Polymorphic input types

[luisobo]

We have an interface Customization and around 20 types implementing this interface. The number of subtypes of Customization will grow over time, we are even considering adding subtypes dinamically.

Each concrete type has it own set of attributes.

On the query side this is easy to represent. The problem is at the mutation side. We want to have a mutation method to add a customization to another object

addCustomizationToNode(nodeId: ID, customizationInput: CustomizationInput)

but this is not currently possible to express since Input Objects cannot have interfaces, we would rather not have one mutation field per subtype, specially since those can change dynamically, potentially.

Do you have any suggestions? Would make sense to have InputObjects take interfaces?

Thank you!

[luisobo]

Maybe some way of escaping the type system on input? Accepting a map os string to anything? as far as I can tell, everything in the input has to be type checked, am I missing something?

[OlegIlyenko]

I also think that this feature would be a valuable addition to GraphQL. I have similar feature in our API.

We model our mutations as UpdateActions. So, for instance, we have a Product type. One can use update actions like SetName(newName), SetDescription(newDescription), AddPrice(price, currency), etc. to update the product. So Ideally I would like to do it with following mutation:

mutation UpdateProduct {
  updateProduct(id: "1234", version: 1, actions: [
    {type: "SetName", newName: "foo"},
    {type: "AddPrice", price: 123, currency: "USD"}
  ])
}

It is also important in our case that all these update actions come in one list, since we guarantee that they all would be applied atomically.

An ability to define an input Interface type would allow us to define ProductUpdateAction which then will have ObjectType children like SetName and AddPrice. I guess union type would also work here, but I would prefer to have an interface type in this particular case.

There is also a discussion around input UnionTypes: graphql/graphql-js#207

[xpepermint]

+1

[siderakis]

+1

[leebyron]

This is something we want to consider. Interfaces may be less valuable because it becomes less clear what the semantics should be, though Unions are pretty interesting. This is all interesting area to explore further.

[GerryG]

I would think support for polymorphic types would be desired as a first class feature. I'm guessing from this issue and the comments that it isn't, yet.

[dylanahsmith]

You could think of a union input type as an Input Object type which only allows a single field to be specified per input object value. Unfortunately that would need to be enforced with runtime checks rather than static validation.

A union input type could be represented in a similar way, where a possible type is used in place of a field, and static validation can ensure that only a single type is specified. E.g. { "MyInputObject": { "foo": "bar" } } could be used to represent the input object value using JSON or maybe ["MyInputObject", { "foo": "bar" }] if you think about it as a tuple. A GraphQL literal would have more options for how to represent the union type, e.g. MyInputObject({ foo: "bar" }) could be one option.

[bwaidelich]

There is another (pretty simple) use case for this feature: a required input parameter that can have one of two possible scalar values.
We could use this to retrieve a node from a tree either by it's path or by a unique identifier. Right now we need to use a string type and do the conversion in the resolving part or have two optional scalar parameters and return an error at runtime if both are missing..

I've seen that the SWAPI-Example suffers from the same issue (with id vs filmId)

[olange]

Same use case as @bwaidelich for me: I'm retrieving an entity from either one of its alternate identifiers.

Currently the eid argument is declared as a GraphQLID (a string merely) and I'm identifying the type of the entity identifier in the resolving part.

But I'd like to use a GraphQLUnionInputType for these eid arguments, that would have a resolveType() function to identify the type, which GraphQL could use to cast and validate the input value accordingly. It would allow to catch the cases where the entity id was not valid.

Current schema

    ...
    product:
      type: productType
      description: "Retrieves product details, given either a Portfolio or Produit entity id."
      args:
        eid:
          type: new GraphQLNonNull( GraphQLID)
          description: "Product entity identifier, or entity identifier of one of its constitutive portfolios."

Query:

query productByCanonicalEID {
  product( eid: "ENTITY-ID-IN-CANONICAL-FORM") { ...ProductFull }
}

query productByAlternateEID {
  product( eid: "ENTITY-ID-IN-ALTERNATE-FORM") { ...ProductFull }
}

Desired schema

    ...
    ProductEntityIDType = new GraphQLScalarType { ... }
    PortfolioEntityIDType = new GraphQLScalarType { ... }

    entityIDUnionInputType = new GraphQLUnionInputType {
      name: 'EntityID'
      types: [ ProductEntityIDType, PortfolioEntityIDType ]
      resolveType(value) {
        # Lets assume the entity identifiers obey a naming convention,
        # they start with specific letters, which we can derive the type from
        if value.startsWith( 'PO')
          return PortfolioEntityIDType
        if value.startsWith( 'PR') 
          return ProductEntityIDType
      }
    }
    ...
    product:
      type: productType
      description: "Retrieves product details, given either a Portfolio or Produit entity id."
      args:
        eid:
          type: new GraphQLNonNull( entityIDUnionInputType) # <– Desired change
          description: "Product entity identifier, or entity identifier of one of its constitutive portfolios."

Query: the same, but argument eid would now be validated and be cast to one of the known entity ID types.

[Cardinal90]

Also was kinda surprised that it is not available. Though I understand why that is. Unlike with queries, this will probably have to be supported by syntax. Something like (using example above):

product( eid#alternate: "ENTITY-ID-IN-ALTERNATE-FORM") { ...ProductFull }

As I could not find a ready solution, I made my own with some workarounds using existing syntax: Union Input Type. You could probably also use it in place of an interface.