The mongo docs specify that you can specify a query hint for count queries using the following syntax:
db.orders.find(
{ ord_dt: { $gt: new Date('01/01/2012') }, status: "D" }
).hint( { status: 1 } ).count()
Can you do this using the mongo template? I have a Query object and am calling the withHint method. I then call mongoTemplate.count(query); However, I'm pretty sure it's not using the hint, though I'm not positive.
Sure, there are a few forms of this including going down to the basic driver, but assuming using your defined classes you can do:
Date date = new DateTime(2012,1,1,0,0).toDate();
Query query = new Query();
query.addCriteria(Criteria.where("ord_dt").gte(date));
query.addCriteria(Criteria.where("status").is("D"));
query.withHint("status_1");
long count = mongoOperation.count(query, Class);
So you basically build up a Query object and use that object passed to your operation, which is .count() in this case.
The "hint" here is the name of the index as a "string" name of the index to use on the collection. Probably something like "status_1" by default, but whatever the actual name is given.
Related
I am working on a nodejs/express app with Mongodb on the backend. In one of my API calls, depending on the presence of a particular querystring parameter or the other I want to issue a query to Mongodb with either a $gt or a $lt.
In some cases we want to ask for everything less than the tokenId using $lt, but in other cases we want everything greater than the tokenId using $gt. How do we do that without duplicating the queries?
Here's an example query:
collection.find({'film_id': {$in : genre}, '_id': {$lt: tokenId}}).sort({'_id': -1}).limit(25).toArray(function(error, films)
Is there a way to dynamically create the query without actually doing 2 different queries?
Build up your query object programmatically:
var query = {'film_id': {$in : genre}};
if (param) {
query._id = {$lt: tokenId};
} else {
query._id = {$gt: tokenId};
}
collection.find(query).sort({'_id': -1}).limit(25).toArray(function(error, films);
Update
Now that Node.js 4+ supports computed property names, you can create query in one step as:
var query = {
film_id: {$in: genre},
_id: {[param ? '$lt' : '$gt']: tokenId}
};
The Above code may not work. The above dynamic query will be resolved to following Ex. Token is an integer 35.
collection.find("_id":"{$gt: 35}")
.sort({'_id': -1}).limit(25).toArray(function(error, films);
resulting in Error
The correct syntax should be:
collection.find("_id":{$gt: 35}).
The double "" quotes should not be there.
How do I formulate a query that uses a sub Object field to return a cursor?
My Object structure looks like this:
_id: "4ncBGvppEs92e4tcZ"
expiryDate: "2017-05-27T21:45:57+03:00"
viewStatisticsArray: Array[1]
0: Object
nrOfViews:155
statesDate:"Fri Mar 24 2017 12:46:21 GMT+0300 (EAT)"
viewedBy: "udEnfEmy5DSBvDsSy"
Please note that the viewedBy (also what I am refering to as a Sub Object) value carries my user id generated from Meteor.user()._id;
var MyUserId = Meteor.user()._id;
I have unsucessfully tried:
Db.find({},{viewedBy: { $in: MyUserId } } ).fetch();
Also unsucessfully tried:
Db.find({},{viewStatisticsArray.viewedBy: { $in: MyUserId } } ).fetch();
Please help! How do I forumlate the query above correctly?
The expected results should yeild in a cursor full of Objects that only have viewedBy: "udEnfEmy5DSBvDsSy".
In mongodb (and therefore Meteor), the correct way to execute this type of query is to use the $elemMatch operator. As an example, your query would look like this.
Db.find({
viewStatisticsArray: {
$elemMatch: {
viewedBy: MyUserId
}
}
});
Since, however, you are only needing to specify a single query predicate, you can alternatively use the below query as well.
Db.find({
'viewStatisticsArray.viewedBy': MyUserId
});
One word of caution, I don't know if minimongo (the mongodb like db that runs on the client in a meteor app) support the $elemMatch operator. If that is the case, and if you are executing this query on the client, then you must use the 2nd option above.
I am trying to use the MongoDB full text indices in Morphia. I need to return the score for each documents as well as have the results sorted. This is what my query looks like without Morphia:
db.getCollection('disease').find( { $text: { $search: "brain" } },
{ score: { $meta: "textScore" } } )
.sort( { score: { $meta: "textScore" } } )
This works correctly and returns hits sorted by score.
I also can do this using the MongoDB Java driver directly without Morphia.
// search with the Java driver
BasicDBObject textSearch = new BasicDBObject("$search", "brain");
BasicDBObject search = new BasicDBObject("$text", textSearch);
BasicDBObject meta = new BasicDBObject("$meta", "textScore");
BasicDBObject score = new BasicDBObject("score", meta);
List<DBObject> diseases = collection.find(search, score).sort(score).toArray();
Assert.assertEquals(2, diseases.size());
Assert.assertEquals("brain", diseases.get(0).get("name"));
Assert.assertEquals("benign-brain", diseases.get(1).get("name"));
I can't figure out how to accomplish the same thing in Morphia. Here is the example from the Morphia documentation (http://mongodb.github.io/morphia/1.0/guides/querying/#text-searching):
List<Greeting> good = datastore.createQuery(Greeting.class)
.search("good")
.order("_id")
.asList();
Assert.assertEquals(4, good.size());
The example does not return score and is ordering by "_id". I don't see any way to handle the $meta operator in Morphia. Has anyone done something similar?
Because Morphia maps back to your type, the only way to expose the score in this situation would be to add a score field to your entity type and map it back to that field. This isn't awesome because it starts to pollute your business types with database metadata fields. You could always try mapping back out a special value object type containing whatever metadata you'd like. That would at least keep your business objects free of this metadata.
Following the advice from #evanchooly and the OP, I was able to resolve my version of this issue as follows:
first I created the query anlong with the search.
Datastore morphiaDS = ...;
Query<myMorphiaModel> query = morphiaDS.createQuery(myMorphiaModel.class)
.field("helloField").equal("world")
.search("yadayadayada"); // Search performs a text search
Next, I transitioned to using the direct Java Mongo drivers. It seems right now, while this issue by #evanchooly is still open, We'll need to use mongo drivers and can't go pure morphia.
BasicDBObject meta = new BasicDBObject("$meta", "textScore");
BasicDBObject score = new BasicDBObject("score", meta);
List<DBObject> results = query.getCollection()
.find(query.getQueryObject(), score)
.sort(score).toArray();
Finally I converted the list of generalized objects to my original morphia model
Morphia morphia = mongoService.getMorphia();
List<myMorphiaModel> searchDocs = results.stream()
.map((result) -> morphia.fromDBObject(myMorphiaModel.class, result))
.collect(Collectors.toList());
One troubleshooting issue to watch out for is that I had to make sure I had 'score' represented in the find, not just in the sort.
Hope this clarifies the helpful answers that others have presented....
Looks like this issue has been fixed with the commit https://github.com/mongodb/morphia/commit/af4d64f6de3c0b1437dd216f5762d03bf98cdcb0 and now you can just do:
List<Greeting> good = datastore.createQuery(Greeting.class)
.search("good")
.project(Meta.textScore("score"))
.order(Meta.textScore("score"))
The only caveat now is that as the project on score is mandatory to be able to sort by score, if no other projections are added, the result just contains the score field. So, projections for all needed fields have to be added into the query.
Hope this helps.
I need to search for the existence of a property that is within another object.
the collection contains documents that look like:
"properties": {
"source": {
"a/name": 12837,
"a/different/name": 76129
}
}
As you can see below, part of the query string is from a variable.
With some help from JohnnyHK (see mongo query - does property exist? for more info), I've got a query that works by doing the following:
var name = 'a/name';
var query = {};
query['properties.source.' + name] = {$exists: true};
collection.find(query).toArray(function...
Now I need to see if I can index the collection to improve the performance of this query.
I don't have a clue how to do this or if it is even possible to index for this.
Suggestions?
2 things happening in here.
First probably you are looking for sparse indexes.
http://docs.mongodb.org/manual/core/index-sparse/
In your case it could be a sparse index on "properties.source.a/name" field. Making indexes on field will dramatically improve your query lookup time.
db.yourCollectionName.createIndex( { "properties.source.a/name": 1 }, { sparse: true } )
Second thing. Always when you want to know whether your query is fast/slow, use mongo console, run your query and on its result call explain method.
db.yourCollectionName.find(query).explain();
Thanks to it you will know whether your query uses indexes or not, how many documents it had to check in order to complete query and some others useful information.
I would like to speed up an query on my mongoDB which uses $where to compare two fields in the document, which seems to be really slow.
My query look like this:
db.mycollection.find({ $where : "this.lastCheckDate < this.modificationDate})
What I would like to do is add a field to my document, i.e. isCheckDateLowerThenModDate, on which I could execute a probably much faster query:
db.mycollection.find({"isCheckDateLowerThenModDate":true})
I quite new to mongoDB an have no idea how to do this. I would appreciate if someone could give me some hints or examples on
How to initialize such a field on an existing collection
How to maintain this field. Which means how to update this field when lastCheckDate or modificationDate changes.
Thanks in advance for your help!
You are thinking in a right way!
1.How to initialize such a field on an existing collection.
Most simple way is to load each document (from your language), calculate this field, update and save.
Or you could perform an update via mongo shell:
db.mycollection.find().forEach(function(doc) {
if(doc.lastCheckDate < doc.modificationDate)
{
doc.isCheckDateLowerThenModDate = true;
}
else
{
doc.isCheckDateLowerThenModDate = false;
}
db.mycollection.save(doc);
});
2.How to maintain this field. Which means how to update this field when
lastCheckDate or modificationDate changes.
You have to do it yourself from your client code. Make some wrapper for update, save operations and recalculate this value each time there. To be absolutely sure that this update works -- write unit tests.
The $where clause is slow because it is evaluating each document using the JavaScript interpreter.
There are a few alternatives:
1) Assuming your use case is "look for records that need updating", take advantage of a sparse index:
add a boolean field like needsChecking and $set this whenever the modificationDate is updated
in your "check" procedure, find the documents that have this field set (should be fast due to the sparse index)
db.mycollection.find({'needsChecking':true});
after you've done whatever check is needed, $unset the needsChecking field.
2) A new (and faster) feature in MongoDB 2.2 is the Aggregation Framework.
Here is an example of adding a "isUpdated" field based on the date comparison, and then filtering the matching documents:
db.mycollection.aggregate(
{ $project: {
_id: 1,
name: 1,
type: 1,
modificationDate: 1,
lastCheckDate: 1,
isUpdated: { $gt:["$modificationDate","$lastCheckDate"] }
}},
{ $match : {
isUpdated : true,
}}
)
Some current caveats of using the Aggregation Framework are:
you have to specify fields to include aside from _id
the result is limited to the current maximum BSON document size (16Mb in MongoDB 2.2)