[DOCS-10869] Expand $project changes in 3.2->3.4 compatibility changes Created: 04/Oct/17  Updated: 30/Oct/23

Status: Closed
Project: Documentation
Component/s: manual, Server
Affects Version/s: None
Fix Version/s: Server_Docs_20231030

Type: Task Priority: Major - P3
Reporter: Charlie Swanson Assignee: Kay Kim (Inactive)
Resolution: Won't Do Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Duplicate
is duplicated by SERVER-31282 $project of nested projection regress... Closed
Participants:
Days since reply: 1 year, 14 weeks, 2 days ago
Epic Link: DOCSP-1769

 Description   

During the 3.4 development cycle we re-wrote the $project stage. Our compatibility notes already list one $project compatibility change, but there are more that are worth mentioning. Specifically, the following:

{$project: {a: {b: "$missingField"}}} used to be {}, now (3.4+) is {a: {}}
{$project: {'a.b': <expression>}} used to be {'a.b': <result of expression>}, now is an error (field names with dots aren't really supported elsewhere)
_id will always show up in explain output for inclusion projections, even if not explicitly mentioned.



 Comments   
Comment by Education Bot [ 31/Oct/22 ]

Hello! This ticket has been closed due to inactivity. If you believe this ticket is still important, please reopen it and leave a comment to explain why. Thank you!

Comment by Pavithra Vetriselvan [ 24/Jan/18 ]

greg.mckeon, I think I handed this ticket back to Kay while it was in CR. Not sure what the progress has been since then.

Comment by Gregory McKeon (Inactive) [ 24/Jan/18 ]

Ping pavithra.vetriselvan, is this now closed?

Comment by Charlie Swanson [ 04/Oct/17 ]

Actually, I misspoke here. See this comment, the second one only impacts $group compatibility, and only when used as the _id argument.

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