Fetching the data optimally in GraphQL

Question

How can I write the resolvers such that I can generate database sub-query in each resolver and effectively combine all of them and fetch the data at once?

For the following schema :

type Node {
    index: Int!
    color: String!
    neighbors(first: Int = null): [Node!]!
}

type Query {
    nodes(color: String!): [Node!]!
}

schema {
    query: Query
}

To perform the following query :

{
    nodes(color: "red") {
        index
        neighbors(first: 5) {
            index
        }
    }
}

Data store:

In my data store, nodes and neighbors are stored in separate tables. I want to write a resolver so that we can fetch the required data optimally.

If there are any similar examples, please share the details. (It would be helpful to get an answer in reference to graphql-java)

Answer 1

DataFetchingEnvironment provides access to sub-selections via DataFetchingEnvironment#getSelectionSet. This means, in your case, you'd be able to know from the nodes resolver that neighbors will also be required, so you could JOIN appropriately and prepare the result.

One limitation of the current implementation of getSelectionSet is that it doesn't provide info on conditional selections. So if you're dealing with interfaces and unions, you'll have to manually collect the sub-selection starting from DataFetchingEnvironment#getField. This will very likely be improved in the future releases of graphql-java.