英文:
`json.Marshal()` converts an array field of a struct to map which it shouldn't
问题
我想将来自github.com/compose-spec的types.Project对象序列化为JSON。
然而，这个结构体中应该是一个数组的字段总是被序列化为一个映射。
package main
import (
"encoding/json"
types "github.com/compose-spec/compose-go/types"
)
func main() {
out := types.Project{
Name: "foo",
Services: []types.ServiceConfig{ // <- 注意这个字段是一个数组
{
Name: "bar",
Image: "hello-world",
},
},
}
buf, err := json.Marshal(out)
if err != nil {
panic(err)
}
println(string(buf)) // <- 注意Services字段现在是一个映射，这是错误的！
var in types.Project
if err := json.Unmarshal(buf, &in); err != nil {
panic(err)
}
}
代码运行失败：
{"name":"foo","services":{"bar":{"command":null,"entrypoint":null,"image":"hello-world"}}}
panic: json: cannot unmarshal object into Go struct field Project.services of type types.Services
goroutine 1 [running]:
main.main()
/tmp/sandbox1081064727/prog.go:29 +0x168
out对象被序列化为：
{
"name": "foo",
"services": {
"bar": {
"command": null,
"entrypoint": null,
"image": "hello-world"
}
}
}
实际上应该是这样的：
{
"name": "foo",
"services": [
{
"name": "bar",
"command": null,
"entrypoint": null,
"image": "hello-world"
}
]
}
英文:
I want to serialize object of types.Project from github.com/compose-spec into JSON
However, a field of ths struct which is supposed to be array, is always serialized into map.
package main
import (
"encoding/json"
types "github.com/compose-spec/compose-go/types"
)
func main() {
out := types.Project{
Name: "foo",
Services: []types.ServiceConfig{ // <- notice this field is an array
{
Name: "bar",
Image: "hello-world",
},
},
}
buf, err := json.Marshal(out)
if err != nil {
panic(err)
}
println(string(buf)) // <- notice the Services field now a map, which is incorrect!
var in types.Project
if err := json.Unmarshal(buf, &in); err != nil {
panic(err)
}
}
The code fails to run:
{"name":"foo","services":{"bar":{"command":null,"entrypoint":null,"image":"hello-world"}}}
panic: json: cannot unmarshal object into Go struct field Project.services of type types.Services
goroutine 1 [running]:
main.main()
/tmp/sandbox1081064727/prog.go:29 +0x168
The out object is serialized as
{
"name": "foo",
"services": {
"bar": {
"command": null,
"entrypoint": null,
"image": "hello-world"
}
}
}
which should really be something like
{
"name": "foo",
"services": [
{
"name": "bar",
"command": null,
"entrypoint": null,
"image": "hello-world"
}
]
}
答案1
得分: 2
你看到的行为是正确的，符合compose文件规范，规范中指出：
Compose文件必须声明一个services根元素，其键是服务名称的字符串表示，值是服务定义。
将列表转换为映射是通过compose-go/types.go中的自定义编组器实现的：
// MarshalYAML使Services实现yaml.Marshaller
func (s Services) MarshalYAML() (interface{}, error) {
services := map[string]ServiceConfig{}
for _, service := range s {
services[service.Name] = service
}
return services, nil
}
// MarshalJSON使Services实现json.Marshaler
func (s Services) MarshalJSON() ([]byte, error) {
data, err := s.MarshalYAML()
if err != nil {
return nil, err
}
return json.MarshalIndent(data, "", " ")
}
英文:
The behavior you're seeing is correct with respect to the compose file specification, which says:
> A Compose file MUST declare a services root element as a map whose keys are string representations of service names, and whose values are service definitions.
The transformation of the list to a map is implemented by the custom marshalers in compose-go/types.go:
// MarshalYAML makes Services implement yaml.Marshaller
func (s Services) MarshalYAML() (interface{}, error) {
services := map[string]ServiceConfig{}
for _, service := range s {
services[service.Name] = service
}
return services, nil
}
// MarshalJSON makes Services implement json.Marshaler
func (s Services) MarshalJSON() ([]byte, error) {
data, err := s.MarshalYAML()
if err != nil {
return nil, err
}
return json.MarshalIndent(data, "", " ")
}
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