I have lots of models in my project like Advertisements, UserDetails etc. Currently I have to delete the entire database every year so as to not create any conflicts between this year data and previous year data.
I want to implement a feature that can allow me to switch between different years. What can be the best way to implement this?
I think you could switch schemas in PostgreSQL. It's not completely straightforward. There are several ways to do that you can look into. The way I did it was to use a default search path for the Django database user account (e.g. user2018, user2019, etc) that only included the schema I wanted to use. I can't check the exact settings right now because my office network is down. You can also do it in settings.py or in each individual model using db_table according to what I've read, although both those solutions seem more convoluted that using the search path.
You would have to shutdown, change the database username in settings.py (or change the search path in PostgreSQL, change the schema over to a new one, and then run migrate to create the tables again. If you have reference data in any of the tables then schema-to-schema copies are easy to do.
Try searching for change django database schema postgresql to see what options there are for specifying the schema.
Related
I'm a beginner at Django, and as a practice project I would like to create a webpage with a dashboard to track investments in a particular p2p platform. They do not have a nice dashboard (but provide excel file with all data). As I see it, main steps that I need to do in this project are as follow:
Create login so that users would have account where they upload their excel files.
Make it possible to import excel file to a database
Manipulate/calculate data for it to be later used in dashboard
Create dashboard.
Host webpage.
After some struggle I have implemented point no. 2, and will deal with 1 and 5 later. But number 3 is my biggest issue now.
I'm completely unsure what I need to do, and google did not help. I need to calculate data before I can make dashboard from it. Union two of the tables, and then join them together with a third table, creating some additional needed calculated fields. Do I create a view in the database and somehow fetch this data to Django? Or do I need to create some rules so that new table would be created at the time of the import? I think having table instead of a view would have better performance. Or maybe I'm doing it completely wrong, and should take completely different approach for this kind of task? Also, is SQLite a good database for a task (I'm using it, because it was a default in Django)?
I assume for vizualization part I will need to do it with some JavaScript library, such as D3? Which then would use data from step 3.
For part 3 there is 2 way, either do these stuff and save the result in your database or you can do it when you need it using django model features like annotation, aggregation and etc.
Option 1 requires to add a table for you calculation which is Models in django.
Option 2 requires to create a doing the annotations in a view or model managers and then using them in views.
Django docs: Aggregation
Which is the best is depended on how big your data is, how complicated the calculation is and how often you need them.
And for database; SQLite is just a database for development use not the production and surly not with a lot of data and a lot of calculations. The recommended database for django is postgresql which is pretty good at handling millions and even billions of data and doing heavy calculation.
And for vizualization you should handle it on the template side which is basically HTML, CSS and JS.
I am recreating a web app in Django that was running in a server but it was terminated, fortunately, I did a backup of all the code. My problem comes with the database because but I do not know how to transfer all the data from the old db.sqlite3 Django database web app into the new one.
I found a similar question as mine Django: transfer data from one database to another but the user wanted to transfer data from specific columns because their models.pyfrom the old and new databases were slightly different. In my case, my models.py from the old and new databases are the same.
Alternatives
I am using the DB Browser for SQLite to explore the content of the old database and I could add manually each row into the Django administration but this will take me too much time.
I could copy the old db.sqlite and replace it in the new web app because the models.py file remains the same but this solution is not appropriate IMO, this solution is rude and I think it goes against the good practices of Software.
How should I proceed for transferring data from the old database to the new one?
This seems like a one time copy of one db to another. I don't see how this goes against good software practice unless you have to be copying this db frequently. I've done it before when migrating servers and it doesn't cause any issues assuming the two instances of the application are the same build.
I was able to do some minor tricks in order to solve my problem because there is not a straightforward functionality that allows you to transfer all your data from two sqlite databases in Django. Here is the trick I did:
Download the sqlite db browser to explore and export the contents of your old database in a .csv file. Open you database with sqlite db browser and hit on the tables option and you will see all your tables, then do a right click on any of those and hit the export as a csv file option to generate the csv file (name_of_your_csv_file.csv). The other alternative is to use the sqlite3.exe to open your database in cmd or powershell and then doing the export with:
.tables #this lets you explore your available tables
headers on
mode csv
output name_of_your_csv_file.csv
2.There are two choices up to this point: You can either insert all the records at once to your new database or you can drop your existing tables from the new database and then recreate them and import the .csv file. I went for the drop option because there were more than 100 records to migrate.
# sqlite3
# check the structure of your table so you can re-create it
.schema <table_name>
#the result might be something like CREATE TABLE IF NOT EXISTS "web_app_navigator_table" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "ticket" varchar(120) NOT NULL);
#drop the table
drop table web_app_navigator_table
#re-create the table
create table web_app_navigator_table(id integer not null primary key autoincrement, ticket varchar(120) not null);
#do the import of the csv file
.import C:/Users/a/PycharmProjects/apps/navigator/name_of_your_csv_file.csv table_name_goes_here
You might see an error such as csv:1: INSERT failed datatype mismatch but this indicates that the first row of your csv file was not inserted because it contains the headers of the exported data from your old database.
I am trying to use django's database routers to shard my database, but I am not able to find a solution for that.
I'd like to define two databases, create the same table in both and then save the even rows in one db, the odd ones in the other one. The examples in the documentation show how to write to a master db and to read from the readonly slaves, which is not what I want, because I don't want to store the whole dataset in both dbs.
Do know any webpage explaining what I am trying to do?
Thank you
PS: I am using Postgresql and I know there are tools to achieve the same goal at DB level. My goal is to study if it can also be done in django and to explore if there are some advantages by doing this.
I need to move a series of tables from one datasource to another. Our hosting company doesn't give shared passwords amongst the databases so I can't write a SQL script to handle it.
The best option is just writing a little coldfusion scripty that takes care of it.
Ordinarily I would do something like:
SELECT * INTO database.table FROM database.table
The only problem with this is that cfquery's don't allow you to use two datasources in the same query.
I don't think I could use a QoQ's either because you can't tell it to use the second datasource, but to have a dbType of 'Query'.
Can anyone think of any intelligent ways of getting this done? Or is the only option to just loop over each line in the first query adding them individually to the second?
My problem with that is that it will take much longer. We have a lot of tables to move.
Ok, so you don't have a shared password between the databases, but you do seem to have the passwords for each individual database (since you have datasources set up). So, can you create a linked server definition from database 1 to database 2? User credentials can be saved against the linked server, so they don't have to be the same as the source DB. Once that's set up, you can definitely move data between the two DBs.
We use this all the time to sync data from our live database into our test environment. I can provide more specific SQL if this would work for you.
You CAN access two databases, but not two datasources in the same query.
I wrote something a few years ago called "DataSynch" for just this sort of thing.
http://www.bryantwebconsulting.com/blog/index.cfm/2006/9/20/database_synchronization
Everything you need for this to work is included in my free "com.sebtools" package:
http://sebtools.riaforge.org/
I haven't actually used this in a few years, but I can't think of any reason why it wouldn't still work.
Henry - why do any of this? Why not just use SQL manager to move over the selected tables usign the "import data" function? (right click on your dB and choose "import" - then use the native client and permissions for the "other" database to specify the tables. Your SQL manager will need to have access to both DBs, but the db servers themselves do not need access to each other. Your manager studio will serve as a conduit.
I have two Django sites: one for development and one for production. Every once in a while, the data from the development database needs to be transferred to the production database or the other way around. I use postgresql.
This works fine: I empty the tables from the database I want to copy to, I generate sql from the applicable tables, and insert the data in the emptied tables. So far, so good.
But when I enter data into the database via the admin interface, Django raises IntegrityErrors, because appname_modelname_pkey already exists.
I think this is because the admin interface wants to add data with id 1, but that's already an imported record. Django isn't aware that id '1' is already taken.
How do I fix this problem? I want Django to increment the id (like SQL auto_increment would do), no matter what data is already stored.
Any help is appreciated!
If you're using postgres on both sides, then the sequence associated with the primary keys are going to be different.
For example, suppose you're moving production data to development. Also, suppose the sequence value in production is 20 and the sequence in development is 10. Then the first new item you add in development will have an id of 11. That id (probably) already exists in the production data, so you get an integrity error.
When you restore tables from a dump, you can reset the sequences by dropping and recreating the existing tables before you restore.
(Or, you can probably use the ALTER SEQUENCE command to sync up the sequences. However, I'm not familiar enough with postgres to say whether that's the right way to do it.)