MongoDB findOne() and updateOne() with embedded document - mongodb

Question

Assume I got the following document with embedded documents in arrays:
{
"name" : "test",
"children" : [
{
"name" : "child1",
"children" : [
{
"name" : "sub1",
"children" : [
{"name" : "c1"},
{"name" : "c2"},
{"name" : "c3"},
{"name" : "c4"},
{"name" : "c5"}
]
}
]
},
{
"name" : "child2",
"children" : [
{
"name" : "sub2",
"children" : [
{"name" : "c1"},
{"name" : "c2"},
{"name" : "c3"},
{"name" : "c4"}
]
},
{
"name" : "sub3",
"children" : [
{"name" : "c1"},
{"name" : "c2"},
{"name" : "c3"},
{"name" : "c4"}
]
},
{
"name" : "sub4",
"children" : [
{"name" : "c1"},
{"name" : "c2"},
{"name" : "c3"},
{"name" : "c4"}
]
}
]
}
]
}
As we can see, test has two children: child1 and child2, while a child has their own children like sub1, sub2, sub3, sub4, etc, and so on.
Currently, I have to update some of the children content, but I ran into the following two issues:
The first issue is about findOne(), when I accidentally made a typo (name child1 should be child2):
db.collection_name.findOne({
'name': 'test',
'children.name': 'child1', // -> should be `child2`
'children.children.name': 'sub2'
})
I can still get document 'test' correctly, but since I made a typo and sub2 is actually under child2, not child1, then how can I still get this correct findOne() result?
The second issue is about updateOne(), when I try to update child1's array children, it works good (the code is also like the sample from the official document):
db.collection_name.updateOne({
'name': 'test',
'children.name': 'child1' // locate child1
}, {
'$set':{'children.$.children':[some other content]}
})
But when I also try to update sub3's array (under child2), the same way failed with error cannot use the part (children of children.children.1.children) to traverse the element, and here is the code with issue:
db.collection_name.updateOne({
'name': 'test',
'children.name': 'child2',
'children.children.name': 'sub3' // locate sub3
}, {
'$set':{'children.children.$.children':[some other content]}
})
I will be really appreaciate if someone can help with these two issues, thanks in advance!

Answer 1

For your first issue, you can use $elemMatch to find the exact element.
db.collection_name.findOne({
'name':'test',
children:{
$elemMatch:{
'name':'child2',
'children.name':'sub2'
}
}
})
I guess that mongo does not support multiple nested array update, but if you know the subarray position you can use this approach.
db.collection_name.updateOne({
'name':'test',
children:{
$elemMatch:{
'name':'child2',
'children.name':'sub3'
}
}
}
, {
$set: {"children.$.children.1.children" :
[
{"name" : "c1"},
{"name" : "c2"},
{"name" : "c3"},
{"name" : "c4"}
]
}
}
)

Answer 2

First Issue: The query return results when querying array as the match is evaluated against all elements of array i.e first match 'children.name': 'child1' matches first element and second 'children.children.name': 'sub2' matches the second element.
Use $elemMatch(query) to match both the conditions to the same array element.
db.collection_name.findOne({
'name': 'test',
'children':{$elemMatch:{'name': 'child2', 'children.name': 'sub2'}}
})
Compare both the above approaches 1 & 2
Second issue: Mongodb 3.6 now supports multiple positional updates through arrayFilters expression.
The below query to replace all children of sub3 children.
db.collection_name.updateOne(
{'name': 'test'},
{'$set':{'children.$[first].children.$[second].children':[some data]}},
{'arrayFilters': [{ 'first.name': 'child2', 'second.name': 'sub3'}]}
)
The below query to push new child in the childrens of sub3 children.
db.collection_name.updateOne(
{'name': 'test'},
{'$push':{'children.$[first].children.$[second].children':new child data}},
{'arrayFilters': [{ 'first.name': 'child2', 'second.name': 'sub3'}]}
)