Dataloader

Dataloader provides an easy way efficiently load data in batches. It’s inspired by https://github.com/facebook/dataloader, although it makes some small API changes to better suite Elixir use cases.

Central to Dataloader is the idea of a source. A single Dataloader struct can have many different sources, which represent different ways to load data.

Here’s an example of a data loader using an ecto source, and then loading some organization data.

source = Dataloader.Ecto.new(MyApp.Repo)

# setup the loader
loader = Dataloader.new |> Dataloader.add_source(:db, source)

# load some things
loader =
  loader
  |> Dataloader.load(:db, Organization, 1)
  |> Dataloader.load_many(:db, Organization, [4, 9])

# actually retrieve them
loader = Dataloader.run(loader)

# Now we can get whatever values out we want
organizations = Dataloader.get_many(loader, :db, Organization, [1,4])

This will do a single SQL query to get all organizations by ids 1,4, and 9. You can load multiple batches from multiple sources, and then when run/1 is called batch will be loaded concurrently.

Here we named the source :db within our dataloader. More commonly though if you’re using Phoenix you’ll want to name it after one of your contexts, and have a different source used for each context. This provides an easy way to enforce data access rules within each context. See the DataLoader.Ecto moduledocs for more details