// Replace
	toy2 := Toy{Name: "toy-has-many-replace"}

	if err := DB.Model(&user2).Association("Toys").Replace(&toy2); err != nil {
		t.Fatalf("Error happened when append toy, got %v", err)
	}

	if toy2.ID == 0 {
		t.Fatalf("toy2's ID should be created")
	}

	user.Toys = []Toy{toy2}
	CheckUser(t, user2, user)

	AssertAssociationCount(t, user2, "Toys", 1, "AfterReplace")

	// Delete

	var updatedUser User
	if err := DB.Preload("Pets").Preload("Toys").Where("id = ?", user.ID).First(&updatedUser).Error; err != nil {
		t.Fatalf("failed to find updated user: %v", err)
	}

	if len(updatedUser.Pets) != 2 {
		t.Fatalf("expected 2 pets, got %d", len(updatedUser.Pets))
	}

	if len(updatedUser.Toys) != 2 {
		t.Fatalf("expected 2 toys, got %d", len(updatedUser.Toys))
	}
}

			relationships.Relations[relation.Name] = relation
		}
	}
}

// User has many Toys, its `Polymorphic` is `Owner`, Pet has one Toy, its `Polymorphic` is `Owner`
//
//	type User struct {
//	  Toys []Toy `gorm:"polymorphic:Owner;"`
//	}
//	type Pet struct {
//	  Toy Toy `gorm:"polymorphic:Owner;"`
//	}
//	type Toy struct {
//	  OwnerID   int
//	  OwnerType string
//	}

			References: []Reference{{"ID", "User", "UserID", "Pet", "", true}},
		},
		{
			Name: "Toys", Type: schema.HasMany, Schema: "User", FieldSchema: "Toy",
			Polymorphic: Polymorphic{ID: "OwnerID", Type: "OwnerType", Value: "users"},
			References:  []Reference{{"ID", "User", "OwnerID", "Toy", "", true}, {"", "", "OwnerType", "Toy", "users", false}},
		},
		{

		Preload("Toys", func(db *gorm.DB) *gorm.DB {
			return db.Table("toys").Select("name")
		}).Count(&count12).Error; err == nil {
		t.Errorf("error should raise when using preload without schema")
	}

	var count13 int64
	if err := DB.Model(User{}).
		Where("name in ?", []string{user1.Name, user2.Name, user3.Name}).
		Preload("Toys", func(db *gorm.DB) *gorm.DB {

				},
				NamedPet: &Pet{
					Name: "generics-nested-joins-manager-namepet-1",
					Toy: Toy{
						Name: "generics-nested-joins-manager-namepet-toy-1",
					},
				},
			},
			NamedPet: &Pet{Name: "generics-nested-joins-namepet-1", Toy: Toy{Name: "generics-nested-joins-namepet-toy-1"}},
		},
		{
			Name:     "generics-nested-joins-2",

And an `APIRoute` subclass to use that custom request class.

### Create a custom `GzipRequest` class { #create-a-custom-gziprequest-class }

/// tip

This is a toy example to demonstrate how it works, if you need Gzip support, you can use the provided [`GzipMiddleware`](../advanced/middleware.md#gzipmiddleware){.internal-link target=_blank}.

///