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.
Related
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.
I am new to Sails and Mongo Db. Currently I am trying to implement a CRUD Function using Sails where I want to save user details in Mongo db.In the model I have the following attributes
"id":{
type:'Integer',
min:100,
autoincrement:true
},
attributes: {
name:{
type:'String',
required:true,
unique:true
},
email_id:{
type:'EMAIL',
required:false,
unique:false
},
age:{
type:'Integer',
required:false,
unique:false
}
}
I want to ensure that the _id is overridden with my values starting from 100 and is auto incremented with each new entry. I am using the waterline model and when I call the Api in DHC, I get the following output
"name": "abc"
"age": 30
"email_id": "abc#gmail.com"
"id": "5587bb76ce83508409db1e57"
Here the Id given is the object Id.Can somebody tell me how to override the object id with an Integer starting from 100 and is auto incremented with every new value.
Attention: Mongo id should be unique as possible in order to scale well. The default ObjectId is consist of a timestamp, machine ID, process ID and a random incrementing value. Leaving it with only the latter would make it collision prone.
However, sometimes you badly want to prettify the never-ending ObjectID value (i.e. to be shown in the URL after encoding). Then, you should consider using an appropriate atomic increment strategy.
Overriding the _id example:
db.testSOF.insert({_id:"myUniqueValue", a:1, b:1})
Making an Auto-Incrementing Sequence:
Use Counters Collection: Basically a separated collection which keeps track the last number of the sequence. Personally, I have found it more cohesive to store the findAndModify function in the system.js collection, although it lacks version control's capabilities.
Optimistic Loop
Edit:
I've found an issue in which the owner of sails-mongo said:
MongoDb doesn't have an auto incrementing attribute because it doesn't
support it without doing some kind of manual sequence increment on a
separate collection or document. We don't currently do this in the
adapter but it could be added in the future or if someone wants to
submit a PR. We do something similar for sails-disk and sails-redis to
get support for autoIncremeting fields.
He mentions the first technique I added in this answer:
Use Counters Collection. In the same issue, lewins shows a workaround.
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.
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).