensuring the request runs outside of a transaction?

Solution

yeah, its not great but that is probably the best way. YOu will likely want to switch on whether or not the given calculation is being loaded

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Loading data from an external API for a calculation

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