Implementation of Django Foreign Key Query

Directory 1. 1 to many 2. Many-to-many (returned query set of objects with related classes inside)

Create 3 tables, as follows:

class Publish(models.Model):
    id = models.AutoField(primary_key=True, auto_created=True)
    pname = models.CharField(max_length=40)
    city = models.CharField(max_length=50)

    def __str__(self):
        return self.pname

class Author(models.Model):
    id = models.AutoField(primary_key=True, auto_created=True)
    aname = models.CharField(max_length=10)

    def __str__(self):
        return self.aname

class Book(models.Model):
    id = models.AutoField(primary_key=True, auto_created=True)
    bname = models.CharField(max_length=30)
    price = models.IntegerField()
    publish = models.ForeignKey(Publish, on_delete=models.CASCADE)
    author = models.ManyToManyField(Author)

    def __str__(self):
        return self.bname

1. 1 to many

Query through class attributes

# get The result of the method is 1 Objects corresponding to classes 
#  Inquire the name of the publishing house of a book 
book = Book.objects.get(id=1)
book.publish.pname

#  Inquire how many books there are under a publishing house 
#  Here book Yes Book The lowercase (must be lowercase) of the table name of this table plus _set
pub = Publish.objects.get(id=1)
pub.book_set.all()

Query through the double underscore (__) of Django

#  Inquire about a certain company through the relevant information of the publishing house 1 Book 
Book.objects.filter(publish__city=' Beijing ')
Book.objects.filter(publish__id=1)

#  Query its publishing house through the relevant information of books 
#  Here book Yes Book The lowercase of the table name of this table (must be lowercase) 
Publish.objects.filter(book__id=1)

#  In values As well as values_list Use in (quotation marks must be added) 
#  Query its publishing house through the relevant information of books 
# values The result is that 1 Query set with dictionary inside 
Book.objects.filter(id=1).values('publish__pname')
# values__list The result is that 1 A query set with Yuan Zu inside 
Book.objects.filter(id=1).values_list('publish__pname')

#  Inquire about a certain company through the relevant information of the publishing house 1 Book 
 Publish.objects.filter(id=1).values('book__bname')
 Publish.objects.filter(id=1).values_list('book__bname')

2. Many-to-many (returned query set of objects with related classes inside)

When many-to-many is used, Django automatically creates an additional table to store their relative relationships. The table name of the additional table here is blogs_book_author.

#  Query one of the authors through their relevant information 1 Book ( The interior of the return is Book Query set of objects of) 
Book.objects.filter(author__id=1)
Author.objects.filter(id=1).values('book')

#  Inquire about 1 Who are the corresponding authors of this book ( The interior of the return is Author Query set of objects of) 
Author.objects.filter(book__id=1)
Book.objects.filter(id=1).values('author')