Question

我在Mac OS X 10.8.2上使用Go 1.0.3，我正在尝试使用json包，尝试将结构封送到json，但我一直空着{} json对象。

err值为nil，因此根据json.Marshal函数没有错误，并且结构是正确的。为什么会这样？

package main

import (
  "encoding/json"
  "fmt"
)

type Address struct {
  street string
  extended string
  city string
  state string
  zip string
}

type Name struct {
  first string
  middle string
  last string
}

type Person struct {
  name Name
  age int
  address Address
  phone string
}

func main() {
  myname := Name{"Alfred", "H", "Eigenface"}
  myaddr := Address{"42 Place Rd", "Unit 2i", "Placeton", "ST", "00921"}
  me := Person{myname, 24, myaddr, "000 555-0001"}

  b, err := json.Marshal(me)

  if err != nil {
    fmt.Println(err)
  }

  fmt.Println(string(b))    // err is nil, but b is empty, why?
  fmt.Println("\n")
  fmt.Println(me)           // me is as expected, full of data
}

Answer 1

您必须制作您想要公开的字段。像这样：

type Address struct {
  Street string
  Extended string
  City string
  State string
  Zip string
}

err为nil，因为所有导出的字段（在这种情况下都没有）都被正确编组。

工作示例：https://play.golang.org/p/9NH9Bog8_C6

查看文档http://godoc.org/encoding/json/#Marshal

Answer 2

请注意，您还可以通过执行以下操作来操纵生成的JSON中字段的名称：

type Name struct {
  First string `json:"firstname"`
  Middle string `json:"middlename"`
  Last string `json:"lastname"` 
}

Answer 3

JSON库无法查看结构中的字段，除非它们是公共的。就您而言，

// GroupJoin Fabrics with some of their OrderPlans:
var result = dbContext.Fabrics
    .GroupJoin(dbContext.OrderPlans.Where(orderPlan => ...)
    fabric => fabric.Id,              // from each Fabric take the primary key
    orderPlan => orderPlan.FabricId,  // from each OrderPlan take the foreign key

    // ResultSelector: take every Fabric with all his matching OrderPlans to make one new object:
    (fabric, orderPlansOfthisFabric) => new
    {
        // Select the Fabric properties you want
        Id = fabric.Id,
        Name = fabric.Name,
        Type = fabric.Type,

        OrderPlans = orderPlansOfThisFabric.Select(orderPlan => new
        {
             // Select the OrderPlan properties you want:
             Width = orderPlan.Width,
             Gsm = orderPlan.Gsm,
        }

        // Weight: calculate the sum of all OrderPlans of this Fabric:
        Weight = orderPlansOfThisFabric
                 .Select(orderPlan => orderPlan.Weight)
                 .Sum(),
    });

字段名称，年龄，地址和电话不是公开的（以小写字母开头）。在golang中，变量/函数以大写字母开头时是公共的。因此，要使其正常工作，您的结构需要看起来像这样：

type Person struct {
  name Name
  age int
  address Address
  phone string
}

我的结构不是编组到json中

3 个答案: