从JSON字符串还原满足定义的接口的结构

Question

I am implementing a task poller (restore unfinished task from a database).

The task must satisfy a defined Task interface:

type Task interface {
    // Identifier returns a unique string of a task
    Identifier() string
    // Data should be persistent
    Data() interface{}
    // Execute a task
    Execute()
}

The data stored in database satisfy the following struct:

type Record struct {
    Identifier string      `json:"identifier"`
    Data       interface{} `json:"data"`
}

When task poller starts, it read the stored data from the database, then (let's just ignore error handling for now):

r := &Record{}
result := database.Get(key)
json.Unmarshal([]byte(result), r)

we restored the saved data from the database into r.

A problem appears that I cannot call the Execute() method because r.Data is actually type of interface{} (map[string]interface{} more specifically ) other than type of Task.

How can I convert or transform the r.Data to become a struct that satisfies Task interface so that I can successfully call Execute() method?

Answer 1

r.Data is actually type of interface{} (map[string]interface{} more specifically).

You need a method set that satisfies the Task interface. For example,

package main

import "fmt"

type Task interface {
    // Identifier returns a unique string of a task
    Identifier() string
    // Data should be persistent
    Data() interface{}
    // Execute a task
    Execute()
}

type Record struct {
    Identifier string      `json:"identifier"`
    Data       interface{} `json:"data"`
}

type Data map[string]interface{}

// Task interface methods
func (d Data) Identifier() string { return "" }
func (d Data) Data() interface{}  { return nil }
func (d Data) Execute()           { fmt.Println("Execute()") }

func main() {
    r := Record{Data: map[string]interface{}{}}
    fmt.Printf("r.Data: %[1]T %[1]v
", r.Data)
    if m, ok := r.Data.(map[string]interface{}); ok {
        r.Data = Data(m)
    }

    var tasks []Task
    if task, ok := r.Data.(Task); ok {
        tasks = append(tasks, task)
    }

    for _, task := range tasks {
        fmt.Printf("%T: ", task)
        task.Execute()
    }
}

Playground: https://play.golang.org/p/SC9Ff8e-_pP

Output:

r.Data: map[string]interface {} map[]
main.Data: Execute()