How can I change the fields of a struct's json marshal?

Question

tl;dr

How can I dynamize the JSON fields of a struct?

I am using gorm as the ORM. I have my model definition as a struct:

type UserAccessToken struct {
    Id        uint           `gorm:"primaryKey" json:"-"`
    CreatedAt time.Time      `json:"createdAt"`
    DeletedAt gorm.DeletedAt `json:"deletedAt"`
    User      User           `gorm:"constraint:OnDelete:CASCADE" json:"-"`
    UserId    uint           `gorm:"not null" json:"-"`
    IpAddress string         `gorm:"not null" json:"ipAddress"`
    Token     string         `gorm:"not null" json:"token"`
}

I have multiple endpoints and I want to use different fields of the struct serialized on each endpoint.

For example, on POST /user-access-tokens/ user will be basic authenticated and a new access token will be created and returned on the response. However, on GET /user-access-tokens/ list API endpoint, the response will be a list of the UserAccessTokens, but the Token won't be on the response. And I am planning to create another endpoint only to be used by the administration interface, and all fields will be available there.

There are two I can think of:

Creating a different struct and reading from the database into this struct.
Adding a method like Map(scenario string) to the model struct which will create a map of the struct according to scenario, but in this case, I also need to add function to handle multiple instances of the struct.

What is the recommended way for this?

Hi Gokhan, knowing more about your application can yield better answers. What are these two endpoints doing? How are they called? How complicated application are you building (lines of code / amount of layers / packages?) — Tomor
Hi Tomor, you are right, I updated my question and added example use cases. — Gokhan Sari

XciD XciD · Accepted Answer · 2021-04-25T18:52:16

You can use another struct:

type UserAccessstruct {
    Id        uint           `gorm:"primaryKey" json:"-"`
    CreatedAt time.Time      `json:"createdAt"`
    DeletedAt gorm.DeletedAt `json:"deletedAt"`
    User      User           `gorm:"constraint:OnDelete:CASCADE" json:"-"`
    UserId    uint           `gorm:"not null" json:"-"`
    IpAddress string         `gorm:"not null" json:"ipAddress"`
   
}


type UserAccessToken {
    UserAccessstruct
    Token     string         `gorm:"not null" json:"token"`
}

func Get() {
   var userAccess UserAccessToken
   db.Select(selectQuery).First(&userAccess)
   

   return userAccess // Full return
   return userAccess.UserAccessstruct // Inner struct without token
}

How can I change the fields of a struct's json marshal?

1 Answers