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"
},
$setOnInsert: {
"firstseen": <TIMESTAMP> # set on insert, not on update
}
},
{upsert:true}
)
There is a feature request for this ( https://jira.mongodb.org/browse/SERVER-340 ) which is resolved in 2.3. Odd releases are actually dev releases so this will be in the 2.4 stable.
So there is no real way in the current stable versions to do this yet. I am afraid the only method is to actually do 3 conditional queries atm: 1 to check the row, then a if to either insert or update.
I suppose if you had real problems with lock here you could do this function with sole JS but that's evil however it would lock this update to a single thread.
Related
I am trying to update the document if the document is found otherwise insert as follows
upserts = [UpdateOne({"$and":[{'_id': x['_id']},{'time':{"$lt": x['time']}}]},
{'$setOnInsert': x, '$set':{'time':x['time']}},
upsert=True) for x in batch]
collection.bulk_write(upserts)
However, I am getting the following error:
Updating the path 'time' would create a conflict at 'time'
I understand that it's happening because time key is getting updated in both set and setOnInsert. I cannot specify fields in setOnInsert as the keys are not fixed. In case excluding a field in setOnInsert is allowed, then I can exclude time in that.
How can I work this around?
When the document is inserted, both the $set and $setOnInsert documents will be processed.
The query executor is refusing to update the same field twice in a single update.
You might try using a dictionary comprehension to remove the time field from the $setOnInsert, like:
'$setOnInsert': {i:x[i] for i in x if i!='time'}
I have to add new value (or edit actual) company. I tried this code in console:
db.users.update({email: /debute/},{company: "test"})
But now, in database I have only _id and company. Why other values removed? Or how can I prevent of removing other values in future?
By default, the update function replaces the entire document with the document you pass. But you can also use it to only replace individual fields and leave the others alone by using the $set operator.
db.users.update({email: /debute/},{ $set: { company: "test"} } );
You might also want to specify a third argument { multi: true } to the update. Otherwise it will only update the first document it finds which matches the condition.
You need to use an update operator on order to update an existing document, your code replaces the document with the new document. Here is how to do an update:
db.users.update({email: /debute/},{$set: {company: "test"}})
In the context of MongoDB, what is upsert?
Is this an update and insert?
Just curious as I see the usage of this term in many articles and documentation on the MongoDB website.
From the documentation: An operation that will either update the first document matched by a query or insert a new document if none matches. The new document will have the fields implied by the operation.
See http://docs.mongodb.org/manual/reference/glossary/#term-upsert
To put it into SQL terms it is much like a ON DUPLICATE KEY ... UPDATE except that it isn't so verbose in how to query for it.
So essentially it is when you query for an update document, MongoDB doesn't find it and so inserts it.
The condition for the upsert accepts all the same stuff as a normal update except it also has the $setOnInsert ( http://docs.mongodb.org/manual/reference/operator/update/setOnInsert/ ) operator which allows you to define a set of fields that will only be taken into consideration on an insert.
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 have a MongoDB collection as follows:
comment_id (number)
comment_title (text)
score (number)
time_score (number)
final_score (number)
created_time (timestamp)
Score is and integer that's usually updated using $inc 1 or -1 whenever someone votes up or down for that record.
but time_score is updated using a function relative to timestamp and current time and other factors like how many (whole days passed) and how many (whole weeks passed) .....etc
So I do $inc and $dec on db directly but for the time_score, I retrieve data from db calculate the new score and write it back. What I'm worried about is that in case many users incremented the "score" field during my calculation of time_score then when I wrote time_score to db it'll corrupt the last value of score.
To be more clear does updating specific fields in a record in Mongo rewrites the whole record or only the updated fields ? (Assume that all these fields are indexed).
By default, whole documents are rewritten. To specify the fields that are changed without modifying anything else, use the $set operator.
Edit: The comments on this answer are correct - any of the update modifiers will cause only relevant fields to be rewritten rather than the whole document. By "default", I meant a case where no special modifiers are used (a vanilla document is provided).
The algorithm you are describing is definitely not thread-safe.
When you read the entire document, change one field and then write back the entire document, you are creating a race condition - any field in the document that is modified after your read but before your write will be overwritten by your update.
That's one of many reasons to use $set or $inc operators to atomically set individual fields rather than updating the entire document based on possibly stale values in it.
Another reason is that setting/updating a single field "in-place" is much more efficient than writing the entire document. In addition you have less load on your network when you are passing smaller update document ({$set:{field:value}}, rather than entire new version of the document).