Creating type register, delete type related functions

Basically it is not an issue, but I don't find the solution, I read about a lot and ask it many times on SO.

What version of Go are you using (`go version`)?

go1.7 linux/amd64

What operating system and processor architecture are you using (`go env`)?

GOARCH="amd64" GOBIN="" GOEXE="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOOS="linux" GOPATH="/home/loow/gopath" GORACE="" GOROOT="/usr/lib/golang" GOTOOLDIR="/usr/lib/golang/pkg/tool/linux_amd64" CC="gcc" GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build217134262=/tmp/go-build -gno-record-gcc-switches" CXX="g++" CGO_ENABLED="1"

The core idea

Creating a Database Manager which is getting a json request which is contain sql related data for example the basic json looks like: {"method": "first", "table": "users"}. The method mean getting the first row from table. There is many of tables, all of them a struct which is represent the table. The database ORM is the gorm so this json is looks like after I connect to the database something like: db.First(&user) where the db is a *gorm.DB and the user is an instance of the Users struct. The core question how I get an instance of the struct where I only have a table name?

First solution

First solution which is working, but there is a problem what I detail after. So there is many of struct where a struct look like:

type Users struct {
    ID uint  
    Name string  
    Email string  
    Token string 
}
func (u *Users) TableName() string {
    return "users"
}

So there is fields and a method which is return the table name. There is a map which stores the table names and return back a pointer instance of the given struct.

var Models = map[string]interface{}{
    "users":   new(Users),
    "categories": new(Categories),
}

The Operation struct have one field, the *gorm.DB and many of functions for example, the first:

func (o Operation) First(model string) string {
    modelStruct := Models[model]
    o.DB.First(modelStruct)
    response, _ := json.Marshal(modelStruct)
    clear(modelStruct)
    return string(response)
}

This function is just doing the database call and return it as a json after clear the pointer.

func clear(v interface{}) {
    p := reflect.ValueOf(v).Elem()
    p.Set(reflect.Zero(p.Type()))
}

This is working but when I want to call the First in concurrancy the clear not working instead of got a panic of nil pointer. If I don't clear the gorm take an extra where because thinking it is an old request.

Second solution

It is not working, but I need something similar. I have a type register.

var typeRegistry = make(map[string]reflect.Type)

func init() {
    typeRegistry["users"] = reflect.TypeOf(Users{})
}

When I get it I want to use the reflect.New function.

var modelStruct = reflect.New(typeRegistry[model]).Elem()

But this is return a reflect.Value, It would be great, but in this case the functions which is related to the struct will disappear. So the gorm return back an error, there isn't function TableName.

Real question

I know the Go is a static language, but how can I handle these types, for always creating the proper instance of the struct?

golang / go