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Creating an opinionated GraphQL server with Go - Part 3

cmelgarejo profile image Christian Melgarejo Bresanovich ・14 min read

This is part of a series, not suited for beginners, but welcome too! You can
check it out from the start

And review how to get up to this part, as always all the code is at github for
part 3


Today we'll add GORM and a database to our project, and the RDBMS of my choice
is PostgreSQL You can use MySQL, SQLite, whatever
you like as long as GORM supports it. And, also you can check out
Part 2 in case you've missed it. I will go even on a faster pace in
this one, check out the comments in the code for more info

Adding GORM into the project

Let's add GORM to our project:

$ go get -u github.com/jinzhu/gorm

So, we need migrations, let's add Gomigrate

$ go get gopkg.in/gormigrate.v1

I don't want the id's to be as easily discoverable as ints [1,2,3] right now
anyone could just send a mutation on deleteUser(userId: 1), this should add
another layer on complexity to reduce the attack surface on our silly API.

Add UUID package from go-frs:

$ go get github.com/gofrs/uuid

And we'll setup the db models to use UUID as primary keys.

Diving into GORM

Now, let's setup GORM into our project, with:

  • Migrations
  • Models

First lets create an entry point for everything DB, where we can initialize and
setup database connection, let's put this code at internal/orm/main.go

// Package orm provides `GORM` helpers for the creation, migration and access
// on the project's database
package orm

import (
    log "github.com/cmelgarejo/go-gql-server/internal/logger"

    "github.com/cmelgarejo/go-gql-server/internal/orm/migration"

    "github.com/cmelgarejo/go-gql-server/pkg/utils"
    //Imports the database dialect of choice
    _ "github.com/jinzhu/gorm/dialects/postgres"

    "github.com/jinzhu/gorm"
)

var autoMigrate, logMode, seedDB bool
var dsn, dialect string

// ORM struct to holds the gorm pointer to db
type ORM struct {
    DB *gorm.DB
}

func init() {
    dialect = utils.MustGet("GORM_DIALECT")
    dsn = utils.MustGet("GORM_CONNECTION_DSN")
    seedDB = utils.MustGetBool("GORM_SEED_DB")
    logMode = utils.MustGetBool("GORM_LOGMODE")
    autoMigrate = utils.MustGetBool("GORM_AUTOMIGRATE")
}

// Factory creates a db connection with the selected dialect and connection string
func Factory() (*ORM, error) {
    db, err := gorm.Open(dialect, dsn)
    if err != nil {
        log.Panic("[ORM] err: ", err)
    }
    orm := &ORM{
        DB: db,
    }
    // Log every SQL command on dev, @prod: this should be disabled?
    db.LogMode(logMode)
    // Automigrate tables
    if autoMigrate {
        err = migration.ServiceAutoMigration(orm.DB)
    }
    log.Info("[ORM] Database connection initialized.")
    return orm, err
}

You might've noticed internal/logger log package, we'll dive into that in the
bonus section, for now, you can even use import "log" package :)

Migration

The migration service called in migration.ServiceAutoMigration that we'll
save in internal/ocm/migration/main.go:

package migration

import (
    "fmt"

    log "github.com/cmelgarejo/go-gql-server/internal/logger"

    "github.com/cmelgarejo/go-gql-server/internal/orm/migration/jobs"
    "github.com/cmelgarejo/go-gql-server/internal/orm/models"
    "github.com/jinzhu/gorm"
    "gopkg.in/gormigrate.v1"
)

func updateMigration(db *gorm.DB) error {
    return db.AutoMigrate(
        &models.User{},
    ).Error
}

// ServiceAutoMigration migrates all the tables and modifications to the connected source
func ServiceAutoMigration(db *gorm.DB) error {
    // Keep a list of migrations here
    m := gormigrate.New(db, gormigrate.DefaultOptions, nil)
    m.InitSchema(func(db *gorm.DB) error {
        log.Info("[Migration.InitSchema] Initializing database schema")
        switch db.Dialect().GetName() {
        case "postgres":
            // Let's create the UUID extension, the user has to ahve superuser
            // permission for now
            db.Exec("create extension \"uuid-ossp\";")
        }
        if err := updateMigration(db); err != nil {
            return fmt.Errorf("[Migration.InitSchema]: %v", err)
        }
        // Add more jobs, etc here
        return nil
    })
    m.Migrate()

    if err := updateMigration(db); err != nil {
        return err
    }
    m = gormigrate.New(db, gormigrate.DefaultOptions, []*gormigrate.Migration{
        jobs.SeedUsers,
    })
    return m.Migrate()
}

Now first we see a couple of packages more dependant on migration,
internal/orm/migration/jobs and internal/orm/models

Defining models

Let's start by setting up the models that can be added in the updateMigration
func, so to define user.go but first, I have a special need for all my models,
I want some of them to be soft deletable (not removed from the table itself)
and some can be utterly destroyed, since we are using GORM we can create structs
by using gorm.Model struct, or define our own, we'll do just that, I
need to be changed, theres another thing, the gorm.Model also uses
autoincremented numeric id's, but I like to complicate things so I want to
use UUID's as primary keys :D

Let's create a internal/orm/models/base.go model file with 2 versions of the
base model, one with hard delete and the other soft delete:

package models

import (
  "time"

  "github.com/gofrs/uuid"
  "github.com/jinzhu/gorm"
)

// BaseModel defines the common columns that all db structs should hold, usually
// db structs based on this have no soft delete
type BaseModel struct {
  // ID should use uuid_generate_v4() for the pk's
  ID        uuid.UUID  `gorm:"primary_key;type:uuid;default:uuid_generate_v4()"`
  CreatedAt time.Time  `gorm:"index;not null;default:CURRENT_TIMESTAMP"` // (My|Postgre)SQL
  UpdatedAt *time.Time `gorm:"index"`
}

// BaseModelSoftDelete defines the common columns that all db structs should
// hold, usually. This struct also defines the fields for GORM triggers to
// detect the entity should soft delete
type BaseModelSoftDelete struct {
  BaseModel
  DeletedAt *time.Time `sql:"index"`
}

Now, with these base models we can define any other one we need for our server,
so here is internal/orm/models/user.go:

package models

// User defines a user for the app
type User struct {
  BaseModelSoftDelete         // We don't to actually delete the users, maybe audit if we want to hard delete them? or wait x days to purge from the table, also
  Email               string  `gorm:"not null;unique_index:idx_email"`
  UserID              *string // External user ID
  Name                *string
  NickName            *string
  FirstName           *string
  LastName            *string
  Location            *string `gorm:"size:1048"`
  Description         *string `gorm:"size:1048"`
}

Since we're going to use a external service for the authentication via Goth
and use it for the Authentication flow, no password column for now.

All right, now with this, we just need to seed the table with at least an user,
we'll use Gomigrate pkg, and prepare a
migration job file, let's call it: internal/orm/migrations/jobs/seed_users.go

package jobs

import (
    "github.com/cmelgarejo/go-gql-server/internal/orm/models"
    "github.com/jinzhu/gorm"
    "gopkg.in/gormigrate.v1"
)

var (
    uname                    = "Test User"
    fname                    = "Test"
    lname                    = "User"
    nname                    = "Foo Bar"
    description              = "This is the first user ever!"
    location                 = "His house, maybe? Wouldn't know"
    firstUser   *models.User = &models.User{
        Email:       "test@test.com",
        Name:        &uname,
        FirstName:   &fname,
        LastName:    &lname,
        NickName:    &nname,
        Description: &description,
        Location:    &location,
    }
)

// SeedUsers inserts the first users
var SeedUsers *gormigrate.Migration = &gormigrate.Migration{
    ID: "SEED_USERS",
    Migrate: func(db *gorm.DB) error {
        return db.Create(&firstUser).Error
    },
    Rollback: func(db *gorm.DB) error {
        return db.Delete(&firstUser).Error
    },
}

Now that we have everything set-up we can modify out cmd/gql-server/main.go

package main

import (
  log "github.com/cmelgarejo/go-gql-server/internal/logger"

  "github.com/cmelgarejo/go-gql-server/internal/orm"
  "github.com/cmelgarejo/go-gql-server/pkg/server"
)

func main() {
  // Create a new ORM instance to send it to our
  orm, err := orm.Factory()
  if err != nil {
    log.Panic(err)
  }
  // Send: ORM instance
  server.Run(orm)
}

Also pkg/server/main.go:

package server

import (
  log "github.com/cmelgarejo/go-gql-server/internal/logger"

  "github.com/cmelgarejo/go-gql-server/internal/orm"

  "github.com/cmelgarejo/go-gql-server/internal/handlers"
  "github.com/cmelgarejo/go-gql-server/pkg/utils"
  "github.com/gin-gonic/gin"
)

var host, port, gqlPath, gqlPgPath string
var isPgEnabled bool

func init() {
  host = utils.MustGet("GQL_SERVER_HOST")
  port = utils.MustGet("GQL_SERVER_PORT")
  gqlPath = utils.MustGet("GQL_SERVER_GRAPHQL_PATH")
  gqlPgPath = utils.MustGet("GQL_SERVER_GRAPHQL_PLAYGROUND_PATH")
  isPgEnabled = utils.MustGetBool("GQL_SERVER_GRAPHQL_PLAYGROUND_ENABLED")
}

// Run spins up the server
func Run(orm *orm.ORM) {
  log.Info("GORM_CONNECTION_DSN: ", utils.MustGet("GORM_CONNECTION_DSN"))

  endpoint := "http://" + host + ":" + port

  r := gin.Default()
  // Handlers
  // Simple keep-alive/ping handler
  r.GET("/ping", handlers.Ping())

  // GraphQL handlers
  // Playground handler
  if isPgEnabled {
    r.GET(gqlPgPath, handlers.PlaygroundHandler(gqlPath))
    log.Info("GraphQL Playground @ " + endpoint + gqlPgPath)
  }
  // Pass in the ORM instance to the GraphqlHandler
  r.POST(gqlPath, handlers.GraphqlHandler(orm))
  log.Info("GraphQL @ " + endpoint + gqlPath)

  // Run the server
  // Inform the user where the server is listening
  log.Info("Running @ " + endpoint)
  // Print out and exit(1) to the OS if the server cannot run
  log.Fatal(r.Run(host + ":" + port))
}

And the GraphQL Handler should also receive the ORM instance, so we can use the
database connection in the resolvers internal/handlers/gql.go:

package handlers

import (
  "github.com/99designs/gqlgen/handler"
  "github.com/cmelgarejo/go-gql-server/internal/gql"
  "github.com/cmelgarejo/go-gql-server/internal/gql/resolvers"
  "github.com/cmelgarejo/go-gql-server/internal/orm"
  "github.com/gin-gonic/gin"
)

// GraphqlHandler defines the GQLGen GraphQL server handler
func GraphqlHandler(orm *orm.ORM) gin.HandlerFunc {
  // NewExecutableSchema and Config are in the generated.go file
  c := gql.Config{
    Resolvers: &resolvers.Resolver{
      ORM: orm, // pass in the ORM instance in the resolvers to be used
    },
  }

  h := handler.GraphQL(gql.NewExecutableSchema(c))

  return func(c *gin.Context) {
    h.ServeHTTP(c.Writer, c.Request)
  }
}

// PlaygroundHandler defines a handler to expose the Playground
func PlaygroundHandler(path string) gin.HandlerFunc {
  h := handler.Playground("Go GraphQL Server", path)
  return func(c *gin.Context) {
    h.ServeHTTP(c.Writer, c.Request)
  }
}

And by this point lets modify the internal/gql/resolvers/main.go for the
Resolver struct to use the ORM instance:

package resolvers

import (
  "github.com/cmelgarejo/go-gql-server/internal/gql"
  "github.com/cmelgarejo/go-gql-server/internal/orm"
)

// Resolver is a modifiable struct that can be used to pass on properties used
// in the resolvers, such as DB access
type Resolver struct {
  ORM *orm.ORM
}

// Mutation exposes mutation methods
func (r *Resolver) Mutation() gql.MutationResolver {
  return &mutationResolver{r}
}

// Query exposes query methods
func (r *Resolver) Query() gql.QueryResolver {
  return &queryResolver{r}
}

type mutationResolver struct{ *Resolver }

type queryResolver struct{ *Resolver }

Oh right! Lets modify our internal/schemas.graphql to reflect the database
model:

scalar Time
# Types
type User {
  id: ID!
  email: String!
  userId: String
  name: String
  firstName: String
  lastName: String
  nickName: String
  description: String
  location: String
  createdAt: Time!
  updatedAt: Time
}

# Input Types
input UserInput {
  email: String
  userId: String
  displayName: String
  name: String
  firstName: String
  lastName: String
  nickName: String
  description: String
  location: String
}

# List Types
type Users {
  count: Int # You want to return count for a grid for example
  list: [User!]! # that is why we need to specify the users object this way
}

# Define mutations here
type Mutation {
  createUser(input: UserInput!): User!
  updateUser(id: ID!, input: UserInput!): User!
  deleteUser(id: ID!): Boolean!
}

# Define queries here
type Query {
  users(id: ID): Users!
}

You've might noticed the way that I'm returning the users query. That's
because we might need to return the count of records to a grid for example,
and I want to filter and search in the future, and that's where list comes in

And, there's no single user query, why is that? I want to KISS always (not you,
stop looking at me like that!) that's why we'll use the same query to retrieve
a single specific record or a bunch of them.

Now, let's modify out scripts/gqlgen.sh with an option to regenerate the
resolver functions at internal/gql/resolvers/generated/resolver.go so you can
copy any new query or mutation resolver into a file of its own

#!/bin/bash
printf "\nRegenerating gqlgen files\n"
# Optional, delete the resolver to regenerate, only if there are new queries
# or mutations, if you are just changing the input or type definition and
# doesn't impact the resolvers definitions, no need to do it
while [[ "$#" -gt 0 ]]; do case $1 in
  -r|--resolvers)
    rm -f internal/gql/resolvers/generated/resolver.go
  ;;
  *) echo "Unknown parameter passed: $1"; exit 1;;
esac; shift; done

time go run -v github.com/99designs/gqlgen
printf "\nDone.\n\n"

Take from internal/gql/resolvers/generated/resolver.go the parts needed, the
func's that have a "not implemented" panic on them, and delete everything
except the package resolvers line, or else you will have impacting func
definitions.

So at last we can create the specific resolver for the users, so a new file with
all the internal/gql/resolvers/users.go:

package resolvers

import (
  "context"

  log "github.com/cmelgarejo/go-gql-server/internal/logger"

  "github.com/cmelgarejo/go-gql-server/internal/gql/models"
  tf "github.com/cmelgarejo/go-gql-server/internal/gql/resolvers/transformations"
  dbm "github.com/cmelgarejo/go-gql-server/internal/orm/models"
)

// CreateUser creates a record
func (r *mutationResolver) CreateUser(ctx context.Context, input models.UserInput) (*models.User, error) {
  return userCreateUpdate(r, input, false)
}

// UpdateUser updates a record
func (r *mutationResolver) UpdateUser(ctx context.Context, id string, input models.UserInput) (*models.User, error) {
  return userCreateUpdate(r, input, true, id)
}

// DeleteUser deletes a record
func (r *mutationResolver) DeleteUser(ctx context.Context, id string) (bool, error) {
  return userDelete(r, id)
}

// Users lists records
func (r *queryResolver) Users(ctx context.Context, id *string) (*models.Users, error) {
  return userList(r, id)
}

// ## Helper functions

func userCreateUpdate(r *mutationResolver, input models.UserInput, update bool, ids ...string) (*models.User, error) {
  dbo, err := tf.GQLInputUserToDBUser(&input, update, ids...)
  if err != nil {
    return nil, err
  }
  // Create scoped clean db interface
  db := r.ORM.DB.New().Begin()
  if !update {
    db = db.Create(dbo).First(dbo) // Create the user
  } else {
    db = db.Model(&dbo).Update(dbo).First(dbo) // Or update it
  }
  gql, err := tf.DBUserToGQLUser(dbo)
  if err != nil {
    db.RollbackUnlessCommitted()
    return nil, err
  }
  db = db.Commit()
  return gql, db.Error
}

func userDelete(r *mutationResolver, id string) (bool, error) {
  return false, nil
}

func userList(r *queryResolver, id *string) (*models.Users, error) {
  entity := "users"
  whereID := "id = ?"
  record := &models.Users{}
  dbRecords := []*dbm.User{}
  db := r.ORM.DB.New()
  if id != nil {
    db = db.Where(whereID, *id)
  }
  db = db.Find(&dbRecords).Count(&record.Count)
  for _, dbRec := range dbRecords {
    if rec, err := tf.DBUserToGQLUser(dbRec); err != nil {
      log.Errorfn(entity, err)
    } else {
      record.List = append(record.List, rec)
    }
  }
  return record, db.Error
}

You sure will have wondered what tf package is: Remember the trasformations
file and folders I mentioned in Part 2? Ok, here is where we need to
transform from the GQL Input to the database user struct to be easily saved
in the database and convert back from the database to the GQL return struct of
the resolver:

package transformations

import (
  "errors"

  gql "github.com/cmelgarejo/go-gql-server/internal/gql/models"
  dbm "github.com/cmelgarejo/go-gql-server/internal/orm/models"
  "github.com/gofrs/uuid"
)

// DBUserToGQLUser transforms [user] db input to gql type
func DBUserToGQLUser(i *dbm.User) (o *gql.User, err error) {
  o = &gql.User{
    ID:          i.ID.String(),
    Email:       i.Email,
    UserID:      i.UserID,
    Name:        i.Name,
    FirstName:   i.FirstName,
    LastName:    i.LastName,
    NickName:    i.NickName,
    Description: i.Description,
    Location:    i.Location,
    CreatedAt:   i.CreatedAt,
    UpdatedAt:   i.UpdatedAt,
  }
  return o, err
}

// GQLInputUserToDBUser transforms [user] gql input to db model
func GQLInputUserToDBUser(i *gql.UserInput, update bool, ids ...string) (o *dbm.User, err error) {
  o = &dbm.User{
    UserID:      i.UserID,
    Name:        i.Name,
    FirstName:   i.FirstName,
    LastName:    i.LastName,
    NickName:    i.NickName,
    Description: i.Description,
    Location:    i.Location,
  }
  if i.Email == nil && !update {
    return nil, errors.New("Field [email] is required")
  }
  if i.Email != nil {
    o.Email = *i.Email
  }
  if len(ids) > 0 {
    updID, err := uuid.FromString(ids[0])
    if err != nil {
      return nil, err
    }
    o.ID = updID
  }
  return o, err
}

Getting back to the users.go resolver, I've separated the helper func's from
the resolver to have them the smallest and more readable way to do this, passing
the resolver to the helper functions will make more sense than just passing the
ORM in the next Part 4 when we'll need to plug-in authentication and
permissions to the resolvers.

Hey, now we can query and mutate our users from the database!

gql is showing db data!

And a specific user from the database:

gql is showing db data!

We can always create a new one:

gql is creating db data!

And update it:

gql is updating db data!

Okay, and as promised let's enhance our little project a bit more by adding a
couple of packages next.

Extra: Bonus section

Logger package

The included "log" package could always be enough for us, but I found this
well structured package called Logrus and
created a wrapper for it to be used through out the project, create the file
internal/logger/main.go:

package logger

import (
  "github.com/sirupsen/logrus"
)

var logger *StandardLogger

func init() {
  logger = NewLogger()
}

// Event stores messages to log later, from our standard interface
type Event struct {
  id      int
  message string
}

// StandardLogger enforces specific log message formats
type StandardLogger struct {
  *logrus.Logger
}

// NewLogger initializes the standard logger
func NewLogger() *StandardLogger {
  var baseLogger = logrus.New()

  var standardLogger = &StandardLogger{baseLogger}

  standardLogger.Formatter = &logrus.TextFormatter{
    FullTimestamp: true,
  }
  // We could transform the errors into a JSON format, for external log SaaS tools such as splunk or logstash
  // standardLogger.Formatter = &logrus.JSONFormatter{
  //   PrettyPrint: true,
  // }

  return standardLogger
}

// Declare variables to store log messages as new Events
var (
  invalidArgMessage      = Event{1, "Invalid arg: %s"}
  invalidArgValueMessage = Event{2, "Invalid value for argument: %s: %v"}
  missingArgMessage      = Event{3, "Missing arg: %s"}
)

// Errorfn Log errors with format
func Errorfn(fn string, err error) {
  logger.Errorf("[%s]: %v", fn, err)
}

// InvalidArg is a standard error message
func InvalidArg(argumentName string) {
  logger.Errorf(invalidArgMessage.message, argumentName)
}

// InvalidArgValue is a standard error message
func InvalidArgValue(argumentName string, argumentValue string) {
  logger.Errorf(invalidArgValueMessage.message, argumentName, argumentValue)
}

// MissingArg is a standard error message
func MissingArg(argumentName string) {
  logger.Errorf(missingArgMessage.message, argumentName)
}

// Info Log
func Info(args ...interface{}) {
  logger.Infoln(args...)
}

// Infof Log
func Infof(format string, args ...interface{}) {
  logger.Infof(format, args...)
}

// Warn Log
func Warn(args ...interface{}) {
  logger.Warnln(args...)
}

// Warnf Log
func Warnf(format string, args ...interface{}) {
  logger.Warnf(format, args...)
}

// Panic Log
func Panic(args ...interface{}) {
  logger.Panicln(args...)
}

// Panicf Log
func Panicf(format string, args ...interface{}) {
  logger.Panicf(format, args...)
}

// Error Log
func Error(args ...interface{}) {
  logger.Errorln(args...)
}

// Errorf Log
func Errorf(format string, args ...interface{}) {
  logger.Errorf(format, args...)
}

// Fatal Log
func Fatal(args ...interface{}) {
  logger.Fatalln(args...)
}

// Fatalf Log
func Fatalf(format string, args ...interface{}) {
  logger.Fatalf(format, args...)
}

Now we have a extendable logger package with nice features

logger stuff

Adding server reloading on change with Realize

If you are annoyed on how every change you make you have to restart you server,
coming from developing quite a while in node.js, I really missed nodemon,
luckily we have something even better in Go:

$ go get github.com/tockins/realize

After this you'll have realize executable in $GOPATH/bin/realize up for use,
so, create a .realize.yml file (or run $GOPATH/bin/realize init in the root
of our project, to create it interactively, here's my yml file:

settings:
  files:
    outputs:
      status: false
      path: ''
      name: .r.outputs.log
    logs:
      status: false
      path: ''
      name: .r.logs.log
    errors:
      status: false
      path: ''
      name: .r.errors.log
  legacy:
    force: false
    interval: 0s
schema:
  - name: gql-server
    path: cmd/gql-server
    commands:
      install:
        status: false
      run:
        status: true
    watcher:
      extensions:
        - go
      paths:
        - ../../
      ignore:
        paths:
          - .git
          - .realize
          - .vscode
          - vendor

This should be enough for running in a script we're making next, copy the
scripts/run.sh to scripts/dev-run.sh and modify it like so:

#!/bin/sh
app="gql-server"
src="$srcPath/$app/$pkgFile"

printf "\nStart running: $app\n"
# Set all ENV vars for the server to run
export $(grep -v '^#' .env | xargs)
time /$GOPATH/bin/realize start run
# This should unset all the ENV vars, just in case.
unset $(grep -v '^#' .env | sed -E 's/(.*)=.*/\1/' | xargs)
printf "\nStopped running: $app\n\n"

And also, change run.shto:

#!/bin/sh
buildPath="build"
app="gql-server"
program="$buildPath/$app"

printf "\nStart app: $app\n"
# Set all ENV vars for the program to run
export $(grep -v '^#' .env | xargs)
time ./$program
# This should unset all the ENV vars, just in case.
unset $(grep -v '^#' .env | sed -E 's/(.*)=.*/\1/' | xargs)
printf "\nStopped app: $app\n\n"

Well, now you can run our project with .scripts/dev-run.sh and have it reload
every time you make a change in your go files! Neat, right?

Again, like the former parts, all the code is available in the
repository here! If you have questions, critiques and comments go ahead and let's learn more together!

And...

Sorry for the long and unwind post, here's a gopher potato: gopher potato

Posted on by:

cmelgarejo profile

Christian Melgarejo Bresanovich

@cmelgarejo

Dev guy, breaks things, fixes them afterwards, usually working as intended or having side effects... I call those: features!

Discussion

markdown guide
 

great work here, but i wanted to make you aware of some possible issues.

first with realize I had to use the following

        commands:
            install:
                status: true
                method: go build -o build/gql-server
            run:
                status: true
                method: build/gql-server

otherwise exec not started occurs.

For mysql users some modifications are needed namely the base.go should have the following ID

    ID        uuid.UUID  `gorm:"primary_key;type:varchar(36)"`

also you need to implement the BeforeCreate

// BeforeCreate will set a UUID rather than numeric ID.
func (base *BaseModel) BeforeCreate(scope *gorm.Scope) error {
    uuid, err := uuid.NewV4()
    if err != nil {
        return err
    }
    return scope.SetColumn("ID", uuid)
}
 

Thank you. I learn a lot from your articles. Waiting for part4.