Insert data not saving to mysql using golang and It shows null while get request

I am trying to perform CRUD operation to golang with Mysql but whenever I try to post data it says 201 but it is not store to mysql.

Here is my controller: data-controller.go

func (c *dataController) Insert(context *gin.Context) {
    var dataCreateDTO dto.DataCreateDTO
    errDTO := context.ShouldBind(&dataCreateDTO)
    if errDTO != nil {
        res := helper.BuildErrorResponse("Failed to process request", errDTO.Error(), helper.EmptyObj{})
        context.JSON(http.StatusBadRequest, res)
    } else {
        result := c.dataService.Insert(dataCreateDTO)
        response := helper.BuildResponse(true, "OK", result)
        context.JSON(http.StatusCreated, response)
    }
}

data-dto.go

//DataCreateDTO is is a model that client use when create a new task
type DataCreateDTO struct {
    ID        uint64 `gorm:"primary_key:auto_increment" json:"id"`
    Title     string `gorm:"type:varchar(255)" json:"title"`
    CreatedAt time.Time
}

my entity file is data.go

//Data struct represents data table in database
type Data struct {
    ID        uint64 `gorm:"primary_key:auto_increment" json:"id"`
    Title     string `gorm:"type:varchar(255)" json:"title"`
    CreatedAt time.Time
}

my repository data-repository.go

//DataRepository is a ....
type DataRepository interface {
    InsertData(b entity.Data) entity.Data
    UpdateData(b entity.Data) entity.Data
    DeleteData(b entity.Data)
    AllData() []entity.Data
    FindDataByID(dataID uint64) entity.Data
}

type dataConnection struct {
    connection *gorm.DB
}

//NewDataRepository creates an instance DataRepository
func NewDataRepository(dbConn *gorm.DB) DataRepository {
    return &dataConnection{
        connection: dbConn,
    }
}

func (db *dataConnection) InsertData(b entity.Data) entity.Data {
    db.connection.Save(&b)
    return b
}

my service data-service.go

//DataService is a ....
type DataService interface {
    Insert(b dto.DataCreateDTO) entity.Data
    Update(b dto.DataUpdateDTO) entity.Data
    Delete(b entity.Data)
    All() []entity.Data
    FindByID(dataID uint64) entity.Data
}

type dataService struct {
    dataRepository repository.DataRepository
}

//NewDataService .....
func NewDataService(dataRepo repository.DataRepository) DataService {
    return &dataService{
        dataRepository: dataRepo,
    }
}

func (service *dataService) Insert(b dto.DataCreateDTO) entity.Data {
    data := entity.Data{}
    err := smapping.FillStruct(&data, smapping.MapFields(&b))
    if err != nil {
        log.Fatalf("Failed map %v: ", err)
    }
    res := service.dataRepository.InsertData(data)
    return res
}

Main file that is server.go

var (
    db             *gorm.DB                  = config.SetupDatabaseConnection()
    dataRepository repository.DataRepository = repository.NewDataRepository(db)
    dataService    service.DataService       = service.NewDataService(dataRepository)
    dataController controller.DataController = controller.NewDataController(dataService)
)

func main() {
    defer config.CloseDatabaseConnection(db)
    r := gin.Default()
    dataRoutes := r.Group("api/datas")
    {
        dataRoutes.GET("/", dataController.All)
        dataRoutes.POST("/", dataController.Insert)
        dataRoutes.GET("/:id", dataController.FindByID)
        dataRoutes.PUT("/:id", dataController.Update)
        dataRoutes.DELETE("/:id", dataController.Delete)
    }

    r.Run() 
}

when I do go run server.go It doesnot show any error but every time I do POST request it says 201k but when I do GET request to get all data it shows null.

my config for database is config.go

func SetupDatabaseConnection() *gorm.DB {
    errEnv := godotenv.Load()
    if errEnv != nil {
        panic("Failed to load env file")
    }
    dbUser := os.Getenv("DB_USER")
    dbPass := os.Getenv("DB_PASS")
    dbHost := os.Getenv("DB_HOST")
    dbName := os.Getenv("DB_NAME")
    dsn := fmt.Sprintf("%s:%s@tcp(%s:3306)/%s?charset=utf8&parseTime=True&loc=Local", dbUser, dbPass, dbHost, dbName)
    db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
    if err != nil {
        panic("Failed to create a connection to database")
    }
    db.AutoMigrate(&entity.Data{})
    return db
}

//CloseDatabaseConnection method is closing a connection between your app and your db
func CloseDatabaseConnection(db *gorm.DB) {
    dbSQL, err := db.DB()
    if err != nil {
        panic("Failed to close connection from database")
    }
    dbSQL.Close()
}

Can you i please help me where I went wrong ? Thank you!