Apollo GraphQL: Augment instead of overriding default resolver behaviour

Question

In the Apollo Server documentation, it describes the behaviour of the default resolver, which is quite handy.

I also gathered from somewhere else (another SO question if I recall), that you can override the default resolver function with your own, by passing a fieldResolver function into the options for the apollo-server instance:

const server = new ApolloServer({ typeDefs, resolvers,
  fieldResolver: function (source, args, context, info) {
    console.log("Field resolver triggered!")
    return null;
  }
});

What I would like to do is augment the default behaviour, rather than overriding it. Specifically, I am integrating with a REST API that returns fields in snake_case, whereas my schema is attempting to follow the advised convention of using camelCase for field names. I would like to wrap this field name conversion around the default resolver behaviour, rather than having to re-write it.

Alternatively, if somebody can point me to the source location for the default resolver implementation, I'd be happy enough to take that and adapt it either!

Daniel Rearden Daniel Rearden · Accepted Answer · 2019-08-16T03:10:18

The default resolver is available through the graphql module:

const { defaultFieldResolver } = require('graphql')

However, converting a field from snake case to camel case can be done without calling the default resolver:

someField: (parent) => parent.some_field

If you want to create a reusable resolver function, you can do something like:

const camelCaseResolver = (parent, args, ctx, info) => {
  return parent[_.snakeCase(info.fieldName)]
}

Or better yet, extract the logic into a schema directive:

class SnakeCaseDirective extends SchemaDirectiveVisitor {
  visitFieldDefinition(field) {
    field.resolve = async function (parent, args, ctx, info) {
      return parent[_.snakeCase(info.fieldName)]
    }
  }
}

Apollo GraphQL: Augment instead of overriding default resolver behaviour

1 Answers