I'm trying to push/insert query results into variable. It gives me error for both the below cases. However, the queries individually gives me correct result. The error is only when trying to push the value into variable.Can you identify what is wrong with the queries?
var aggVal =db.zeroDimFacts.aggregate(
{$group: {_id: '', maxi: {$max: "$_id"}}},
{$project: {_id:0, maxe:"$maxi"}})
printjson(aggVal)
var ss = db.zeroDimFacts.find({},{_id:1}).sort({"_id": -1}).limit(1)
printjson(ss)
Both the codes give some similar errors like:
DBQuery: Agronomics.zeroDimFacts -> { "query" : { }, "orderby" : { "_id" : 1 } }
Using the aggregation framework you would need to run the following pipeline;
Note - the pipeline should be an array of aggregation operators piped together
var cursor = db.zeroDimFacts.aggregate([
{ "$group": { "_id": null, "maximumId": { "$max": "$_id" } } }
]);
var maximumId = cursor.toArray()[0]["maximumId"];
printjson(maximumId);
This may not be perfect way to get max value. However, it still continues to give correct result.
If someone can provide/ suggest a correct way, I will mark it as answer after two days.
After a long trial n errors, I have found an answer to this. First push the values into an array and the zeroth element of an array will have your max value. Now push that value to another variable.
var ss = db.zeroDimFacts.find({},{_id:1}).limit(1).sort({_id:-1}).toArray()
var vi =Number(ss[0]._id)
print(vi)
Related
Currently I use the following find query to get the latest document of a certain ID
Conditions.find({
caveId: caveId
},
{
sort: {diveDate:-1},
limit: 1,
fields: {caveId: 1, "visibility.visibility":1, diveDate: 1}
});
How can I use the same using multiple ids with $in for example
I tried it with the following query. The problem is that it will limit the documents to 1 for all the found caveIds. But it should set the limit for each different caveId.
Conditions.find({
caveId: {$in: caveIds}
},
{
sort: {diveDate:-1},
limit: 1,
fields: {caveId: 1, "visibility.visibility":1, diveDate: 1}
});
One solution I came up with is using the aggregate functionality.
var conditionIds = Conditions.aggregate(
[
{"$match": { caveId: {"$in": caveIds}}},
{
$group:
{
_id: "$caveId",
conditionId: {$last: "$_id"},
diveDate: { $last: "$diveDate" }
}
}
]
).map(function(child) { return child.conditionId});
var conditions = Conditions.find({
_id: {$in: conditionIds}
},
{
fields: {caveId: 1, "visibility.visibility":1, diveDate: 1}
});
You don't want to use $in here as noted. You could solve this problem by looping through the caveIds and running the query on each caveId individually.
you're basically looking at a join query here: you need all caveIds and then lookup last for each.
This is a problem of database schema/denormalization in my opinion: (but this is only an opinion!):
You could as mentioned here, lookup all caveIds and then run the single query for each, every single time you need to look up last dives.
However I think you are much better off recording/updating the last dive inside your cave document, and then lookup all caveIds of interest pulling only the lastDive field.
That will give you immediately what you need, rather than going through expensive search/sort queries. This is at the expense of maintaining that field in the document, but it sounds like it should be fairly trivial as you only need to update the one field when a new event occurs.
I have a mongo collection in which the documents have a field that is an array. I want to be able to publish everything in the documents except for the elements in the array that were created more than a day ago. I suspect the answer will be somewhat similar to this question.
Meteor publication: Hiding certain fields in an array document field?
Instead of limiting fields in the array, I just want to limit the elements in the array being published.
Thanks in advance for any responses!
EDIT
Here is an example document:
{
_id: 123456,
name: "Unit 1",
createdAt: (datetime object),
settings: *some stuff*,
packets: [
{
_id: 32412312,
temperature: 70,
createdAt: *datetime object from today*
},
{
_id: 32412312,
temperature: 70,
createdAt: *datetime from yesterday*
}
]
}
I want to get everything in this document except for the part of the array that was created more than 24 hours ago. I know I can accomplish this by moving the packets into their own collection and tying them together with keys as in a relational database but if what I am asking were possible, this would be simpler with less code.
You could do something like this in your publish method:
Meteor.publish("pubName", function() {
var collection = Collection.find().fetch(); //change this to return your data
_.each(collection, function(collectionItem) {
_.each(collectionItem.packets, function(packet, index) {
var deadline = Date.now() - 86400000 //should equal 24 hrs ago
if (packet.createdAt < deadline) {
collectionItem.packets.splice(index, 1);
}
}
}
return collection;
}
Though you might be better off storing the last 24 hours worth of packets as a separate array in your document. Would probably be less taxing on the server, not sure.
Also, code above is untested. Good luck.
you can use the $elemMatch projection
http://docs.mongodb.org/manual/reference/operator/projection/elemMatch/
So in your case, it would be
var today = new Date();
var yesterday = new Date(today);
yesterday.setDate(today.getDate() - 1);
collection.find({}, //find anything or specifc
{
fields: {
'packets': {
$elemMatch: {$gt : {'createdAt' : yesterday /* or some new Date() */}}
}
}
});
However, $elemMatch only returns the FIRST element matching your condition. To return more than 1 element, you need to use the aggregation framework, which will be more efficient than _.each or forEach, particularly if you have a large array to loop through.
collection.rawCollection().aggregate([
{
$match: {}
},
{
$redact: {
$cond: {
if : {$or: [{$gt: ["$createdAt",yesterday]},"$packets"]},
then: "$$DESCEND",
else: "$$PRUNE"
}
}
}], function (error, result ){
});
You specify the $match in a way similar to find({}). Then all the documents that match your conditions get pipped into the $redact which is specified by the $cond.
$redact scans the document from top level to bottom. At the top level, you have _id, name, createdAt, settings, packets; hence {$or: [***,"$packets"]}
The presence of $packets in the $or allows the $redact to scan the second level which contain the _id, temperature and createdAt; hence {$gt: ["$createdAt",yesterday]}
This is async, you can use Meteor.wrapAsync to wrap around the function.
Hope this help
I have a collection of documents that have a value that is known to be a number, but is stored as a string. It is out of my control to change the type of the field, but I want to use that field in an aggregation (say, to average it).
It seems that I should be using a projection prior to grouping, and in that projection convert the field as needed. I can't seem to get the syntax just right - everything I try either gives me NaN, or the new field is simply missing from the next step in the aggregation.
$project: {
value: '$value',
valueasnumber: ????
}
Given the very simple example above, where the contents of $value in all documents are string type, but will parse to a number, what do I do to make valueasnumber a new (non-existing) field that is of type double with the parsed version of $value in it?
I've tried things like the examples below (and about a dozen similar things):
{ $add: new Number('$value').valueOf() }
new Number('$value').valueOf()
Am I barking up the wrong tree entirely? Any help would be greatly appreciated!
(To be 100% clear, below is how I would like to use the new field).
$group {
score: {
$avg: '$valueasnumber'
}
}
One of the way which I can think of is to use a mongo shell javascript to modify the document by adding new number field, valuesasnumber (number conversion of existing string 'value' field) in the existing document or in the new doc. Then using this numeric field for further calculations.
db.numbertest.find().forEach(function(doc) {
doc.valueasnumber = new NumberInt(doc.value);
db.numbertest.save(doc);
});
Using the valueasnumber field for numeric calculation
db.numbertest.aggregate([{$group :
{_id : null,
"score" : {$avg : "$valueasnumber"}
}
}]);
The core operation is to convert value from string to number which is unable to handled in aggregate pipeline operation currently.
mapReduce is an alternative as below.
db.c.mapReduce(function() {
emit( this.groupId, {score: Number(this.value), count: 1} );
}, function(key, values) {
var score = 0, count = 0;
for (var i = 0; i < values.length; i++) {
score += values[i].score;
count += values[i].count;
}
return {score: score, count: count};
}, {finalize: function(key, value) {
return {score: value.score / value.count};
}, out: {inline: 1}});
Now there is $toInt conversion operators in aggregation, you can check:
https://jira.mongodb.org/browse/SERVER-11400
Here is a few documents from my collections:
{"make":"Lenovo", "model":"Thinkpad T430"},
{"make":"Lenovo", "model":"Thinkpad T430", "problems":["Battery"]},
{"make":"Lenovo", "model":"Thinkpad T430", "problems":["Battery","Brakes"]}
As you can see some documents have no problems, some have only one problem and some have few problems in a list.
I want to calculate how many reviews have a specific "problem" (like "Battery") in problems list.
I have tried to use the following aggregate command:
{ $match : { model : "Thinkpad T430"} },
{ $unwind : "$problems" },
{ $group: {
_id: '$problems',
count: { $sum: 1 }
}}
And for battery problem the count was 382. I also decided to double check this result with find() and count():
db.reviews.find({model:"Thinkpad T430",problems:"Battery"}).count()
Result was 362.
Why do I have this difference? And what is the right way to calculate it?
You likely have documents in the collection where problems contains more than one "Battery" string in the array.
When using $unwind, these will each result in their own doc, so the subsequent $group operation will count them separately.
I am totally new to MongoDB... I am missing a "newbie" tag, so the experts would not have to see this question.
I am trying to update all documents in a collection using an expression. The query I was expecting to solve this was:
db.QUESTIONS.update({}, { $set: { i_pp : i_up * 100 - i_down * 20 } }, false, true);
That, however, results in the following error message:
ReferenceError: i_up is not defined (shell):1
At the same time, the database did not have any problem with eating this one:
db.QUESTIONS.update({}, { $set: { i_pp : 0 } }, false, true);
Do I have to do this one document at a time or something? That just seems excessively complicated.
Update
Thank you Sergio Tulentsev for telling me that it does not work. Now, I am really struggling with how to do this. I offer 500 Profit Points to the helpful soul, who can write this in a way that MongoDB understands. If you register on our forum I can add the Profit Points to your account there.
I just came across this while searching for the MongoDB equivalent of SQL like this:
update t
set c1 = c2
where ...
Sergio is correct that you can't reference another property as a value in a straight update. However, db.c.find(...) returns a cursor and that cursor has a forEach method:
Queries to MongoDB return a cursor, which can be iterated to retrieve
results. The exact way to query will vary with language driver.
Details below focus on queries from the MongoDB shell (i.e. the
mongo process).
The shell find() method returns a cursor object which we can then iterate to retrieve specific documents from the result. We use
hasNext() and next() methods for this purpose.
for( var c = db.parts.find(); c.hasNext(); ) {
print( c.next());
}
Additionally in the shell, forEach() may be used with a cursor:
db.users.find().forEach( function(u) { print("user: " + u.name); } );
So you can say things like this:
db.QUESTIONS.find({}, {_id: true, i_up: true, i_down: true}).forEach(function(q) {
db.QUESTIONS.update(
{ _id: q._id },
{ $set: { i_pp: q.i_up * 100 - q.i_down * 20 } }
);
});
to update them one at a time without leaving MongoDB.
If you're using a driver to connect to MongoDB then there should be some way to send a string of JavaScript into MongoDB; for example, with the Ruby driver you'd use eval:
connection.eval(%q{
db.QUESTIONS.find({}, {_id: true, i_up: true, i_down: true}).forEach(function(q) {
db.QUESTIONS.update(
{ _id: q._id },
{ $set: { i_pp: q.i_up * 100 - q.i_down * 20 } }
);
});
})
Other languages should be similar.
//the only differnce is to make it look like and aggregation pipeline
db.table.updateMany({}, [{
$set: {
col3:{"$sum":["$col1","$col2"]}
},
}]
)
You can't use expressions in updates. Or, rather, you can't use expressions that depend on fields of the document. Simple self-containing math expressions are fine (e.g. 2 * 2).
If you want to set a new field for all documents that is a function of other fields, you have to loop over them and update manually. Multi-update won't help here.
Rha7 gave a good idea, but the code above is not work without defining a temporary variable.
This sample code produces an approximate calculation of the age (leap years behinds the scene) based on 'birthday' field and inserts the value into suitable field for all documents not containing such:
db.employers.find({age: {$exists: false}}).forEach(function(doc){
var new_age = parseInt((ISODate() - doc.birthday)/(3600*1000*24*365));
db.employers.update({_id: doc._id}, {$set: {age: new_age}});
});
Example to remove "00" from the beginning of a caller id:
db.call_detail_records_201312.find(
{ destination: /^001/ },
{ "destination": true }
).forEach(function(row){
db.call_detail_records_201312.update(
{ _id: row["_id"] },
{ $set: {
destination: row["destination"].replace(/^001/, '1')
}
}
)
});