I have models based on schemas, for ex. Users, Events, Rooms. All of these entities can have comments enabled. Comments are stored on a seperate model Comments, since I cannot control how many comments each entity might end up having. I want to be able to Find the entity by id of a comment and make the search through all the models I have. Basically something like this:
[list of models to search].Find( { comment_id: id });
Any ideas?
mongodb can search only one collection per command, so for your use case you would need a separate query for each collection.
You may consider storing all your comments in a single collection and associating them back out to their parent model by reference with modelId and modelName fields. I have used that schema successfully. It sounds like you are storing your comments as an array of comment IDs in your parent model, which seems less practical than either fully embedding the comments or fully separating them.
And there's nothing to stop you from saving the data into multiple collections, so in the 'search' collection and also the separate 'users', 'events' collections.
You might even want to use a technology like solr or elastic search, to index your data.
Related
I am trying to implement relations on collections. My requirement is
Post request 1, json body:
{
"username":"aaa",
"password":"bbb",
"role":"owner",
"company":"SAS"
}
Post request 2, creating from first document so I got company name from previous json body:
{
"username":"eee",
"password":"fff",
"role":"engineer",
"company":"SAS"
}
Post request 3, creating from first document so I got company name from previous json body:
{
"username":"uuu",
"password":"kkk",
"role":"engineer",
"company":"SAS"
}
Post request 4, next company json body:
{
"username":"hhh",
"password":"ggg",
"role":"owner",
"company":"GVG"
}
Here company is foreign key field. How can I achieve company with id field without failing one another like transactions.
In mysql I will create two tables company, user and using transactions i will insert in both tables in single post using id's if any update in company name id will remain same for owner and engineer.
How can I achieve these in mongodb, with node.js?
In online searches I have found most suggest avoid transactions and using mongodb functionalities like mongodb embedded.
I would suggest you to start with making schemas for user and company using mongoose. Its an ODM(object document mapper) which is almost always used with node.js and mongodb
Now this is one to many relations. In relational databases as you have mentioned, you would make a company table and a user table.
In mongodb it "depends". If its one to "few" relationship you would just nest the users array into company's collection. Then since you are only updating a single document(pushing user to users array in company's document), you wont be needing any transactions. Single document update is always atomic(no matter how many fields you update on the same document).
But if each company can have large number of users(ever growing nested array is not good, as it can cause data fragmentation and bad performance), then its better to store the company's id in user's document. And even in this case you would not need transaction, since you are not updating the company's document.
Another reason for storing user as separate collection, is query issues. If you just want to query users its difficult if they are nested in companies. So basically you need to consider how you will query and figure out the number of relations then decide to nest of store is separate collections.
First of all, you should notice that Mongo is document-oriented DB, not a relation one. So if you need transactions and relation model, probably you should try to use any SQL relative database? Especially if you are more familiar with them?
About relation and data modeling: you should this article (or even entire part) at official Mongo docs, Data Modelling.
TL:DR, you could create two separate collections (the same as tables in SQL) like employees, and companies (by default, collection's name will be in plural forms). And store data separately.
So you employees will be stored like you mention above, but companies will be like:
{
_id: ObjectID("35473645632")
name: "SAS"
}, ...
and as for your employees collection, you should store not like, "company":"SAS", but, "company":"ObjectID("35473645632"), or even as array if you want it too. But don't forgot to edit you schema than.
You could use not just MongoDB's default _id but your own one, it could be any unique number/string combination
So, if your company will be renamed, your connection with other documents (employees) still will be there.
To request all/any of your employees with company name's you should use .aggregation framework with $lookup, instead of .find.
Im using MongoDB for storing information for a nodeJS application and a doubt came to my mind, after finding that it is possible to use ObjectID to ref another document. As it is known, MongoDB is a no-SQL db, so there is no need for consistency whatsoever and information can be repeated.
So, lets say, I have a collection for users and one of their field values is 'friends', which is an array of this user friends (another users). What is the best practice, saving all the user info there (thus repeating the same thing over and over again throughout the DB) or saving only the ObjectID of the friendUser (makes way more sense to me, but it sounds kinda SQL mindset). I'm not really getting when should I use each of the options, so a professional opinion would be very appreciated.
To model relationships between connected data, you can reference a document or embed it in another document as a subdocument.
Referencing a document does not create a “real” relationship between these two documents as does with a relational database.
Referencing documents is also known as normalization. It is good for data consistency but creates more queries in your system.
Embedding documents is also known as denormalization.
The benefit of Embedding approach is getting all the data you need about a document and it’s sub-document(s) with a single query. Therefore, this approach is very fast. The drawback is that data may not stay as consistent in the database.
Important
If one document is to be used by many documents then better create a referenced doc.
i. Will Save Space.
ii. if any change required, we will have to update only the referenced doc
instead of updating many docs.
Create sub doc(embedded)
i. If another document is not dependent on the subdocument.
Source: https://vegibit.com/mongoose-relationships-tutorial/
Recommended reading:
MongoDB Applied Design Patterns by Rick Copeland
To Embed or Reference
So I have this MEAN-project I hobby on in my spare time.
Right now I'm setting up users and rooms, and am a bit hesitant about progressing further, as I am unsure about the proper protocol of db's in general.
As I recall, you're not supposed to have a Many-To-Many relationship; rather, you're supposed to have a relation table.
Right now, my User schema has an array of rooms he is in, and my Room schema has an array of users tied to it (the third and last schema being Message).
Is it better to have a userroomrelation doc that holds a PK, an id of one room, and then a list of all users in this room?
Thanks,
Rasmus
MongoDB isn't a relational database like *SQL databases (hence why MongoDB is called NoSQL), so using a relation table is fairly inefficient in Mongo. Holding an array of user _id's in the room collection is about as ideal as you could get, if you don't want repeat data.
Here are some more indepth answers on many-to-many in MongoDB.
How can a User be in more than one room? Isn't that just a property on the User? And if you index that why would you also need to store it on the Room?
There is no one right way, it really depends on how many of each object you have and if it's a small number (as rooms and users implies) you may be better with a simpler and more robust (cannot store impossible values) approach like having a single property on a user RoomId. That's never going to be inconsistent and if you need to find the set of users in a given room it's a cheap query.
In MongoDB you CAN denormalize the data and store an array on each object containing part or all of the other object, but you can also create an effective join collection if you want to.
For example you could have a collection {UserId, RoomId, DateTimeEntered, DateTimeLeft} with appropriate indexes which allows you to quickly find all the users in a given room at a given time. Once you have the set of Ids you could go load them if you need them for display OR you could add the fields you need for display to this table {UserId, UserName, ...} BUT then you have the problem of maintaining that data if it ever changes OR keeping it intact if you need to know that when they entered the room that's what it was called.
There are also a TON of other questions on StackOverflow relating to how you should store related data, I suggest you go read those also.
Mongoose doesn't appear to support Mongo DBRefs. Apparently they released "DBRef" support but it was actually just plain references (no ability to reference documents from different collections). I've finally managed to craft a schema that allows me to hold an array of ObjectID references and populate them, which is great for certain parts of my schema, but it would be extremely convenient if I could use proper DBRefs to create an array that lets me refer to documents from a number of collections.
Luckily(?) there's a module that can monkey patch DBRef support into mongoose: https://github.com/goulash1971/mongoose-dbref
Unluckily, I can't make any sense of the documents. The best I can tell is that there is no ability to use DBRefs in an array (there is a 'fetch' method to dereference, but it takes a single dbref); 'populate' doesn't seem to be patched to fill in DBRefs, and I can't tell how I'm supposed to assign a DBRef given a source document [collection.items.push(?????)].
From the internet, it appears that I can assign an object of the form { $id: document._id, $ref: 'Collection' } -- when logging the result, it appears to have "taken" as a DBRef data type, but I am unsure if this is correct since I cannot seem to do anything useful with it (turn the ref back into a document).
What I really want is a way to represent an ordered list of items from multiple collections; any solution to this is fine by me, but so far DBRefs are the best I've got. Help?
A DBRef (as explained in detail here) is a tuple containing the ObjectId, collection name, and possibly the database container name of a referenced object in another collection.
Internally in the MongoDB server these serve no purpose and are just data within a document. The point is for use in some drivers and ODM implementations to allow for some sort of automatic expansion by issuing additional queries to the server in order to have the data that is elsewhere appear to be an ordinary sub-document part of the referencing document. This can be automatic or a lazy load depending on the implementation, but is always done over the wire and processed on the client side. The server will do nothing to traverse or join this data.
Additionally, MongoDB collections are schemaless, so there is nothing as in the relational sense that says all documents in a collection have to have the same structure.
In the case of Mongoose, there are built in functions to do this sort of loading for you as a convenience, and while not strictly a DBRef and utilizing documents with a different schema in the same collection is the same means as storing the documents external to the referencing document.
It is important to consider the data access patterns of your application and not to simply opt for the same sort of relational design you are used to. Keeping in mind that you are only ever reading from one collection at a time, it is most desirable to get at the data you need in a single read or write, without multiple operations over the wire, which will slow things down considerably.
In short, you should always consider embedding sub-documents first, and then use external references any your best supported form only when you absolutely have to. Your application users will thank you in the end.
Is there a way to create and query a collection thats inside another collection...
Can any one direct me to literature that can teach me how to do this?
I've checked the mongodb
docs tutorial and i havent come across this scenario
No code example because i don't know where to start.
Here is what im trying to do.
Im modelling an online shop. So shop object details are in a collection holding many shops.
Now each shop has got products and each product its own unique details. I want to a void using references and rather append but from tutorial from mongodb docs its not quite clear how to do it.
Im fairly new to mongodb
Thanks.
There isn't any such thing as a collection inside another collection with mongo. A collection is a collection of documents.
There are a couple of ways to link documents to other documents, or collections of other data. The correct one to choose is up to you, your data, and your application.
Any document can point to another ObjectId from any field
You can have an array inside a document
Combine the two, and you can have an array of document ids
Mongo is a document store, not a relational database. My suggestion is don't try to use it as a relational database. If what you need is an RDBMS, use one.
Arrays:
http://docs.mongodb.org/manual/reference/operator/query-array/
http://docs.mongodb.org/manual/reference/operator/update-array/
ObjectId:
http://docs.mongodb.org/manual/core/document/