Preload / load Polymorphism Association

tsdevelopment commented 2 years ago

Your Question

I have a Polymorphism Association described as follow:

type UserTypeA struct {
    Id uint64 `json:"-"`
    Firstname   string         `json:"firstname" gorm:"size:255;not null"`
    Lastname    string         `json:"lastname" gorm:"size:255;not null"`
    Message []Message  `json:"-" gorm:"polymorphic:User;polymorphicValue:UserTypeA"`
}

type UserTypeB struct {
    Id uint64 `json:"-"`
    Firstname   string         `json:"firstname" gorm:"size:255;not null"`
    Lastname    string         `json:"lastname" gorm:"size:255;not null"`
    Message []Message  `json:"-" gorm:"polymorphic:User;polymorphicValue:UserTypeB"`
}

type Message struct {
    Id uint64 `json:"-"`
    UserID    uint64 `json:"userId" gorm:"not null"`
    UserType  string `json:"userType" gorm:"size:255;not null"`
    Message   string `json:"message" gorm:"type:text;not null"`
}

Now I want to fetch all Messages and want to have the user in the json response in it. Is this possible in gorm? So far I tried the following:

var messages []Message
DB.Preload("UserTypeB").Find(&messages, Message{})

The relation "UserTypeB" can not be found. How can I get the following output? Is there another way to get the wanted result?

{
  "message": "Lorem ipsum...",
  "user": { // Gorm should either select UserTypeA or UserTypeB automatically by column "UserType"
    "id": 1234,
    "firstname": "John",
    "Lastname": "Doe"
  }
}

The document you expected this should be explained

https://gorm.io/docs/has_many.html#Polymorphism-Association

Expected answer

The documentation only describes how to create new entries. But the part of getting entries with polymorphism associations is still missing. I also searched on google & co. But I only found a solution when I would fetch UserTypeA or UserTypeB, but not Messages .

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