英文:
Golang cannot display retrieved data in view
问题
希望这是我最后一个关于指针的问题：
我正在调用一个存储库方法来获取一组健身课程。我在视图中这样显示它们：
{{ range .}}
{{.VideoPath}} << 正确
<br>
{{.Instructor.Email}} << 空白
<br>
{{.ClassType.ClassTypeCode}} << 空白
{{end}}
指导员和课程类型字段显示为空结构体，但是在ClassRepository中，我进行了一些Printlns，正确的数据被打印出来了。某处可能存在指针问题或其他问题。我做错了什么？
这是存储库的代码：
package repositories
type ClassRepository struct {
Gorp gorp.SqlExecutor
}
func (c ClassRepository) ClassesForLastNDays(days int) []entities.Class {
var classes []entities.Class
// 获取课程 - 省略部分代码
c.populateClassRelationships(classes)
return classes
}
func (c ClassRepository) populateClassRelationships(classes []entities.Class) {
for i := range classes {
class := classes[i]
// 课程类型
obj, err := c.Gorp.Get(entities.ClassType{}, class.ClassTypeCode)
if err != nil {
panic(err)
}
class.ClassType = *obj.(*entities.ClassType)
fmt.Println(class.ClassType) << 返回正确的数据
// 指导员和设备
指导员和设备的代码类似
}
}
更新：
经过大量的printlns，我可以确认问题出在populateClassRelationships之后，填充的值都丢失了。
func (c ClassRepository) ClassesForLastNDays(days int) []entities.Class {
var classes []entities.Class
// 获取课程 - 省略部分代码
c.populateClassRelationships(classes) <<<< 在该方法中，Println有值
return classes <<<< 值已丢失
}
英文:
Hopefully this is my last question to do with pointers ever:
I am calling a repository method to get a slice of gym classes. I am displaying them in a view like this:
{{ range .}}
{{.VideoPath}} << Correct
<br>
{{.Instructor.Email}} << Blank
<br>
{{.ClassType.ClassTypeCode}} << Blank
{{end}}
The instructor and classtype fields are coming up as empty structs, but in the ClassRepository I did some Printlns and the correct data gets printed. Somewhere there is a pointer issue or something. What have I done wrong?
Here is the repository:
package repositories
type ClassRepository struct {
Gorp gorp.SqlExecutor
}
func (c ClassRepository) ClassesForLastNDays(days int) []entities.Class {
var classes []entities.Class
// Gets the classes - omitted for brevity
c.populateClassRelationships(classes)
return classes
}
func (c ClassRepository) populateClassRelationships(classes []entities.Class) {
for i := range classes {
class := classes[i]
// ClassType
obj, err := c.Gorp.Get(entities.ClassType{}, class.ClassTypeCode)
if err != nil {
panic(err)
}
class.ClassType = *obj.(*entities.ClassType)
fmt.Println(class.ClassType) << Returns correct data
// Instructor and Equipment
Same for instructor and Equipment
}
}
UPDATE:
After a whole lot of printlns I can confirm that the issue is here after populateClassRelationships the populated values are all lost.
func (c ClassRepository) ClassesForLastNDays(days int) []entities.Class {
var classes []entities.Class
// Gets the classes - omitted for brevity
c.populateClassRelationships(classes) <<<< In the method,Println has values
return classes <<<< Values have been lost
}
答案1
得分: 1
我相信问题出在你的函数populateClassRelationships上，它没有修改原始的数据结构，如下面的代码所示，最终输出的结果是：
[1]
[]
不起作用的代码：
func myFunc(data []int) {
data = append(data, 1)
fmt.Println(data)
}
func main() {
d := []int { }
myFunc(d)
fmt.Println(d)
}
通过将参数作为指针引入，可以修改原始数据：
func myFuncNew(data *[]int) {
*data = append(*data, 1)
fmt.Println(*data)
}
英文:
I believe the issue is with your function populateClassRelationships where it is not modifying the original data structure as illustrated by the following code which finally outputs:
[1]
[]
Not working
func myFunc(data []int) {
data = append(data, 1)
fmt.Println(data)
}
func main() {
d := []int { }
myFunc(d)
fmt.Println(d)
}
With the introduction of the parameters as a pointer the original data can be modified
func myFuncNew(data *[]int) {
*data = append(*data, 1)
fmt.Println(*data)
}
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