如何将JSON文档中的字符串值解组为int类型的变量？

Question

My struct:

type User struct {
    FirstName     string `json:"firstname, omitempty" validate:"required"` 
    LastName      string `json:"lastname, omitempty" validate:"required"`
    NumberofDays  int   `json:"numberofdays, string" validate:"min=0,max=100"`
}

Value for NumberofDays is passed as string from the server but I want to check if it is within range and store as int.

Ex: user := &User{"Michael","Msk","3"}

I'm getting 'cannot unmarshal string into Go value of type int'.

I'm not sure how to typecast to int and do the validation

Answer 1

Remove the space after the comma in the struct tags, e.g. json:"numberofdays, string" should be json:"numberofdays,string". With the space, the json package ignores the string part, hence the error message you're getting. Without the space, the error goes away and behavior is as expected.

Demo comparing the two here: https://play.golang.org/p/AUImnw_PIS

Documentation of json package struct tags: https://golang.org/pkg/encoding/json/#Marshal