How to call Interface function in go-gin?

Question

This is repository + controller

package brand

import (
    "path/to/models"
    "gorm.io/gorm"

    "github.com/gin-gonic/gin"
)

type ResponseBrand struct {
    Items      []models.MasterBrand `json:"items"`
    TotalCount int                  `json:"total"`
}

type Repository interface {
    GetAll() (ResponseBrand, error)
}

type DBRepo struct {
    db *gorm.DB
}


func (repo *DBRepo) GetAll() (ResponseBrand, error) {
    var response ResponseBrand
    var brands []models.MasterBrand

    repo.db.Find(&brands)

    response.Items = brands
    response.TotalCount = len(brands)

    return response, nil
}

func list(c *gin.Context) {
    // this is an error
    res, _ := Repository.GetAll()
}

This for routing group

func ApplyRoutes(r *gin.RouterGroup) {
    brand := r.Group("/brand") {
        brand.GET("/", list)
    }
}

I try to implement repository in my project, but still stuck to call Repository.GetAll() in our controller function list. i use gin & gorm for this

question from:https://stackoverflow.com/questions/65660925/how-to-call-interface-function-in-go-gin

Answer 1

Interface is just a set of method signatures that type must have in order to implement that particular interface. So you can't call interface.

In your example code DBRepo is supposed to implement Repository interface and function list() is a function that allows to list contents of any type that implements Repository. In to do so obviously list() needs to know which instance of Repository-like type to list - e.g. receive it as an argument. Like this:

func list(ctx *gin.Context, repo Repository) {
    // here call GetAll() which MUST exist on all types passed (otherwise they don't
    // implement Repository interface
    res, _ := repo.GetAll()
    // ...
}

Now gin wouldn't be able to take modified list as a router function because signature of such is just (ctx *gin.Context) but you can use anonymous function and wrap your Repository-aware list() in it.

func ApplyRoutes(repo Repository, r *gin.RouterGroup) {
    brand := r.Group("/brand") {
        brand.GET("/", func(ctx *gin.Context) {
            list(repo)
        })
    }
}

Also your ApplyRoutes() function needs to know on which Repository routes should operate - I added it here as argument for simplicity, other elegant solution would be to wrap entire controller in type and obtain the Repository instance as a field of receiver.