Golang数据库管理器API概念，错误与类型断言 [英] Golang database manager api concept, error with type assertion

问题描述

创建数据库管理器API的基本概念，用于通过API获取数据。我正在使用GORM来获取这些strcuts实例的数据。所以有300-400代表表格的结构。

The base concept creating a Database Manager API for getting data through an API. I am using the GORM for getting data of the instances of the strcuts. So there is 300-400 struct which represents the tables.

type Users struct {
  ID int64
  Name string
}

type Categories struct {
  ID int64
  Category string
}

下一步我实现了一个函数，该函数通过表名返回结构的正确实例，我通过API端点参数获得。

The next step I implement a function which is return the correct instance of the struct by table name, what I get through the API endpoint param.

func GetModel(model string) interface{} {
  switch model {
  case "users":
    return Users{}
  case "categories"
    return Categories{}
  }
  return false
}

有一个操作结构，其中唯一的一个字段是数据库。有一些方法，例如我想使用GORM db.Last（&用户）函数的GetLast（）。

After there is an operations struct where the only one field is the DB. There is methods, for example the GetLast() where I want to use the GORM db.Last(&users) function.

func (o Operations) GetLast(model string) interface{} {
  modelStruct := GetModel(model)
  .
  .
  .
  return o.DB.Last(&modelStruct)
}

是点，所以这是我不知道的。当前的解决方案不起作用，因为在这种情况下，它是一个接口{}我需要进行类型断言更多信息在这个问题。类型断言看起来像：

There is points so this is what I don't know. The current solution is not working because in this case it is an interface{} I need make a type assertion more info in this question. The type assertion is looks like:

func (o Operations) GetLast(model string) interface{} {
  modelStruct := GetModel(model)
  .
  test := modelStruct.(Users)
  .
  return o.DB.Last(&test)
}

解决方案工作，但在这种情况下，我失去了模块化。我尝试使用 reflect.TypeOf（modelStruct），但它也不起作用，因为reflect.TypeOf的结果是一个reflect.Type，它不是golang类型。

This solution working, but in this case I lost the modularity. I try using the reflect.TypeOf(modelStruct), but it is also not working because the result of the reflect.TypeOf is a reflect.Type, with is not a golang type.

推荐答案

基本上，我解决了这个问题，将模型作为指针，并在将其作为json文件返回之后解决。

Basically I solved the problem, for getting the model as a pointer, and after I return it back as a json file.

所以我的模型如下：

So my model is the following:

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

它通过表格类型返回一个新模型。我可以使用gorm First（）函数。然后json将它统一起来，然后返回。

And it is return back a new model by table type. what I can use for gorm First() function. Then json Marshal it, and return.

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

清除模型指针，因为First（）函数存储最新查询的回调函数。

Before the return I clear the model pointer because the First() function store callbacks for the latest queries.

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

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