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80 lines
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3.5 KiB
Markdown
80 lines
No EOL
3.5 KiB
Markdown
# Flows
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A flow is a static definition of a set of steps to be run.
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Flows are backed by `executors`, which determine how the workflow steps are performed.
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The executor can be overriden on invocation, but not all executors will be capable of running all flows.
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As of this writing, the default executor is the only one. It runs all steps in parallel unless values must be provided from one step to another, or in steps that are enclosed by a transaction.
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Ash.Flow is still in its early days, so expect many features, step types, and executors to come in the future.
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All explanations here pertain to the builtin executor, so be sure to read the documentation of any other executor you may use.
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Flows are comprised of steps, which each have an `input` and an `result`. By default, each step is executed concurrently (or at least *may* be executed concurrently). When the result of one step is used in another, that will cause them to run in sequence. In the following flow, for example, the `:create_user` and `:create_blank_project` steps would happen concurrently, but both would wait on the `:create_org` step.
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```elixir
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flow do
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# Flow arguments allow you to parameterize the flow
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argument :org_name, :string do
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allow_nil? false
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end
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argument :user_name, :string do
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allow_nil? false
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end
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# The flow returns the result of the `:create_user` step.
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returns :create_user
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end
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steps do
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# The step is called `:create_org`, and it creates an `Organization` using the `register_org` action.
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create :create_org, MyApp.Accounts.Organization, :register_org do
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# The input to the action refers to an argument of the flow
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input %{
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name: arg(:org_name)
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}
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end
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# The step is called :create_user, and it creates a `User` using the `:register_user` action.
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create :create_user, MyApp.Accounts.User, :register_user do
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input %{
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# The input refers to an argument of the flow
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name: arg(:user_name),
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# and to the result of another step
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org: result(:create_org)
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}
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end
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# The step is called :create_blank_project, and it creates a `Project` using the `:register_user` action.
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create :create_blank_project, MyApp.Accounts.Project, :create_example do
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input %{
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# The input refers to the result of another step
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org: result(:create_org)
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}
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end
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end
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```
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## Return Values
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`returns` determines what the flow returns, and may be one of three things:
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- `:step_name` - will return the result of the configured step
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- `%{step_name: :key}` will return a map of each key to the provided step name, i.e `%{key: <step_name_result>}`
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- `[:step_name]` - which is equivalent to `%{step_name: :step_name}`
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## Errors
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Currently, any error anywhere in the flow will simply fail the flow and will return an error. Over time, error handling behavior will be added, as well as the ability to customize how transactions are rolled back, and to handle errors in a custom way.
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## Custom steps
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Custom steps allow you to implement any custom logic that you need. There aren't really any restrictions on what you do in a custom step, but there is one main consideration if you want your custom step to play nicely with transactions:
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Generally speaking you should set the `touches_resources` if you set `async?` to true.
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This ensures that the custom step will be run synchronously if any of those resource's data
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layers is in a corresponding transaction. You don't necessarily need to set *all* of the
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resources that will be touched. For example, all AshPostgres resources that share the same
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repo share the same transaction state. |