I am trying to get by code the next sequence number but it always says "undefined".
I did this in my mongoDB before:
db.PresentationCollection.insert(
{
_id: "editorID",
seq: 0
}
)
my code (name is editorID):
function getNextSequence(name, db) {
var collection = db.get('PresentationCollection');
var ret = collection.findAndModify(
{
query: { _id: name },
update: { $inc: { seq: 1 } },
new: true
}
);
return ret.seq;
}
You're missing the callback. Callback-based asynchronous functions generally do not return anything meaningful. See the documentation for findAndModify in the node binding's readme.
I had the same problem from following this link and it is indeed the callback not being specified and your code not waiting for the returned result - mongo db documents create auto increment
Here is what I did to solve it. Keep in mind I am using Q for promise helping but you could use straight up javascript promises.
function _getNextSequence(name) {
var deferred = Q.defer();
db.counters.findAndModify(
{ _id: name }, //query
[], //sort
{ $inc: { seq: 1 } }, //update
{ new:true }, //options
function(err, doc) { //callback
if (err) deferred.reject(err.name + ': ' + err.message);
if (doc){
deferred.resolve(doc.value.seq);
}
});
return deferred.promise;
}
Related
var config = require('config.json');
var mongo = require('mongoskin');
var db = mongo.db(config.connectionString, { native_parser: true });
module.exports.getNextSequence = function (name) {
var temp;
db.collection("counters").findAndModify(
{ _id: name }, // query
[], // represents a sort order if multiple matches
{ $inc: { seq: 1 } }, // update statement
{ new: true }, // options - new to return the modified document
function (err, doc) {
temp = doc.value.seq;
console.log(temp); // <-- here the temp is getting printed correctly
}
);
return temp;
}
Using the above code, I am not able to return the value of doc.value.seq. When doing console.log(obj.getNextSequence) it prints undefined.
I want the function to return the value of doc.value.seq.
I'm not familiar with mongoskin so I'm not positive this is correct, but a database query is typically asynchronous, so you need to access the queried value via a callback.
I'm guessing your "getNextSequence" function is returning the "temp" variable before the database query completes (i.e. before the "temp = doc.value.seq" statement).
Try something like this:
module.exports.getNextSequence = function (name, callback) {
var temp;
db.collection("counters").findAndModify(
{ _id: name }, // query
[], // represents a sort order if multiple matches
{ $inc: { seq: 1 } }, // update statement
{ new: true }, // options - new to return the modified document
function (err, doc) {
temp = doc.value.seq;
callback(temp);
}
);
}
Then access "temp" from within the callback passed to getNextSequence.
findAndModify is an asynchronous function. Your console.log line will run after you return temp, which will therefore be undefined. In order to get this to work, you'll want to use an asynchronous approach of your own. There are two available approaches in your situation.
Callbacks:
You're already using a callback, which you provide as the final argument to findAndModify. You could extend this approach and feed this into a callback of your own, as follows:
module.exports.getNextSequence = function (name, callback) {
db.collection("counters").findAndModify(
{ _id: name },
[],
{ $inc: { seq: 1 } },
{ new: true },
function (err, doc) {
if (err) {
return callback(err);
}
callback(null, doc.value.seq);
}
);
}
Of course, this will require you to pass a callback into getNextSequence and follow the callback pattern upstream. You might also want to handle the error from mongoskin and do some handling of your own.
Promises:
If you don't provide a callback to findAndModify, it will return a promise, which you can chain on to, as follows:
module.exports.getNextSequence = function (name) {
return db.collection("counters").findAndModify(
{ _id: name },
[],
{ $inc: { seq: 1 } },
{ new: true }
).then(function (doc) {
return doc.value.seq;
});
}
Again, this will require you to follow the promise pattern upstream. You'll want to read up on promises if you choose this approach, so that you can correctly handle errors, which I have not addressed in the example above.
So here's the deal :
I have an array of objects with a child array of objects
askedAdvices
askedAdvice.replayAdvices
I'm looping trough the parent and foreach looping trough the childs and need to populate() two obejcts (I'm using sails)
The child looks like :
askedAdvices = {
replayAdvices : [{
bookEnd : "<ID>",
user : "<ID>"
}]
}
So my goal is to cycle and populate bookEnd and user with two findOne query, but I'm going mad with the callback hell.
Here's the Models code :
AskedAdvices Model
module.exports = {
schema : false,
attributes: {
bookStart : {
model : 'book'
},
replayAdvices : {
collection: 'replybookend'
},
user : {
model : 'user',
required : true
},
text : {
type : "text"
}
}
};
ReplyBookEnd Model
module.exports = {
schema : false,
attributes: {
bookEnd : {
model : 'book'
},
user : {
model : 'user',
required : true
},
text : {
type : "text"
}
}
};
Here's the Method code :
getAskedAdvices : function(req, res) {
var queryAskedAdvices = AskedAdvices.find()
.populate("replayAdvices")
.populate("user")
.populate("bookStart")
queryAskedAdvices.exec(function callBack(err,askedAdvices){
if (!err) {
askedAdvices.forEach(function(askedAdvice, i){
askedAdvice.replayAdvices.forEach(function(reply, i){
async.parallel([
function(callback) {
var queryBook = Book.findOne(reply.bookEnd);
queryBook.exec(function callBack(err,bookEndFound) {
if (!err) {
reply.bookEnd = bookEndFound;
callback();
}
})
},
function(callback) {
var queryUser = User.findOne(reply.user)
queryUser.exec(function callBack(err,userFound){
if (!err) {
reply.user = userFound;
callback();
}
})
}
], function(err){
if (err) return next(err);
return res.json(200, reply);
})
})
})
} else {
return res.json(401, {err:err})
}
})
}
I can use the async library but need suggestions
Thanks folks!
As pointed out in the comments, Waterline doesn't have deep population yet, but you can use async.auto to get out of callback hell. The trick is to gather up the IDs of all the children you need to find, find them with single queries, and then map them back onto the parents. The code would look something like below.
async.auto({
// Get the askedAdvices
getAskedAdvices: function(cb) {
queryAskedAdvices.exec(cb);
},
// Get the IDs of all child records we need to query.
// Note the dependence on the `getAskedAdvices` task
getChildIds: ['getAskedAdvices', function(cb, results) {
// Set up an object to hold all the child IDs
var childIds = {bookEndIds: [], userIds: []};
// Loop through the retrieved askedAdvice objects
_.each(results.getAskedAdvices, function(askedAdvice) {
// Loop through the associated replayAdvice objects
_.each(askedAdvice.replayAdvices, function(replayAdvice) {
childIds.bookEndIds.push(replayAdvice.bookEnd);
childIds.userIds.push(replayAdvice.user);
});
});
// Get rid of duplicate IDs
childIds.bookEndIds = _.uniq(childIds.bookEndIds);
childIds.userIds = _.uniq(childIds.userIds);
// Return the list of IDs
return cb(null, childIds);
}],
// Get the associated book records. Note that this task
// relies on `getChildIds`, but will run in parallel with
// the `getUsers` task
getBookEnds: ['getChildIds', function(cb, results) {
Book.find({id: results.getChildIds.bookEndIds}).exec(cb);
}],
getUsers: ['getChildIds', function(cb, results) {
User.find({id: results.getChildIds.userIds}).exec(cb);
}]
}, function allTasksDone(err, results) {
if (err) {return res.serverError(err);
// Index the books and users by ID for easier lookups
var books = _.indexBy(results.getBookEnds, 'id');
var users = _.indexBy(results.getUsers, 'id');
// Add the book and user objects back into the `replayAdvices` objects
_.each(results.getAskedAdvices, function(askedAdvice) {
_.each(askedAdvice.replayAdvices, function(replayAdvice) {
replayAdvice.bookEnd = books[replayAdvice.bookEnd];
replayAdvice.user = users[replayAdvice.bookEnd];
});
});
});
Note that this is assuming Sails' built-in Lodash and Async instances; if you're using newer versions of those packages the usage of async.auto has changed slightly (the task function arguments are switched so that results comes before cb), and _.indexBy has been renamed to _.keyBy.
I am trying to get count of data fetched from the database using find() query in mongoose. Now can anyone tell me can i do something like below or do i have to write other function to do that
merchantmodel.find({merchant_id: merchant_id, rating: {'$ne': -1 }, review: {'$ne': "" }}, {'review':1, '_id':0}, {sort: {time_at: -1}}, function(err, docs) {
if (err) {
} else {
if (docs) {
console.log(docs[1].review);
console.log(docs.size()); // Here by writing something is it possible to get count or not
res.json({success: 1, message : "Successfully Fetched the Reviews"});
}
}
});
Convert returned value to array and then use length property
var query = { merchant_id : merchant_id, rating : { '$ne': -1 }, review: { '$ne': "" }};
var projection = { 'review':1, '_id':0 };
var options = { sort: { time_at: -1 } };
merchantmodel.find(query, projection, options).toArray(function(err, docs) {
if (err) {
throw(err);
}
console.log(docs[1].review);
console.log(docs.length);
res.json({success: 1, message : "Successfully Fetched the Reviews"});
});
You can simply do this:
console.log(docs.length);
The docs variable returned by the find() method is an array so docs.length would do the job.
The mongodb native way to do this would be:
db.collection.find( { a: 5, b: 5 } ).count()
I am trying to update the floor_num value from 1 to 9000 in an object in a nested array, in Mongoose:
thingSchema.findById(thingID, function(err, lm) {
if (!lm){
console.log(err);
}
else {
lm.update({'style.maps.localMapArray.map_marker_viewID': req.body.map_marker_viewID},
{'$set': {
'style.maps.localMapArray.$.floor_num': 9000,
}
}, function(err) {
//update success
});
}
});
But I'm getting this Mongo error:
MongoError: cannot use the part
(localMapArray of style.maps.localMapArray.map_marker_viewID) to traverse
the element ({localMapArray: [ { map_marker_viewID: "acympqswmkui",
floor_num: 1 } ]} code: 16837
My schema:
var thingSchema = new Schema({
style: {
maps: {
localMapArray: [{
map_marker_viewID : String,
floor_num : Number
}],
}
}
});
Here is my noob way of solving such kind of problems. I am also new to MongoDB and Mongoose.
thingSchema.findById(thingID, function(err, lm) {
if (err)
console.log(err);
var localMaps = lm.style.maps.localMapArray;
for (var i = 0; i < localMaps.length; i++) {
if (lm.style.maps.localMapArray[i].map_marker_viewId == req.body.map_marker_viewID) {
lm.style.maps.localMapArray[i].floor_num = 9000;
}
}
lm.save();
});
I wish somewhere here can give better example with Mongoose. Hope it will help you.
Using Mongoose, I'd like to make a query with MongoDB and order and limit the results I get. I am doing this with Node.js so I am using callbacks.
So far, I have managed to order my results like this:
myModel.find({ $query: {}, $orderby: { created_at : -1 }}, function (err, items) {
callback( null, items )
});
How can I limit the results I get selecting and index and the number of items I want to get?
Using mongodb native:
http://mongodb.github.io/node-mongodb-native/api-generated/collection.html#find
myModel.find(filter)
.limit(pageSize)
.skip(skip)
.sort(sort)
.toArray(callback);
You can also specify the items in your query:
myModel.find(filter, {sort: {created_at: -1}, limit: 10}, function(err, items){
});
There is no $orderby in node mongodb native, so I'm not sure what library or other tool you're using.
...
Now that you've clarified Mongoose (which in general I recommend against):
myModel.find(filter).limit(10).exec(function(err, items){
//process
});
To sort documents, we can apply sort on a cursor object. To enforce order of sort, instead of passing an object, we need to pass an array to the sort method.
var MongoClient = require('mongodb').MongoClient,
commandLineArgs = require('command-line-args'),
assert = require('assert');
var options = commandLineOptions();
MongoClient.connect('mongodb://localhost:27017/crunchbase', function(err, db) {
assert.equal(err, null);
console.log("Successfully connected to MongoDB.");
var query = queryDocument(options);
var projection = {
"_id": 0,
"name": 1,
"founded_year": 1,
"number_of_employees": 1
};
var cursor = db.collection('companies').find(query);
cursor.project(projection);
cursor.limit(options.limit);
cursor.skip(options.skip);
cursor.sort([
["founded_year", 1],
["number_of_employees", -1]
]);
var numMatches = 0;
cursor.forEach(
function(doc) {
numMatches = numMatches + 1;
console.log(doc.name + "\n\tfounded " + doc.founded_year +
"\n\t" + doc.number_of_employees + " employees");
},
function(err) {
assert.equal(err, null);
console.log("Our query was:" + JSON.stringify(query));
console.log("Documents displayed: " + numMatches);
return db.close();
}
);
});
function queryDocument(options) {
console.log(options);
var query = {
"founded_year": {
"$gte": options.firstYear,
"$lte": options.lastYear
}
};
if ("employees" in options) {
query.number_of_employees = {
"$gte": options.employees
};
}
return query;
}
function commandLineOptions() {
var cli = commandLineArgs([{
name: "firstYear",
alias: "f",
type: Number
}, {
name: "lastYear",
alias: "l",
type: Number
}, {
name: "employees",
alias: "e",
type: Number
}, {
name: "skip",
type: Number,
defaultValue: 0
}, {
name: "limit",
type: Number,
defaultValue: 20000
}]);
var options = cli.parse()
if (!(("firstYear" in options) && ("lastYear" in options))) {
console.log(cli.getUsage({
title: "Usage",
description: "The first two options below are required. The rest are optional."
}));
process.exit();
}
return options;
}
One thing to notice is the order in which MongoDB applies skip, limit and sort
sort
skip
limit
There's also a possibility that we can sort data on the MongoDB side as well, provided that we've setup the indexing.
Notice that MongoDB driver will send a query when we call a cursor method passing a callback function to process query results.