Do GraphQL fields support polymorphism based on passed in arguments?

Question

I would like to define the following queries

{
// return all individuals
individuals {
    id
  }
}

// return ONE individual by id
individuals(id:"123") {
   id
  }
}

note that the query name is the same, only the parameters are different.

Today, the only workaround I found is to define different query names.

How can I define polymorphic queries? Is it even possible?

I'm not sure what you mean here by "query name" - are you referring to the field name on the root query type? — stubailo, Oct 21 '16 at 19:55
It's explained here http://graphql.org/learn/queries/ In the examples above, the query name is "individuals" — Olivier Refalo, Oct 21 '16 at 20:54

score 15 · Accepted Answer · answered Oct 22 '16 at 06:45

The fields accessible at the root of your GraphQL query are defined in a GraphQL schema as fields on the root query type, commonly simply named Query. This type is exactly the same as any other GraphQL Object type in a schema. So this question can be restated as:

Do GraphQL fields have the ability to return different results based on the arguments or argument types passed in?

The short answer is "no". One important property of GraphQL is that a particular field must always return the same type; this means that a field that returns an array must always return an array, and a field that returns an object type must always return that particular type, regardless of the arguments passed in.

However, there are a few ways you can achieve similar results to avoid needing to create too many different named fields:

GraphQL fields can have optional arguments. So for example if you have a field called individuals, you could use optional arguments to supply different kinds of filters, for example: individuals(search: "Dan") or individuals(status: "admin"), or individuals (with no arguments) or individuals(status: "admin", search: "Dan") (both arguments provided at once.
GraphQL fields can return a union of several object types. So if your field can return several different types of things, you can use a union. This is represented in the SearchResult example in the docs: http://graphql.org/learn/schema/#union-types Unfortunately that doesn't apply here since you can't have a union of an array with an object type.

In many cases though, you will need to create multiple fields because GraphQL doesn't currently have method overloading or polymorphism.

For an item by `id`, I am returning an array of `1`, without an `id`, an array of `n`. Seems to work well. — Jazzy, Dec 16 '16 at 00:48

Do GraphQL fields support polymorphism based on passed in arguments?

1 Answers1