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)
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?
Using ForeignKey relationships, I want to be able to copy data and store it in another model. For example, think of how you would handle past Invoices and billed Services.
The Invoice would have one or more Services associated with it and with prices for the Services. This prices for a Service can / will change over time - but the Service price recorded with the Invoice should remain as it was when the Invoice was created.
My first thought was to create a pdf from the resulting data and store it. But this would make the data somewhat inaccessible.
Is there somehow a way to copy the data and keep them accessible?
This is a pretty broad problem with multiple solutions. I dont think that what you're aiming to is the correct one.
One rule for saving invoices is, that invoices never change. You should never update an invoice. So not only your 'copies' of invoices should remain the same, but the original too.
Also, you should have a InvoiceItem (or InvoiceRow) model which are the items on your invoice. Don't bind Products to a Invoice directly.
Here are 2 solutions I've used:
Solution 1
You can normalize the data on your invoice(items). So, don't use foreignkeys, but normalize all data about the product, so product info (incl. price) is saved within the invoice(item).
Solution 2
Give your products revision numbers. So everytime a product is updated (name or price change for example), a new product is created in the database. Now you can link the InvoiceItem to a Product with a Foreign Key, and it will will be historically accurate.
Im sure there are some guides/best practices for creating Invoice backends. Language or Framework is not important. Invoicing is really important, so do alot of research before starting to build something. That's just my two pennies
We are building a Sitecore site that will pull in some product data from an external database. On a nightly basis we will query the external database and either Add, Update or Archive/Delete/Remove product content items in Sitecore as needed. Our data template has some fields that will be populated directly from the external database (and will be read-only for content authors) and other fields that they will populate themselves. Included in our custom fields will be the SKU of the item from the external database. It is possible that over time a product could disappear from the external database. In this case we would want Sitecore to somehow remove this item from our list of products, but not completely delete it. The reason for this is that the products that have been removed could reappear in the future and we would not want to lose all of the data that had been added to other custom fields on the item. I can think of a number of different approaches for this:
Use Archiving/Recycling features of Sitecore. When we find that there is a product item in Sitecore that no longer appears in the external database, then we could archive it. That works well. However I can't seem to figure out a way to restore that item later if it reappears in the external database. I don't have any access to any custom fields when an item is archived (from what I have read online). So when I come across a SKU in the external database that is not in Sitecore, I have no way of figuring out if there is an archived item that has that SKU.
Use a custom status field on each product content item. I could set each product content item to "active" or "inactive". This would make it easy to reactivate items that reappear in the external database. However I worry about things like search and publishing. It seems messy to me to have some content items that are inactive in the folder of all products in the master database. It could be confusing to content authors and I worry that they will find their way in to the web database, etc. It seems like I would have to do a lot of custom coding to make sure that those products do not show up on any pages, etc.
When a product disppears from the external database I could then move those content items to a different location in Sitecore. Then when they reappear I could move them back. This also feels messy.
I just wonder if there is some better solution that I am missing. Thanks in advance for any help.
I would go with option 2 "Setting status field on each product "Active" or "Inactive", as its more clear and keep the data in one place.
Additional thing to do (as suggested by Vasiliy) is to set the "Publishable" checkbox on product to "False", this way the product will disappear from web database, hence no extra filter in your search methods.
You can implement custom content editor warning to inform content editor that the current product is "inactive":
Creating Custom Content Editor warnings
Hope this helps
Just a thought what if you just unpublished the items that were removed from the external database and set the ones in the authoring db unpublishable until they reappear again. With this scenario, you could also have a task running archiving items that have been unpublished and not republished for a given period of time.
The best solution really depends on the number and frequency of items appearing / disappearing and the cost benefit of keeping those items in the authoring database vs. deleting them.
My django application need to collect user data(name age country etc) based on his email domain( 'gmail' as in xyz#gmail.com).I wist to create a new table every time i encounter a new email domain.
Can this be done in django ?
This is a bad idea. Your tables would all have the same structure. All of your data should be stored in a single table, with a domain column to keep the data separate. Why would you want a different table for each domain? Whatever reason you have, there's a better way to do it.
This idea goes against everything in the design of the relational database, and the Django ORM on top of it.