django orm

Innocent Iguana answered on November 14, 2021 Popularity 10/10 Helpfulness 2/10

answer django orm

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django orm

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############################## Tables ##############################
CREATE TABLE Course (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    -- Other Course fields );
CREATE TABLE Project (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    course_id INTEGER REFERENCES Course(id) ON DELETE CASCADE,
    -- Other Project fields );
CREATE TABLE Learner (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    user_id INTEGER UNIQUE REFERENCES auth_user(id) ON DELETE CASCADE,
    -- Other Learner fields );
CREATE TABLE AssignedProject (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    learner_id INTEGER REFERENCES Learner(id) ON DELETE CASCADE,
    project_id INTEGER REFERENCES Project(id) ON DELETE CASCADE,
    assigned_date DATE,
    UNIQUE (learner_id, project_id));
################################ Django equivalent Models ##############################
class Course(models.Model):
    # Course fields
class Project(models.Model):
    course = models.ForeignKey(Course, on_delete=models.CASCADE)
class Learner(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    projects_completed = models.ManyToManyField(Project, through='AssignedProject')
class AssignedProject(models.Model):
    learner = models.ForeignKey(Learner, on_delete=models.CASCADE)
    project = models.ForeignKey(Project, on_delete=models.CASCADE)
    assigned_date = models.DateField()
    class Meta:
        unique_together = ('learner', 'project') # Ensure uniqueness of learner-project pairs
################################ CRUD operations using ORM  ##############################
### Create
course = Course.objects.create(name="Django Course") # Create a Course
project = Project.objects.create(course=course, name="Django Project") # Create a Project
user = User.objects.create(username="john_doe") # Create a User
learner = Learner.objects.create(user=user) # # Create a User associated Learner
AssignedProject.objects.create(learner=learner, project=project, assigned_date=date.today()) # Assign Project to Learner (many-to-many relationship)
### Read
all_courses = Course.objects.all() # Retrieve all courses
course = Course.objects.get(pk=1) # Retrieve a specific course by ID
projects_of_course = course.project_set.all() # Retrieve all projects associated with a course
user = User.objects.get(username="john_doe").learner # Retrieve a specific learner by user
projects_completed_by_learner = learner.projects_completed.all() # Retrieve all projects completed by a learner
# Update a learner
learner = Learner.objects.get(pk=1)
learner.user.first_name = "John"
learner.user.save()
### Delete
project.delete()
### Adding related objects
projects = Project.objects.filter(course__name='Django Course')
learner.projects_completed.add(*projects) # Adding new related objects
learner.projects_completed.remove(*projects) # Removing related objects
learner.projects_completed.clear() # Remove all related objects
################################ Accessing Related objects  ##############################
# Learner has foreign key of User (with one-to-one relationship: user = models.OneToOneField(User))
learner = Learner.objects.get(name="abir")
learner.user # forward access
user.learner # backward access
# Project has foreign key of Course (with many-to-one relationship: course = ForeignKey(Course))
project.course # Forward access
course.project_set.all() # backward access. all because there are many courses
# Learner has foreign key of Project (with many-to-many relationship: projects_completed = models.ManyToManyField('Project', related_name='completed_by'))
learner.projects_completed.all() # forward access
project.completed_by.all() # backward access
# Learner is a subclass of User (class Learner(User) , and it is one-to-one relationship)
learner.user_ptr # Forward access to parent object
user.learner # Backward access to child object 
# Learner has foreign key of Project through intermediate table ("AssignedProject")
assigned_projects = AssignedProject.objects.filter(learner=learner).all() # Access all projects for specified learner
assigned_learners = AssignedProject.objects.filter(project=project).all() # Access all learners for specified project
################################ Some Other Common Operations  ##############################
queryset = EntityName.objects.all().delete() # .count()
queryset = EntityName.objects.order_by('-colName')[2] # Second row after sorting in descending order
print(str(queryset.query)) # See SQL equivalent query
queryset = EntityName1.objects.filter(foreignEntityField__colName__gt=5)  # Filtering: foreignEntityKey is relation to another table
queryset = EntityName.objects.exclude(colName__gt=5)  # Filtering with NOT operation
queryset = queryset1.union(queryset2) # UNION
from django.db.models import Q
queryset = EntityName.objects.filter(Q(colName__startswith='R')|Q(colName__startswith='D'))  # Alternative approach for OR
queryset = EntityName.objects.filter(~Q(colName__startswith='R'))  # Alternative approach for NOT

Popularity 10/10 Helpfulness 2/10 Language python

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Tags: django-orm python

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Contributed on Mar 07 2024

Innocent Iguana

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what is the django orm

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The Django web framework includes a default object-relational mapping layer (ORM) that can be used to interact with application data from various relational databases such as SQLite, PostgreSQL and MySQL. The Django ORM is an implementation of the object-relational mapping (ORM) concept.

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Tags: django-orm d

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Contributed on Nov 14 2021

Odd Osprey

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django orm

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