Convert JSON.RawMessage to JSON

Question

I am using gqlgen, sqlx and pgx. And I'm trying to use a custom scalar for sqlx's types.JSONText.

I have this attributes jsonb field in items table.

-- migrations/001_up.sql

CREATE TABLE IF NOT EXISTS items (
    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
    quantity INT NOT NULL,
    attributes JSONB
);

I have these model structs:

// graph/model/item.go

type Item struct {
    ID         string       `json:"id,omitempty" db:"id,omitempty"`
    Quantity   int          `json:"quantity" db:"quantity"`
    Attributes *Attributes  `json:"attributes,omitempty" db:"attributes,omitempty"`
}

type Attributes types.JSONText

I have this graphql schema:

// graph/schema.graphql

type Item {
  id: ID!
  quantity: Int!
  attributes: Attributes
}
 
scalar Attributes

I can successfully inserted into database, but got error at retrieving.

| id            | quantity | attributes                         |
|---------------|----------|------------------------------------|
| 031e1489-...  | 100      | {"size": "medium", "color": "red"} |

This is the log I got from db query:

>> items.Db: &{
  031e1489-02c9-46d3-924d-6a2edf1ca3ba // id
  100                                  // quantity
  0xc000430600                         // attributes
}

I tried to marshal attributes scalar:

// graph/model/item.go

...

func (a *Attributes) MarshalGQL(w io.Writer) {
    b, _ := json.Marshal(a)
    w.Write(b)
}

// Unmarshal here
...

Add custom scalar type in gqlgen.yml:

...

  Attributes:
    model:
      - github.com/my-api/graph/model.Attributes

But I got the string instead of json:

{
  "data": {
    "item": {
      "id": "031e1489-02c9-46d3-924d-6a2edf1ca3ba",
      "quantity": 100,
      "attributes": "eyJjb2xvciI6ICJyZWQifQ==",
    }
  }
}

The desired output is:

{
  "data": {
    "item": {
      "id": "031e1489-02c9-46d3-924d-6a2edf1ca3ba",
      "quantity": 100,
      "attributes": {
        "size": "medium",
        "color": "red",
      }
    }
  }
}

What I am doing wrong?

---

Here are my attempts:

If I removed pointer from Attributes in Item struct, gqlgen throws error:

go generate ./...
go: finding module for package github.com/my-api/graph/generated
generating core failed: type.gotpl: template: type.gotpl:49:28: executing "type.gotpl" at <$type.Elem.GO>: nil pointer evaluating *config.TypeReference.GOexit status 1
graph/resolver.go:3: running "go": exit status 1
make: *** [Makefile:2: gengql] Error 1

This returns the desired result, but I don't know how to use it with real data:

func (a *Attributes) MarshalGQL(w io.Writer) {
    raw := json.RawMessage(`{"foo":"bar"}`)
    j, _ := json.Marshal(&raw)
    s := string(j)

    w.Write([]byte(s))
}

Query result:

{
  "data": {
    "item": {
      "id": "031e1489-02c9-46d3-924d-6a2edf1ca3ba",
      "quantity": 100,
      "attributes": {
        "foo": "bar"
      }
    }
  }
}

Answer 1

Attributes is defined using types.JSONText which is defined using json.RawMessage which is defined using []byte. This means that the underlying type of all 4 types, including []byte, is []byte, which in turn means that all of the 4 types can be converted to []byte.

Hence it should be enough to do this:

func (a *Attributes) MarshalGQL(w io.Writer) {
    w.Write([]byte(*a))
}