1. models

              class Customer(models.Model):
                first_name = models.CharField(max_length=255)
                last_name = models.CharField(max_length=255)
                email = models.EmailField(unique=True)

                def __str__(self):
                    return f"{self.first_name} {self.last_name}"


            class Category(models.Model):
                name = models.CharField(max_length=255)

                def __str__(self):
                    return self.name


            class Product(models.Model):
                name = models.CharField(max_length=255)
                description = models.TextField()
                price = models.DecimalField(max_digits=10, decimal_places=2)
                category = models.ForeignKey(Category, related_name='products', on_delete=models.CASCADE)
                stock = models.PositiveIntegerField(default=0)

                def __str__(self):
                    return self.name

            

1. Basic where

               product= Product.objects.filter(name="Smartphone")
               

Output :

               'SELECT
                      "product"."id",
                      "product"."name",
                      "product"."description",
                      "product"."price",
                      "product"."category_id",
                      "product"."stock"
              FROM 
                  "product" 
              WHERE 
                  "product"."name" = \'Smartphone\

              

2. Multiple where

                # 1. AND (2 ways)
                Emp.objects.filter(age=28,name="Ava Martinez")
                Emp.objects.filter(Q(age=28) & Q(name="Ava Martinez"))

                # 2. OR 
                Emp.objects.filter(Q(age=28) | Q(name="Ava Martinez"))

                # 3. NOT
                Emp.objects.filter(~Q(age=28))

                

1. Contains (substring search):

name__containsis a field lookup that checks for the presence of the substring "art" anywhere in the name field, regardless of its position. “art” in their name, such as “Smartphone,” “Artisan,” or “Cart.”

            Product.objects.filter(name__contains="art")
            

Output:

            'SELECT
                    "product"."id",
                    "product"."name",
                    "product"."description",
                    "product"."price",
                    "product"."category_id",
                    "product"."stock"
            FROM
                 "product"
            WHERE
                "product"."name" LIKE \'%art%\'

            

2. Starts with:

name__startswith : It returns a queryset containing all products whose names start with “T,” such as “Tablet,” “TV,” or “T-shirt.”

            Product.objects.filter(name__startswith="T")
            

Output:

            'SELECT
                "product"."id",
                "product"."name",
                "product"."description",
                "product"."price",
                "product"."category_id",
                "product"."stock"
            FROM 
                "product"
            WHERE
                 "product"."name" LIKE \'T%\' 
        

3. Ends with:

name__endswith : It returns a queryset containing all products whose names end with “top,” such as “Laptop,” “Desktop,” or “Teapot.”

        Product.objects.filter(name__endswith="top")
        

Output:

        'SELECT
                "product"."id",
                "product"."name",
                "product"."description",
                "product"."price",
                "product"."category_id",
                "product"."stock"
        FROM 
            "product"
        WHERE 
            "product"."name" LIKE \'%top\' 
        

1. Greater than

        Product.objects.filter(price__gt=199)
        

Output:

        'SELECT
            "product"."id",
            "product"."name",
            "product"."description",
            "product"."price",
            "product"."category_id",
            "product"."stock"
    FROM 
        "product"
    WHERE 
        "product"."price" > \'199\'
            

2. Less than:

            Product.objects.filter(price__lt=199)
            

1. BETWEEN

            Product.objects.filter(stock__range=(50, 200))
            

Output:

            'SELECT 
                "product"."id",
                "product"."name",
                "product"."description",
                "product"."price",
                "product"."category_id",
                "product"."stock"
        FROM 
            "product"
        WHERE 
            "product"."stock" BETWEEN 50 AND 200

        

2. NOT BETWEEN

        # filter records that do not have an ID in the range of 1 to 3 
        Emp.objects.filter(~Q(id__range=(1,3)))
        </pre>


              

1. IN OPERATOR

        # fetch objects that have age value 25, 28, or 30
        Emp.objects.filter(age__in=[25,28,30])
        

2. NOT IN OPERATOR

        Product.objects.exclude(category_id=1)
        

Output:

        'SELECT
                "product"."id",
                "product"."name",
                "product"."description",
                "product"."price",
                "product"."category_id",
                "product"."stock"
        FROM 
            "product"
        WHERE NOT 
            ("product"."category_id" = 1)

        

        # fetch objects that do not have age value 25, 28, 30
        Emp.objects.exclude(age__in=[25,28,30])
        

        # STARTS WITH CASE SENSITIVE
        Emp.objects.filter(name__startswith="J")

        # STARTS WITH CASE INSENSITIVE
        # i ignores casing
        Emp.objects.filter(name__istartswith="j")

        # ENDS WITH CASE SENSITIVE
        Emp.objects.filter(name__endswith="e")

        # CONTAINS 
        # checks for 'doe' in name irrespective of the case
        Emp.objects.filter(name__icontains='doe')

        # IS NULL
        Emp.objects.filter(age__isnull=True)

        # IS NOT NULL
        Emp.objects.filter(age__isnull=False)