How to query a single embedded document in an array in MongoDB? - arrays

Question

I am trying to query a single embedded document in an array in MongoDB. I don't know what I am doing wrong. Programmatically, I will query this document and insert new embedded documents into the currently empty trips arrays.
{
"_id" : ObjectId("564b3300953d9d51429163c3"),
"agency_key" : "DDOT",
"routes" : [
{
"route_id" : "6165",
"route_type" : "3",
"trips" : [ ]
},
{
"route_id" : "6170",
"route_type" : "3",
"trips" : [ ]
},
...
]
}
Following queries -I run in mongo shell- return empty:
db.tm_routes.find( { routes : {$elemMatch: { route_id:6165 } } } ).pretty();
db.tm_routes.find( { routes : {$elemMatch: { route_id:6165,route_type:3 } } } ).pretty();
db.tm_routes.find({'routes.route_id':6165}).pretty()
also db.tm_routes.find({'routes.route_id':6165}).count() is 0.
The following query returns every document in the array
db.tm_routes.find({'routes.route_id':'6165'}).pretty();
{
"_id" : ObjectId("564b3300953d9d51429163c3"),
"agency_key" : "DDOT",
"routes" : [
{
"route_id" : "6165",
"route_type" : "3",
"trips" : [ ]
},
{
"route_id" : "6170",
"route_type" : "3",
"trips" : [ ]
},
...
]}
but db.tm_routes.find({'routes.route_id':'6165'}).count() returns 1.
And finally, here is how I inserted data in the first place -in Node.JS-:
async.waterfall([
...
//RETRIEVE ALL ROUTEIDS FOR EVERY AGENCY
function(agencyKeys, callback) {
var routeIds = [];
var routesArr = [];
var routes = db.collection('routes');
//CALL GETROUTES FUNCTION FOR EVERY AGENCY
async.map(agencyKeys, getRoutes, function(err, results){
if (err) throw err;
else {
callback(null, results);
}
});
//GET ROUTE IDS
function getRoutes(agencyKey, callback){
var cursor = routes.find({agency_key:agencyKey});
cursor.toArray(function(err, docs){
if(err) throw err;
for(i in docs){
routeIds.push(docs[i].route_id);
var routeObj = {
route_id:docs[i].route_id,
route_type:docs[i].route_type,
trips:[]
};
routesArr.push(routeObj);
/* I TRIED 3 DIFFERENT WAYS TO PUSH DATA
//1->
collection.update({agency_key:agencyKey}, {$push:{"routes":{
'route_id':docs[i].route_id,
'route_type':docs[i].route_type,
'trips':[]
}}});
//2->
collection.update({agency_key:agencyKey}, {$push:{"routes":routeObj}});
*/
}
// 3->
collection.update({agency_key:agencyKey}, {$push:{routes:{$each:routesArr}}});
callback(null, routeIds);
});
};
},
...
var collection = newCollection(db, 'tm_routes',[]);
function newCollection(db, name, options){
var collection = db.collection(name);
if (collection){
collection.drop();
}
db.createCollection(name, options);
return db.collection(name);
}
Note: I am not using Mongoose and don't want to use if possible.

Answer 1

Melis,
I see what you are asking for, and what you need is help understanding how things are stored in mongodb. Things to understand:
A document is the basic unit of data for MongoDB and can be roughly compared to a row in a relational database.
A collection can be thought of as a table with a dynamic schema
So documents are stored in collections.Every document has a special _id, that is unique within a collection. What you showed us above in the following format is One document.
{
"_id" : ObjectId("564b3300953d9d51429163c3"),
"agency_key" : "DDOT",
"routes" : [
{
"route_id" : "6165",
"route_type" : "3",
"trips" : [ ]
},
{
"route_id" : "6170",
"route_type" : "3",
"trips" : [ ]
},
...
]}
If you run a query in your tm_routes collection. The find() will return each document in the collection that matches that query. Therefore when you run the query db.tm_routes.find({'routes.route_id':'6165'}).pretty(); it is returning the entire document that matches the query. Therefore this statement is wrong:
The following query returns every document in the array
If you need to find a specific route in that document, and only return that route, depending on your use, because its an array, you may have to use the $-Positional Operator or the aggregation framework.

Answer 2

For Node and Mongodb users using Mongoose, this is one of the ways to write the query to the above problem:
db.tm_routes.updateOne(
{
routes: {
$elemMatch: {
route_id: 6165 (or if its in a route path then **6165** could be replaced by **req.params.routeid**
}
}
},
{
$push: {
"routes.$.trips":{
//the content you want to push into the trips array goes here
}
}
}
)