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  1. Core Server
  2. SERVER-58680

$ifNull behaves differently in latest

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    • Type: Icon: Bug Bug
    • Resolution: Fixed
    • Priority: Icon: Major - P3 Major - P3
    • 5.1.0-rc0
    • Affects Version/s: None
    • Component/s: None
    • Labels:
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      Behavior in 5.0.0 and earlier:

      MongoDB Enterprise > db.version()
5.0.0
MongoDB Enterprise > db.test.find()
{ "_id" : 1 }
{ "_id" : 2, "X" : null }
{ "_id" : 3, "X" : 3 }
MongoDB Enterprise > db.test.aggregate([{ $project : { Z : { $ifNull : ["$X", null] } } }])
{ "_id" : 1, "Z" : null }
{ "_id" : 2, "Z" : null }
{ "_id" : 3, "Z" : 3 }
MongoDB Enterprise >

      Unexpected behavior in latest:

      MongoDB Enterprise > db.version()
5.0.0-alpha0-1698-gf4169a7
MongoDB Enterprise > db.test.find()
{ "_id" : 1 }
{ "_id" : 2, "X" : null }
{ "_id" : 3, "X" : 3 }
MongoDB Enterprise > db.test.aggregate([{ $project : { Z : { $ifNull : ["$X", null] } } }])
{ "_id" : 1 } // NOTE: the Z field is missing
{ "_id" : 2, "Z" : null }
{ "_id" : 3, "Z" : 3 }
MongoDB Enterprise >

       

      Show
      Behavior in 5.0.0 and earlier: MongoDB Enterprise > db.version() 5.0.0 MongoDB Enterprise > db.test.find() { "_id" : 1 } { "_id" : 2, "X" : null } { "_id" : 3, "X" : 3 } MongoDB Enterprise > db.test.aggregate([{ $project : { Z : { $ifNull : [ "$X" , null ] } } }]) { "_id" : 1, "Z" : null } { "_id" : 2, "Z" : null } { "_id" : 3, "Z" : 3 } MongoDB Enterprise > Unexpected behavior in latest: MongoDB Enterprise > db.version() 5.0.0-alpha0-1698-gf4169a7 MongoDB Enterprise > db.test.find() { "_id" : 1 } { "_id" : 2, "X" : null } { "_id" : 3, "X" : 3 } MongoDB Enterprise > db.test.aggregate([{ $project : { Z : { $ifNull : [ "$X" , null ] } } }]) { "_id" : 1 } // NOTE: the Z field is missing { "_id" : 2, "Z" : null } { "_id" : 3, "Z" : 3 } MongoDB Enterprise >  
    • QE 2021-08-23, QE 2021-09-06, QE 2021-09-20, QE 2021-10-04
    • 153

      $ifNull behaves differently in latest when the replacement value is null. In earlier versions it returned null. In latest it omits the field entirely.

      While it may sound silly to use a replacement value of null, the LINQ provider in the C# driver uses this construct to replace a missing field with an explicit null-valued field.

            Assignee:
            ethan.zhang@mongodb.com Ethan Zhang (Inactive)
            Reporter:
            robert@mongodb.com Robert Stam
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              Created:
              Updated:
              Resolved: