I'm a MongoDB beginner previously MySQL user. I was wondering what the correct way is to store and update data that relates to one another in MongoDB.
Say I have 2 entities User and Item. Everytime I display an item, i want to show all user information together with it, so I copy the user information into my Item object when creating an Item:
Item
------
itemID
itemName
userName
userID
userLocation
Say I update the userName of the user related to that item. That means I need to target all the Items that has the userID to update the userName of those Items. Is that the right way of doing it? Or would you reference the user inside the Item Object like this?
Item
------
itemID
itemName
userID
and perform a specific query? What's the MongoDB way of storing data and updating it?
So far I've just been doing this "Bulk" update kind of way doing it but I'm not sure what's the best practice in this case.
Related
I'm wondering if it's possible to auto update the User's column('number of posts') if the Posts table updates. The Post entity has a ManyToOne relation with User('userId'). Is there a way to make the User Table "listen" to the Post Table and automatically updates the number of post column, or i need to write it in the post service create function to do so. I'm new to sql so i'm just trying new stuff. I'm using NestJS,typeORM, Postgres and Graphql
#Kendle's answer does work and has the advantage of pushing the computation and complexity down onto your DB server. Alternatively, you can keep that logic in the application by leveraging TypeORM's Subscribers functionality. Documentation can be found here.
In your specific use case, you could register a subscriber for your Post entity implementing afterInsert and afterRemove (or afterSoftRemove if you soft delete posts) to increment and the decrement the counter respectively.
You don't want to duplicate that data. That's the whole idea of a relational database that different data is kept in different tables.
You can create a view if you want to avoid typing a query with a JOIN each time.
For example you might create the view below:
CREATE VIEW userPosts AS
SELECT
user.id,
user.name,
COUNT(posts.id)
FROM users
LEFT JOIN posts ON user.id = posts.user_id
ORDER BY user.id;
Once you have created the view your can query it as if it were a table.
SELECT * FROM userDate WHERE id = '0001';
Of course I don't have your table definitions and data so you will need to adapt this code to your tables.
So in a traditional database I might have 2 tables like users, company
id
username
companyid
email
1
j23
1
something#gmail.com
2
fj222
1
james#aol.com
id
ownerid
company_name
1
1
A Really boring company
This is to say that user 1 and 2 are apart of company 1 (a really boring company) and user 1 is the owner of this company.
I could easily issue an update statement in MySQL or Postgresql to update the company name.
But how could I model the same data from a NoSQL perspective, in something like Dynamodb or Mongodb?
Would each user record (document in NoSQL) contain the same company table data (id, ownerid (or is owner true/false, and company name)? I'm unclear how to update the record for all users containing this data then if the company name needed to be updated.
In case you want to save the company object as JSON in each field (for performance reasons), indeed, you have to update a lot of rows.
But best way to achieve this is to have a similar structure as you have above, in MySQL. NoSql schema depends a lot on the queries you will be making.
For example, the schema above is great for:
Find a particular user by username, along with his company name. First you need to query User by username (you can add an index), get the companyId and do another query on Company to fetch the name.
Let's assume company name changes often
In this case company name update is easy. To execute the read query, you need 2 queries to get your result (but they should execute fast)
Embedded company JSON would work better for:
Find all users from a specific city and show their company name
Let's assume company name changes very rarely
In this case, we can't use the "relational" approach, because we will do 1 query to fetch Users by city and then another query for all users found to fetch the company name
Using embedded approach, we need only 1 query
To update a company name, a full (expensive) scan is needed, but should be ok if done rarely
What if company name changes ofter and I want to get users by city?
This becomes tricky, NoSQL is not a replacement for SQL, it has it's shortcomings. Solution may be a platform dependent feature (from mongo, dynamodb, firestore etc.), an additional layer above (elasticSearch) or no solution at all (consider not using key-value NoSQL)
Depends on the programming language used to handle NoSQL objects/documents you have variety of ORM libraries to model your schema. Eg. for MongoDB plus JS/Typescript I recommend Mongoose and its subdocuments. Here is more about it:
https://mongoosejs.com/docs/subdocs.html
I'm creating a kind of project management app which consists of 'jobs' and 'entities' (or tasks) within those jobs. As part of it I'm creating a todo list which should be unique to each user and I'm wondering what the best design is for the database?
Entities exist in their own collection and are related to jobs through a jobId field.
My initial thought was to structure it like:
Entity
Todos[]
User1
Todo1
Todo2
...
User2
...
I also have a users collection so would it better to store the todos there like:
User
Todos[]
Entity
Todo1
Todo2
...
Or some other method?? I think updating and deleting todos will be quite tricky..
Update
Option 3 - I could remove the user array and store the user on each todo object, like:
Entity
Todos[]
Todo{
User: John
Text: some todo
Done: false
Then filter all todos by a specific user. I will get some duplicate data (the user) but I don't think that's so bad..
Also when updating/deleting a todo is it safe to match it based on the text field or do I need to store a unique id on each todo?
I believe that your initial thought is the best of the two. In it, the User is referenced. In the second it looks like a user document with the todos in it. I think that is a little too much coupling, the first method being better decomposed and easier to modify/maintain as the reasons dictate in the future.
I have 2 Mongoose.js Schemas that work together with the 'populate' feature: A 'user' schema and another based on their role. E.g. 'admin'. When a user is assigned a role, a corresponding document needs to be created in a different collection with a link to the _id of the document in the users collection. (Yes, more like an SQL database than non-relational, I know)
Currently I manually create the second document in my code whenever a user with a specialized role is created or a role is added to a user. |
I'd like to know if there is a way to automatically create this corresponding record from my schema whenever a 'user' document is created or updated with a role.
Any advice?
Nothing will do it automatically, but you can use the mongoose middleware to insert our update a document in another collection pre or post save.
The post hook will have the _id populated.
If you want to do it in the pre hook (to enforce some transactional integrity) you can assign the _id manually.
I have a Customer table and another Orders table. Each Customer can have many orders (One to many relationship).
I want to get a Customer object and from it get how many orders he has (the actual order data is not relevant at this point). So as I see it I have 2 options:
create a view with another OrdersCount field - and that will be another object in my system.
in my app, when I need the count get the Customer.Orders.Count - but for my understanding that will cause an extra query to run and pull all the orders from the database to that collection.
Is there a correct way to do such thing?
Thanks
You do need a new type, but you don't need to recreate all relevant properties.
from c in context.Customers
// where ...
select new {
Customer = c,
OrderCount = c.Orders.Count()
}
Update code that looks for e.g. the Name property of an item in the result, to look for Customer.Name.