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Python Using Databases in Python Meet Peewee Queries Are Your Friend

zakaria arr
zakaria arr
6,347 Points

I keep getting this error StudentDoesNotExist and OperationalError Everything else looks fine. What wrong with my code?

from peewee import *

db = SqliteDatabase('students.db')


class Student(Model):
    username = CharField(max_length=255, unique=True)
    points = IntegerField(default=0)

    class Meta:
        database = db


students = [
  {'username': 'bigman',
   'points': 3324},
  {'username': 'knucklehead',
   'points': 3343},
  {'username': 'strongman',
   'points': 33434},
  {'username': 'hench',
   'points': 34524},
]

def top_student():
  student = Student.select().order_by(Student.points.desc()).get()
  return student

def add_students():
  for student in students:
    try:
      Student.create(username=student['username'],
                      points=student['points'])
    except IntegrityError:
      student_record = Student.get(username=student['points'])
      student_record.save()


if __name__ == '__main__':
    db.connect()
    db.create_tables([Student], safe=True)
    add_students()
    print('our top student is: {0.username}.'.format(top_student()))

in workspaces I get

File "/usr/local/pyenv/versions/3.4.1/lib/python3.4
/site-packages/peewee.py", line 2439, in get
% self.sql())
peewee.StudentDoesNotExist: Instance matching query d
oes not exist:
SQL: SELECT "t1"."id", "t1"."username", "t1"."points"
FROM "student" AS t1 WHERE ("t1"."username" = ?)
PARAMS: ['3324']

and in idle I get it somehow works can someone please explain why?? on idle I get

our top student is: hench.

3 Answers

Hi Zakaria I created a function that checks to see if each user exists before adding it to the database. see below.

def add_students():
  for student in students:
    uname = student['username']
    upoints = student['points']
    try:
      if student_exists(uname,upoints) < 1:
        Student.create(username=uname,
                      points=upoints)
    except IntegrityError:
      print("Error adding students")

def student_exists(uname,upoints):
  student = Student.select().where(Student.username==uname,Student.points==upoints)
  return student.count()

I ran the code over and over with no errors. I also added new students to the dictionary with higher points and it all seems to work fine now.

hope this helps.

zakaria arr
zakaria arr
6,347 Points

Wow thanks pal its works perfectly everytime.

zakaria arr
zakaria arr
6,347 Points

Kenneth Love can you help me

Hi Zakaria

the line that prints out the top student, what is {0.username}?? I changed your code slightly, in the function top_student, i returned the student.username rather than just student and also changed the print statement, i then ran your code with no errors. see below

from peewee import  *

db = SqliteDatabase('students.db')

class Student(Model):
  username = CharField(max_length=255, unique=True)
  points = IntegerField(default=0)


  class Meta:
    database = db

students = [
  {'username': 'bigman',
   'points': 3324},
  {'username': 'knucklehead',
   'points': 3343},
  {'username': 'strongman',
   'points': 33434},
  {'username': 'hench',
   'points': 34524},
]

def top_student():
  student = Student.select().order_by(Student.points.desc()).get()
 # changed the return statement from student to student.username
  return student.username

def add_students():
  for student in students:
    try:
      Student.create(username=student['username'],
                      points=student['points'])
    except IntegrityError:
      student_record = Student.get(username=student['points'])
      student_record.save()




if __name__ == '__main__':
  db.connect()
  db.create_tables([Student],safe=True)
  add_students()
 # i changed the {0.username} to just the placeholder
  print('our top student is: {}.'.format(top_student()))

hope this helps

zakaria arr
zakaria arr
6,347 Points

Thank you Andreas My apologies I didn't define the error very well and I only recently realised what was causing the problem. The error is being caused due to an IntegrityError because when I run the script the first time it works because all of the usernames and points are unique. However, once the database saves these into a table I will get an error if I run the program. For the meanwhile I have been able to fix this integrity error by using this piece of code that I have posted below. If you have a better way of dealing with this error I would really appreciate it.

And Thank You again

zakaria arr
zakaria arr
6,347 Points
def add_students():
  for student in students:
    try:
      Student.create(username=student['username'],
                      points=student['points'])
    except IntegrityError:
      #I am dealing with the IntegrityError  by
      #Telling the user that student already exists
      print('student already exists')
zakaria arr
zakaria arr
6,347 Points

running this code the first time gives

treehouse:~/workspace$ python students.py
our top student is: hench.

and the second time gives

treehouse:~/workspace$ python students.py
student already exists
student already exists
student already exists
student already exists
our top student is: hench.