Querying nested objects

Working with Data
1

Dear Mongo Community,

I’m look back to 25 years of relational database and are now diving into document-based-mongodb. And I have a question how to model the following case:

Assuming I have I forum with posts:

{
 "UserName": "The only one user",
 "Posts": [
   {
     "Date": "01.01.2023 23:40:02",
     "Type": 3
     "Message": "Hello world"
   },
{
     "Date": "02.01.2023 22:42:02",
     "Type": 2
     "Message": "Hello earth"
   }
 ]
}

Imaging there are a lot of messages per user and a lot of user.
If I want to display the last 20 messages across all users what would the query look like?
Or do i have to reorganize the posts into a seperate collection?

Thank you, for your input.
Lukas

2

Please do not store your date as string.

Dates as strings take more space, are slower to compare and in your specific format cannot be sorted.

You could use a projection that uses something:

{ "Posts" : { "$slice" : [ -1 , 20 ] }
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