Use $lookup to populate area children

Author: zichongkao

src/__tests__/areas.ts

@@ -202,7 +202,6 @@ describe('areas API', () => {
       })
       expect(areaClimbsResponse.statusCode).toBe(200)
       const areaResult = areaClimbsResponse.body.data.area
-      console.log(areaClimbsResponse.body)
       // In leftRightIndex order
       expect(areaResult.climbs[0]).toMatchObject({ name: 'left', metadata: { leftRightIndex: 0 } })
       expect(areaResult.climbs[1]).toMatchObject({ name: 'middle', metadata: { leftRightIndex: 1 } })

src/graphql/resolvers.ts

@@ -200,13 +200,6 @@ const resolvers = {
     // New camel case field
     areaName: async (node: AreaType) => node.area_name,
 
-    children: async (parent: AreaType, _, { dataSources: { areas } }: Context) => {
-      if (parent.children.length > 0) {
-        return await areas.findChildren(parent.children)
-      }
-      return []
-    },
-
     aggregate: async (node: AreaType) => {
       return node.aggregate
     },

src/model/AreaDataSource.ts

@@ -105,14 +105,23 @@ export default class AreaDataSource extends MongoDataSource<AreaType> {
             as: 'climbs' // clobber array of climb IDs with climb objects
           }
         },
+        { // Self-join to populate children areas.
+          $lookup: {
+            from: 'areas',
+            localField: 'children',
+            foreignField: '_id',
+            as: 'children'
+          }
+        },
         {
           $set: {
             'climbs.gradeContext': '$gradeContext' // manually set area's grade context to climb
           }
         },
         {
           $set: {
-            climbs: { $sortArray: { input: '$climbs', sortBy: { 'metadata.left_right_index': 1 } } }
+            climbs: { $sortArray: { input: '$climbs', sortBy: { 'metadata.left_right_index': 1 } } },
+            children: { $sortArray: { input: '$children', sortBy: { 'metadata.leftRightIndex': 1 } } }
           }
         }
       ])