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?
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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.
We have two documents that have merged and they now have one one ObjectId.
There exists a configuration document that may have references to the old ObjectId. The old ObjectID can exist all over this document which is full of nested arrays and lists.
We want to do a simple find and replace on this document, preferably without replacing the entire document itself.
Is there a generic way to set every field that has ObjectIdA as a value and replace it with ObjectIdB?
There's no way to do that, no. You need to perform updates on all possible paths explicitly.
I have some JSON entries in MongoDB but I plan to add new attributes into all my entries, like how you would create a new column and appoint a default value in RDBMS.
Is there any way to do it with MongoDB?
If you mean that every new document needs to be guaranteed to have the new fields, I'm afraid that it's not possible in MongoDB itself, because it is schemaless. I am however not familiar with mongoose, and there can be a solution using it.
If, like your title suggests, you just want to add the new fields to all existing documents you can do it with an update with empty filter like this:
db.collection.updateMany({}, {"newfield1":"val1","newfield2":"val2"})
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.
I have collections with huge amount of Documents on which I need to do custom search with various different queries.
Each Document have boolean property. Let's call it "isInTop".
I need to show Documents which have this property first in all queries.
Yes. I can easy do sort in this field like:
.sort( { isInTop: -1 } );
And create proper index with field "isInTop" as last field in it. But this will be work slowly, as indexes in mongo works best with unique fields.
So is there is solution to show Documents with field "isInTop" on top of each query?
I see two solutions here.
First: set Documents wich need to be in top the _id from "future". As you know, ObjectId contains timestamp. So I can create ObjectId with timestamp from future and use natural order
Second: create separate collection for Ducuments wich need to be in top. And do queries in it first.
Is there is any other solutions for this problem? Which will work fater?
UPDATE
I have done this issue with sorting on custom field which represent rank.
Using the _id field trick you mention has the problem that at some point in time you will reach the special time, and you can't change the _id field (without inserting a new document and removing the old one).
Creating a special collection which just holds the ones you care about is probably the best option. It gives you the ability to logically (and to some extent, physically) separate the documents.
Newly introduced in mongodb there is also support for a "sparse" index which may fulfill your needs as well. You could only set the "isInTop" field when you want it to be special, and then create a sparse index on it which would not have the problems you would normally have with a single indexed boolean field (in btrees).