Same field in multiple conditions in match or find: they are treated as "OR"?

Working with Data
#1

Looks like that when same field is used in multiple conditions in match or find, those sonditions are treated as joinned by logical “OR”, not “AND”:
match {
{‘responseMessage’: { $exists: true }},
{‘responseMessage’: {$ne: “No Suggestions Found”}}
}
returns all documents where responseMessage exists OR responseMessage is not equal to “No Suggestions Found”, which actually returns documents where responseMessage DOES NOT EXIST.
If I need to have those confitions to be joined with “AND”, I need to put them like:

{ $and: [
{‘responseMessage’: { $exists: true }},
{‘responseMessage’: {$ne: “No Suggestions Found”}}
]}

This is different from behavior when 2 conditions are using different fields - those conditions will be treated as joined by “AND”

#2

Hi @SERGIY_MITIN. Welcome to the community.

Yes, here’s the documentation when specifying the same field. Your query can be rewritten with an implicit AND, like below

db.coll.find({ responseMessage: { $exists: true, $ne: "no suggestions found"}})

Hope this adds clarity.

  • Mahi
#3

This is not what really happen.

The reason for that is that in most JSON implementations when a field name is repeated only the last occurrence is kept.

So in your case, responseMessage:{$exists:true} is not even seen by the server.

You may experiment in mongosh with :

query = {
    "responseMessage" : "any value" ,
    "responseMessage" : { "$exists" : true } ,
    "responseMessage" : { "$ne" : "No Suggestions Found" }
}

You will see that mongosh outputs:

{ responseMessage: { '$ne': 'No Suggestions Found' } }

showing that all other occurrences of responseMessage are ignored.