How to update document in an object in an array in an object in an array using MongoDB?

Question

Using MongoDB queries:
1. How do I find the object with _id A3?
2. How would I update object with _id A3 to A4?

Please note: Database is an array of objects where one key has an array of objects

[{
"project_name": "ProjectA",
"issues":[{"issue_title":"TitleA1", "_id":"A1"},
          {"issue_title":"TitleA2","_id":"A2"},
          {"issue_title":"TitleA3","_id":"A3"}]
},
{
"project_name": "ProjectB",
"issues":[{"issue_title":"TitleB1", "_id":"B1"},
          {"issue_title":"TitleB2","_id":"B2"},
          {"issue_title":"TitleB3","_id":"B3"}]
}
]

mickl · Accepted Answer · 2020-02-29 05:43:55Z

2

You can use the dot notation to $match your object by nested _id and use $unwind with $replaceRoot to promote nested object to the top level:

db.collection.aggregate([
    {
        $unwind: "$issues"
    },
    {
        $match: { "issues._id": "A3" }
    },
    {
        $replaceRoot:{ newRoot: "$issues" }
    }
])

Mongo Playground

the positional operator can be used to update that one:

db.col.updateOne({ "project_name": "ProjectA", "issues._id": "A3" }, { $set: { "issues.$._id": "A4" } })

edited Feb 29, 2020 at 5:43

answered Feb 29, 2020 at 5:27

mickl

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5 Comments

wongx Over a year ago

I'm not sure that works because the starting dataset is an array... could you please confirm that your code can bypass 2 arrays? I'm not sure if I'm testing the code wrong or if the code can't access double arrays. Maybe it needs $elemMatch somewhere but I tried so many times and couldn't get it to work

mickl Over a year ago

So is it like this: mongoplayground.net/p/8yPdPJ1C2cB ? or can you show exactly how single object looks like?

wongx Over a year ago

Ah yes, just like in that playground. Question 1 would be how to return this object {"issue_title":"TitleA3","_id":"A3"} by itself. I tried the code you suggested but it's giving me error and maybe we need to integrate "aggregate" somehow?

mickl Over a year ago

@wongz modified my answer

wongx Over a year ago

thanks, the first code works. The second one may need aggregate as well?

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