Querying the database

A student wanted to join 2 tables and display the results but he was not making any headway and couldn't figure out what was wrong with his code. After some debugging via printing to the console, I realised that he was not getting any data and that's why nothing was being displayed on his template. And there was a simple reason for this, his model was not set up to allow such a query. He was joining a table that had no foreign keys to various other tables that were linked to each other rather than to the first table.

class Players(models.Model):
    PlayerName = models.CharField(max_length=100)
    PlayerAddress = models.CharField(max_length=100)
    PlayerEmailAddress = models.CharField(max_length=100)
    PlayerPhoneNumber = models.IntegerField()
    TeamID = models.ForeignKey(Team, on_delete=models.CASCADE)
    Coach = models.ForeignKey(Coaches, on_delete=models.CASCADE)

I did what I always do in such situations where I encounter problems I have not seen before, I pulled his branch and started working on my own solution. I changed the table he was joining and added another foreign key to that table to ensure that I could get all the data I wanted. This small exercise made me realise just how important it is to design your database well.

def team_home(request):
    jointables= Players.objects.select_related('TeamID', 'Coach')
    playerQueryset = jointables.order_by('-TeamID', 'PlayerName')
    context = {'team' : playerQueryset}
    return render(request, 'SoccerApp/SoccerApp_page.html', context)

Printing to the console showed me I was getting all the data I wanted to, and then it was just a matter of passing it to the template. This was fun. I really should play with the database more often!

Comments

Deviants in a normal world

It's definitely been a bit since I've seen this graphy. Anyone who has learnt about standard deviation knows this graph. Standard Deviation Standard deviation shows us how spread out all the values in a set are from the mean. The higher the standard deviation, the more spread out the values are over a wider range and the flatter this curve. In a normal distribution, most values are within 1 standard deviation from the mean(the green part of the graph). Apparently NumPy can calculate standard deviation too! import numpy numSet = [ *lots of numbers* ] numSetStdDev = numpy.std(numSet) Variance The variance also indicates how spread out the values in a set are. It measures the average degree to which each value differs from the mean. variance = standard deviation ^2 import numpy numSet = [ *lots of numbers * ] numSetVar = numpy.var(numSet) Source: https://www.w3schools.com/python/python_ml_standard_deviation.asp

Snakes and ladders

I've started on my Python course. So far, the code has been familiar because the first few basic codes are similar to Javascript. And then modules happened. Confusion and despair! What is the world is 'if __name__ == "__main__": ' and why must I reach this section of my course on a public holiday when none of the instructors are in :( Stack overflow to the rescue, providing me a lifeline while I was drowning in a pit of serpents. I feel eternally indebted to a particular Mr Fooz. Picture from here From my understanding, when the Python interpreter reads a source file, it first sets the variable __name__ and then it executes all the code in the file. If that particular file that you are running(i.e. your module) is the main program, the interpreter will assign '__name__ = "__main__" '. Thereafter, any code in the aforementioned 'if' statement is run. If you have, instead, imported a module, the interpreter assigns '__name__ ...

Fizzbuzz

I was today years old when I found out what fizzbuzz was. Yes, I'm late to the party. I was in an interview where the interviewer mentioned that ordinarily they would ask interviewees in for a round of fizzbuzz challenges, as I know. Actually sir, no, I don't know 👀 But he sounded so certain that I must surely know what it is that I was afraid to say anything so I did what I always do when I panic. Look right back saying not a word. I googled this mysterious fizzbuzz problem: It looks pretty easy. I don't think he meant this actual problem, but problems like this. Because this problem is way too easy to be an actual problem someone asks in an interview. I decided to work on it for fun: Yup. Super easy. I wish this is all I were asked in an interview 😄

I do it for my cat

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