Value does not exist - elasticsearch

Question

I am familiar with checking if a field exists using the exists query. I am wondering if there is a way to check if a value does not exist instead; something like this:
GET /_search
{
"query": {
"bool": {
"must_not": {
"exists": {
"field": "user",
"value": "id"
}
}
}
}
}
Update:
I want to add that it is a compound query so counting the result will not work.

Answer 1

If you want to check that if a particular field value exists or not, then you can simply use a match query. There is no need to use exists query with the must_not clause.
If the document matching the field value is there in your index, then its count will come in the search result. hits.total.value will you the count of matching documents.
Adding a working example
Index Data:
{
"user": "abc"
}
Search Query:
{
"size":0,
"query": {
"match": {
"user": "abc"
}
}
}
Search Result:
"hits": {
"total": {
"value": 1, // note this
"relation": "eq"
},
"max_score": null,
"hits": []
}
Search Query:
{
"size":0,
"query": {
"match": {
"user": "def"
}
}
}
Search Result:
"hits": {
"total": {
"value": 0, // note this
"relation": "eq"
},
"max_score": null,
"hits": []
}
Another option is to use count API
GET /_count
{
"query": {
"match": {
"user": "def"
}
}
}
Search Result:
{
"count": 0, // note this
"_shards": {
"total": 1,
"successful": 1,
"skipped": 0,
"failed": 0
}
}