Let's say I have a collection named products. I want to make sure whenever a document in this collection is inserted or updated, I check if there is a viewCount field present or not. If it is, I let the create/update operation complete. Else, I want to add this field and set the value to zero.
The challenge is, there are a lot of such operations in the application code. So, I am looking for a way to accomplish this at DB level. Is this possible ?
Use findAndModify:
db.products.findAndModify({
query:{ yourQuery},
update:{ fieldsToCreate, $inc: { viewCount:1} },
new: true,
upsert: true
})
where fieldsToCreate is a partial document of the values you want to create if the document does not exist. The new document will be returned with viewCount set to 1, which is correct, since it was viewed 1 time when returned.
Related
I need to create a TTL Index in MongoDB and for that, I'm adding a new field "last_modified". I'm using the latest Python and pymongo in case this makes any difference.
After reading information on sparse and non-sparse indexes I understand that all documents that do not have "last_modified" will have this field added with the null value.
Is there a way to set some default value instead of null for those documents?
Alternatively, I'll have to update all documents in all DB instances using some migration function, but I would really like to do it clean...
Thanks in advance for any links or ideas!
I understand that all documents that do not have "last_modified" will have this field added with the null value.
No this is not true, sparse indexes just index documents where the field exists. documents without this field will just be out of the index converage.
Is there a way to set some default value instead of null for those documents? ... I'll have to update all documents in all DB instances ... to do it clean...
You have to run an update, there is no magic solution. Not sure why doing this is "not clean".
The update is super simple:
// this query will allow you to execute the update even if you started streaming new events with this field.
db.collection.updateMany({ last_modified: {$exists: false} }, { $set: { last_modified: defaultValue }})
EDIT(15/04/2016): As per the comments received in this question I think there is no direct method in mongodb to do so. In that case is it possible to do this with MongooseJS?
I am using mongodb, For one collection I need an 'lastModified' field, which should show me when in the last time any value of the document actually modified. That means, If I did an update query and all the other values are same, then the 'lastModified' shouldn't get updated.
Example:
Suppose I have a document in collection as :
{ _id: 1, status: "a", lastModified: ISODate("2016-04-02T01:11:18.965Z") }
when I update with
{$set:{"status":"a", "lastModified":"Current Time Here"}}
then the "lastModified" should not change
when I update with
{$set:{"status":"b", "lastModified":"Current Time Here"}}
then the "lastModified" should change
How to achieve this?
In my case I will call the update operation multiple times, and I don't want to get the 'lastModified' changed each in this case. Instead it should change only when the 'status' is actually modified.
I want to know how to reference the returned document attributes
from find and use it within modify. E.x. :
var totalNoOfSubjects = 5;
db.people.findAndModify( {
query: { name: "Tom", state: "active", rating: { $gt: 10 } },
sort: { rating: 1 },
update: { $set: { average: <reference score value returned by find>/totalNoOfSubjects} }
} );
My understanding is that findAndModify locks the document, hence I want to perform the update in the modify using the attributes found in the find. This will make the operation
atomic.
I am wondering if this is supported by mongo.
No, you cannot refer to values in the found document during the update portion of a findAndModify. It's the same as update in this respect.
As such, you cannot do this atomically as you need to first fetch the document and then craft the update or findAndMondify to contain the value computed from your fetched doc.
See https://jira.mongodb.org/browse/SERVER-458 for one way this may be addressed in the future.
Atomicity is exactly the reason for findAndModify.
As stated in the docs, Mongo will find one or more documents (matching the query specified) modify one document (using the update specified). The whole process is atomic. Default implementation has Mongo returning the found document (in its unchanged state). This can be modified using the new option.
I am trying to use upsert in MongoDB to update a single field in a document if found OR insert a whole new document with lots of fields. The problem is that it appears to me that MongoDB either replaces every field or inserts a subset of fields in its upsert operation, i.e. it can not insert more fields than it actually wants to update.
What I want to do is the following:
I query for a single unique value
If a document already exists, only a timestamp value (lets call it 'lastseen') is updated to a new value
If a document does not exists, I will add it with a long list of different key/value pairs that should remain static for the remainder of its lifespan.
Lets illustrate:
This example would from my understanding update the 'lastseen' date if 'name' is found, but if 'name' is not found it would only insert 'name' + 'lastseen'.
db.somecollection.update({name: "some name"},{ $set: {"lastseen": "2012-12-28"}}, {upsert:true})
If I added more fields (key/value pairs) to the second argument and drop the $set, then every field would be replaced on update, but would have the desired effect on insert. Is there anything like $insert or similar to perform operations only when inserting?
So it seems to me that I can only get one of the following:
The correct update behavior, but would insert a document with only a subset of the desired fields if document does not exist
The correct insert behavior, but would then overwrite all existing fields if document already exists
Are my understanding correct? If so, is this possible to solve with a single operation?
MongoDB 2.4 has $setOnInsert
db.somecollection.update(
{name: "some name"},
{
$set: {
"lastseen": "2012-12-28"
},
$setOnInsert: {
"firstseen": <TIMESTAMP> # set on insert, not on update
}
},
{upsert:true}
)
There is a feature request for this ( https://jira.mongodb.org/browse/SERVER-340 ) which is resolved in 2.3. Odd releases are actually dev releases so this will be in the 2.4 stable.
So there is no real way in the current stable versions to do this yet. I am afraid the only method is to actually do 3 conditional queries atm: 1 to check the row, then a if to either insert or update.
I suppose if you had real problems with lock here you could do this function with sole JS but that's evil however it would lock this update to a single thread.
I am trying to use upsert in MongoDB to update a single field in a document if found OR insert a whole new document with lots of fields. The problem is that it appears to me that MongoDB either replaces every field or inserts a subset of fields in its upsert operation, i.e. it can not insert more fields than it actually wants to update.
What I want to do is the following:
I query for a single unique value
If a document already exists, only a timestamp value (lets call it 'lastseen') is updated to a new value
If a document does not exists, I will add it with a long list of different key/value pairs that should remain static for the remainder of its lifespan.
Lets illustrate:
This example would from my understanding update the 'lastseen' date if 'name' is found, but if 'name' is not found it would only insert 'name' + 'lastseen'.
db.somecollection.update({name: "some name"},{ $set: {"lastseen": "2012-12-28"}}, {upsert:true})
If I added more fields (key/value pairs) to the second argument and drop the $set, then every field would be replaced on update, but would have the desired effect on insert. Is there anything like $insert or similar to perform operations only when inserting?
So it seems to me that I can only get one of the following:
The correct update behavior, but would insert a document with only a subset of the desired fields if document does not exist
The correct insert behavior, but would then overwrite all existing fields if document already exists
Are my understanding correct? If so, is this possible to solve with a single operation?
MongoDB 2.4 has $setOnInsert
db.somecollection.update(
{name: "some name"},
{
$set: {
"lastseen": "2012-12-28"
},
$setOnInsert: {
"firstseen": <TIMESTAMP> # set on insert, not on update
}
},
{upsert:true}
)
There is a feature request for this ( https://jira.mongodb.org/browse/SERVER-340 ) which is resolved in 2.3. Odd releases are actually dev releases so this will be in the 2.4 stable.
So there is no real way in the current stable versions to do this yet. I am afraid the only method is to actually do 3 conditional queries atm: 1 to check the row, then a if to either insert or update.
I suppose if you had real problems with lock here you could do this function with sole JS but that's evil however it would lock this update to a single thread.