I'm trying to solve the relational model in order to make a Django app.
I't will be something like a McDonald's crew scheduler. I mean the grid with colored pins marking who will be working at a given hour a given weekday.
I did try to Google out some example, but I didn't find anything. I need some theory/bibliography in order to build up my model and code it into my app.
Thanks in advance
From the short description, you probably wouldn't have just one model in your app.
From your question I'm assuming you don't have a lot of experience with databases... Here are a few suggestions:
Start here because if you don't understand the basic principles of database design, foreign keys, one-to-one, one-to-many, many-to-many, etc etc etc; you will have a hard time designing your Django models.
It would be nice to learn SQL too. Django models are supposed to insulate you from it, but in reality it is using SQL underneath and knowing SQL will enable you to check and fix performance issues in the future. There are some resources online too. And if you are using SQLite, learn its syntax too.
The above is stuff that you will be able to reuse regardless of the web framework you end up with. Django, Rails, the next big thing... whatever.
Study other people's data models. Here are several different ones - maybe you can find the one you are looking for (employee shifts? shift scheduling?).
Then read the basic django model documentation and really understand it. What django models are doing is mapping python objects to relational database tables (ORM is the acronym; Object Relational Mapping) and this article may very well help you in coming up with good designs.
Don't get discouraged. Everybody had to start somewhere.
Hope you find all you need. Have fun with Django.
Related
I am looking for a simple way to create geographical maps in Django, in which I could then select, highlight and annotate countries or groups thereof.
"Annotate": insert a label displaying textual information about the said country.
Is there anything that comes to mind?
Many thanks
EDIT: I checked GeoDjango already and it looks like much work in order to get where I need to. Don't get me wrong: I'm not trying to minimize my own investment in learning new tools, but for this project, I have a trade-off between time allocated to learning and the relative importance of this geographical feature in my app. It's more of a nice-to-have feature I'd like to add to an already 'complete' app. So I wondered whether there exists a 'simpler' python library for this task.
I think this is more of a question for if there is a front-end library to elegantly handle this. However if you need to generate the maps you could try something like this
https://kartograph.org/
I have personally used this http://jvectormap.com/ and found it to be really good.
In your database you could just have a Countries model with any associated information you might need to display, and create a view to handle that appropriately.
Using more number of ForeignKey's in Django cause any problem in production? Is there any limits of using models. I'm using cache to handle some views.But I'm really worried about my database design.
In my project, I'm using 30 FK's to store information about users and activities.right now all working fine on the production server.In future, more FK will present.Using more number DB's cause any problem in future?
Thanks in advance.
There is not really a limit on the use of models/tables/foreign keys/relations, that's where database are for: handling big loads of data. The way you handle your database operations are of more importance here.
In combination with Django: this is the best book I know to explain it all to you with nice and ably examples.
https://www.twoscoopspress.com/products/two-scoops-of-django-1-11
I'm build a Django app with Neo4j (along with Postgres), I found this Django integration called neo4django, I was wondering if it's possible to use neo4restclient only, like, what would be the disadvantages of not using Neo4django? Does using neo4-rest-client only, give me more flexibility?
When I was creating my models with Neo4Django, it seemed that there is no difference between modeling a graph db and relational db. Am I missing anything?
Thanks!
You can absolutely go ahead with neo4j-rest-client or py2neo, without using neo4django. In the same way, you can use any other database driver you'd like any time using Django, any REST client, etc.
What'll you lose? The model DSL, the built-in querying (eg, Person.objects.filter(name="Mohamed")), the built-in indexing, and the Lucene, Gremlin and Cypher behind that. Some things will be much easier- like setting an arbitrary property on a node- but you'll need to learn more about how Neo4j works.
You'll also lose some of the shortcuts Django provides that work with neo4django, like get_object_or_404() and some of the class-based views that work with querysets.
What'll you gain? Absolute power over the DB, and an easier time tweaking DB performance. Though neo4django isn't nearly as good a lib as some traditional ORMs in the Python sphere, the trade-off of power vs provided ease is similar.
That said, the two can work together- you can drop down from neo4django to the underlying REST client nodes and relationships anytime. Just use model_instance.node to get the underlying neo4j-rest-client node object from a model, and from neo4django.db import connection to get a wrapped neo4j-rest-client GraphDatabase.
On whether you're missing something: neo4django was written to re-use a powerful developer interface- the Django ORM- so it should feel similar to writing models for Postgres. I've written a bit about that odd feeling in the past. I think part of the problem might be that the lib doesn't highlight the graph terminology new graph-interested devs expect- like traversals and pattern matching- and instead dresses those techniques in Django query clothing.
I'd love your thoughts, or to know anything you'd like the library to do that it isn't doing :) Good luck!
I have a little project that involved article archive browsing by year of publication.
I used the trick given in this other question to build a list of article publication years and article counts for those years. It works pretty well on my test server with SQLite. Since the production server will rely on PostgreSQL I am looking for a way to achieve the same thing in PostgreSQL and ended up toying with the EXTRACT keyword. I use something like "import settings" to detect the current database backend and execute the right query.
My point is all of that look more and more like a dirty & crappy hack to solve an issue in a very inelegant, untestable and poorly maintainable way. As a web programmer beginner I ask my experienced elder,
How would you deal with that correctly ?
As an option to the raw sql:
You can calculate the count per year with the ORM (e.g. How to use Django ORM to get a list by year of all articles with an article count )
Then you store that value somewhere (in a model or in cache ...) in order not to be overwhelmed by the slowness of the ORM calculation.
I am working on a Google App Engine application and I am relatively new at this.
I have built an app already in Django and have a model using a field type of ManyToMany.
I am aware that django-nonrel does not support many-to-many field types of Django. So I am considering using ListField instead.
Questions:
- What is the implication of using ListField instead of ManyToMany?
- I am aware that this means that Django's JOIN API cannot be used. But what does this mean for my app?
- Am I going to have problems when it comes to doing a search for something in a many-to-many field?
Apologies if these are programming 101 questions. I'm a designer trying to get my head around development.
Thanks
Well as you probably know, you will be spanning the relationship more manually.
Django cannot help quite as much as when using ManyToMany, but it should not be that big a problem.
Depending on the complexity of the relationship, you might want to consider building a model just for this purpose.
I have never used that approach on GAE, since IMO its only valid when an object has alot relations (more than 50 I would say) or when the lookups you plan to do, will benefit from this. Maybe because they start at either end of the relationship with equal frequency or it would be nice to be able to loop over the relationships to display them or something along those lines.
Last time I made something on GAE I used the ListField (or ListProperty as it was known then) since most of the objects only had about 20 related objects and the lookups would rarely go the other way.
So all in all, its not a big deal and I don't remember it as any kind of a pain to work with/around.
Hope this was helpful despite it being rather "IMO"