How to update the Embedded Data which is inside of another Embedded Data? - mongodb

Question

I have document like below in MongoDB:
{
"_id": "test",
"tasks": [
{
"Name": "Task1",
"Parameter": [
{
"Name": "para1",
"Type": "String",
"Value": "*****"
},
{
"Name": "para2",
"Type": "String",
"Value": "*****"
}
]
},
{
"Name": "Task2",
"Parameter": [
{
"Name": "para1",
"Type": "String",
"Value": "*****"
},
{
"Name": "para2",
"Type": "String",
"Value": "*****"
}
]
}
]
}
There is Embedded Data Structure (Parameter) inside of another Embedded Data Structure (Tasks). Now I want to update the para1 in Task1's Parameter.
I have tried many ways but I can only use query tasks.Parameter.name to find the para1 but cannot update it. the example in the doc are using .$. to update the value in a Embedded Data Structure but it doesn't work in my case.
Anyone have any ideas ?

Answer 1

MongoDB currently only supports the positional operator once, and only for the top level array. There is a ticket SERVER-831 to change this behavior for your use case. You can follow the issue there and up vote it.
However, you might be able to change your approach to accomplish what you want to do. One way is to change your schema. Collapse the tasks name into the array so the document looks like this:
{
_id:test,
tasks:
[
{
Task:1
Name:para1,
Type:String,
Value:*****
},
{
Task:1
Name:para2,
Type:String,
Value:*****
},
{
Task:2
Name:para1,
Type:String,
Value:*****
},
{
Task:2
Name:para2,
Type:String,
Value:*****
}
]
}
Another approach that may work for you is to use $pull and $push. For instance something like this to replace a task (this assumes that tasks.Parameter.Name is unique to an array of Parameters):
db.test2.update({$and: [{"tasks.Name": "Task3"}, {"tasks.Parameter.Name":"para1"}]}, {$pull: {"tasks.$.Parameter": {"Name": "para1"}}})
db.test2.update({"tasks.Name": "Task3"}, {$push: {"tasks.$.Parameter": {"Name": "para3", Type: "String", Value: 1}}})
With this solution you need to be careful with regard to concurrency, as there will be a brief moment where the document doesn't exist.