Implement eager fetch by inner join

model/book.go

@@ -18,20 +18,34 @@ type Book struct {
 	Format     *Format   `json:"format"`
 }
 
+// RecordBook defines struct represents the record of the database.
+type RecordBook struct {
+	ID           uint
+	Title        string
+	Isbn         string
+	CategoryID   uint
+	CategoryName string
+	FormatID     uint
+	FormatName   string
+}
+
+const selectBook = "select b.*, c.id as category_id, c.name as category_name, f.id as format_id, f.name as format_name " +
+	"from book b inner join category_master c on c.id = b.category_id inner join format_master f on f.id = b.format_id "
+
 // TableName returns the table name of book struct and it is used by gorm.
 func (Book) TableName() string {
 	return "book"
 }
 
 // NewBook is constructor
-func NewBook(title string, isbn string, category *Category, format *Format) *Book {
-	return &Book{Title: title, Isbn: isbn, Category: category, Format: format}
+func NewBook(title string, isbn string, categoryID uint, formatID uint) *Book {
+	return &Book{Title: title, Isbn: isbn, CategoryID: categoryID, FormatID: formatID}
 }
 
 // FindByID returns a book full matched given book's ID.
 func (b *Book) FindByID(rep *repository.Repository, id uint) (*Book, error) {
 	var book Book
-	if error := rep.Preload("Category").Preload("Format").Where("id = ?", id).Find(&book).Error; error != nil {
+	if error := rep.Where("id = ?", id).Find(&book).Error; error != nil {
 		return nil, error
 	}
 	return &book, nil
@@ -40,7 +54,7 @@ func (b *Book) FindByID(rep *repository.Repository, id uint) (*Book, error) {
 // FindAll returns all books of the book table.
 func (b *Book) FindAll(rep *repository.Repository) (*[]Book, error) {
 	var books []Book
-	if error := rep.Preload("Category").Preload("Format").Find(&books).Error; error != nil {
+	if error := rep.Find(&books).Error; error != nil {
 		return nil, error
 	}
 	return &books, nil
@@ -49,26 +63,38 @@ func (b *Book) FindAll(rep *repository.Repository) (*[]Book, error) {
 // FindAllByPage returns the page object of all books.
 func (b *Book) FindAllByPage(rep *repository.Repository, page int, size int) (*Page, error) {
 	var books []Book
-	p := createPage(rep, &books, page, size)
 
-	if error := rep.Preload("Category").Preload("Format").Offset(page * p.Size).Limit(size).Find(&books).Error; error != nil {
-		return nil, error
+	var rec RecordBook
+	rows, err := rep.Raw(selectBook+" limit ? offset ? ", size, page*size).Rows()
+	if err != nil {
+		return nil, err
+	}
+	for rows.Next() {
+		rep.ScanRows(rows, &rec)
+		book := converToEntity(&rec)
+		books = append(books, *book)
 	}
 
-	p.Content = &books
+	p := createPage(rep, &books, page, size)
 	return p, nil
 }
 
 // FindByTitle returns the page object of books partially matched given book title.
 func (b *Book) FindByTitle(rep *repository.Repository, title string, page int, size int) (*Page, error) {
 	var books []Book
-	p := createPage(rep, &books, page, size)
 
-	if error := rep.Preload("Category").Preload("Format").Where("title LIKE ?", "%"+title+"%").Offset(page * p.Size).Limit(size).Find(&books).Error; error != nil {
-		return nil, error
+	var rec RecordBook
+	rows, err := rep.Raw(selectBook+" where title like ? limit ? offset ? ", "%"+title+"%", size, page*size).Rows()
+	if err != nil {
+		return nil, err
+	}
+	for rows.Next() {
+		rep.ScanRows(rows, &rec)
+		book := converToEntity(&rec)
+		books = append(books, *book)
 	}
 
-	p.Content = &books
+	p := createPage(rep, &books, page, size)
 	return p, nil
 }
 
@@ -77,9 +103,9 @@ func createPage(rep *repository.Repository, books *[]Book, page int, size int) *
 	p.Page = page
 	p.Size = size
 	p.NumberOfElements = p.Size
-
-	rep.Preload("Category").Preload("Format").Find(&books).Count(&p.TotalElements)
+	p.TotalElements = len(*books)
 	p.TotalPages = int(math.Ceil(float64(p.TotalElements) / float64(p.Size)))
+	p.Content = books
 
 	return p
 }
@@ -116,6 +142,12 @@ func (b *Book) Delete(rep *repository.Repository) (*Book, error) {
 	return b, nil
 }
 
+func converToEntity(rec *RecordBook) *Book {
+	c := &Category{ID: rec.CategoryID, Name: rec.CategoryName}
+	f := &Format{ID: rec.FormatID, Name: rec.FormatName}
+	return &Book{ID: rec.ID, Title: rec.Title, Isbn: rec.Isbn, CategoryID: rec.CategoryID, Category: c, FormatID: rec.FormatID, Format: f}
+}
+
 // ToString is return string of object
 func (b *Book) ToString() (string, error) {
 	bytes, error := json.Marshal(b)

model/category.go

@@ -31,6 +31,15 @@ func (c *Category) FindByID(rep *repository.Repository, id uint) (*Category, err
 	return &category, nil
 }
 
+// CountByID returns a size of categories full matched given category's ID.
+func (c *Category) CountByID(rep *repository.Repository, id uint) (int, error) {
+	var count int
+	if error := rep.Model(&Category{}).Where("id = ?", id).Count(&count).Error; error != nil {
+		return 0, error
+	}
+	return count, nil
+}
+
 // FindAll returns all categories of the category table.
 func (c *Category) FindAll(rep *repository.Repository) (*[]Category, error) {
 	var categories []Category

model/dto/book.go

@@ -22,9 +22,7 @@ func NewRegBookDto() *RegBookDto {
 
 // Create creates a book model from this DTO.
 func (b *RegBookDto) Create() *model.Book {
-	c := model.NewCategory("")
-	f := model.NewFormat("")
-	return model.NewBook(b.Title, b.Isbn, c, f)
+	return model.NewBook(b.Title, b.Isbn, b.CategoryID, b.FormatID)
 }
 
 // Validate performs validation check for the each item.

model/format.go

@@ -31,6 +31,15 @@ func (f *Format) FindByID(rep *repository.Repository, id uint) (*Format, error)
 	return &format, nil
 }
 
+// CountByID returns a size of formats full matched given format's ID.
+func (f *Format) CountByID(rep *repository.Repository, id uint) (int, error) {
+	var count int
+	if error := rep.Model(&Format{}).Where("id = ?", id).Count(&count).Error; error != nil {
+		return 0, error
+	}
+	return count, nil
+}
+
 // FindAll returns all formats of the format table.
 func (f *Format) FindAll(rep *repository.Repository) (*[]Format, error) {
 	var formats []Format

repository/repository.go

@@ -1,6 +1,7 @@
 package repository
 
 import (
+	"database/sql"
 	"fmt"
 
 	"github.com/jinzhu/gorm"
@@ -60,6 +61,11 @@ func GetDB() *gorm.DB {
 	return rep.db
 }
 
+// Model specify the model you would like to run db operations
+func (rep *Repository) Model(value interface{}) *gorm.DB {
+	return rep.db.Model(value)
+}
+
 // Find find records that match given conditions.
 func (rep *Repository) Find(out interface{}, where ...interface{}) *gorm.DB {
 	return rep.db.Find(out, where...)
@@ -115,6 +121,11 @@ func (rep *Repository) Scopes(funcs ...func(*gorm.DB) *gorm.DB) *gorm.DB {
 	return rep.db.Scopes(funcs...)
 }
 
+// ScanRows scan `*sql.Rows` to give struct
+func (rep *Repository) ScanRows(rows *sql.Rows, result interface{}) error {
+	return rep.db.ScanRows(rows, result)
+}
+
 // Transaction start a transaction as a block.
 // If it is failed, will rollback and return error.
 // If it is sccuessed, will commit.

service/book.go

@@ -1,6 +1,8 @@
 package service
 
 import (
+	"fmt"
+
 	"github.com/ybkuroki/go-webapp-sample/logger"
 	"github.com/ybkuroki/go-webapp-sample/model"
 	"github.com/ybkuroki/go-webapp-sample/model/dto"
@@ -53,16 +55,17 @@ func RegisterBook(dto *dto.RegBookDto) (*model.Book, map[string]string) {
 
 		err := rep.Transaction(func(txrep *repository.Repository) error {
 			var err error
+			var count int
 			book := dto.Create()
 
 			category := model.Category{}
-			if book.Category, err = category.FindByID(txrep, dto.CategoryID); err != nil {
-				return err
+			if count, err = category.CountByID(txrep, dto.CategoryID); err != nil || count == 0 {
+				return fmt.Errorf("Not found category entity")
 			}
 
 			format := model.Format{}
-			if book.Format, err = format.FindByID(txrep, dto.FormatID); err != nil {
-				return err
+			if count, err = format.CountByID(txrep, dto.FormatID); err != nil || count == 0 {
+				return fmt.Errorf("Not found format entity")
 			}
 
 			if result, err = book.Create(txrep); err != nil {
@@ -73,7 +76,7 @@ func RegisterBook(dto *dto.RegBookDto) (*model.Book, map[string]string) {
 		})
 
 		if err != nil {
-			logger.GetEchoLogger().Error(err.Error)
+			logger.GetEchoLogger().Error(err)
 			return nil, map[string]string{"error": "transaction error"}
 		}
 
@@ -93,6 +96,7 @@ func EditBook(dto *dto.ChgBookDto) (*model.Book, map[string]string) {
 
 		err := rep.Transaction(func(txrep *repository.Repository) error {
 			var err error
+			var count int
 			var book *model.Book
 
 			b := model.Book{}
@@ -102,15 +106,17 @@ func EditBook(dto *dto.ChgBookDto) (*model.Book, map[string]string) {
 
 			book.Title = dto.Title
 			book.Isbn = dto.Isbn
+			book.CategoryID = dto.CategoryID
+			book.FormatID = dto.FormatID
 
 			category := model.Category{}
-			if book.Category, err = category.FindByID(txrep, dto.CategoryID); err != nil {
-				return err
+			if count, err = category.CountByID(txrep, dto.CategoryID); err != nil || count == 0 {
+				return fmt.Errorf("Not found category entity")
 			}
 
 			format := model.Format{}
-			if book.Format, err = format.FindByID(txrep, dto.FormatID); err != nil {
-				return err
+			if count, err = format.CountByID(txrep, dto.FormatID); err != nil || count == 0 {
+				return fmt.Errorf("Not found format entity")
 			}
 
 			if result, err = book.Save(txrep); err != nil {
@@ -121,7 +127,7 @@ func EditBook(dto *dto.ChgBookDto) (*model.Book, map[string]string) {
 		})
 
 		if err != nil {
-			logger.GetEchoLogger().Error(err.Error)
+			logger.GetEchoLogger().Error(err)
 			return nil, map[string]string{"error": "transaction error"}
 		}
 
@@ -156,7 +162,7 @@ func DeleteBook(dto *dto.ChgBookDto) (*model.Book, map[string]string) {
 		})
 
 		if err != nil {
-			logger.GetEchoLogger().Error(err.Error)
+			logger.GetEchoLogger().Error(err)
 			return nil, map[string]string{"error": "transaction error"}
 		}