doushu7588 2017-09-30 16:14
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Golang抽象函数从db获取数据并填充数组

I want to create an abstract function, that gets data from DB and fills array by this data. Types of array can be different. And I want to do it without reflect, due to performance issues. I just want to call everywhere some function like GetDBItems() and get array of data from DB with desired type. But all implementations that I create are owful.

Here is this function implementation:

type AbstractArrayGetter func(size int) []interface{}

func GetItems(arrayGetter AbstractArrayGetter) {
    res := DBResponse{}
    DB.Get(&res)
    arr := arrayGetter(len(res.Rows))
    for i := 0; i < len(res.Rows); i++ {
        json.Unmarshal(res.Rows[i].Value, &obj[i])
    }
}

Here I call this function:

var events []Event
GetFullItems("events", "events_list", map[string]interface{}{}, func(size int) []interface{} {
        events = make([]Event, size, size)
        proxyEnt := make([]interface{}, size, size)
        for i, _ := range events {
            proxyEnt[i] = &events[i]
        }
        return proxyEnt
    })

It works, but there are to much code to call this function, also there is some perfomance issue about copying events array to interfaces array.

How can I do it without reflect and do it with a short function call code? Or reflect not to slow in this case?

  • 写回答

1条回答 默认 最新

  • drkjzk3359 2017-10-05 17:13
    关注

    I tested performance with reflect, and it is similar to the mentioned above solution. So here is solution with reflect, if someone needs it. This function gets data from DB and fills abstract array

    func GetItems(design string, viewName string, opts map[string]interface{}, arrayType interface{}) (interface{}, error) {
        res := couchResponse{}
        opts["limit"] = 100000
        bytes, err := CouchView(design, viewName, opts)
        if err != nil {
            return nil, err
        }
        err = json.Unmarshal(bytes, &res)
        if err != nil {
            return nil, err
        }
        dataType := reflect.TypeOf(arrayType)
        slice := reflect.MakeSlice(reflect.SliceOf(dataType), len(res.Rows), len(res.Rows))
        for i := 0; i < len(res.Rows); i++ {
            if opts["include_docs"] == true {
                err = json.Unmarshal(res.Rows[i].Doc, slice.Index(i).Addr().Interface())
            } else {
                err = json.Unmarshal(res.Rows[i].Value, slice.Index(i).Addr().Interface())
            }
            if err != nil {
                return nil, err
            }
        }
        x := reflect.New(slice.Type())
        x.Elem().Set(slice)
        return x.Interface(), nil
    }
    

    and getting data using this function:

    var e Event
    res, err := GetItems("data", "data_list", map[string]interface{}{}, e)
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论

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