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Craft GraphQL APIs in Elixir with Absinthe

Implement Callback Approach

Explore how to implement the middleware/3 callback in Absinthe for cleaner and more efficient error handling in GraphQL mutations. Learn to apply schema-wide middleware logic to reduce duplication and improve maintainability as your API grows.

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Callback approach

Every field in our mutation object so far can return Ecto changeset errors. Those resolvers would be a lot cleaner if they could use this middleware instead. If we take the macro-based approach we have covered so far, it looks like this:

mutation do
  field :ready_order, :order_result do
    arg :id, non_null(:id)
    resolve &Resolvers.Ordering.ready_order/3 
    middleware Middleware.ChangesetErrors
  end
  field :complete_order, :order_result do
    arg :id, non_null(:id)
    resolve &Resolvers.Ordering.complete_order/3 
    middleware Middleware.ChangesetErrors
  end
  field :place_order, :order_result do
    arg :input, non_null(:place_order_input) 
    resolve &Resolvers.Ordering.place_order/3 
    middleware Middleware.ChangesetErrors
  end
  field :create_menu_item, :menu_item_result do 
    arg :input, non_null(:menu_item_input) 
    resolve &Resolvers.Menu.create_item/3 
    middleware Middleware.ChangesetErrors
  end 
end

Not only does this seem like an unnecessary duplication of code, but it’s ...