Given this $elemMatch: {"title":"xyz","passed_year":2005,"univercity":"abc"} I think you want to exclude any documents which contain an sub document in the educations array which contains all of these pairs:
- "title" : "xyz"
- "passed_year" : 2005
- "univercity" : "abc"
This query will achieve that:
db.persons.find({
"educations": {
$not: {
$elemMatch:{"title": "xyz", "passed_year": 2005, "univercity": "abc"}
}
}
})
In your question you wrote:
both of them are giving me the output
I suspect this is because your query is specifying education whereas the correct attribute name is educations. By specifying education you are adding a predicate which cannot be evaluated since it references a non existent document attribute so regardless of whether that predicate uses $ne or $not it will simply not be applied.
In answer to the question of which operator to use: $not or $ne: if you run the above query with .explain(true) you'll notice that the parsed query produced by Mongo is very different for each of these operators.
Using $ne
"parsedQuery" : {
"$not" : {
"educations" : {
"$eq" : {
"$elemMatch" : {
"title" : "xyz",
"passed_year" : 2005,
"univercity" : "abc"
}
}
}
}
}
Using $not:
"parsedQuery" : {
"$not" : {
"educations" : {
"$elemMatch" : {
"$and" : [
{
"passed_year" : {
"$eq" : 2005
}
},
{
"title" : {
"$eq" : "xyz"
}
},
{
"univercity" : {
"$eq" : "abc"
}
}
]
}
}
}
}
So, it looks like use of $ne causes Mongo to do something like this psuedo code ...
not educations equalTo "$elemMatch" : {"title" : "xyz", "passed_year" : 2005, "univercity" : "abc"}
... i.e. it treats the elemMatch clause as if it is the RHS of an equality operation whereas use of $not causes Mongo to actually evaluate the elemMatch clause.
