GraphQL: Inline Fragment on Array Fields

[Moumouls]

#5894
#5863

Allow to dive into pointers contained in an array field

• Spec
• Implementation
• Optimization

[Moumouls]

@davimacedo Do you have any feedback on the Spec?

[davimacedo]

It looks really good to me! It's for sure the best solution for the issue. Let's move forward with this spec.

[Moumouls]

So a bad news is that GraphQL don't currently support the union with Scalar.
I will create a new type Element with a field value that contain the value of the array element.

graphql/graphql-spec#215

[davimacedo]

So what do you think about the schema below?

type ArrayItem {
  value: Any
  pointer: Class # we already have an interface called Class
}

type SomeClass {
  arrayField: [ArrayItem!]
}

[Moumouls]

The new spec look like this:

query GetCustomer($objectId: ID!) {
  objects {
    getCustomer(objectId: $objectId) {
      objectId
      manyRelations {
        ... on CustomerClass {
          objectId
          someCustomerField
          arrayField {
            ... on Element {
              value
            }
          }
        }
        ... on SomeClassClass {
          objectId
          someClassField
        }
      }
      createdAt
      updatedAt
    }
  }
}

[davimacedo]

With my suggestion it would be:

query GetCustomer($objectId: ID!) {
  objects {
    getCustomer(objectId: $objectId) {
      objectId
      manyRelations {
        pointer {
          ... on CustomerClass {
            objectId
            someCustomerField
            arrayField {
              value
            }
          }        
          ... on SomeClassClass {
            objectId
            someClassField
          }
        }
      }
      createdAt
      updatedAt
    }
  }
}

It is little bit harder for returning the pointers (but still intuitive) and a lot easier for returning no pointer values (most common scenario).

[davimacedo]

You can also return objectId, createdAt, and updatedAt without using the inline fragment (a lot easier):

query GetCustomer($objectId: ID!) {
  objects {
    getCustomer(objectId: $objectId) {
      objectId
      manyRelations {
        pointer {
          objectId
          createdAt
          updatedAt
        }
      }
      createdAt
      updatedAt
    }
  }
}

[codecov]

Codecov Report

Merging #5908 into master will decrease coverage by 10.73%.
The diff coverage is 98.14%.

@@             Coverage Diff             @@
##           master    #5908       +/-   ##
===========================================
- Coverage   93.69%   82.95%   -10.74%     
===========================================
  Files         153      153               
  Lines       10769    10801       +32     
===========================================
- Hits        10090     8960     -1130     
- Misses        679     1841     +1162

Impacted Files	Coverage Δ
src/GraphQL/ParseGraphQLSchema.js	97.39% <100%> (+0.02%)	⬆️
src/GraphQL/loaders/parseClassQueries.js	97.36% <100%> (+0.14%)	⬆️
src/GraphQL/parseGraphQLUtils.js	92.3% <100%> (+17.3%)	⬆️
src/GraphQL/loaders/parseClassMutations.js	98.83% <100%> (ø)	⬆️
src/GraphQL/loaders/parseClassTypes.js	85.97% <100%> (-0.67%)	⬇️
src/GraphQL/loaders/defaultGraphQLTypes.js	97.17% <92.85%> (-0.26%)	⬇️
...dapters/Storage/Postgres/PostgresStorageAdapter.js	3% <0%> (-93.68%)	⬇️
src/Adapters/Storage/Postgres/PostgresClient.js	78.57% <0%> (-7.15%)	⬇️
src/Controllers/UserController.js	93.45% <0%> (-0.94%)	⬇️
src/Routers/UsersRouter.js	93.54% <0%> (-0.65%)	⬇️
... and 4 more

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[Moumouls]

I think inline fragment will do the job to dive into arrays, i don't really see real benefits of data architecture like:

type ArrayItem {
  value: Any
  pointer: Class # we already have an interface called Class
}

because it's the native behavior of Inline Fragment.
Using only Inline Fragment we allow developers to .map() easly on the array too.

It's now fully functional and tested, i invite you to give it a try on localhost 🚀

[Moumouls]

I currently don't understand why Postgres fail, do you have an idea @davimacedo ?

[davimacedo]

I am not sure but I guess it is something related to the selectedFields. Because of the inline fragment, it is probably returning more keys than what you expected, you are sending these keys to Postgres and it is failing because the field does not exist in the class. Try to debug the selectedValues that you are passing to the rest api. If you prefer I can also take a look on this later today.

[Moumouls]

@davimacedo so the postgres error is due to keys (alias select) passed to the REST API. I think it's a Parse Server Postgres Error, it fail to query on an array with multi Pointers types and a deep select constraint. To fix this bug i'm currently using the root field on the select.

Effects: More data returned to Parse Server GraphQL on field Objects and Postgres compatible.

[davimacedo]

Great job! I added few questions.

[davimacedo]

Everything else seems good to me!

[davimacedo]

Great job! LGTM!