CODEWITHSUNDEEP
mongodb
Alveoli
Alveoli

Reputation: 1202

MongoDB: find() query to select nothing

What's an elegant way to set the query parameter so find() intentionally returns no documents?

Obviously I could just hardcode a query that I know would never return a result for my dataset. But that would be no fun.

Upvotes: 3

Views: 483

Answers (3)

Justin R
Justin R

Reputation: 31

I have a similar concern in that I want to build queries based on conditional logic. I could write full BSON for each condition but I think it makes the code less readable. What I ended up doing was using AND with a filters list

 List<Bson> filters=new ArrayList<>();
                filters.add(eq("title", job.getTitle()));
                filters.add(eq("companyName", job.getCompanyName()));
                if (job.getPostingDate() != null) {
                    filters.add(eq("postingDate", job.getPostingDate()));
                }

                if(job.getMinYearlySalary()!=null){
                    filters.add(eq("minYearlySalary", job.getMinYearlySalary()));
                }

                if(job.getMaxYearlySalary()!=null){
                    filters.add(eq("maxYearlySalary", job.getMaxYearlySalary()));
                }

                if(job.getMinHourlySalary()!=null){
                    filters.add(eq("minHourlySalary", job.getMinHourlySalary()));
                }

                if(job.getMaxHourlySalary()!=null){
                    filters.add(eq("maxHourlySalary", job.getMaxHourlySalary()));
                }

                Bson query=and(filters);
                CountOptions options = new CountOptions();
                options.limit(1);
                if (collection.countDocuments(query, options) > 0) {
                    containsJob = true;
                }

What I did is not the OPs exact question. I think this using an empty list would return everything but I have not tested it and could see it also returning nothing. That being said this approach will not waste time with pointless comparisons and is at least an interesting starting point.

Upvotes: 0

Dev
Dev

Reputation: 13753

you won't gonna save negative _id. So you can try:

db.collection.find({"_id":-1})

Upvotes: 3

Neo-coder
Neo-coder

Reputation: 7840

Query on _id field like following use any one of this :

db.collectionName.find({"_id":0})
db.collectionName.find({"_id":""})
db.collectionName.find({"_id":null})

Upvotes: 3

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