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  1. Core Server
  2. SERVER-58680

$ifNull behaves differently in latest

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • None
    • 5.1.0-rc0
    • None
    • None
    • Fully Compatible
    • ALL
    • Hide

      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

    Description

      $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.

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        Issue Links

          is caused by

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-55295 Short circuit $ifNull expression if the condition always evaluates to a constant or null

          • Major - P3 - Major loss of function.
          • Closed
          is depended on by

          Task - A task that needs to be done. CSHARP-3726 Fix GroupJoin_syntax_with_select_many_and_DefaultIfEmpty failure on latest

          • Unknown - Priority not determined yet.
          • Closed

          Activity

            People

              ethan.zhang@mongodb.com Ethan Zhang (Inactive)
              robert@mongodb.com Robert Stam
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              Dates

                Created:
                Updated:
                Resolved: