gorm_pager.go

package store

import (
	"math"

	"gorm.io/gorm"
)

// Param 分页参数
type Param struct {
	DB      *gorm.DB
	Page    int `form:"page"`
	Limit   int `form:"limit"`
	OrderBy []string
	ShowSQL bool
}

// Page 分页返回
type Page struct {
	TotalRecord int64       `json:"totalRecord"`
	TotalPage   int         `json:"totalPage"`
	Items       interface{} `json:"items"`
	Offset      int         `json:"offset"`
	Page        int         `form:"page" json:"page"`
	Limit       int         `form:"limit" json:"limit"`
	PrevPage    int         `json:"prevPage"`
	NextPage    int         `json:"nextPage"`
}

// Paging 分页
func Paging(param Param, result interface{}) (Page, error) {
	db := param.DB

	if param.ShowSQL {
		db = db.Debug()
	}
	if param.Page < 1 {
		param.Page = 1
	}
	if param.Limit == 0 {
		param.Limit = 10
	}

	var page Page
	var offset int
	var count int64
	var err error

	if count, err = countRecords(db, result); err != nil {
		return page, err
	}

	if param.Page == 1 {
		offset = 0
	} else {
		offset = (param.Page - 1) * param.Limit
	}

	if len(param.OrderBy) > 0 {
		for _, o := range param.OrderBy {
			db = db.Order(o)
		}
	}

	// 不知道为什么，一旦在countRecords用Model(anyType)执行过后， 再次查询时不会用指定的Select
	// 所以这里要判断一下是否有指定的Select，然后重新指定Select
	if len(db.Statement.Selects) > 0 {
		db = db.Select(db.Statement.Selects)
	}
	if err := db.Limit(param.Limit).Offset(offset).Find(result).Error; err != nil {
		return page, err
	}

	page.TotalRecord = count
	page.Items = result
	page.Page = param.Page

	page.Offset = offset
	page.Limit = param.Limit
	page.TotalPage = int(math.Ceil(float64(count) / float64(param.Limit)))

	if param.Page > 1 {
		page.PrevPage = param.Page - 1
	} else {
		page.PrevPage = param.Page
	}

	if param.Page == page.TotalPage {
		page.NextPage = param.Page
	} else {
		page.NextPage = param.Page + 1
	}
	return page, nil
}

func countRecords(db *gorm.DB, anyType interface{}) (int64, error) {
	var count int64
	result := db.Model(anyType).Count(&count)

	return count, result.Error
}