GraphQL and variable schemas

[hluz]

Maybe I'm missing the obvious, but how will we be able to retrieve / mutate data with variable schema? Consider the following scenario:

• Mongo collection where each document contains a the schema definition for a sub-document. This schema is not fixed but varies from document to document. How can we retrieve such documents when we don't know in advance its schema?

Example collection:

[
  {
    "_id": "1",
    "name": "A",
    "fldDef": [
      {
        "name": "f1",
        "type": "str",
        "opt": false
      },
      {
        "name": "f2",
        "type": "bool"
      }
    ],
    "flds": {
      "f1": "value1",
      "f2": true
    }
  },
  {
    "_id": "2",
    "name": "B",
    "fldDef": [
      {
        "name": "f3",
        "type": "str",
        "opt": true
      },
      {
        "name": "f4",
        "type": "str",
        "opt": true
      },
      {
        "name": "f5",
        "type": "num"
      }
    ],
    "flds": {
      "f3": "value3",
      "f5": 25
    }
  }
]

[dmitry]

we don't know in advance its schema

Do you mean the structure is not strictly structured?

I think he means documents with different fields in the same collection.

I imagine it can be hard to query for data, when you don't know what to query for explicitly. Maybe there's some kind of wildcard in graphQL that'll allow for implicit field queries?

[hluz]

I mean, in schema-less dbs, like Mongo, you don't have to define a schema that constrains the documents structure for that collection. So, you can have two documents in the same collection with different structures. Since the documents are stored in JSON like format, they are self-described, since each document contains both the name and the value of each field or subdocument. You will know the structure when you retrieve the document. but GraphQL requires the structure to be part of the query. So, how to use GraphQl with those dbs?

[dmitry]

Check out this one: graphql/graphql-spec#101

[hluz]

Gee... That is frightening... Such a lengthy discussion and surfaced complexity to solving stuff as basic as retrieving all values of a field array? :-(

[justinsb]

GraphQL encourages use of a well-defined schema. There are definitely benefits to doing so (and trade-offs).

In your example, you would probably currently just tweak the "variable" bit of your schema to be

"flds": [
      { "name": "f1", "value": "value1" },
      { "name": "f2", "value": "true" }
    ]

[ianserlin]

Yes, it is sorta like mustache's (precursor to handlebars) dogmatic refusal to provide any conditional logic within a ui template. Perfection of one theory can (and often is) at the expense of the development experience.

[hluz]

GraphQL encourages use of a well-defined schema. There are definitely benefits to doing so (and trade-offs).

Encouraging is fine. Requiring it not so much.

In your example, you would probably currently just tweak the "variable" bit of your schema to be

"flds": [
      { "name": "f1", "value": "value1" },
      { "name": "f2", "value": "true" }
    ]

Sure. It the end, anything can be represented by a key-value-par. Although that does not make it very functional to query and manipulate... (btw, how are the array search capabilities of GraphQL?)

But the main issue is that people can't afford to restructure the database just because a supposedly db-agnostic query/manipulation syntax cannot handle current db structures. Can you imagine the rippling impact to other applications that use that data?

In my opinion, attempting to be 100% compatible with Facebook's specs is fine. We should support the spec, but that should not stop us having extensions to the spec to cover shortfalls like this. We need a way to specify the equivalent of mongo projections without having to use a schema. If only for mongo. And to be able to use each criteria for fields not defined in the schema.

[justinsb]

@hluz the GraphQL structure does not need to reflect the database structure.

[hluz]

I understand that, but will be increased complexity having to remap that on the server side for no benefit.

[hluz]

justinsb closed this an hour ago

@justinsb, does the closing of the issue mean that there will be no support to retrieve a mongo document (in its JSON format) via GraphQL when the schema is unknown?