Below code is being used many a times in the mongo shell.
db.CourseContent.find({Actor: a, Object: obj})
So, I have pushed the query results in a variable for further use. However, it seems the query is being changed or modified which cannot be used further.
OLD CODE: (THIS IS WORKING FINE)
var bag={}
bag.$sri=[]; bag.$idz=[]
bag.$sri =db.CourseContent.find({Actor: a, Object: obj}).map( function(sri) {return sri.StatementRefId});
bag.$idz =db.CourseContent.find({Actor: a, Object: obj}).map( function(sri) {return sri._id});
NEW CODE: (NOT WORKING WHEN USING VARIABLE TO STORE QUERY RESULTS) bag.$idz does not contain any value where has it succeeds in OLD CODE.
var bag={}
bag.$sri=[]; bag.$idz=[]
var qry = db.CourseContent.find({Actor: a, Object: obj})
bag.$sri =qry.map( function(sri) {return sri.StatementRefId});
bag.$idz = qry.map( function(sri) {return sri._id});
Can someone help me find where I have been doing wrong?
The problem is that the find() method and his companion in crime aggregate() return a Cursor which can be consumed only once. So you need to convert the query result using the toArray() method like this:
var qry = db.CourseContent.find({ Actor: a, Object: obj }).toArray()
I suggest you use the aggregation framework to return those values:
db.CourseContent.aggregate([
{ "$match": { Actor: a, Object: obj } },
{ "group": {
"_id": null,
"sri": { "$push": "$StatementRefId" },
"idz": { "$push": "$_id" }
}}
])
The resulted Cursor object contains a single document. If you are in the shell, it yield that document but using some driver, you need to iterate the cursor.
Related
I have an array inside a document of a collection called pown.
{
_id: 123..,
name: pupies,
pups:[ {name: pup1, location: somewhere}, {name: pup2, ...}]
}
Now a user using my rest-service sends the entire first entry as put request:
{name: pup1, location: inTown}
After that I want to update this element in my database.
Therefore I tried this:
var updatedPup = req.body;
var searchQuery = {
_id : 123...,
pups : { name : req.body.name }
}
var updateQuery = {
$set: {'pups': updatedPup }
}
db.pown.update(searchQuery, updateQuery, function(err, data){ ... }
Unfortunately it is not updating anythig.
Does anyone know how to update an entire array-element?
As Neil pointed, you need to be acquainted with the dot notation(used to select the fields) and the positional operator $ (used to select a particular element in an array i.e the element matched in the original search query). If you want to replace the whole element in the array
var updateQuery= {
"$set":{"pups.$": updatedPup}
}
If you only need to change the location,
var updateQuery= {
"$set":{"pups.$.location": updatedPup.location}
}
The problem here is that the selection in your query actually wants to update an embedded array element in your document. The first thing is that you want to use "dot notation" instead, and then you also want the positional $ modifier to select the correct element:
db.pown.update(
{ "pups.name": req.body.name },
{ "$set": { "pups.$.locatation": req.body.location }
)
That would be the nice way to do things. Mostly because you really only want to modify the "location" property of the sub-document. So that is how you express that.
I have the following Document:
{
"_id": 100,
"Version": 1,
"Data": "Hello"
}
I have a function which return a number from a sequence:
function getNextSequence(name) {
var ret = db.Counter.findAndModify(
{
query: { _id: name },
update: { $inc: { value: 1 } },
new: true,
upsert: true
}
);
return ret.value;
}
I can use this for optimistic concurrency by performing the following Mongo command:
db.CollectionName.findAndModify({
query: { "_id" : NumberLong(100), "Version" : 1 },
update: { "$set" : {
"Data": "Here is new data!",
"Version" : db.eval('getNextSequence("CollectionName")') }
},
new: true
}
);
This will update the document (as the _id and Version) match, with the new Data field, and also the new number out of the eval call.
It also returns a modified document, from which I can retrieve the new Version value if I want to make another update later (in the same 'session').
My problem is:
You cannot create an Update document using the MongoDB C# client that will serialize to this command.
I used:
var update = Update.Combine(
new UpdateDocument("$set", doc),
Update.Set(versionMap.ElementName, new BsonJavaScript("db.eval('getNextSequence(\"Version:CollectionName\")')")))
);
If you use what I first expected to perform this task, BsonJavascript, you get the following document, which incorrectly sets Version to a string of javascript.
update: { "$set" : {
"Data": "Here is new data!",
"Version" : { "$code" : "db.eval('getNextSequence(\"Version:CollectionName\")')" }
}
}
How can I get MongoDB C# client to serialize an Update document with my db.eval function call in it?
I have tried to add a new BsonValue type in my assembly which I would serialize down to db.eval(''); However there is a BsonType enum which I cannot modify, without making a mod to MongoDB which I would not like to do incase of any issues with the change, compatibility etc.
I have also tried simply creating the Update document myself as a BsonDocument, however FindAndModify will only accept an IMongoUpdate interface which a simply a marker that at present I find superfluous.
I have just tried to construct the command manually by creating a BsonDocument myself to set the Value: db.eval, however I get the following exception:
A String value cannot be written to the root level of a BSON document.
I see no other way now than drop down to the Mongo stream level to accomplish this.
So I gave up with trying to get Mongo C# Client to do what I needed and instead wrote the following MongoDB function to do this for me:
db.system.js.save(
{
_id : "optimisticFindAndModify" ,
value : function optimisticFindAndModify(collectionName, operationArgs) {
var collection = db.getCollection(collectionName);
var ret = collection.findAndModify(operationArgs);
return ret;
}
}
);
This will get the collection to operate over, and execute the passed operationArgs in a FindAndModify operation.
Because I could not get the shell to set a literal value (ie, not a "quoted string") on a javascript object, I had to to this in my C# code:
var counterName = "Version:" + CollectionName;
var sequenceJs = string.Format("getNextSequence(\"{0}\")", counterName);
var doc = entity.ToBsonDocument();
doc.Remove("_id");
doc.Remove(versionMap.ElementName);
doc.Add(versionMap.ElementName, "SEQUENCEJS");
var findAndModifyDocument = new BsonDocument
{
{"query", query.ToBsonDocument()},
{"update", doc},
{"new", true},
{"fields", Fields.Include(versionMap.ElementName).ToBsonDocument() }
};
// We have to strip the quotes from getNextSequence.
var findAndModifyArgs = findAndModifyDocument.ToString();
findAndModifyArgs = findAndModifyArgs.Replace("\"SEQUENCEJS\"", sequenceJs);
var evalCommand = string.Format("db.eval('optimisticFindAndModify(\"{0}\", {1})');", CollectionName, findAndModifyArgs);
var modifiedDocument = Database.Eval(new EvalArgs
{
Code = new BsonJavaScript(evalCommand)
});
The result of this is that I can now call my Sequence Javascript, the getNextSequence function, inside the optimisticFindAndModify function.
Unforunately I had to use a string replace in C# as again there is no way of setting a BsonDocument to use the literal type db.eval necessary, although Mongo Shell likes it just fine.
All is now working.
EDIT:
Although, if you really want to push boundaries, and are actually awake, you will realize this same action can be accomplished by performing an $inc on the Version field.... and none of this is necessary....
However: If you want to follow along to the MongoDB tutorial on how they to say to implement concurrency, or you just want to use a function in a FindAndModify, this will help you. I know I'll probably refer back to it a few times in this project!
I have an array of mongoose queries like so
var q = [{"_id":'5324b341a3a9d30000ee310c'},{$addToSet:{"Campaigns":'532365acfc07f60000200ae9'}}]
and I would like to apply them to a mongoose method like so
var q = [{"_id":'5324b341a3a9d30000ee310c'},{$addToSet:{"Campaigns":'532365acfc07f60000200ae9'}}]
Account.update.apply(this, q);
How can I do this ? How can I convert an array of mongoose query objects to mongoose parameters?
I tried the following but it doesnt work.
var q = [{
"_id": '5324b341a3a9d30000ee310c'
}, {
$addToSet: {
"Campaigns": '532365acfc07f60000200ae9'
}
}]
Account.update(q).exec(function (e, r) {
console.log(r)
console.log('ERROR')
console.log(e)
console.log('ERROR')
cb(e, r);
});
All you need to do is pass in the correct object context via apply to the update method:
Account.update.apply(Account, q)
.exec(function(e, r) {
// your code here ...
});
The this needs to be the Model instance, not the global scope context (or whatever else this may have been at the time it was called).
Basically seems to be just the way the prototype of the function seems to be passed in. So if you want to build your arguments dynamically then you need to do something like this:
var q = [
{ "_id": account._id },
{ "$addToSet": { "Campaigns": campaign._id } },
];
Account.update( q[0], q[1], (q[2]) ? q[2] : {}, function(err, num) {
Essentially then you are always passing in the query, update and options documents as arguments. This uses the ternary condition to put an empty {} document in as the options parameter, where it does not exist in your dynamic entry.
I have an aggregation query on a students collection that is returning two sets of results
for each student like this
{ _id: 1543,
name: 'Bill Jackson',
scores: { type: 'homework', score: 38.86823689842918 } }
{ _id: 1543,
name: 'Bill Jackson',
scores: { type: 'homework', score: 15.861613903793295 } }
That's working fine. Now in the callback I want to remove one of the scores for each student. I use ugly nested conditionals below to isolate which of the two records I want to remove, and, once that's achieved I create a find and Modify query to remove the doc but there's no evidence of it getting run. Neither the error or success callback to the findAndModify are getting run, however I am able to log that I'm inside the area where the findAndModify is getting called.
Is it possible to query the db in the callback to an aggregation? If not, how should I perform an operation that persists in the db?
//aggregation query ommitted
, function(err, result) { //callbackstarts here with result of aggregation query that returns two records for each student
for (var i=0; i<result.length; i++) {
var id = result[i]['_id'];
if (id === result[i]['_id']){
if (foo && foo === result[i]['_id']){
//if we're in here, we know we need to remove score associated with this result[i]['_id']
//create findAndModify to remove the record
var query = { '_id' : result[i]['_id']}
var sort = []
var operation = { '$pull' : { 'scores.score' : result[i]['scores']['score'] } };
var options = []
console.log('this code is getting called but findAndModify not')
db.collection('students').findAndModify(query, sort, operation, options,function(err, doc) {
if(err) throw err;
if (!doc) {
console.log("record not found");
}
else {
console.log("changed doc" + doc);
}
});
}else {
var foo = result[i]['_id'] //part of logic to isolate which of two records to remove
}
I'm doing a MapReduce in Mongo to generate a reverse index of tokens for some documents. I am having trouble accessing document's _id in the map function.
Example document:
{
"_id" : ObjectId("4ea42a2c6fe22bf01f000d2d"),
"attributes" : {
"name" : "JCDR 50W38C",
"upi-tokens" : [
"50w38c",
"jcdr"
]
},
"sku" : "143669259486830515"
}
(The field ttributes['upi-tokens'] is a list of text tokens I want to create reverse index for.)
Map function (source of the problem):
m = function () {
this.attributes['upi-tokens'].forEach(
function (token) { emit(token, {ids: [ this._id ]} ); }
); }
Reduce function:
r = function (key, values) {
var results = new Array;
for (v in values) {
results = results.concat(v.ids);
}
return {ids:results};
}
MapReduce call:
db.offers.mapReduce(m, r, { out: "outcollection" } )
PROBLEM Resulting collection has null values everywhere where I'd expect an id instead of actual ObjectID strings.
Possible reason:
I was expecting the following 2 functions to be equivalent, but they aren't.
m1 = function (d) { print(d['_id']); }
m2 = function () { print(this['_id']); }
Now I run:
db.offers.find().forEach(m1)
db.offers.find().forEach(m2)
The difference is that m2 prints undefined for each document while m1 prints the ids as desired. I have no clue why.
Questions:
How do I get the _id of the current object in the map function for use in MapReduce? this._id or this['_id'] doesn't work.
Why exactly aren't m1 and m2 equivalent?
Got it to work... I made quite simple JS mistakes:
inner forEach() in the map function seems to overwrite 'this' object; this is no longer the main document (which has an _id) but the iterated object inside the loop)...
...or it was simply because in JS the for..in loop only returns the keys, not values, i.e.
for (v in values) {
now requires
values[v]
to access the actual array value. Duh...
The way I circumvented mistake #1 is by using for..in loop instead of ...forEach() loop in the map function:
m = function () {
for (t in this.attributes['upi-tokens']) {
var token = this.attributes['upi-tokens'][t];
emit (token, { ids: [ this._id ] });
}
}
That way "this" refers to what it needs to.
Could also do:
that = this;
this.attributes['upi-tokens'].forEach( function (d) {
...
that._id...
...
}
probably would work just fine.
Hope this helps someone.