Objects are no longer treated as literals inside of an array of an aggregation expression

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    • Type: Bug
    • Resolution: Won't Fix
    • Priority: Critical - P2
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    • Affects Version/s: 3.2.1
    • Component/s: Aggregation Framework
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      STEP ONE: Set up a collection (e.g. named j_bug) with the following two documents:

      { 
    "_id" : ObjectId("569fbe30f6916b01e49b27b7"), 
    "rand" : NumberInt(456), 
    "entities" : [
        {
            "name" : "Test Entity"
        }
    ]
}
{ 
    "_id" : ObjectId("569fbe8cf6916b01e49b27b9"), 
    "rand" : NumberInt(123)
}

      STEP TWO: in mongo version 3.2.1 run the following aggregation

      db.j_bug.aggregate([
{$project:{entities:{$ifNull:["$entities", [  {'name' : 'No Entity'} ] ]}}}
])
>>Error from description will be produced.

      In mongo version 3.0.7 run the exact same aggregation query and you should get the desired output as follows:

      { "_id" : ObjectId("569fbe30f6916b01e49b27b7"), "entities" : [ { "name" : "Test Entity" } ] }
{ "_id" : ObjectId("569fbe8cf6916b01e49b27b9"), "entities" : [ { "name" : "No Entity" } ] }
      Show
      STEP ONE: Set up a collection (e.g. named j_bug) with the following two documents: { "_id" : ObjectId("569fbe30f6916b01e49b27b7"), "rand" : NumberInt(456), "entities" : [ { "name" : "Test Entity" } ] } { "_id" : ObjectId("569fbe8cf6916b01e49b27b9"), "rand" : NumberInt(123) } STEP TWO: in mongo version 3.2.1 run the following aggregation db.j_bug.aggregate([ {$project:{entities:{$ifNull:["$entities", [ {'name' : 'No Entity'} ] ]}}} ]) >>Error from description will be produced. In mongo version 3.0.7 run the exact same aggregation query and you should get the desired output as follows: { "_id" : ObjectId("569fbe30f6916b01e49b27b7"), "entities" : [ { "name" : "Test Entity" } ] } { "_id" : ObjectId("569fbe8cf6916b01e49b27b9"), "entities" : [ { "name" : "No Entity" } ] }
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      On 3.0, an expression like the following will work:

      { $project: { _id: 0, entities:{ $ifNull : [ '$entities', [  {'name' : 'No Entity'} ] ] } }

      but on 3.2.1, it will generate the following error, since it tries to interpret the object literal {name: 'No Entity'} as an expression:

      assert: command failed: {
	"ok" : 0,
	"errmsg" : "field inclusion is not allowed inside of $expressions",
	"code" : 16420
} : aggregate failed
_getErrorWithCode@src/mongo/shell/utils.js:23:13
doassert@src/mongo/shell/assert.js:13:14
assert.commandWorked@src/mongo/shell/assert.js:266:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1215:5
@(shell):1:1

2016-01-20T13:02:55.869-0400 E QUERY    [thread1] Error: command failed: {
	"ok" : 0,
	"errmsg" : "field inclusion is not allowed inside of $expressions",
	"code" : 16420
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:23:13
doassert@src/mongo/shell/assert.js:13:14
assert.commandWorked@src/mongo/shell/assert.js:266:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1215:5
@(shell):1:1

      The workaround is to wrap the object in a $literal expression, like so:

      { $project: { _id: 0, entities:{ $ifNull : [ '$entities', [  {$literal: {'name' : 'No Entity'} } ] ] } }

            Assignee:
            Benjamin Murphy (Inactive)
            Reporter:
            Jesse English
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            0 Vote for this issue
            Watchers:
            9 Start watching this issue

              Created:
              Updated:
              Resolved: