# Workflows

Workflows compose jobs with dependency relationships: sequential, fan-out, and fan-in patterns.

```elixir
alias Oban.Pro.Workflow

Workflow.new()
|> Workflow.add(:extract, ExtractWorker.new(%{source: "db"}))
|> Workflow.add(:transform, TransformWorker.new(%{}), deps: :extract)
|> Workflow.add(:notify, NotifyWorker.new(%{}), deps: :extract)  # fan-out
|> Workflow.add(:load, LoadWorker.new(%{}), deps: [:transform, :notify])  # fan-in
|> Oban.insert_all()
```

## Patterns

- **Sequential**: `deps: :previous_job`
- **Fan-out**: Multiple jobs depend on the same parent
- **Fan-in**: One job depends on multiple parents with `deps: [:a, :b, :c]`

## Accessing upstream results

Use `recorded: true` workers:

```elixir
def process(job) do
  {:ok, data} = Workflow.fetch_recorded(job, :extract)
end
```

## Cascading Functions

Function captures that automatically receive context and upstream results:

```elixir
Workflow.new()
|> Workflow.put_context(%{source: source})
|> Workflow.add_cascade(:extract, &extract/1)
|> Workflow.add_cascade(:transform, &transform/1, deps: :extract)
|> Workflow.add_cascade(:load, &load/1, deps: :transform)
|> Oban.insert_all()

def extract(%{source: source}), do: %{records: fetch_records(source)}
def transform(%{extract: %{records: records}}), do: %{data: process(records)}
def load(%{transform: %{data: data}}), do: insert_all(data)
```

Fan-out with `{enumerable, function/2}`:

```elixir
Workflow.add_cascade(:accounts, {account_ids, &sync_account/2})
```

## Sub-workflows

Compose from reusable pieces:

```elixir
extract_flow =
  Workflow.new()
  |> Workflow.add(:fetch, FetchWorker.new(%{}))
  |> Workflow.add(:parse, ParseWorker.new(%{}), deps: :fetch)

Workflow.new()
|> Workflow.add(:setup, SetupWorker.new(%{}))
|> Workflow.add_workflow(:extract, extract_flow, deps: :setup)
|> Workflow.add(:cleanup, CleanupWorker.new(%{}), deps: :extract)
|> Oban.insert_all()
```

## Unique workflows

Ensure only one active workflow per name with `unique: true`. Duplicates while the first is still
running come back flagged `conflict?: true` and aren't inserted:

```elixir
Workflow.new(unique: true, name: "nightly-etl")
|> Workflow.add(:extract, ExtractWorker.new(%{}))
|> Oban.insert_all()
```