22/12/2020 - GO
Assume that you have a service class that depends on two database repository classes. This will require you to store both of them in the service struct. This is ok for small amount of dependencies but if you need more, you would have a big struct and messy code to work with. You might have other services do the same thing but for different repository classes. Finally you have a lot of duplicates all over the place. The solution to this problem is simple. We are going to create a main repository struct which will store all the other/sub repository interfaces in it. We than just use the main repository where we need. This will allow us to access all the embedded repositories form it. A bit like a strategy pattern.
├── cmd
│ └── client
│ └── main.go
└── internal
├── dao
│ ├── article.go
│ └── label.go
├── repository
│ ├── article.go
│ ├── label.go
│ └── repository.go
└── service
├── article.go
└── label.go
package dao
import "time"
type ArticleRepository interface {
Insert(article *Article) error
Find(ID string) (*Article, error)
}
type Article struct {
ID string
Title string
PublishedAt time.Time
}
package dao
type LabelRepository interface {
Insert(label *Label) error
List(limit uint8) ([]*Label, error)
}
type Label struct {
ID string
Name string
}
package repository
import "github.com/you/client/internal/dao"
type Repository struct {
Article dao.ArticleRepository
Label dao.LabelRepository
}
func New() Repository {
return Repository{
Article: article{},
Label: label{},
}
}
package repository
import (
"log"
"github.com/you/client/internal/dao"
)
type article struct{}
func (a article) Insert(article *dao.Article) error {
log.Println("inserting article")
return nil
}
func (a article) Find(ID string) (*dao.Article, error) {
log.Println("finding article")
return nil, nil
}
package repository
import (
"log"
"github.com/you/client/internal/dao"
)
type label struct{}
func (l label) Insert(label *dao.Label) error {
log.Println("inserting label")
return nil
}
func (l label) List(limit uint8) ([]*dao.Label, error) {
log.Println("listing labels")
return nil, nil
}
package service
import (
"github.com/you/client/internal/dao"
"github.com/you/client/internal/repository"
)
type Article struct {
repo repository.Repository
}
func NewArticle(repo repository.Repository) Article {
return Article{repo: repo}
}
func (a Article) DoSomething() {
_ = a.repo.Article.Insert(&dao.Article{})
_, _ = a.repo.Article.Find("id")
}
package service
import (
"github.com/you/client/internal/dao"
"github.com/you/client/internal/repository"
)
type Label struct {
repo repository.Repository
}
func NewLabel(repo repository.Repository) Label {
return Label{repo: repo}
}
func (l Label) DoSomething() {
_ = l.repo.Label.Insert(&dao.Label{})
_, _ = l.repo.Label.List(1)
}
package main
import (
"github.com/you/client/internal/repository"
"github.com/you/client/internal/service"
)
func main() {
repo := repository.New()
articleService := service.NewArticle(repo)
articleService.DoSomething()
labelService := service.NewLabel(repo)
labelService.DoSomething()
}
$ go run -race cmd/client/main.go
2020/12/22 23:26:14 inserting article
2020/12/22 23:26:14 finding article
2020/12/22 23:26:14 inserting label
2020/12/22 23:26:14 listing labels