NoSQL aggregation query Shakespeare’s dataset - mongodb

Question

I'm trying to learn NoSQL aggregation queries and here is dataset (name - shakespeare_plays) structure:
"_id" : "Romeo and Juliet",
"acts" : [
{
"title" : "ACT I",
"scenes" : [
{
"title" : "SCENE I. Verona. A public place.",
"action" : [
{
"character" : "SAMPSON",
"says" : [
"Gregory, o' my word, we'll not carry coals."
]
},
{
"character" : "GREGORY",
"says" : [
"No, for then we should be colliers."
]
},
// ...
{
"character" : "GREGORY",
"says" : [
"To move is to stir; and to be valiant is to stand:",
"therefore, if thou art moved, thou runn'st away."
]
},
{
"character" : "SAMPSON",
"says" : [
"A dog of that house shall move me to stand: I will",
"take the wall of any man or maid of Montague's."
]
},
{
"character" : "GREGORY",
"says" : [
"That shows thee a weak slave; for the weakest goes",
"to the wall."
]
},
// ...
},
// ...
]
},
// ...
]
}
What tasks am I trying to do:
What characters are found in more than one play
How many replicas does Juliet have
Number of characters in Othello
Any tips how to do it via aggregate?

Answer 1

You're on the right track. Sharing some queries to achieve your goal.
From where you're right now, you can get a list of all characters by adding $group stage
db.getCollection('shakespeare_plays').aggregate([{
$unwind: "$acts"
}, {
$unwind: "$acts.scenes"
}, {
$unwind: "$acts.scenes.action"
}, {
$group: {
_id: "$acts.scenes.action.character"
}
}])
Going further, you want to see who has appeared how many times, you can use $sum operator inside $group
db.getCollection('shakespeare_plays').aggregate([{
$unwind: "$acts"
}, {
$unwind: "$acts.scenes"
}, {
$unwind: "$acts.scenes.action"
}, {
$group: {
_id: "$acts.scenes.action.character",
count: {$sum: 1}
}
}])
//Results : [{ "_id" : "GREGORY", "count" : 4 }]
You can export the results to an array and perform any logic you want to perform on the results which will give you all the answers you needed
var myResults = db.getCollection('shakespeare_plays').aggregate([pipelineQuery]).toArray();
//Here you can perform any logic on the variable myResults in your programming language
Read more about $group and $sum