Apollo-server: Resolving a list of Unions

[sandervanhooft]

Hi @helfer @stubailo ,

I just found out how to implement a Resolver for a single Union (#172), but how about resolving a list of Unions?

In relation to the example provided in #172: how would I resolve a list of Characters? ([Character]!)

For me this is a practical issue. I am using this in a real-life case with an AvailableSearchFilters Union List, which can contain for example a GeoPointDistanceFilter and a PriceRangeFilter.

Of course I'm willing to update the docs if you can point me to the solution.

Kind regards,

Sander

[helfer]

Just return a list where each item implements one of the union types. Or return a list of promises that resolve to one of those types. I believe the resolveType method will still apply to each individual item, but if that doesn't work, you can try defining ofType on each of the implementing types.

[sandervanhooft]

Hi @helfer,

Thanks for pointing that out.

I got it to work with a list of interfaces using __resolveType, but not with the list of unions.

I cannot find any documentation on ofType. Can you give me an example, or point me to the documentation?

Kind regards,

Sander

Edit: using "graphql": "^0.7.2", "graphql-tools": "^0.7.2"

[sandervanhooft]

Addendum
So when resolving a list of NodeInterfaces, this works:

  NodeInterface: {
    __resolveType(root:Object, context:Object, info:Object) {
      if(root._graphQLType === 'Offer'){
        return 'Offer';
      }

      return null;
    },
  }, 

But when resolving a list of SearchFilterUnions, the specific resolver isn't called. The array is available on the parent resolver though.

SearchFilterUnion: {
    __resolveType(root:Object, context:Object, info:Object) {
    console.log('\n\nSEARCHFILTERUNION: ', root) // TODO remove
      if( root.offerCategoryFilter) {
        return 'OfferCategorySearchFilter'
      }
      if( root.geoBoundingBoxFilter) {
        return 'GeoBoundingBoxSearchFilter'
      }
      if( root.geoDistanceFilter) {
        return 'GeoDistanceSearchFilter'
      }
      if( root.priceRangeFilter) {
        return 'PriceRangeSearchFilter'
      }
      return null
    }
  },

Example array logged from parent:

[ offerCategoryFilter: { id: '6ca46120-8a42-11e6-8692-553a5a80fc35' },
  geoBoundingBoxFilter: { topLeft: { lat: 86.5, lon: 86.5 },
    bottomRight: { lat: 5.5, lon: 5.5 } },
  geoDistanceFilter: { location: { lat: 5.5, lon: 5.5 },
    distance: 15000,
    units: 'km' },
  priceRangeFilter: { min: 6, max: 44 } ]

Any clue?

[sandervanhooft]

Phew... I've found the issue.

Do not name array elements like this, as _named array elements seem not to be passed to the resolver_:

// WRONG!
[ offerCategoryFilter: { id: '6ca46120-8a42-11e6-8692-553a5a80fc35' },
  geoBoundingBoxFilter: { topLeft: { lat: 86.5, lon: 86.5 },
    bottomRight: { lat: 5.5, lon: 5.5 } },
  geoDistanceFilter: { location: { lat: 5.5, lon: 5.5 },
    distance: 15000,
    units: 'km' },
  priceRangeFilter: { min: 6, max: 44 } ]
// END-WRONG!

Instead, use a default array like this, you can pass the ofType to resolve the Union type:

[ { id: '6ca46120-8a42-11e6-8692-553a5a80fc35',
    ofType: 'offerCategoryFilter' },
  { topLeft: { lat: 86.5, lon: 86.5 },
    bottomRight: { lat: 5.5, lon: 5.5 },
    ofType: 'geoBoundingBoxFilter' },
  { location: { lat: 5.5, lon: 5.5 },
    distance: 15000,
    units: 'km',
    ofType: 'geoDistanceFilter' },
  { min: 6, max: 44, ofType: 'priceRangeFilter' } ]

Now you can resolve the union type like this:

SearchFilterUnion: {
    __resolveType(root:Object, context:Object, info:Object) {
      if( root.ofType === 'offerCategoryFilter') {
        return 'OfferCategorySearchFilter'
      }
      if( root.ofType === 'geoBoundingBoxFilter') {
        return 'GeoBoundingBoxSearchFilter'
      }
      if( root.ofType === 'geoDistanceFilter') {
        return 'GeoDistanceSearchFilter'
      }
      if( root.ofType === 'priceRangeFilter') {
        return 'PriceRangeSearchFilter'
      }
      return null
    }
  },

[sandervanhooft]

I was surprised the resolver skips named array elements. Is this intended behaviour? Took me a while to figure this out :)

[stubailo]

@sandervanhooft that sounds like something that would need to be fixed in GraphQL.js - this package doesn't deal with execution at all. However, if you have some ideas for where documentation could be improved, please file an issue here: https://github.com/apollostack/tools-docs