Go-Gin binding data with one-to-many relationship - go

Question

I'm new to Golang and Gin framework, I have created two models
type Product struct {
gorm.Model
Name string
Media []Media
}
type Media struct {
gorm.Model
URI string
ProductID uint
}
and I send a POST request to save a new product, the body was:
{
"name": "Product1",
"media": [
"https://server.com/image1",
"https://server.com/image2",
"https://server.com/image3",
"https://server.com/video1",
"https://server.com/video2"
]
}
And I save a new product using this code
product := Product{}
if err := context.ShouldBindJSON(product); err != nil { // <-- here the error
context.String(http.StatusBadRequest, fmt.Sprintf("err: %s", err.Error()))
return
}
tx := DB.Create(&product)
if tx.Error != nil {
context.String(http.StatusBadRequest, fmt.Sprintf("err: %s", tx.Error))
return
}
the return error message is
err: json: cannot unmarshal string into Go struct field Product.Media of type models.Media
I know that ShouldBindJSON can't convert media-string to media-object, but what is the best practice to do this?

Answer 1

Your payload doesn't match the model. In the JSON body, media is an array of strings, whereas in the model it's a struct with two fields and the embedded gorm model.
If you can't change anything of your current setup, implement UnmarshalJSON on Media and set the URI field from the raw bytes. In the same method you may also initialize ProductID to something (if needed).
func (m *Media) UnmarshalJSON(b []byte) error {
m.URI = string(b)
return nil
}
Then the binding will work as expected:
product := Product{}
// pass a pointer to product
if err := context.ShouldBindJSON(&product); err != nil {
// handle err ...
return
}
fmt.Println(product) // {Product1 [{"https://server.com/image1" 0} ... }