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Gloo Resolvers

Gloo resolvers are the primary means of resolving schema fields using QLoo. This document explains the structure of a Gloo resolver and how to write one.

Request Templates

Let's take a look at the structure of a Gloo resolver (usually written by users as YAML, stored by QLoo as Proto).

  request_template: '{{ marshal (index .Parent "pet_ids") }}'
  response_template: '{{ "success" }}'
    upstream: petstore
    function: ListPets
  • request_template is optional. If provided, QLoo will use the provided template to construct the request body sent to the resolver function.

Request templates follow the conventions of Go templates.

Available parameters for use in Request Templates come from the Params object.

The Params Object has the following structure (defined in Go):

type Params struct {
    Args   map[string]interface{}
    Parent map[string]interface{}

Args represent arguments that were passed to QLoo as part of the Client Query.

Parent represents the root object the field under query belongs to. Parent is nil for root types (Query and Mutation type).

The marshal function is available for use in QLoo templates. marshal will encode any value into JSON.

Here's an example of a Gloo Resolver using multiple destinations, with load balancing:

  request_template: '{{ marshal (index .Parent "friend_ids") }}'
  response_template: '{{ marshal (index .Parent "friend_ids") }}'
    - weight: 1
        upstream: petstore-v1
        function: ListPets
    - weight: 1
        upstream: petstore-v2
        function: ListPets

Response Templates

Response templates also use Go template syntax. Response templates can refer to (sub)fields of the response body, provided that it is JSON-encoded.