How to update particular value inside array - Mongodb - 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-"}}
)

Answer 1

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.

Answer 2

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+" } ]
}
)