Error Handling

You can configure your schema to rescue application errors during field resolution. Errors during batch loading will also be rescued.

Thanks to @exAspArk for the graphql-errors gem which inspired this behavior and @thiago-sydow who suggested an implementation like this.

Add error handlers

Handlers are added with rescue_from configurations in the schema:

class MySchema < GraphQL::Schema
  # ...

  rescue_from(ActiveRecord::RecordNotFound) do |err, obj, args, ctx, field|
    # Raise a graphql-friendly error with a custom message
    raise GraphQL::ExecutionError, "#{field.type.unwrap.graphql_name} not found"
  end

  rescue_from(SearchIndex::UnavailableError) do |err, obj, args, ctx, field|
    # Log the error
    Bugsnag.notify(err)
    # replace it with nil
    nil
  end
end

The handler is called with several arguments:

• err is the error that was raised during field execution, then rescued
• obj is the object which was having a field resolved against it
• args is the Hash of arguments passed to the resolver
• ctx is the query context
• field is the GraphQL::Schema::Field instance for the field where the error was rescued

Inside the handler, you can:

• Raise a GraphQL-friendly GraphQL::ExecutionError to return to the user
• Re-raise the given err to crash the query and halt execution. (The error will propagate to your application, eg, the controller.)
• Report some metrics from the error, if applicable
• Return a new value to be used for the error case (if not raising another error)