Gorm GORM v2 Many to Many does not create new record in join table

Your Question

Two structs Thread & Interest have a many to many relationship with each other. According to the documentation this is how both structs looks like:

type Thread struct {
    ID        uuid.UUID `gorm:"primaryKey" json:"threadId"`
    Title     string    `gorm:"not null" json:"title"`
    Body      string    `gorm:"not null" json:"body"`
    CreatedAt time.Time
    UpdatedAt time.Time

    // Foreign keys
    UserID uuid.UUID `json:"userId"`

    // Has many association
    Comments []Comment `json:"comments"`

    // many to many associations
    Interests     []Interest `gorm:"many2many:thread_interests;" json:"interests"`
    UsersLiked    []User     `gorm:"many2many:post_likes;" json:"usersLiked"`
    UsersDisliked []User     `gorm:"many2many:post_dislikes;" json:"usersDisliked"`
}

type Interest struct {
    ID        uuid.UUID `gorm:"primaryKey" json:"interestId"`
    Name      string    `json:"name"`
    CreatedAt time.Time `json:"createdAt"`
    UpdatedAt time.Time `json:"updatedAt"`

    // Many to many associations
    UserProfiles []UserProfile `gorm:"many2many:user_interests;" json:"userProfiles"`
    Threads      []Thread      `gorm:"many2many:thread_interests;" json:"threads"`
}

Since it is many to many between both structs I created another struct to act as join table named ThreadInterest. The code:

type ThreadInterest struct {
    ThreadID   uuid.UUID `gorm:"primaryKey;"`
    InterestID uuid.UUID `gorm:"primaryKey;"`
    CreatedAt  time.Time
    UpdatedAt  time.Time
}

The problem is that whenever I create a new thread with the corresponding interests it creates the thread record but no new record is created in the join table ThreadInterest. I tried reading the documentation and searching online but I can't find a solution. I hope you guys could help me on this.

UPDATE: Here is how I create the thread

handler:

func HandleCreateThread(context *gin.Context) {

    var threadInput apimodels.ThreadInput

    err := context.ShouldBindJSON(&threadInput)

    if err != nil {
        // return error
        context.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }

    userId, err := api.GetTokenUserId(context)

    if err != nil {
        // return error
        context.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }

    var interests []databasemodels.Interest

    interests, err = dataaccess.FindInterestByIds(threadInput.Interests)

    if err != nil {
        context.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }

    thread := databasemodels.Thread{
        Title:     threadInput.Title,
        Body:      threadInput.Body,
        Interests: interests,
        UserID:    userId,
    }

    newThread, err := dataaccess.CreateNewThread(&thread)

    if err != nil {
        context.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
        return
    }

    context.JSON(http.StatusOK, gin.H{"thread": newThread})
}

dataaccess:

func CreateNewThread(thread *databasemodels.Thread) (*databasemodels.Thread, error) {
    // Generate ID and hash password
    thread.ID = api.GenerateUUID()

    // store to database
    err := database.Database.Create(&thread).Error
    if err != nil {
        return &(databasemodels.Thread{}), err
    }
    return thread, nil
}

And this is how I migrate my database:

var Database *gorm.DB

// start a connection to the specified postgresql db from env file
func ConnectDb() {
    var err error
    host := os.Getenv("DB_HOST")
    username := os.Getenv("DB_USER")
    password := os.Getenv("DB_PASSWORD")
    databaseName := os.Getenv("DB_NAME")
    port := os.Getenv("DB_PORT")

    dsn := fmt.Sprintf("host=%s user=%s password=%s dbname=%s port=%s sslmode=disable TimeZone=Africa/Lagos", host, username, password, databaseName, port)
    Database, err = gorm.Open(postgres.Open(dsn), &gorm.Config{})

    if err != nil {
        panic(err)
    } else {
        fmt.Println("Successfully connected to the database")
    }
}

// conducts migrations to the connected database (built-in GORM functionality)

func AutoMigrateDb() {

    Database.AutoMigrate(
        &(databasemodels.User{}),
        &(databasemodels.UserProfile{}),
        &(databasemodels.Interest{}),
        &(databasemodels.UserInterest{}),
        &(databasemodels.Comment{}),
        &(databasemodels.Thread{}),
        &(databasemodels.ThreadInterest{}),
        &(databasemodels.PostLike{}),
        &(databasemodels.PostDislike{}),
        &(databasemodels.CommentLike{}),
        &(databasemodels.CommentDislike{}),
    )
}

Expected answer

Insert a new record storing both keys of the two structs that has a many to many relationship after creating thread.

Comment From: roskee

Hi, I ran your sample code and it works fine. Maybe check if FindInterestByIds is correctly returning its values.

Comment From: github-actions[bot]

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