I would like to know how to delete, for example, the last 100 documents inserted in my collection.
How is it possible from the shell?
You should be able to use the _id to sort on last inserted, as outlined in the answer here:
db.coll.find().sort({_id:-1}).limit(100);
It looks like using limit on the standard mongo remove operation isn't supported though, so you might use something like this to delete the 100 documents:
for(i=0;i<100;i++) {
db.coll.findAndModify({query :{}, sort: {"_id" : -1}, remove:true})
}
See the docs for more on findAndModify.
Related
I am looking to a way to FindAndModify not more than 5 documents in MongoDB.
This is collection for queue which will be processed from multiple workers, so I want to put it into single query.
While I cannot control amount of updates in UpdateOptions parameter, is it possible to limit number of rows which will be found in filterDefinition?
Problem 1: findAndModify() can only update a single document at a time, as per the documentation. This is an inherent limit in MongoDB's implementation.
Problem 2: There is no way to update a specific number of arbitrary documents with a simple update() query of any kind. You can update one or all depending on the boolean value of your multi option, but that's it.
If you want to update up to 5 documents at a time, you're going to have to retrieve these documents first then update them, or update them individually in a foreach() call. Either way, you'll either be using something like:
db.collection.update(
{_id: {$in: [ doc1._id, doc2._id, ... ]}},
{ ... },
{multi: true}
);
Or you'll be using something like:
db.collection.find({ ... }).limit(5).forEach(function(doc) {
//do something to doc
db.collection.update({_id: doc._id}, doc);
});
Whichever approach you choose to take, it's going to be a workaround. Again, this is an inherent limitation.
I've done a bit of research on this and haven't come across anything that jumps out at me immediately as what I'm looking for.
Say we have a document (or documents) in a collection that look something like this:
//First example document
{
"_id": "JK",
"letters": ["J", "K"]
}
//Second example document
{
"_id": "LM",
"letters": ["L"]
}
So I run a query like the one below to see if I have any matching documents and of course I don't so I expect to get null.
> db.example.findOne({"_id": "LM", "letters": {"$in": ["M"]}})
null
So I do an update and add "M" to the letters array on the documents (syntax may not be quite right):
> db.example.update({"_id": "LM"}, {"$addToSet": {"letters": "M"}})
I run the possibility of not having a matching _id, so the findOne would would also return null given the example documents in the collection for this query.
> db.example.findOne({"_id": "AB", "letters": {"$in": ["A"]}})
null
Based on the way I've constructed the above query, I get null back when "A" is not found in letters or the _id of "AB" is not found on any document. In this case I know that this document isn't in there because I know what is in the collection.
What I'd like to do is keep my update query from above with $addToSet and modify it to use upsert WHILE ALSO specifying the document to insert in the event that $addToSet fails due to the document not existing to cut down on database transactions. Is this possible? Or will I have to break up my queries a bit in order to accommodate this?
Because this information may influence answers:
I do my querying through mongo shell and pymongo.
mongo version: 2.6.11
pymongo version: 2.8
Thanks for any help!
EDIT: So after a break and a bit more digging, it seems setOnInsert does what I was looking for. I do believe that this probably solves my issue, but I've not had a chance to test yet.
Hello I'm new to Mongodb, I am currently trying to update the last document in a query result but having trouble doing so.
I know how to get the last document using
db.collection.find().sort({$natural:-1}).limit(1)
but how do I update this? I tried doing:
db.collection.update(db.collection.find().sort({$natural:-1}).limit(1))
But that didn't work. And I don't think:
db.collection.update(query,update,option).sort({$natural:-1}).limit(1))
would do what i want. I checked the official documentation but couldn't find anything on querying only for the last document.
You can use findAndModify to perform an update that requires sorting to identify the document to update:
db.test.findAndModify({
query: {},
sort: {$natural: -1},
update: {$set: {foo: 'bar'}}
})
You can also do it this way:
var id = db.collection.find().sort({$natural:-1}).limit(1)[0]['_id'];
db.collection.update({_id: id},{...})
I'm using MongoDB 2.6.8. According to the $maxTimeMS reference, these two queries should behave identically:
> db.collection.find({}).maxTimeMS(100)
> db.collection.find({}, {$maxTimeMS: 100})
The first query does exactly what I want, but the second query restricts only returns the object IDs of the documents. I tried increasing $maxTimeMS to 100000000 and there was no change in behavior.
Why am I getting different results for these two commands?
You found a bug in the documentation.
The reason that db.collection.find({}, {$maxTimeMS: 100}) returns only the _id of each object is because mongoDB is interpreting the {$maxTimeMS: 100} portion of the query as a projection.
So it thinks you want to see all the documents and you want to see the fields _id and the field $maxTimeMS. Of course, none of your documents have a $maxTimeMS field, so they only show the _id.
The proper way to perform the query you want without the shortcut is:
db.collection.find({ $query: {}, $maxTimeMS: 100 })
I have sample products table and would like to update multiple documents using _id field. Every time, I try this it only updates the first doc in the $in clause I mentioned , not updating all.
db.products.update({_id:{$in:[ObjectId("507d95d5719dbef170f15bff"),
ObjectId("507d95d5719dbef170f15c01"), ObjectId("507d95d5719dbef170f15c00")]}},
{$set:{'monthly_price':7865}}, {multi:true})
You can first try running find on the products table to make sure that all the object ids actually exist.
You can also try explain command
give this a try:
db.<collection>.update( { query }, {$set: {monthly_price:7865}}, false, true)
I think the object id's which you have given doesn't exist in the collection.
I tried using the following query and it worked for me.
db.test.update({_id:{$in:[ObjectId("57b33483e5b9ce24f4910855"),
ObjectId("57b33483e5b9ce24f4910856"),
ObjectId("57b33489e5b9ce24f4910857"),
ObjectId("57b33491e5b9ce24f4910858")
]
}
},
{$set{'isCurrentStatus':true}},
{multi:true}
)