How to update particular value inside array - Mongodb

Question

I have a mongodb collection Users that looks like this:

{
    "_id" : ObjectId("5dba8987b4a39c13bc104a23"),
    "contact" : {
        "firstName" : "Mark",
        "lastName" : "Doe",
        "parentsBloodType" : [ 
            {
                "type" : "AB+",
            }, 
            {
                "type" : "A+",
            }, 
        ],
    },
    "createdAt" : ISODate("2019-10-31T07:13:11.278Z"),
    "updatedAt" : ISODate("2019-11-26T09:59:41.611Z")
}

I need to run a raw query to update from AB+ to O-. I would also like to check if they match before updating.

I tried this but it added an extra field to the User:

  db.getCollection('users').update(
    {"_id": ObjectId("5dba8987b4a39c13bc104a23")},
    {"$set" : { 'parentsBloodType.' + '0' + '. type' : "O-"}}
    )

What happens if both parents have AB+? Do you like to update both or just one? — Wernfried Domscheit
– Wernfried Domscheit, Commented Dec 18, 2019 at 8:22

Wernfried Domscheit · Accepted Answer · 2019-12-18 08:50:36Z

This one would do the update:

db.users.update(
   { "_id": ObjectId("5dba8987b4a39c13bc104a23") },
   { "$set": { 'contact.parentsBloodType.0.type' : "O-"} }
)

You an check match with this:

db.users.update(
   {
      "_id": ObjectId("5dba8987b4a39c13bc104a23"),
      "contact.parentsBloodType.type": "AB+"
   },
   { "$set": { 'contact.parentsBloodType.0.type': "AB+" } }
)

This updates the document only if type AB+ exist (at any parent).

Or if you like to check whether the first type is AB+ then use

db.users.update(
   {
      "_id": ObjectId("5dba8987b4a39c13bc104a23"),
      "contact.parentsBloodType.0.type": "AB+"
   },
   { "$set": { 'contact.parentsBloodType.0.type': "AB+" } }
)

However, I assume you are actually looking for this:

db.users.update(
   { "_id": ObjectId("5dba8987b4a39c13bc104a23") },
   { "$set": { 'contact.parentsBloodType.$[p].type': "0-" } },
   { arrayFilters: [{ "p.type": "AB+" }] }
)

Which will update any AB+ to 0- no matter on which position it appears in the array.

Fraction · Accepted Answer · 2019-12-18 10:43:25Z

0

You could use the positional $ operator to update the first element that matches the query document:

db.getCollection('users').update(
  { "_id": ObjectId("5dba8987b4a39c13bc104a23"), "parentsBloodType.type": "AB+" },
  { "$set" : { 'parentsBloodType.$.type' : "O-" } }
)

note that:

the positional $ operator acts as a placeholder for the first element that matches the query document, and

the array field must appear as part of the query document.

Or use the filtered positional operator $[] if you want to update all elements that match an array filter condition or conditions:

db.students.update(
   { "_id": ObjectId("5dba8987b4a39c13bc104a23") },
   { $set: { "parentsBloodType.$[element].type" : "O-" } },
   { 
     arrayFilters: [ { "element.type": "AB+" } ]
   }
)

edited Dec 18, 2019 at 10:43

answered Dec 18, 2019 at 9:13

Fraction

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1 Comment

Wernfried Domscheit Over a year ago

Just a note, multi: true means update multiple documents - not update multiple values of an array. I.e. regardless of multi: true or multi: false it will update all matching values in the array. Acctually when you filter on primary key _id: ObjectId(...) then multi: true is pointless.

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