Bulk Actions

Bulk actions are ways to create, update or destroy many records at once, backed by scalable patterns.

Currently, only bulk creates are implemented. Bulk updates and bulk destroys will come next.

Bulk Creates

Bulk creates take a list or stream of inputs for a given action, and batches calls to the underlying data layer. For example, with an action like this: 

create :create do
  accept [:title, :subtitle]
end

You could then call YourApi.bulk_create like so: 

YourApi.bulk_create([ %{title: "foo", subtitle: "bar"}, %{title: "baz", subtitle: "buz"}], Resource, :action)

Considerations

Generally speaking, all regular Ash create actions are compatible (or can be made to be compatible) with bulk create actions. However, there are some important considerations.

  • Ash.Resource.Change modules can be optimized for bulk actions by implementing batch_change/3 , before_batch/3 and after_batch/3 . If you implement batch_change/3 , the change function will no longer be called, and you should swap any behavior implemented with before_action and after_action hooks to logic in the before_batch and after_batch callbacks.

  • Actions that reference arguments in changes, i.e change set_attribute(:attr, ^arg(:arg)) will prevent us from using the batch_change/3 behavior. This is usually not a problem, for instance that change is lightweight and would not benefit from being optimized with batch_change/3

  • If your action uses after_action hooks, or has after_batch/3 logic defined for any of its changes, then we must ask the data layer to return the records it inserted. Again, this is not generally a problem because we throw away the results of each batch by default. If you are using return_records?: true then you are already requesting all of the results anyway.

Returning a Stream

Returning a stream allows you to work with a bulk action as an Elixir Stream. For example: 

input_stream()
|> YourApi.bulk_create(Resource, :action, return_stream?: true, return_records?: true)
|> Stream.map(fn {:ok, result} -> 
  # process results
  {:error, error} ->
  # process errors
end)
|> Enum.reduce(%{}, fn {:ok, result}, acc -> 
   # process results
   {:error, error} ->
   # process errors
end)

Considerations

Because streams are lazily evaluated, if you were to do something like this: 

[input1, input2, ...] # has 300 things in it
|> YourApi.bulk_create(Resource, :action, return_stream?: true, return_records?: true, batch_size: 100) # the default is 100
|> Enum.take(150)

What would happen is that we would insert 200 records (assuming no errors were emitted). Because the stream would end after we process the first two batches. If you want to make sure that everything happens, just be sure you aren’t using things like Stream.take or Enum.take to limit the amount of things pulled from the stream.