Question:

How to create a query to unwind the array and filter out elements after an element with a certain value?

Problem

I have a document like this in a collection:

{

_id: '123',

locations: [

{uuid:'1-1'},

{uuid:'2-2'},

{uuid:'3-3'},

{uuid:'4-4'}

]

}

I would like to create a query that returns this:

[

{ location: { uuid:'3-3'} }

{ location: { uuid:'4-4'} }

]

Looks like a job for aggregate

Start off by:

{ $match: { _id: 123 } }

then maybe

{ $unwind: '$locations' }

Then

{ $project: { _id: 0, location: '$locations'} }

Cool, this gives me:

[

{ location: { uuid: '1-1'} }

{ location: { uuid: '2-2'} }

{ location: { uuid: '3-3'} }

{ location: { uuid: '4-4'} }

]

Now I need a way only to return elements that come after '3-3' (but also keep 3-3). Any ideas?

Solution

Here the approach I took is to $slice the array from index 2 to end of array so to get the position of 3-3 i used $indexOfArray.
Now since locations is sliced there is fewer to $unwind

db.collection.aggregate([

{ $match: { _id: "123" } },

{

$project: {

_id: 0,

locations: {

$slice: [ "$locations", { $indexOfArray: [ "$locations", { uuid: "3-3" } ] }, { $size: "$locations" } ]

}

{ $unwind: "$locations" },

{ $project: { _id: 0, location: "$locations" } }

])

Answered by: >cmgchess

Credit: >StackOverflow

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