MongoDB - query in denormalized model - mongodb

Question

I have to show the advantages to use normalized model(in this case), with two collections in MongoDB: the first for coaches and the second for teams.
So, I use a denormalized model to show the differences.
For example, if I want to update the palmarès of Barcellona(from 23 Liga to 24 Liga), with denormalized model, I have to find all coaches that coached Barcellona and then I have to update the palmarès inside each coach. Clearly it's too expensive. I want to do this example.
I have this denormalized model of soccer coaches and teams they have coached.
Here is an example:
"_id" : "LEMG_1970",
"name" : "Luis",
"surname" : "Enrique Martinez Garcia",
"age" : 45,
"date_Of_birth" : {
"day" : 8,
"month" : 5,
"year" : 1970
},
"place_Of_birth" : "Gijòn",
"nationality" : "Spanish",
"preferred_formation" : "4-3-3 off",
"coached_Team" : [
{
"_id" : "Bar.43",
"official_name" : "Futbol Club Barcelona"
"common_name" : "Barcellona",
"country" : "Spain",
"started_by" : {
"day" : 28,
"month" : 11,
"year" : 1899
},
"championship" : "La Liga",
"stadium" : {
"name" : "Camp Nou",
"capacity" : 99354
},
"palmarès" : {
"La Liga" : 23,
"Copa del Rey" : 27,
"Supercopa de Espana" : 11,
"UEFA Champions League" : 4,
"UEFA Cup Winners Cup" : 4,
"UEFA Super Cup" : 4,
"FIFA Club World cup" : 2
},
"average age" : 26.9,
"squad value(in mln)" : 591.5,
"foreigners" : 13,
"uniform" : [
"blue",
"dark red"
],
"in_charge" : {
"from" : {
"day" : 1,
"month" : 7,
"year" : 2014
}
},
"matches" : 59
},
{
{
"_id" : "Rom.01",
"official_name" : "Associazione Sportiva Roma SpA",
"common_name" : "Roma",
"country" : "Italy",
"started_by" : {
"day" : 22,
"month" : 6,
"year" : 1927
},
"championship" : "Serie A",
"stadium" : {
"name" : "Olimpico di Roma",
"capacity" : 73261
},
"palmarès" : {
"Serie A" : 3,
"Coppa Italia" : 9,
"Supercoppa Italiana" : 2,
"Serie B" : 1
},
"average age" : 28.3,
"squad value(in mln)" : 253.7,
"foreigners" : 22,
"uniform" : [
"red",
"yellow"
],
"in_charge" : {
"from" : {
"day" : 7,
"month" : 6,
"year" : 2011
},
"to" : {
"day" : 10,
"month" : 5,
"year" : 2012
}
},
"matches" : 41
}
]
As you can see information about teams are into coach document. Now, I want to update the palmarès of Barcellona. I tried this query, but I got an error:
db.coach.update({_id:"LEMG_1970"}, {$set:{"coached_Team.palmarès.La Liga":24}})
This is the advice:
"code" : 16837,
"errmsg" : "cannot use the part (coached_Team of coached_Team.palmarès.La Liga) to traverse the element
What can I do to update the palmarès with denormalized model?

Answer 1

Use the $ positional operator in your update, this identifies an element in an array to update without explicitly specifying the position of the element in the array. Since the positional $ operator acts as a placeholder for the first element that matches the query document, the the array field must appear as part of the query document hence you need the coached_Team array field in your query:
var query = {
"_id" : "LEMG_1970",
"coached_Team._id" : "Bar.43"
},
update = {
"$set": {
"coached_Team.$.palmarès.La Liga": 24
}
};
db.coach.update(query, update);