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  1. Core Server
  2. SERVER-37392

In $graphLookup the query planner in mongo/master treats undefined and null as equivalent, while in 4.0 it does not

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    • Type: Icon: Bug Bug
    • Resolution: Unresolved
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: None
    • Component/s: Querying
    • Query Optimization
    • ALL
    • Hide 
      (function() {
    "use strict";

    const coll = db.fuzzer_coll;
    coll.drop();
    assert.writeOK(coll.insert({_id: 293,obj: {}}));
    assert.writeOK(coll.insert({_id: 322,obj: {str: undefined}})); 
    assert.commandWorked(coll.createIndex( {"obj.str": 1}));

    const agg = {
        $graphLookup: {
            from: 'fuzzer_coll', startWith: null, connectFromField: 'missing',
            connectToField: 'obj.str', as: 'arrayAs'
        }
    }

    const res1 = coll.aggregate([agg]);
    print(tojson(res1.toArray()));
}) ();
      Show
      (function() { "use strict"; const coll = db.fuzzer_coll; coll.drop(); assert.writeOK(coll.insert({_id: 293,obj: {}})); assert.writeOK(coll.insert({_id: 322,obj: {str: undefined}})); assert.commandWorked(coll.createIndex( {"obj.str": 1})); const agg = { $graphLookup: { from: 'fuzzer_coll', startWith: null, connectFromField: 'missing', connectToField: 'obj.str', as: 'arrayAs' } } const res1 = coll.aggregate([agg]); print(tojson(res1.toArray())); }) ();

      Aggregation output:

      4.0: 
[
	{
		"_id" : 293,
		"obj" : {

		},
		"arrayAs" : [
			{
				"_id" : 293,
				"obj" : {

				}
			}
		]
	},
	{
		"_id" : 322,
		"obj" : {
			"str" : undefined
		},
		"arrayAs" : [
			{
				"_id" : 293,
				"obj" : {

				}
			}
		]
	}
]

master:
[
	{
		"_id" : 293,
		"obj" : {

		},
		"arrayAs" : [
			{
				"_id" : 293,
				"obj" : {

				}
			},
			{
				"_id" : 322,
				"obj" : {
					"str" : undefined
				}
			}
		]
	},
	{
		"_id" : 322,
		"obj" : {
			"str" : undefined
		},
		"arrayAs" : [
			{
				"_id" : 293,
				"obj" : {

				}
			},
			{
				"_id" : 322,
				"obj" : {
					"str" : undefined
				}
			}
		]
	}
]

      The query plan shows different index bounds in 4.0 and master:
      4.0:

      [js_test:ReproAgg] 2018-09-28T17:50:43.152-0500 d20021| ---------bounds = field #0['obj.str']: [null, null]

      master:

      [js_test:ReproAgg] 2018-09-28T17:50:43.147-0500 d20020| ---------bounds = field #0['obj.str']: [undefined, undefined], [null, null]

       

            Assignee:
            backlog-query-optimization [DO NOT USE] Backlog - Query Optimization
            Reporter:
            vlad.rachev@mongodb.com Vlad Rachev (Inactive)
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            Watchers:
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              Created:
              Updated: