How can I create a unique index for my mongodb collection that will be incremented for each insert into the collection? I want to do it from my mongodb, not using mongoose. Is there any possible way ?
Each driver provides an ObjectId generator which creates unique ids.
No driver can generate sequential integers in a globally unique manner, hence this isn't something that is provided. If you want this functionality you need to implement it yourself.
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I am using MongoDB with Spring Boot. And I saw the below option:
#Indexed(unique=true)
which means that field is both indexed and unique, can we make it only unique.
I mean for my case unique is enough, I do not want to index that field, can we achieve that?
i am new to NOSQL(mongo db),i am having a specific question, if i want to create multiple auto incremented field in multiple collections,do i need to create counter collection for each an every collection or is there any alternative way and how is it possible?
Is there a way I can find the last inserted document and the field, i.e. _id or id such that I can increment and use when inserting a new document?
The issue is that I create my own id count, but I do not store this, now I've deleted records, I cannot seem to add new records because I am attempting to use the same id.
There is no way to check insertion order in MongoDB, because the database does not keep any metadata in the collections regading the documents.
If your _id field is generated server-side then you need to have a very good algorithm for this value in order to provide collision avoidance and uniqueness while at the same time following any sequential constraints that you might have.
Is MongoDB _id unique by default, or do I have to set it to unique?
For the most part, _id in mongodb is unique enough. There is one edge case where it's possible to generate a duplicate id though:
If you generate more than 16,777,215 object ids in the same single second, while running in one process while on the same machine then you will get a duplicate id due to how object ids are generated. If you change any one of those things like generating an id in a different process or on a different machine, or at a different unix time, then you won't get a duplicate.
Let me know if you ever manage to pull this off with a realistic use case. Apparently google only gets around 70,000 searches a second and those are all processed on different machines.
All documents contain an _id field. All collections (except for capped ones) automatically create unique index on _id.
Try this:
db.system.indexes.find()
ok .. short version
YES YES YES
_id uniqid by default , mongoDB creates index on _id by default and you do not need any settings
According to MongoDB's manual the answer is yes, it's unique by default:
MongoDB creates the _id index, which is an ascending unique index on the _id field, for all collections when the collection is created. You cannot remove the index on the _id field.
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Different from other RDBMS, Mongodb document's Id is generated on the client side. This functionality is usually implemented in the drivers of various programming languages.
The Id is string with 12 bytes length, which consists of several parts as follows:
TimeStamp(4 bytes) + MachineId(3 bytes) + ProcessId(2 bytes) + Counter(3 bytes)
Based on this pattern, it's extremely unlikely to have two Ids duplicated.
{ "_id" : ObjectId("4c2209f9f3924d31102bd84a"), "name" : "mongo" }
what exactly is the purpose of objectId? It's a big number that is generated using a timestamp.
If I see any nosql which is key-value, I query with key the value.
Here we use key and value in the as the data and use find () function.
So, I am trying to understand when we really need the objectid?
What are the reasons behind that giving access to the user to view the value of the object ID?
After reading the docs, one basic question is mongo DB as hash table type implementation?
After readying doc..one basic question is mongo DB as hash table type implementation?
MongoDB used BSON, a binary form of JSON. A JSON object is basically just a "hashtable" or a set of key / value pairs.
what exactly is the use of object id? that is a big number that is generated with time.
In MongoDB, each document you store must have an _id. If you do not set a value for _id, then MongoDB will automatically generate one for you. If you have a unique key when you are inserting the object, you can use that instead. For details on the ObjectId see here.
If I see any nosql which is key-value, I query with key the value.
MongoDB is not just key-value. MongoDB supports multiple indexes on a single collection, you can query on many different fields, not just the "key" or "id".
Object ID is similar to primary key in RDBMS
Whenever u insert a new document, mongodb will generate object ID.
Object ID is a 12 byte BSON Type.
First 4 Byte represents timestamp
next 3 byte unique machine identifier
next 2 byte process id
next 3 byte random increment counter
Returns the equivalent 16 digit hex