Pagination ​

This guide discusses pagination in Go, specifically on how to implement pagination in the UserController and userService.

Structs and Methods ​

The pagination process uses several structs and methods:

• GetPageOptions() method: Retrieves the PageOptions.

GetPageOptions() *PageOptions

• GetPageOptionsWithOptions(options *PageOptionsOptions) method: Retrieves the PageOptions with options specified.

GetPageOptionsWithOptions(options *PageOptionsOptions) *PageOptions

• PageOptionsOptions struct: Defines allowed orderings.

type PageOptionsOptions struct {
	OrderByAllowed []string
}

• Pagination(c core.IHTTPContext) method: This function handles pagination. It creates a new UserService and calls its Pagination method, returning the JSON representation of the response.

func (m UserController) Pagination(c core.IHTTPContext) error {
	userSvc := services.NewUserService(c)
	res, ierr := userSvc.Pagination(c.GetPageOptions())
	if ierr != nil {
		return c.JSON(ierr.GetStatus(), ierr.JSON())
	}

	return c.JSON(http.StatusOK, res)
}

• Pagination(pageOptions *core.PageOptions) method: This function handles the logic for user pagination.

func (s userService) Pagination(pageOptions *core.PageOptions) (*repository.Pagination[models.User], core.IError) {
	// Implementation for user pagination
	return repo.User(s.ctx, repo.UserOrderBy(pageOptions)).Pagination(pageOptions) // Calling the Pagination method of the repo.User repository
}

• Pagination[M any] struct: The generic struct representing the Pagination result. It includes the page, total, limit, count, and items.

type Pagination[M any] struct {
	Page  int64 `json:"page" example:"1"`
	Total int64 `json:"total" example:"45"`
	Limit int64 `json:"limit" example:"30"`
	Count int64 `json:"count" example:"30"`
	Items []M   `json:"items"`
}

Flow of Pagination ​

1. When a pagination request comes in, it is handled by the Pagination(c core.IHTTPContext) method of the UserController.
2. A new userService is instantiated via services.NewUserService(c).
3. The Pagination(c.GetPageOptions()) method of the userService is called with the PageOptions fetched from the context.
4. Within the userService pagination method, the repo.User(s.ctx, repo.UserOrderBy(pageOptions)).Pagination(pageOptions) call is made. It is responsible for actual data retrieval and pagination.
5. The Pagination method of the User repository returns the paginated data based on the options passed.
6. If an error occurs during the process, it is caught and returned in a JSON response. If the process is successful, the data is returned in a JSON response with the HTTP status 200.

Conclusion ​

The above code and guide demonstrate how to perform pagination in Go. Remember to adjust the implementation according to the specifics of your database or data source.