Ok, I edited to make it clear.
I have sort kind of problem here. I cannot find the best way to do this:
I have a "table" at my MongoDB with my Mongoose Model like that:
var machineSchema = new Schema({
uuid : String,
data : String
});
So the UUID is my machine UUID. I can have something like this on the database:
{"uuid":"bla1","data":"RAM 1024MB"},
{"uuid":"bla1","data":"LINUX"},
{"uuid":"bla1","data":"CPU: Xeon"},
{"uuid":"bla2","data":"RAM 512MB"},
{"uuid":"bla2","data":"LINUX"},
{"uuid":"bla2","data":"CPU: Pentium Dual Core"}
What I want to do is, having two UUIDs (like bla1 and bla2) find what they have in common (data). So it should return:
{"uuid":"bla1","data":"LINUX"},
{"uuid":"bla2","data":"LINUX"}
or just
{"data":"LINUX"}
I could do two queries for bla1 and bla2 and them compare manually, but I think it has a better way to do that. I'm not used to Mongoose queries, there is anyway to do it? On MySQL I would do a Query with two subqueries only selecting the results that field1 matches between two. On Mongoose how should I do that?
Thanks!
It sounds like you require classic SQL 'join' functionality.
Unfortunately MongoDB (as well as most NoSQL databases) do not support joins, the functionality is more geared towards dealing with separate entities rather than sets.
Related
We are in the process of writing tests for our Node/MongoDB backend and I have a question about finding documents.
My understanding is it's preferable to use Mongoose to get your documents as opposed to the MongoDB driver. In other words, doing Customer.findOne().exec() instead of setting up a db connection and then doing db.collection("customers").findOne().
Other than the first option (using Mongoose to find the doc) being slightly less verbose, I'm curious what the other reasons are. Is a straight MongoDB lookup a bigger drag on the database?
One of the great feature of mongoose is the built in validation mechanism. Also the Populate method to get data from multiple collections is an awesome characteristic of Mongoose.
In terms of query performance, here is a good read:
https://medium.com/#bugwheels94/performance-difference-in-mongoose-vs-mongodb-60be831c69ad
Hope this helps :)
MongoDB is schemaless, which means a collection (table in relational DB) can contain documents (rows) of different structure - having different fields, for instance.
I'm new to Mongo, so I decided to use Mongoose which should make things a bit easier. Reading the guide:
Defining your schema
Everything in Mongoose starts with a Schema. Each schema maps to a
MongoDB collection and defines the shape of the documents within that
collection.
Notice at the last sentence. Doesn't it conflict with the schemaless philosophy of MongoDB? Or maybe it's that in 99% of cases, I want a collection of documents of the same structure, so in the introductory guide only that scenario is discussed? Does Mongoose even allow me to create schemaless collection?
MongoDB does not require a schema, but that confuses a lot of people from a standard SQL background so Mongoose is aimed at trying to bridge the gap between SQL and NoSQL. If you want to maintain a collection with different document types, than by all means do not use Mongoose.
If you're okay with the schemaless nature of MongoDB there is no reason to add additional abstractions and overhead to MongoDB which is what Mongoose surely applies.
The purpose of Mongoose is to use a Schema, there are other database drivers you can use to take advantage of MongoDBs Schemaless nature such as Mongoskin.
If you want to utilize the Mongoose's Schema Design and make an exeception you can use: Mongoose Strict.
According to the docs:
The strict option, (enabled by default), ensures that values passed to our model constructor that were not specified in our schema do not get saved to the db.
NoSQL doesn't mean no schema. It means, the database doesn't control schema. For instance, with MongoDB, you can look hard to find anything that determines a field in a document is a string, or a number or a date. The database doesn't care. You could store a number in a field in one document and in another document in the same collection, and in the same field, you could store a string. But, from a coding perspective, that can become quite hairy and would be bad practice. This is why you still have to define data types. So, you still need a schema of sorts and why Mongoose offers and, in fact, enforces this functionality.
Going a conceptual level higher now, the major concept of NoSQL is to put schema inside your code and not in some file of SQL commands i.e. not telling the DB what to expect in terms of data types and schema to be controlled by the database. So, instead of needing to have migration files/paths and versioning on database schema, you just have your code. ORMs, for example, try to bridge this issue too, where they often have automated migration systems.
ORMs also try to avoid the Object Relational Impedance Mismatch problem, which MongoDB avoids completely. Well, it doesn't have relationships per se, so the problem is avoided out of necessity.
Getting back to schema, with MongoDB and Mongoose, if you or one of your team make a change to the schema in the code, all your other team members need to do to get the database to work with it is pull in that new code. Voila, the schema is up-to-date and will work. No need to also pull in a copy of the newer migration file (to determine the new schema of the DB) to then have to run it on a (copy of the) db to update it too, just to continue programming. There is no need to make changes in schema in multiple places.
So, in the end, if you can imagine your schema is always in your code (only), making changes to an application with a database persisting state like MongoDB is a good bit simpler and even safer. (Safer, because code and schema can't get out of sync, as it's the one and the same.)
I'm new to mongoDB and in a node project i'm using mongoose to create a schema for my database. I have come to understand that in my case i should be using embedded data instead of by reference. (http://docs.mongodb.org/manual/core/data-modeling-introduction/)
The structure that i need to store in the database is something like this:
book
| title
| | chapter
| | | content (url to a html file)
Coming from a mySQL world, i'm trying to understand the noSQL database concepts and i was wondering how one would design the mongoose schema.
Thx,
You can nest documents, and document arrays in a MongoDB document:
db.books.findOne();
can return a JSON:
{
isbn:"253GHST78F6",
title:"some book",
author:"Earnest Hemmingway",
chapters:[
{title:"chapter 1",content:"http://api.com/chapters/1.html"},
{title:"chapter 2",content:"http://api.com/chapters/2.html"}
]
}
But, there are a few more things to keep in mind when modeling a collection in MongoDB:
Model data as close as possible to what will be asked for: There are no Joins in MongoDB, so, try to keep all such data together (pre joined), that is supposed be queried together in future.
Nesting is good for queries but nested update and search is bad:
Indexing and searching inside nested documents, especially arrays, will be expensive.
Avoid placing any data in nested arrays, that is very frequently updated.
There are no Foriegn Keys in MongoDB. So, if you have multiple copies of same document nested under different collections, keeping all of them updated is your responsibility.
First take a look at this Martin Fowlers excellent video:
I think there is no better authority that can explain nosql, then Fowler. Especially knowing his sql background.
Second, MongoDB follows json schema. If you know how to work with json, you will know how to work with nosql (mongodb). Basic thing that needs to be understand is that Mongo schema is expressed in a language that is using it.
So, if you are using NodeJS with Mongo, you still have objects and array to work with. In simple words, Mongo is not forcing any particular schema. It is on developer to create his scheme based on his language/mongo driver.
So how would you express you data logic in your language ? If it is in form of JS object, then move that form to db.
I really like MongoDB, becuse it can be combined with some great JS tools like Underscore.js for all kind of data manipulations.
I am a super newbie to mongodb. I am using mongoose to access mongodb from node.js, and know how to get things to work, but I don't think I understand why it works the way it does.
Most importantly, I don't understand why mongoose has 'schema' when one of the standout features of mongodb is that it doesn't have schema. Could someone enlighten me? thank you.
Data without a schema is useless. You get a document from MongoDB, what do you do with it? Read some fields? You need to know the names, types and meanings of those fields. That’s a schema.
When people say that MongoDB “has no schema”, they really mean that it does not enforce schema the way SQL databases do. MongoDB pushes schema concerns up to your application level, where you can handle them more flexibly. For example, in order to add a new field to your documents, you don’t need to do an all-or-nothing ALTER on your collection—potentially millions of entries. You just add that field to your ODM (Mongoose) schema and you’re done.
I'm building a small product system to try and get me into Node.js, Mongo and the like.
I was drawn to Mongo for the possibilities of storing products of different types in the same collection instead of having multiple tables, eav or any of the other MySQL-methods that didn't quite fit.
I was reading through tutorials and at first fell over writing a Provider for the ProductModel, but then someone suggested i should use Mongoose.
However, the issue with Mongoose seems to be that i need a set schema for each model. My first idea was that a product should have a title and a type attribute. Then type would decide the overall product structure. So for example a dvd product might have a director while a t-shirt product would not have a director but would have different sizes.
Is it possible to implement this kind of structure in Mongoose, and how? It's my understanding that if i provide a schema for each produt type i won't be able to query them simultaneously? Does different schemas mean different collection? - I couldn't quite figure that out.
Any help and guidance is appreciated, would like to be able to use a framework instead of writing the DB handling myself (although that what was i planning to do initially, but if someone else allready did it better than me :))
Mongoose has a schemaless type which can be very useful in your case, but might not be the best solution.
ProductSchema = new Schema({any: {}});
If you change anything on this object you need to notify Mongoose about it with obj.markModified('field-name') before saving.
My suggestion is to use your own wrapper over node-mongodb-native, which I'm running on production for 7~8 months without problems.
There's another lib called mongous that you can check it out.