Mongo query inside Hashmap with unknown hash key

Question

Platform: MongoDB, Spring, SpringDataMongoDB

I have a collection called "Encounter" with below structure

Encounter:

{ "_id" : "49a0515b-e020-4e0d-aa6c-6f96bb867288", 
    "_class" : "com.keype.hawk.health.emr.api.transaction.model.Encounter",  
    "encounterTypeId" : "c4f657f0-015d-4b02-a216-f3beba2c64be", 
    "visitId" : "8b4c48c6-d969-4926-8b8f-05d2f58491ae", 
    "status" : "ACTIVE", 
    "form" : 
    { 
        "_id" : "be3cddc5-4cec-4ce5-8592-72f1d7a0f093", 
        "formCode" : "CBC", 
        "fields" : { 
            "dc" : { 
                "label" : "DC", 
                "name" : "tc", 
            }, 
            "tc" : { 
                "label" : "TC", 
                "name" : "tc", 


            }, 
            "notes" : { 
                "label" : "Notes", 
                "name" : "notes", 
            } 
        }, 
        "notes" : "Blood Test", 
        "dateCreated" : NumberLong("1376916746564"), 
        "dateModified" : NumberLong("1376916746564"), 
        "staffCreated" : 10013, 
        "staffModified" : 10013

    }, 
}

The element "fields" is represented using a Java Hashmap as:

protected LinkedHashMap<String, Field> fields;

The Key to the hashmap () is not fixed, but generated at run time.

How do I query to get all documents in the collection where "label" = "TC"?

It's not possible to query like db.encounter.find({'form.fields.dc.label':'TC'}) because the element name 'dc' is NOT known. I want to skip that postion and the execute query, something like:

db.encounter.find({'form.fields.*.label':'TC'});

Any ideas?

Also, how do I best use indexes in this scenario?

Unfortunately your schema is at a disadvantage here since there is no easy way to do that, you would need to make fields an array of objects — Sammaye
– Sammaye, Commented Sep 10, 2013 at 21:40
Thanks. I'm getting it and moving in the direction you advised. — Firdous Amir
– Firdous Amir, Commented Sep 11, 2013 at 5:55

drmirror · Accepted Answer · 2013-09-10 21:43:08Z

4

If fields were an array and your key a part of the sub-document instead:

"fields" : [
   { "key"   : "dc",
     "label" : "DC",
     "name"  : "dc"
   },
   { "key"   : "tc",
     "label" : "TC",
     "name"  : "tc"
   }
]

In this case, you could simply query for any sub-element inside the array:

db.coll.find({"form.fields.label":"TC"})

Not sure how you would integrate that with Spring, but perhaps the idea helps? As far as indexes are concerned, you can index into the array, which gives you a multi-key index. Basically, the index will have a separate entry pointing to the document for each array value.

answered Sep 10, 2013 at 21:43

drmirror

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1 Comment

Firdous Amir Over a year ago

It sure helps. Thank you.

awgtek · Accepted Answer · 2024-03-29 19:11:44Z

0

Faced a similar issue and found this: https://stackoverflow.com/a/75338607/1527469, i.e. just convert the object to array, do the filter, then convert back:

db.encounter.aggregate([
    {
        "$set": {
            "form.fields": {
                "$objectToArray": "$form.fields"
            }
        }
    }, {

        "$match":
            {
                "form.fields.v.label": "TC"
            }
    },
    {
        "$set": {
            "form.fields": {
                "$arrayToObject": "$form.fields"
            }
        }
    }
])

answered Mar 29, 2024 at 19:11

awgtek

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