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I got the following Entities:
A User Entity, it has OneToMany Products and OneToMany Images
A Product Entity that has ManyToMany Images
An Image Entity, having the ManyToOne to User, and the (inverted) ManyToMany Products
The Images connected to the Product are also always connected to the same User Entity too.
I want to display for the Current User the Products and their Images in a Table.
For this, the User is loaded by the User Provider. (1 Query)
Then it gets the N Products for the User (1 Query)
Then it ask Images joined by the ManyToMany table which Images are connected to the Products (N Queries)
The Last Queries I want to optimize somehow if able. My thought because I already know what kind of Images there will be because of the User OneToMany Relationship.
What could I do it make it better? Try to build my own Query? My own Hydrator? Maybe Caching of the Images Entities will be enough?
I tried making the Entities and their relationships Cacheable but that doesn't seems to reduce the amount of queries.
From what you explain:
You need to load from both user side (product and image). It can happen to load image not linked to the user (and product not linked to the user).
Your problem com from the many to many between product and image, that will force you to load image from product and not from user.
The solution would be to change your database to match this:
where the linked table containing all 3 foreign key has a uniq constraint on all 3.
This way, you just have to load everything in 1 query from user if you use DQL or SQL.
Related
I want to create a small app that creates a kind off receipt record in to a db table, from two other tables. very much like a receipt from a grocery store where a cashier makes a sell and the ticket contains multiple items, calculates a total and subtotal and return values to the database. I currently have 3 tables: the Ticket table where i would like to insert the values of all calculations and ticket info, the services table that acts like an inventory of services available. this has the service name and price for each service and my responsible table that has a list of "cashiers" or people that will make the sale and their percentage for their commissions, i have the views to create , edit and delete cashier's and services.
What I don't have is a way to create the ticket. I am completely lost. can you guys point me in to the correct path on what to look for. i am learning to program son i don't have a lot of knowledge in this if its even possible. i don't need the system to print i just want to have all record stored this way later on i can expand on it and create reports of sold items and who sold them and how much commissions each seller has won.
You need to create relationships to two other models (tables) from the Ticket model (table). Luckily you don't have to create the relations in the database tables itself. Use django model's Foreign key fields to accomplish this. Here is the documentation link:
Django Models
You may need to read it several times to get the concepts thoroughly.
A little background. I've been developing the core code of an application in python, and now I want to implement it as a website for the user, so I've been learning Django and have come across a problem and not sure where to go with it. I also have little experience dealing with databases
Each user would be able to populate their own list, each with the same attributes. What seems to be the solution is to create a single model defining the attributes etc..., and then the user save records to this, and at the same time very frequently changing the values of the attributes of the records they have added (maybe every 5~10 seconds or so), using filters to filter down to their user ID. Each user would add on average 4000 records to this model, so say just for 1000 users, this table would have 4 million rows, 10,000 users we get 40million rows. To me this seems it would impact the speed of content delivery a lot?
To me a faster solution would be to define the model, and then for each user to have their own instance of this table of 4000ish records. From what I'm learning this would use more memory and disk-space, but I'd rather get a faster user experience as my primary end point.
Is it just my thinking because I don't have experience with databases? Or are my concerns warranted and I should find a solution as to how to be able to do the latter?
This post asked the same question I believe, but no solution on how to achieve it. How to create one Model (table) for each user on django?
I have been trying to create a Schema for my Android application in Amazon Dynamo DB. I have very less experience with NoSQL Databases.
I have created a Survey based Android Application, now I have certain tables to store in Amazon Dynamo DB.
The Tables are Employees table, Survey table, Question table and the Response table.
The Employees table stores the information for all the employees, the survey table holds the name of the surveys and the employees, who has taken the survey.
My Issue is with the Question table and the Response table. The Questions are dynamic and are based on the employees who is taking the survey.
The answers in the Answer table depends on the number of Questions asked in the survey.
I want to know what should be my #DynamoDBHashKey, #DynamoDBIndexHashKey, #DynamoDBIndexRangeKey in the Question and the Response table, so that I can map question to respones and what should be the #DynamoDBAttribute in both the tables.
The Use Case can be: An Employee of the company posted 12 questions for all the other employees of the company.
Image was taken earlier, later on I added survey table as well
DynamoDB is good at some things and bad at others. Its great at scaling massively and horizontally while maintaining low read/write latency, but introduces eventual consistency, and forces you to make major schema decisions up front, such as what should be in a table, and how should data be partitioned, and what should be the indexes. It demands that you adopt its horizontal scaling model by partitioning your tables into pieces via the partition key.
From the way you have phrased the question it is clear that you are more comfortable in a relational database. DynamoDB is not a great place to start learning about NoSQL schema(less) design - I would have found it quite unforgiving if it was my first NoSQL database, especially trying to model a domain such as the one you describe. Its simply not a great domain modelling environment full stop - its all about horizontal scaling and performance.
If you are more comfortable in a relational database, then use a relational database. If you want to try NoSQL it is necessary to adopt a different mindset when it comes to modelling your domain into persist-able entities. For example, you might include closely related child objects within the schema of a parent record - in your example you might include Questions as children of a Survey and store them in one record, unlike in relational modelling where you would put these in separate tables.
Also stems from this question : Rails naming convention for join table
I want to create more than one join tables which link 2 models together with different relation. Let's say I have models User and Post. The first relationship table relate users with their created posts, and the another one relate users with their liked posts. How should I named these tables ? Or am I doing anything wrong with database design ?
I have a project that looks like a simple shopping site that sells different kinds of products. For example, I have 4 models: Brand, Product, Consignment. Consignment is linked to Product, and Product is linked to Brand. To reduce count of queries to databases, I want to save current state of these models(or at least some of them). I want to do it, because I show a sidebar with brands and products. So every time when user opens some page, it will execute the query to database to get those brands and products.
But when admin add some new product or brand, I want to handle database changing and resave it. How to implement it?
Your answer is by using Cache. Cache is a method to store your objects in memory/other app like redis temporarily so that you do not need send queries to database. You can read the full description here.
Or, you can use this third party library that helps you to cache Django ORM Model. Here are the example.
Brand.objects.filter(name='stackoverlow').cache()
After doing an update to the model, you need to clear or invalidate the cache.
invalidate_model(Brand)