MongoDB Aggregate and Update Exercise - database

Question

I was practicing on mongoDB. Currently, this is my first attempt on NoSql databases. I have a generic movie collection(video_movieDetails). In it, there are "_id" "title" "year" "director" "writers" "countries". I am able to write queries like "Construct a query and return all movies where Ian McKellen or Elijah Woods played in, but not both in movies.
db.video_movieDetails.find({$or:[{$and:[{"actors":"Ian McKellen"},{"actors":{$ne:"Elijah Woods"}}]},{$and:[{"actors":"Elijah Woods"},{"actors":{$ne:"Ian McKellen"}}]}]})
Now I am trying to achieve,
Titles and number of movies of each movie director.(For aggregation)
Updating a director's name from "Tim Burton" to "T. Burton". Eventually, all of the names should be updated on corresponding movie. (Updating)
How may I achieve this two queries? Thank you.

Answer 1

With this setup:
db.foo.insert([
{"_id": 0,title: "Movie A", year: 2010, director: "D1", actors: ["A1","A2"] }
,{"_id": 1,title: "Movie B", year: 2010, director: "D1", actors: ["A1","A5","A6"]}
,{"_id": 2,title: "Movie C", year: 2010, director: "D2", actors: ["A4"]}
,{"_id": 3,title: "Movie D", year: 2012, director: "D3", actors: ["A7"]}
,{"_id": 4,title: "Movie E", year: 2015, director: "D3", actors: ["A7"]}
]);
c = db.foo.aggregate([
{$group: {_id: "$director", movies: {$push: "$title"}, count: {$sum:1}}}
]);
show(c, true);
// For update(), note the option multi:true. Without it, mongodb will update ONLY the
// first doc matching the query criteria, not ALL the docs.
rc = db.foo.update({director: "D3"},{$set: {"director":"T. Burton"}},{multi:true});
printjson(rc);
c = db.foo.aggregate([]);
show(c, true);
you get this:
{ "_id" : "D1", "movies" : [ "Movie A", "Movie B" ], "count" : 2 }
{ "_id" : "D2", "movies" : [ "Movie C" ], "count" : 1 }
{ "_id" : "D3", "movies" : [ "Movie D", "Movie E" ], "count" : 2 }
found 3
{ "nMatched" : 2, "nUpserted" : 0, "nModified" : 2 }
{
"_id" : 0,
"title" : "Movie A",
"year" : 2010,
"director" : "D1",
"actors" : [
"A1",
"A2"
]
}
{
"_id" : 1,
"title" : "Movie B",
"year" : 2010,
"director" : "D1",
"actors" : [
"A1",
"A5",
"A6"
]
}
{
"_id" : 2,
"title" : "Movie C",
"year" : 2010,
"director" : "D2",
"actors" : [
"A4"
]
}
{
"_id" : 3,
"title" : "Movie D",
"year" : 2012,
"director" : "T. Burton",
"actors" : [
"A7"
]
}
{
"_id" : 4,
"title" : "Movie E",
"year" : 2015,
"director" : "T. Burton",
"actors" : [
"A7"
]
}
The $match stage will work on arrays as if they were scalars. For example, to find all movies in which actor A1 or A4 appears:
db.foo.aggregate([
{$match: {"actors": {$in: ["A1","A4"]} }}
]);
A simple $lookup example:
db.foo2.insert([
{_id:0, location: "Spain"},
{_id:1, location: "Italy"},
{_id:2, location: "Italy"},
{_id:3, location: "USA"},
{_id:4, location: "Sweden"},
]);
c = db.foo2.aggregate([
{$match: {"location": "Italy"}}
,{$lookup: {from: "foo", localField: "_id", foreignField: "_id", as: "X"}}
// Lookup can produce a one-to-many relationship; thus, "X" will come back
// as an array. Since we know that the _id-to-_id relationship is 1:1, we
// can just grab the first element of X and reset X to be that. In this
// case, $addFields acts like an assignment expression "x = x + 1" where
// x is overwritten by a new x.
,{$addFields: {X: {$arrayElemAt:["$X",0]} }}
// At this point, if you really want, you can $project just the title and
// location or whatever you want. Sometimes it is more flexible just to
// return the whole shape. Comment out the next line as an experiment:
,{$project: {_id:true, location:true, title: "$X.title"}}
]);
yields:
{ "_id" : 1, "location" : "Italy", "title" : "Movie B" }
{ "_id" : 2, "location" : "Italy", "title" : "Movie C" }