Update Field in Array of Objects MongoDb [duplicate] - mongodb

Question

This question already has answers here:
How do I update Array Elements matching criteria in a MongoDB document?
(2 answers)
Closed 4 years ago.
I have an object that looks like the following:
> db.delegate_list.find({"name": "delegateList"}).pretty()
{
"_id" : ObjectId("5becd1e0adeb2717c087cec5"),
"name" : "delegateList",
"delegates" : [
{
"address" : "tz1SUgyRB8T5jXgXAwS33pgRHAKrafsdkjhc",
"sync" : false
},
{
"address" : "tz1MecudVJnFZN5FSrriu8ULz2d6dDTR7KaM",
"sync" : false
}
]
}
I am trying to update the sync field for specific object in the array. So for example if I update the sync field for the object at index 0 or address tz1SUgyRB8T5jXgXAwS33pgRHAKrafsdkjhc by doing the following it yields:
> db.delegate_list.update({"name":"delegateList"}, {$set:{"delegates.0.sync": true}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.delegate_list.find({"name": "delegateList"}).pretty()
{
"_id" : ObjectId("5becd1e0adeb2717c087cec5"),
"name" : "delegateList",
"delegates" : [
{
"address" : "tz1SUgyRB8T5jXgXAwS33pgRHAKrafyg87Yc",
"sync" : true
},
{
"address" : "tz1MecudVJnFZN5FSrriu8ULz2d6dDTR7KaM",
"sync" : false
}
]
}
It works as expected, but if I perform the same update command to switch back sync:false, it gives me a malformed object, while deleting the rest of the array:
> db.delegate_list.update({"name":"delegateList"}, {$set:{"delegates.0.sync": false}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.delegate_list.find({"name": "delegateList"}).pretty()
{
"_id" : ObjectId("5becd1e0adeb2717c087cec5"),
"name" : "delegateList",
"delegates" : {
"address" : "tz1SUgyRB8T5jXgXAwS33pgRHAKrafyg87Yc",
"sync" : true,
"0" : {
"sync" : false
}
}
}

Answer 1

You can update specific array item, if item match your case using $ operator
db.delegate_list.update({"delegates.address":"tz1SUgyRB8T5jXgXAwS33pgRHAKrafyg87Yc"}, {$set:{"delegates.$.sync": false}})
It will update the sync filed which address is "tz1SUgyRB8T5jXgXAwS33pgRHAKrafyg87Yc"
only, and not going to add any extra field.