Mongodb projection exclude one of my field when another is present - mongodb

Question

I am running a simple query using mongoDB compass using filter and project and I'm having a behaviour I can't explain.
Here is my filter:
{
"$and": [
{
"_id": ObjectId('611ee5ee6b93815ee436969e')
},
{
"type": "article"
}
]
}
I get the following result:
{
"_id": {
"$oid": "611ee5ee6b93815ee436969e"
},
"type": "article",
"history": [],
"liked": [],
"parentId": "61105f00cc11ec10406fd1c4",
"permissionList": [],
"title": "Test",
"wikiId": "610de623fbfa1e58cdba9d2c"
}
As expected I get all the fields, in particular type and wikiId
However if i add the following projection:
{
"_id": 1,
"wikiId": 1,
"parentId": 1,
"title": 1,
"type": 1,
"permissionList": 1,
"liked": 1,
"history": 1
}
I would expect the same result, however i get:
{
"_id": {
"$oid": "611ee5ee6b93815ee436969e"
},
"type": "article",
"history": [],
"liked": [],
"parentId": "61105f00cc11ec10406fd1c4",
"permissionList": [],
"title": "Test"
}
This time i don't have the field wikiId, however it was requested in the projection.
And what's bug me is that if I do this projection instead:
{
"_id": 1,
"wikiId": 1,
"parentId": 1,
"title": 1,
"permissionList": 1,
"liked": 1,
"history": 1
}
Then I got the wikiId field as expected in the result again.
Anyone can provide me an insight of what is going on with those queries and where i'm mistaken.
Edit 1: The fact I want to use a projection is that depending on the type field I can use different document with different field.
In my Java code I'm using #BsonDiscriminator(key = "type") but when I explicitly want a kind of document I'm creating the appropriate projection to be sure. However in this case I just wanted to simplify the issue I'm facing to the simplest.
Thanks

Answer 1

in compass by default filters are having and condition so your filter can be refactored as below:
{ "_id": ObjectId('611ee5ee6b93815ee436969e'), "type": "article" }
And regarding projection you can just simply mention fields to Exclude or include like below:
{
"_id": 1,
"wikiId": 1,
"parentId": 1,
"title": 1,
"type": 1,
"permissionList": 1,
"liked": 1,
"history": 1
}
if you need all fields then there is no need to mention anything by default in compass you get all fields, but lets say you want all but few fields(_id,wikiId) then use below projection:
{
"_id": 0,
"wikiId": 0,
}
Also in compass you can try clicking find again or refresh button to see as sometimes it does not reflects current filter as as we change filter it fetches data so just hit refresh or find and see it should work.