Regarding nested or sub queries is there some best practice

Question

Regarding nested or sub queries is there some best practice Given the following example there is a query for A there is a query for B B is a property of A and can be resolved if requested This is how it looks from the interface level ``` import com expediagroup graphql annotations GraphQLDescription import com expediagroup graphql spring operations Query import org springframework stereotype Component Component interface QueryB Query SubQuery GraphQLDescription Get B suspend fun queryB B corresponds to the field name in parent model e g A b override val fieldName String get = b Component interface QueryA Query GraphQLDescription Get A suspend fun queryA A data class A val aValue String val b B corresponds with field name data class B val bValue String interface SubQuery Name when used in parent model val fieldName String ``` To implement the resolver for A including B it s needed to Inject resolver for B into A Execute some custom logic to see if the query for A also requested field B This kina works but is a bit cumbersome and works against the benefits of graphql magic resolving what is needed ```class QueryAImpl private val queryB QueryB QueryA override suspend fun queryA A val aValue = A A val `was b requested as part of a ` = true return if `was b requested as part of a ` aValue copy b = queryB queryB else aValue ``` I think the DataLoader approach could help here or <https github com ExpediaGroup graphql kotlin blob master examples server spring server src main kotlin com expediagroup graphql examples server spring dataloaders CompanyDataLoader kt|https github com ExpediaGroup graphql kotlin blob master examples server spring graphql examples server spring dataloaders CompanyDataLoader kt>

Dariusz Kuc · Answer

You dont have to return data classes if your object returns a function then it will only be invoked when requested ie ```class A val aValue String suspend fun b B ``` If computation of B requires some beans you could either add them as private ignored values to the constructor of A OR autowire them directly to `fun b Autowired private service SomeService `

Robert · Answer

Thanks for the hint But that is more or less the same approach With other graphql libraries kickstart of nodeJS you just register the DataLoaders and the Framework will resolve the graph of objects nested resolvers

Dariusz Kuc · Answer

Not exactly

Dariusz Kuc · Answer

The way that GraphQL Java works since it was based on the JS implementation I assume it is similar there as well is that on incoming requests our queries are parsed into a tree which is then resolved in a breadth first manner When resolving a field we invoke underlying resolver aka data fetcher The difference between `graphql kotlin` and `graphql java` is that we abstract away the resolver piece and just invoke the underlying function doesn t matter if it is a getter or a regular function `graphql java` gives you the property getters for free as well uses reflections on the parent object to find getter based on the field name since we build schema from a reflection we can register this when we build schema As for the other resolvers you have to write those yourself you could put all the logic within a resolver and don t have any extra function calls Keep in mind though that if your resolver returns an object gt in Kotlin and I guess in Java if you use `final` you have to initialize those objects with ALL properties It doesn t matter whether all or any of those fields will be resolved you still need to populate them to create an object That is why in `graphql kotlin` if instead of a property you use a function that function will only be invoked IF requested by a query

Dariusz Kuc · Answer

`DataLoader` won t magically solve your problem It can potentially help with caching and optimizing some of the batching calls but you still need to instruct your resolver to invoke it It doesn t matter whether you invoke the data loader directly from a resolver OR from invoked function i e in your example above you still can use data loader from `b ` that returns `B`