I'm new in MongoDB, and i would like to know if there is a way to create a dynamic view inside MongoDB.
Let me be more precise :
In mongo i have a collection with financial datas, and an GUI interface wich display the datas.
But each users could reduce the datas by adding or removing columns to the grid, and filter the grid : a classic usecase.
What i would like to do, is to create a collection for each user that listen to the master table, according to the users filters: something like this :
mongo.createView(masterCollection, filters, mapReduce)
In this scenario, mongo update each view, each time a modification is done in the master collection (update, delete, insert).
I could do something like this manualy : create a table for a user, and use a tailable cursor on my master collection with the user filters and mapReduce, and the add, remove, or update the document in the user collection.
But, i have up to 100 simultaneous users, and it would open and keep alive 100 tailable cursors on the primary collection. I don't know enough mongo, but i think it's not a best practice to do something like this.
Actualy i have a thread for each user that get data for the collection, according to the user filters, every 5 secondes.
Could you please let me now if there is a native mongo way to handle this scenario or a way to create a user view in mongo.
Thank you
Starting with MongoDB v3.4 (community and enterprise edition), there is a support for creating read only views from existing collections or other views. This feature utilises MongoDB aggregation pipeline.
To create a view from the mongo shell, you could do:
db.createView(<view>, <source>, <pipeline>, <collation> )
Using your scenario above, you could create:
db.createView(<"user_view_name">, <"source_collection_name">, <"aggregation pipeline operators">)
See all the available Aggregation Pipeline Operators - i.e. not only you could filter, you could also modify the document structure.
See MongoDB Views behaviour for more information.
MongoDB Enterprise has a feature called 'Single View' which implements database views. It's more for aggregating data from multiple tables (e.g. parent/child relationships), and may be more than what you're looking for but is worth checking out. The downside, it's only available in the pricey Enterprise edition.
Check out the description here
Related
Does mongodb have some analogue of SHOW CREATE TABLE in mysql which shows create query for collection?
Or can I create another collection like existing one with all settings?
There no analogs for SHOW CREATE TABLE.
But maybe you will find a some usufull functions there https://docs.mongodb.com/manual/reference/command/nav-administration/
For example the information about indexes you can retrieve with getIndexes function.
Create the indexes you can via createIndexes function.
Example:
var indexes = db.collection.getIndexes();
db.collection.createIndexes(indexes);
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There is no good answer to this question because the schema involved when dealing with schema-less databases like MongoDB is dictated by the application, not the database.
The database will shove in whatever it is given as there is nothing enforcing a consistent document structure within a given collection, even though all access to the database should be controlled through some kind of wrapper. In conclusion, the only place you should look at for the schema is your model classes.
Is there a way to switch off the ability of mongo to sporadically create dbs and collections as soon as it sees one in a query. I run queries on the mongo console all the time and mistype a db or collection name, causing mongo to just create one. There should be a switch to have mongo only explicitly create dbs and collections. I can't find one on the docs.
To be clear, MongoDB does not auto create collections or databases on queries. For collections, they are auto created when you actually save data to them. You can test this yourself, run a query on a previously unknown collection in a database like this:
use unknowndb
db.unknowncollection.find()
show collections
No collection named "unknowncollection" shows up until you insert or save into it.
Databases are a bit more complex. A simple "use unknowndb" will not auto create the database. However, if after you do that you run something like "show collections" it will create the empty database.
I agree, an option to control this behavior would be great. Happy to vote for it if you open a Jira ticket at mongoDB.
No, implicit creation of collections and DBs is a feature of the console and may not be disabled. You might take a look at the security/authorization/role features of 2.6 and see if anything might help (although there's not something that exactly matches your request as far as I know).
I'd suggest looking through the MongoDB issues/bug/requests database system here to and optionally add the feature request if it doesn't already exist.
For people who are using Mongoose, a new database will get created automatically if your Mongoose Schema contains any form of index. This is because Mongo needs to create a database before it can insert said index.
Is there a way to switch off the ability of mongo to sporadically create dbs and collections as soon as it sees one in a query. I run queries on the mongo console all the time and mistype a db or collection name, causing mongo to just create one. There should be a switch to have mongo only explicitly create dbs and collections. I can't find one on the docs.
To be clear, MongoDB does not auto create collections or databases on queries. For collections, they are auto created when you actually save data to them. You can test this yourself, run a query on a previously unknown collection in a database like this:
use unknowndb
db.unknowncollection.find()
show collections
No collection named "unknowncollection" shows up until you insert or save into it.
Databases are a bit more complex. A simple "use unknowndb" will not auto create the database. However, if after you do that you run something like "show collections" it will create the empty database.
I agree, an option to control this behavior would be great. Happy to vote for it if you open a Jira ticket at mongoDB.
No, implicit creation of collections and DBs is a feature of the console and may not be disabled. You might take a look at the security/authorization/role features of 2.6 and see if anything might help (although there's not something that exactly matches your request as far as I know).
I'd suggest looking through the MongoDB issues/bug/requests database system here to and optionally add the feature request if it doesn't already exist.
For people who are using Mongoose, a new database will get created automatically if your Mongoose Schema contains any form of index. This is because Mongo needs to create a database before it can insert said index.
It is not recommended to use ElasticSearch as the only storage from some obvious reasons like security, transactions etc. So how it is usually used together with other database?
Say, I want to store some documents in MongoDB and be able to effectively search by some of their properties. What I'd do would be to store full document in Mongo as usual and then trigger insertion to ElasticSearch but I'd insert only searchable properties plus MongoDB ObjectID there. Then I can search using ElasticSearch and having ObjectID found, go to Mongo and fetch whole documents.
Is this correct usage of ElasticSearch? I don't want to duplicate whole data as I have them already in Mongo.
The best practice is for now to duplicate documents in ES.
The cool thing here is that when you search, you don't have to return to your database to fetch content as ES provide it in only one single call.
You have everything with ES Search Response to display results to your user.
My 2 cents.
You may like to use mongodb river take a look at this post
There are more issue then the size of the data you store or index, you might like to have MongoDB as a backup with "near real time" query for inserted data. and as a queue for the data to indexed (you may like to use mongodb as cluster with the relevant write concern suited for you application
I am currently evaluating mongodb for a project I have started but I can't find any information on what the equivalent of an SQL view in mongodb would be. What I need, that an SQL view provides, is to lump together data from different tables (collections) into a single collection.
I want nothing more than to clump some documents together and label them as a single document. Here's an example:
I have the following documents:
cc_address
us_address
billing_address
shipping_address
But in my application, I'd like to see all of my addresses and be able to manage them in a single document.
In other cases, I may just want a couple of fields from collections:
I have the following documents:
fb_contact
twitter_contact
google_contact
reddit_contact
each of these documents have fields that align, like firstname lastname and email, but they also have fields that don't align. I'd like to be able to compile them into a single document that only contains the fields that align.
This can be accomplished by Views in SQL correct? Can I accomplish this kind of functionality in MongoDb?
The question is quite old already. However, since mongodb v3.2 you can use $lookup in order to join data of different collections together as long as the collections are unsharded.
Since mongodb v3.4 you can also create read-only views.
There are no "joins" in MongoDB. As said by JonnyHK, you can either enormalize your data or you use embedded documents or you perform multiple queries
However, you could also use Map-Reduce.
or if you're prepared to use the development branch, you could test the new aggregation framework though maybe it's too much? This new framework will be in the soon-to-be-released 2.2, which is production-ready unlike 2.1.x.
Here's the SQL-Mongo chart also, which may be of some help in your learning.
Update: Based on your re-edit, you don't need Map-Reduce or the Aggregation Framework because you're just querying.
You're essentially doing joins, querying multiple documents and merging the results. The place to do this is within your application on the client-side.
MongoDB queries never span more than a single collection as there is no support for joins. So if you have related data you need available in the results of a query you must either add that related data to the collection you're querying (i.e. denormalize your data), or make a separate query for it from another collection.
I am currently evaluating mongodb for a project I have started but I
can't find any information on what the equivalent of an SQL view in
mongodb would be
In addition to this answer, mongodb now has on-demand materialized views. In a nutshell, this feature allows you to use aggregate and $merge (in 4.2) to create/update a quick view collection that you can query from faster. The strategy is used to update the quick view collection whenever the main collection has a record change. This has the side effect unlike SQL of increasing your data storage size. But the benefits can be huge depending on your querying needs.