Find and replace a sub sub array element in MongoDB - arrays

Question

Hi I am developing MeteorJS app, I am stuck at updating a sub sub array element.
It is a poll application and I have the following database structure:
Under each question there are options and when a user clicks a button of an option, I want to increment that options votes by one and every user should have one vote right for each question.
From the button, I am passing name and questionId data in order to find the right option to increment vote. I should find the specific question with the questionId and then the specific array with the name under the Options.
Where I am stuck at is I can't find it.
Please help, thanks
Collection Name: Polls
Each Poll has the following structure:
{
"_id" : "uJtBt8mM2pbTYfwND",
"createdAt" : ISODate("2017-04-03T22:40:14.678Z"),
"pollName" : "First Poll",
"entryOwner" : "gdAHxDrxFuTvYiFt8",
"question" : [
{
"name" : "Question number 1",
"questionId" : "xgYQxGxpwBXaQpjXN",
"options" : [
{
"name" : "John",
"votes" : 0
},
{
"name" : "Adam",
"votes" : 0
},
{
"name" : "Robert",
"votes" : 0
}
]
},
{
"name" : "Question number 2",
"questionId" : "zviwYHHsaATBdG6Jw",
"options" : [
{
"name" : "John",
"votes" : 0
},
{
"name" : "Adam",
"votes" : 0
},
{
"name" : "Robert",
"votes" : 0
}
]
}
],
}

Answer 1

You can use $and which performs a logical AND operation on an array of two or more expressions.
{ $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }
The first expression here would be to get the question with questionId.
'question.questionId': "xgYQxGxpwBXaQpjXN"
And second expression to specify the object with matching name in options array.
To find the object with the name in options array, you can use $elemMatch which allows to specify queries.
{ <field>: { $elemMatch: { <query1>, <query2>, ... } } }
To get the object in options array having name as "John".
'question.options': {
$elemMatch: {
name: "John"
}
}
And finally, use $inc to increase the votes (here by 1).
It will get the first matching element (with $).
'question.options.$.votes': 1
Here's the full code:
db.Polls.update({
$and: [{
'question.questionId': "xgYQxGxpwBXaQpjXN"
},
{
'question.options': {
$elemMatch: {
name: "John"
}
}
}
]
}, {
$inc: {
'question.options.$.votes': 1
}
})