MongoDB Java conditional find

Question

I have a mongoDB ( collection with documents possibly containing two dates, dateA and dateB. These dates aren't guaranteed to be set, and can be null.

I want to write a find query that expresses:

    if dateA is not null:
            if dateA is less than someArbitraryDate
    or
    if dateB is not null:
            if dateB is less than someArbitraryDate

Looking at this answer, I know I probably need to use $expr and $cond. I'm just not sure how to write the find.

are you saying you want the query alone? or do you need it in spring data? — Yadhukrishna
– Yadhukrishna, Commented Jun 30, 2020 at 17:48
I'm not using spring, just the Java driver. I think the query alone would suffice for me to figure out how to use it in Java. — niebula
– niebula, Commented Jun 30, 2020 at 17:53

Yadhukrishna · Accepted Answer · 2020-06-30 18:07:08Z

1

You do not need $expr or $cond for the simple use case that you stated. We can achieve the same with just $or.

The query will be something like:

db.collection.find({
    "$or": [
        {"dateA": {"$exists": true, "$ne": null, "$lt":  ISODate("<YYYY-mm-ddTHH:MM:ss>")}},
        {"dateB": {"$exists": true, "$ne": null, "$lt":  ISODate("<YYYY-mm-ddTHH:MM:ss>")}},
    ]
})

Here $exists ensures the field is present, $ne: null ensures the value is not null and then just a less than match to a date string will give you what you want in one if-if block you wrote

Combining them with $or will just combine the results from each of the dateA and dateB matches.

Read more on the operators from: https://docs.mongodb.com/manual/reference/operator/query-comparison/

answered Jun 30, 2020 at 18:07

Yadhukrishna

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1 Comment

niebula Over a year ago

Good point. I think this should work for my scenario, thanks!

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