Java – retrieves values from nested JSON arrays in mongodb

My Mongo collection has entries in the following format

{
    "myobj" : {
        "objList" : [
            { "location" : "Texas" },{ "location" : "Houston"},{ "name":"Sam" }
        ]
    },"category" : "cat1"
}


{
"myobj" : 
{
    "objList" : [
        { "location" : "Tennesy" },{ "location" : "NY"},{ "location" : "SF" }
    ]
},"category" : "cat2"

}

I want to extract the * * category * * located in "Houston" In the case of a simple JSON object, I must pass it as a query, such as:

BasicDBObject place = new BasicDBObject();
place.put("location","Houston");

But in the case of nested JSON, I don't know how to pass it as a query and get the appropriate category That is, if I pass my location as "Houston", it should return its corresponding category "CAT1"... I hope my problem is clear now

Solution

OK, you have your documents:

db.coll1.insert({
    "myobj" : {
        "objList" : [
            { "location" : "Texas" },"category" : "cat1"
})

and

db.coll1.insert({
    "myobj" : {
        "objList" : [
            { "location" : "Tennesy" },{ "location" : "SF" }
        ]
    },"category" : "cat1"
})

Now you can use the dot operator to find what you want:

db. coll1. find({“myobj.objList.location”：“Texas”}). Pretty () will return an object with Texas

db. coll1. find({“myobj.objList.location”：“SF”}). Pretty () will return an object with SF

db. coll1. find({“myobj.objList.location”：“Houston”}). Pretty () will return two objects

Now I hope you can write it in Java I've never used java, but based on this question, you can do such a thing If it doesn't work, just look at how to use the dot operator for Mongo in the Java driver:

DBCursor cursor = coll1.find(new BasicDBObject("myobj.objList.location","Texas"));

PS: you said you wanted to retrieve categories In this way, you will need to use projection dB coll1. Find ({< my query}, {category: 1, _id: 0})