How to search in array of object in mongodb

Question

Suppose the mongodb document(table) 'users' is

{
    _id: 1,
    name: {
        first: 'John',
        last: 'Backus'
    },
    birth: new Date('Dec 03, 1924'),
    death: new Date('Mar 17, 2007'),
    contribs: ['Fortran', 'ALGOL', 'Backus-Naur Form', 'FP'],
    awards: [
        {
            award: 'National Medal',
            year: 1975,
            by: 'NSF'
        },
        {
            award: 'Turing Award',
            year: 1977,
            by: 'ACM'
        }
    ]
}
// ...and other object(person)s

I want to find the person who has the award 'National Medal' and must be awarded in year 1975 There could be other persons who have this award in different years.

How can I find this person using award type and year. So I can get exact person.

kookaburra · Accepted Answer · 2021-08-06 07:48:47Z

599

The right way is:

db.users.find({awards: {$elemMatch: {award:'National Medal', year:1975}}})

$elemMatch allows you to match more than one component within the same array element.

Without $elemMatch mongo will look for users with National Medal in some year and some award in the year 1975, but not for users with National Medal in 1975.

See MongoDB $elemMatch Documentation for more info. See Read Operations Documentation for more information about querying documents with arrays.

edited Aug 6, 2021 at 7:48

kookaburra

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answered Dec 26, 2012 at 15:00

Leonid Beschastny

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4 Comments

Aditya Mittal Over a year ago

i.e. elemMatch matches award 'and' year (as opposed to award 'or' year)

Venkatesh Kolla - user2742897 Over a year ago

how do we query only those documents that has first name as John and award as national medal in simple way? we do it with aggregate and iterating through awards array but wanted to know simple query

Gobliins Over a year ago

if year would be an array of strings, how would the query look like?

Leonid Beschastny Over a year ago

@Gobliins the same, except year would be a string

turivishal · Accepted Answer · 2021-05-31 14:51:09Z

33

Use $elemMatch to find the array of a particular object

db.users.findOne({"_id": id},{awards: {$elemMatch: {award:'Turing Award', year:1977}}})

edited May 31, 2021 at 14:51

turivishal

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answered Apr 28, 2017 at 6:09

KARTHIKEYAN.A

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1 Comment

Native Coder Over a year ago

passing two objects to findOne, is this essentially a "subquery"? IE, we find the _ID = ID then search inside of that using $elemMatch?

Mohammad Yaser Ahmadi · Accepted Answer · 2021-06-10 11:53:44Z

18

as explained in above answers Also, to return only one field from the entire array you can use projection into find. and use $

db.getCollection("sizer").find(
  { awards: { $elemMatch: { award: "National Medal", year: 1975 } } },
  { "awards.$": 1, name: 1 }
);

will be return

{
    _id: 1,
    name: {
        first: 'John',
        last: 'Backus'
    },
    awards: [
        {
            award: 'National Medal',
            year: 1975,
            by: 'NSF'
        }
    ]
}

edited Jun 10, 2021 at 11:53

answered Feb 14, 2021 at 13:11

Mohammad Yaser Ahmadi

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Comments

alistair · Accepted Answer · 2020-08-28 15:35:18Z

12

You can do this in two ways:

ElementMatch - $elemMatch (as explained in above answers)

db.users.find({ awards: { $elemMatch: {award:'Turing Award', year:1977} } })
Use $and with find

db.getCollection('users').find({"$and":[{"awards.award":"Turing Award"},{"awards.year":1977}]})

edited Aug 28, 2020 at 15:35

alistair

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answered Jun 11, 2020 at 9:44

Joby Wilson Mathews

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