Concat and get all matching nested arrays across entire collection - mongodb

Question

I have question, in database I have model :
board.model.js
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var BoardSchema = new Schema({
name: { type: String, maxlength: 20 },
lists : { type: Array },
users : [{ type : Schema.Types.ObjectId, ref: 'User' }],
});
module.exports = mongoose.model('Board', BoardSchema);
Inside lists is added array cards.
In practice it looks like this:
{
"_id" : ObjectId("59df60fb6fad6224f4f9f22a"),
"name" : "1",
"users" : [
ObjectId("59cd114cea98d9326ca1c421")
],
"lists" : [
{
"list" : "1",
"cards" : [
{
"name" : "1",
"Author" : [
ObjectId("59df60fb6fad6224f4f9f22a")
],
},
{
"name" : "2"
},
{
"name" : "3"
}
]
},
{
"list" : "2",
"cards" : [
{
"name" : "1",
"Author" : [
ObjectId("59df60fb6fad6224f4f9f22a")
],
},
{
"name" : "2",
"Author" : [
ObjectId("59df60fb6fad6224f4f9f22a")
],
},
{
"name" : "3"
}
]
}
],
"__v" : 0
}
Okay this is an example of one board, the question is can I pull only the cards in which the author is "Author": ObjectId ("59df60fb6fad6224f4f9f22a") of all boards?

Answer 1

You can try below aggregation in 3.4.
Concat all the matching ($filter) cards in each board followed by $unwind and push to collect all cards across boards.
Breakdown:
$reduce to concat all the cards arrays in a single document.
$filter operates on $$this ( cards array ) arguments and filters for matching cards while $$value keeps the previous values.
$concatArrays to merge the previous values with the current filtered values.
$unwind to deconstruct cards arrays and $group with $push to get all cards arrays across boards.
db.collection.aggregate([
{
"$project": {
"boardcards": {
"$reduce": {
"input": "$lists.cards",
"initialValue": [],
"in": {
"$concatArrays": [
"$$value",
{
"$filter": {
"input": "$$this",
"as": "result",
"cond": {
"$eq": [
"$$result.Author",
ObjectId("59df60fb6fad6224f4f9f22a")
]
}
}
}
]
}
}
}
}
},
{
"$unwind": "$boardcards"
},
{
"$group": {
"_id": null,
"allboardcards": {
"$push": "$boardcards"
}
}
}
])
As asked in the comment to get just the names of cards you have to wrap the $filter in $map operator to only map card names.
So replace $filter with $map + $filter
{
"$map": {
"input": {
"$filter": {
"input": "$$this",
"as": "result",
"cond": {
"$eq": [
"$$result.Author",
ObjectId("59df60fb6fad6224f4f9f22a")
]
}
}
},
"as": "result",
"in": {
"name": "$$result.name"
}
}
}