GraphQL是否有一种无需明确的“…on”查询即可获取已解决的联合类型字段的方法？

Question

I have the following Union defined in my schema file:

union ContentUnion = Content | Setting | Page | Picture

and for example this type defintion for Setting

type Setting {
    id: String!
    doctype: String!
    name: String!
}

I also have a working Type resolver for ContentUnion .

Using this query

{ 
 content(id: "113804"){
  ... on Setting{
      id
  }
 }
}

I am able to retrieve a value. But this feels weird for me because I do not understand why I have to explicitly tell that the Type is Setting . I thought that is what the TypeResolver is actually for?

I would like to simply use this query

  { 
     content(id: "113804"){
      id
    }
  }

But the result therefore is:

{
  "data": null,
  "errors": [
    {
      "message": "Validation error of type FieldUndefined: Field 'id' in type 'ContentUnion' is undefined @ 'content/id'",
      "locations": [
        {
          "line": 1,
          "column": 26
        }
      ],
      "description": "Field 'id' in type 'ContentUnion' is undefined",
      "validationErrorType": "FieldUndefined",
      "queryPath": [
        "content",
        "id"
      ],
      "errorType": "ValidationError",
      "path": null,
      "extensions": null
    }
  ],
  "extensions": null,
  "dataPresent": false
}

That is because the schema was not able to locate an id field on the ContentUnion union type since it is an union. I wonder if there is a way to get this to work maybe? Because it would remove a lot of headache for me in my implementation.

Answer 1

I'm sorry you have to use the query with typed fragments.

Per unions in the GraphQL specification , GraphQL Unions represent an object that could be one of a list of GraphQL Object types, but provides for no guaranteed fields between those types. No fields may be queried on union without the use of typed fragments.