mongo/jstests/aggregation/sources/graphLookup/nested_objects.js

// Cannot implicitly shard accessed collections because unsupported use of sharded collection
// for target collection of $lookup and $graphLookup.
// @tags: [assumes_unsharded_collection]

// In MongoDB 3.4, $graphLookup was introduced. In this file, we test the behavior of graphLookup
// when the 'connectToField' is a nested array, or when the 'connectFromField' is a nested array.

(function() {
"use strict";

var local = db.local;
var foreign = db.foreign;

local.drop();
foreign.drop();

// 'connectFromField' is an array of objects.
var bulk = foreign.initializeUnorderedBulkOp();
for (var i = 0; i < 100; i++) {
    bulk.insert({_id: i, neighbors: [{id: i + 1}, {id: i + 2}]});
}
assert.commandWorked(bulk.execute());

assert.commandWorked(local.insert({starting: 0}));

var res = local
                  .aggregate({
                      $graphLookup: {
                          from: "foreign",
                          startWith: "$starting",
                          connectFromField: "neighbors.id",
                          connectToField: "_id",
                          as: "integers"
                      }
                  })
                  .toArray()[0];
assert.eq(res.integers.length, 100);

foreign.drop();

// 'connectToField' is an array of objects.
var bulk = foreign.initializeUnorderedBulkOp();
for (var i = 0; i < 100; i++) {
    bulk.insert({previous: [{neighbor: i}, {neighbor: i - 1}], value: i + 1});
}
assert.commandWorked(bulk.execute());

var res = local
                  .aggregate({
                      $graphLookup: {
                          from: "foreign",
                          startWith: "$starting",
                          connectFromField: "value",
                          connectToField: "previous.neighbor",
                          as: "integers"
                      }
                  })
                  .toArray()[0];
assert.eq(res.integers.length, 100);

foreign.drop();

// Both 'connectToField' and 'connectFromField' are arrays of objects.
var bulk = foreign.initializeUnorderedBulkOp();
for (var i = 0; i < 100; i++) {
    bulk.insert({
        previous: [{neighbor: i}, {neighbor: i - 1}],
        values: [{neighbor: i + 1}, {neighbor: i + 2}]
    });
}
assert.commandWorked(bulk.execute());

var res = local
                  .aggregate({
                      $graphLookup: {
                          from: "foreign",
                          startWith: "$starting",
                          connectFromField: "values.neighbor",
                          connectToField: "previous.neighbor",
                          as: "integers"
                      }
                  })
                  .toArray()[0];
assert.eq(res.integers.length, 100);
}());