How to make complex json data with go struct? [closed] - json

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I want to build a json like
{
"data": {
"posts": [
{"title": "first", "body": "first body"},
{"title": "second", "body": "second body"}
],
"categories": [
{"name": "red"},
{"name": "white"}
]
}
}
It includes two parts of data: post and category. They are different structure. But want to send them together one time.
With this code
package main
import (
"net/http"
"github.com/labstack/echo/v4"
)
type Article struct {
Data struct {
Post []struct {
Title string `json:"title"`
Body string `json:"body"`
} `json:"posts"`
Category []struct {
Name string `json:"name"`
} `json:"categories"`
} `json:"data"`
}
func main() {
e := echo.New()
e.GET("/", func(c echo.Context) error {
article := &Article{}
data := article.Data
post := data.Post
post[0].Title = "first"
post[0].Body = "first body"
post[1].Title = "second"
post[1].Body = "second body"
category := data.Category
category[0].Name = "red"
category[1].Name = "white"
return c.JSON(http.StatusOK, article)
})
e.Logger.Fatal(e.Start(":8008"))
}
I tried to make a root struct Article, then define its children, then set data to tree one by one.
When run the server and call / endpoint, got error
echo: http: panic serving [::1]:49501: runtime error: index out of range [0] with length 0
goroutine 35 [running]:
net/http.(*conn).serve.func1(0xc00012afa0)
/Users/user/.goenv/versions/1.15.7/src/net/http/server.go:1801 +0x147
panic(0x1314380, 0xc00001a200)
/Users/user/.goenv/versions/1.15.7/src/runtime/panic.go:975 +0x47a
main.main.func1(0x139b160, 0xc000208000, 0x0, 0x0)
/Users/user/test/testecho/server.go:28 +0x13b
github.com/labstack/echo/v4.(*Echo).add.func1(0x139b160, 0xc000208000, 0x0, 0x0)
/Users/user/go/1.15.7/pkg/mod/github.com/labstack/echo/v4#v4.2.0/echo.go:536 +0x62
github.com/labstack/echo/v4.(*Echo).ServeHTTP(0xc000180000, 0x1397680, 0xc000200000, 0xc000072000)
/Users/user/go/1.15.7/pkg/mod/github.com/labstack/echo/v4#v4.2.0/echo.go:646 +0x187
Then tried this
e.GET("/", func(c echo.Context) error {
article := &Article{
Data: struct{
"Post": {
{
"Title": "first",
"Body": "first body",
},
{
"Title": "second",
"Body": "second body",
},
},
"Category": {
{
"Name": "red",
},
{
"Name": "white",
},
},
}
a, err := json.Marshal(article)
if err != nil {
fmt.Println(err)
}
return c.JSON(http.StatusOK, a)
})
But the Data: struct{ line got expected expression.

Answer 1

You can simplify the code required by declaring a named type for each object in the output:
type Post struct {
Title string `json:"title"`
Body string `json:"body"`
}
type Category struct {
Name string `json:"name"`
}
type Data struct {
Posts []Post `json:"posts"`
Categories []Category `json:"categories"`
}
type Article struct {
Data Data
}
With this change, it's easy to write the composite literal:
article := &Article{
Data: Data{Posts: []Post{
{
Title: "first",
Body: "first body",
},
{
Title: "second",
Body: "second body",
},
},
Categories: []Category{
{
Name: "red",
},
{
Name: "white",
},
},
},
}