在golang中通用处理CRUD动作

Question

I'm trying to create view that will handle all basic CRUD operations on my gorm models. The goal is to pass model to the view and let all the magic happen.

I found topics about using reflections, so I did, but also read that is not "golang way".

The first problem that I head with this is gorm using always "value" table. So temporary solution for that is to force using "users" table or table name from CommonView

package controllers

import (
    "encoding/json"
    "fmt"
    "github.com/jinzhu/gorm"
    "net/http"
    "reflect"
)

type CommonView struct {
    db        *gorm.DB
    modelType reflect.Type
    model     interface{}
    tableName string
}

func NewCommonView(db *gorm.DB, model interface{}, tableName string) *CommonView {
    return &CommonView{
        db:        db,
        modelType: reflect.TypeOf(model),
        model:     model,
        tableName: tableName,
    }
}

func (cv *CommonView) HandleList(w http.ResponseWriter, r *http.Request) {
    modelSliceReflect := reflect.SliceOf(cv.modelType)
    models := reflect.MakeSlice(modelSliceReflect, 0, 10)

    fmt.Println(modelSliceReflect)
    fmt.Println(models)

    //modelsDirect := reflect.MakeSlice(reflect.TypeOf(cv.model), 0, 0)
    cv.db.Table("users").Find(&models)

    fmt.Println("From db: ")
    fmt.Println(models)

    modelType := reflect.TypeOf(modelSliceReflect)
    fmt.Println("Type name: " + modelType.String())


    modelsJson, _ := json.Marshal(models)

    fmt.Fprint(w, string(modelsJson))
}

Model: package models

import "golang.org/x/crypto/bcrypt"

type User struct {
    Id        string `json:"id" gorm:"type:uuid;primary_key;default:uuid_generate_v4()"`
    FirstName string `json:"firstName"`
    LastName  string `json:"lastName"`
    Email     string `json:"email" gorm:"unique;not null"`
    Password  string `json:"-"`
}

func (User) TableName() string {
    return "user"
}

Gorm finding the rows in DB (know that from gorm log). But json don't dump them - guess it's in wrong type and can't handle that. Any ideas how do handle this problem?

If you also have any other solutions how to solve problem of CRUD view, I will be also very grateful.

Answer 1

The problem rises from the fact that the json package handles reflect.Value not as expected. You can find a similar discussion here: https://github.com/golang/go/issues/7846

As you can see in the following code snippet, reflect.MakeSlice returns a type Value, not a slice.

slice_empty_reflect_make := reflect.MakeSlice(
                                    reflect.SliceOf(
                                            reflect.TypeOf(5)),
                                    10, 10)

fmt.Printf("Type of reflect.MakeSlice(): %s
",
           reflect.TypeOf(slice_empty_reflect_make).Name())

This yields:

Type of reflect.MakeSlice(): Value

When you feed the Value in the json marshaller, it will return an object, not an array:

Json: {}
Error: <nil>

You need to get back to the interface of the Value by using .Interface():

jsonBytes, err := json.Marshal(slice_empty_reflect_make.Interface())

And this is a duplicate in disguise of How do I serialize a map of type [string]reflect.Value?