GORM 2.0 Release Note

GORM 2.0 это перезапись с нуля, представляет некоторые изменения несовместимых API и много улучшений

Ключевые моменты

• Улучшение производительности
• Модульность
• Context, Batch Insert, Prepared Statement Mode, DryRun Mode, Join Preload, Find To Map, Create From Map, FindInBatches supports
• Вложенная транзакция/SavePoint/RollbackTo
• SQL Builder, Named Argument, Group Conditions, Upsert, Locking, Optimizer/Index/Comment Hints supports, SubQuery improvements, CRUD with SQL Expr and Context Valuer
• Full self-reference relationships support, Join Table improvements, Association Mode for batch data
• Multiple fields allowed to track create/update time, UNIX (milli/nano) seconds supports
• Field permissions support: read-only, write-only, create-only, update-only, ignored
• New plugin system, provides official plugins for multiple databases, read/write splitting, prometheus integrations…
• New Hooks API: unified interface with plugins
• New Migrator: allows to create database foreign keys for relationships, smarter AutoMigrate, constraints/checker support, enhanced index support
• New Logger: context support, improved extensibility
• Unified Naming strategy: table name, field name, join table name, foreign key, checker, index name rules
• Better customized data type support (e.g: JSON)

Как обновить

• GORM’s developments moved to github.com/go-gorm, and its import path changed to gorm.io/gorm, for previous projects, you can keep using github.com/jinzhu/gorm GORM V1 Document
• Database drivers have been split into separate projects, e.g: github.com/go-gorm/sqlite, and its import path also changed to gorm.io/driver/sqlite

Установка

go get gorm.io/gorm
// **ПРИМЕЧАНИЕ** GORM `v2.0.0` релиз выложен с тегом `v1.20.0`

Быстрый старт

import (
  "gorm.io/gorm"
  "gorm.io/driver/sqlite"
)

func init() {
  db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{})

  // Most CRUD API kept compatibility
  db.AutoMigrate(&Product{})
  db.Create(&user)
  db.First(&user, 1)
  db.Model(&user).Update("Age", 18)
  db.Model(&user).Omit("Role").Updates(map[string]interface{}{"Name": "jinzhu", "Role": "admin"})
  db.Delete(&user)
}

Основные возможности

Примечание к выпуску содержит только основные изменения, внесенные в GORM V2 в качестве краткого справочного списка

Поддержка контекста

• Операции с БД поддерживают context.Context при помощи метода WithContext
• Logger также принимает контекст для отслеживания

db.WithContext(ctx).Find(&users)

Пакетная вставка

To efficiently insert large number of records, pass a slice to the Create method. GORM will generate a single SQL statement to insert all the data and backfill primary key values, hook methods will be invoked too.

var users = []User{{Name: "jinzhu1"}, {Name: "jinzhu2"}, {Name: "jinzhu3"}}
db.Create(&users)

for _, user := range users {
  user.ID // 1,2,3
}

You can specify batch size when creating with CreateInBatches, e.g:

var users = []User{{Name: "jinzhu_1"}, ...., {Name: "jinzhu_10000"}}

// batch size 100
db.CreateInBatches(users, 100)

Prepared Statement Mode

Prepared Statement Mode creates prepared stmt and caches them to speed up future calls

// globally mode, all operations will create prepared stmt and cache to speed up
db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{PrepareStmt: true})

// session mode, create prepares stmt and speed up current session operations
tx := db.Session(&Session{PrepareStmt: true})
tx.First(&user, 1)
tx.Find(&users)
tx.Model(&user).Update("Age", 18)

Режим DryRun

Generates SQL without executing, can be used to check or test generated SQL

stmt := db.Session(&Session{DryRun: true}).Find(&user, 1).Statement
stmt.SQL.String() //=> SELECT * FROM `users` WHERE `id` = $1 // PostgreSQL
stmt.SQL.String() //=> SELECT * FROM `users` WHERE `id` = ?  // MySQL
stmt.Vars         //=> []interface{}{1}

Join с предварительной загрузкой

Preload associations using INNER JOIN, and will handle null data to avoid failing to scan

db.Joins("Company").Joins("Manager").Joins("Account").Find(&users, "users.id IN ?", []int{1,2})

Поиск в Map

Scan result to map[string]interface{} or []map[string]interface{}

var result map[string]interface{}
db.Model(&User{}).First(&result, "id = ?", 1)

Создать из Map

Create from map map[string]interface{} or []map[string]interface{}

db.Model(&User{}).Create(map[string]interface{}{"Name": "jinzhu", "Age": 18})

datas := []map[string]interface{}{
  {"Name": "jinzhu_1", "Age": 19},
  {"name": "jinzhu_2", "Age": 20},
}

db.Model(&User{}).Create(datas)

Найти в пакете(FindInBatches)

Query and process records in batch

result := db.Where("age>?", 13).FindInBatches(&results, 100, func(tx *gorm.DB, batch int) error {
  // batch processing
  return nil
})

Вложенные транзакции

db.Transaction(func(tx *gorm.DB) error {
  tx.Create(&user1)

  tx.Transaction(func(tx2 *gorm.DB) error {
    tx.Create(&user2)
    return errors.New("rollback user2") // rollback user2
  })

  tx.Transaction(func(tx2 *gorm.DB) error {
    tx.Create(&user3)
    return nil
  })

  return nil // commit user1 and user3
})

SavePoint, RollbackTo

tx := db.Begin()
tx.Create(&user1)

tx.SavePoint("sp1")
tx.Create(&user2)
tx.RollbackTo("sp1") // rollback user2

tx.Commit() // commit user1

Именованные аргументы

GORM supports use sql.NamedArg, map[string]interface{} as named arguments

db.Where("name1 = @name OR name2 = @name", sql.Named("name", "jinzhu")).Find(&user)
// SELECT * FROM `users` WHERE name1 = "jinzhu" OR name2 = "jinzhu"

db.Where("name1 = @name OR name2 = @name", map[string]interface{}{"name": "jinzhu2"}).First(&result3)
// SELECT * FROM `users` WHERE name1 = "jinzhu2" OR name2 = "jinzhu2" ORDER BY `users`.`id` LIMIT 1

db.Raw(
  "SELECT * FROM users WHERE name1 = @name OR name2 = @name2 OR name3 = @name",
  sql.Named("name", "jinzhu1"), sql.Named("name2", "jinzhu2"),
).Find(&user)
// SELECT * FROM users WHERE name1 = "jinzhu1" OR name2 = "jinzhu2" OR name3 = "jinzhu1"

db.Exec(
  "UPDATE users SET name1 = @name, name2 = @name2, name3 = @name",
  map[string]interface{}{"name": "jinzhu", "name2": "jinzhu2"},
)
// UPDATE users SET name1 = "jinzhu", name2 = "jinzhu2", name3 = "jinzhu"

Группировка условий

db.Where(
  db.Where("pizza = ?", "pepperoni").Where(db.Where("size = ?", "small").Or("size = ?", "medium")),
).Or(
  db.Where("pizza = ?", "hawaiian").Where("size = ?", "xlarge"),
).Find(&pizzas)

// SELECT * FROM pizzas WHERE (pizza = 'pepperoni' AND (size = 'small' OR size = 'medium')) OR (pizza = 'hawaiian' AND size = 'xlarge')

Под Запрос

// Where SubQuery
db.Where("amount > (?)", db.Table("orders").Select("AVG(amount)")).Find(&orders)

// From SubQuery
db.Table("(?) as u", db.Model(&User{}).Select("name", "age")).Where("age = ?", 18}).Find(&User{})
// SELECT * FROM (SELECT `name`,`age` FROM `users`) as u WHERE age = 18

// Update SubQuery
db.Model(&user).Update(
  "price", db.Model(&Company{}).Select("name").Where("companies.id = users.company_id"),
)

Upsert (обновить или создать)

clause.OnConflict provides compatible Upsert support for different databases (SQLite, MySQL, PostgreSQL, SQL Server)

import "gorm.io/gorm/clause"

db.Clauses(clause.OnConflict{DoNothing: true}).Create(&users)

db.Clauses(clause.OnConflict{
  Columns:   []clause.Column{{Name: "id"}},
  DoUpdates: clause.Assignments(map[string]interface{}{"name": "jinzhu", "age": 18}),
}).Create(&users)
// MERGE INTO "users" USING *** WHEN NOT MATCHED THEN INSERT *** WHEN MATCHED THEN UPDATE SET ***; SQL Server
// INSERT INTO `users` *** ON DUPLICATE KEY UPDATE name="jinzhu", age=18; MySQL

db.Clauses(clause.OnConflict{
  Columns:   []clause.Column{{Name: "id"}},
  DoUpdates: clause.AssignmentColumns([]string{"name", "age"}),
}).Create(&users)
// MERGE INTO "users" USING *** WHEN NOT MATCHED THEN INSERT *** WHEN MATCHED THEN UPDATE SET "name"="excluded"."name"; SQL Server
// INSERT INTO "users" *** ON CONFLICT ("id") DO UPDATE SET "name"="excluded"."name", "age"="excluded"."age"; PostgreSQL
// INSERT INTO `users` *** ON DUPLICATE KEY UPDATE `name`=VALUES(name),`age=VALUES(age); MySQL

Блокировка

db.Clauses(clause.Locking{Strength: "UPDATE"}).Find(&users)
// SELECT * FROM `users` FOR UPDATE

db.Clauses(clause.Locking{
  Strength: "SHARE",
  Table: clause.Table{Name: clause.CurrentTable},
}).Find(&users)
// SELECT * FROM `users` FOR SHARE OF `users`

Optimizer/Index/Comment Hints

import "gorm.io/hints"

// Optimizer Hints
db.Clauses(hints.New("hint")).Find(&User{})
// SELECT * /*+ hint */ FROM `users`

// Index Hints
db.Clauses(hints.UseIndex("idx_user_name")).Find(&User{})
// SELECT * FROM `users` USE INDEX (`idx_user_name`)

// Comment Hints
db.Clauses(hints.Comment("select", "master")).Find(&User{})
// SELECT /*master*/ * FROM `users`;

Check out Hints for details

CRUD из SQL Expr/Context Valuer

type Location struct {
    X, Y int
}

func (loc Location) GormDataType() string {
  return "geometry"
}

func (loc Location) GormValue(ctx context.Context, db *gorm.DB) clause.Expr {
  return clause.Expr{
    SQL:  "ST_PointFromText(?)",
    Vars: []interface{}{fmt.Sprintf("POINT(%d %d)", loc.X, loc.Y)},
  }
}

db.Create(&User{
  Name:     "jinzhu",
  Location: Location{X: 100, Y: 100},
})
// INSERT INTO `users` (`name`,`point`) VALUES ("jinzhu",ST_PointFromText("POINT(100 100)"))

db.Model(&User{ID: 1}).Updates(User{
  Name:  "jinzhu",
  Point: Point{X: 100, Y: 100},
})
// UPDATE `user_with_points` SET `name`="jinzhu",`point`=ST_PointFromText("POINT(100 100)") WHERE `id` = 1

Check out Customize Data Types for details

Права доступа к полю

Field permissions support, permission levels: read-only, write-only, create-only, update-only, ignored

type User struct {
  Name string `gorm:"<-:create"` // allow read and create
  Name string `gorm:"<-:update"` // allow read and update
  Name string `gorm:"<-"`        // allow read and write (create and update)
  Name string `gorm:"->:false;<-:create"` // createonly
  Name string `gorm:"->"` // readonly
  Name string `gorm:"-"`  // ignored
}

Отслеживать создание/обновление времени/unix (мили/нано) секунд для нескольких полей

type User struct {
  CreatedAt time.Time // Set to current time if it is zero on creating
  UpdatedAt int       // Set to current unix seconds on updaing or if it is zero on creating
  Updated   int64 `gorm:"autoUpdateTime:nano"` // Use unix Nano seconds as updating time
  Updated2  int64 `gorm:"autoUpdateTime:milli"` // Use unix Milli seconds as updating time
  Created   int64 `gorm:"autoCreateTime"`      // Use unix seconds as creating time
}

Множественные базы данных, разделение чтения/записи

GORM provides multiple databases, read/write splitting support with plugin DB Resolver, which also supports auto-switching database/table based on current struct/table, and multiple sources、replicas supports with customized load-balancing logic

Check out Database Resolver for details

Prometheus

GORM provides plugin Prometheus to collect DBStats and user-defined metrics

Check out Prometheus for details

Cтратегия именования

GORM allows users change the default naming conventions by overriding the default NamingStrategy, which is used to build TableName, ColumnName, JoinTableName, RelationshipFKName, CheckerName, IndexName, Check out GORM Config for details

db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{
  NamingStrategy: schema.NamingStrategy{TablePrefix: "t_", SingularTable: true},
})

Logger

• Context support
• Customize/turn off the colors in the log
• Slow SQL log, default slow SQL time is 200ms
• Optimized the SQL log format so that it can be copied and executed in a database console

Режим транзакции

By default, all GORM write operations run inside a transaction to ensure data consistency, you can disable it during initialization to speed up write operations if it is not required

db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{
  SkipDefaultTransaction: true,
})

Типы данных (JSON в качестве примера)

GORM optimizes support for custom types, so you can define a struct to support all databases

The following takes JSON as an example (which supports SQLite, MySQL, Postgres, refer: https://github.com/go-gorm/datatypes/blob/master/json.go)

import "gorm.io/datatypes"

type User struct {
  gorm.Model
  Name       string
  Attributes datatypes.JSON
}

db.Create(&User{
  Name:       "jinzhu",
  Attributes: datatypes.JSON([]byte(`{"name": "jinzhu", "age": 18, "tags": ["tag1", "tag2"], "orgs": {"orga": "orga"}}`)),
}

// Query user having a role field in attributes
db.First(&user, datatypes.JSONQuery("attributes").HasKey("role"))
// Query user having orgs->orga field in attributes
db.First(&user, datatypes.JSONQuery("attributes").HasKey("orgs", "orga"))

Умный выбор

GORM allows select specific fields with Select, and in V2, GORM provides smart select mode if you are querying with a smaller struct

type User struct {
  ID     uint
  Name   string
  Age    int
  Gender string
  // hundreds of fields
}

type APIUser struct {
  ID   uint
  Name string
}

// Select `id`, `name` automatically when query
db.Model(&User{}).Limit(10).Find(&APIUser{})
// SELECT `id`, `name` FROM `users` LIMIT 10

Пакетный режим связей

Association Mode supports batch data, e.g:

// Find all roles for all users
db.Model(&users).Association("Role").Find(&roles)

// Delete User A from all user's team
db.Model(&users).Association("Team").Delete(&userA)

// Get unduplicated count of members in all user's team
db.Model(&users).Association("Team").Count()

// For `Append`, `Replace` with batch data, argument's length need to equal to data's length or will returns error
var users = []User{user1, user2, user3}
// e.g: we have 3 users, Append userA to user1's team, append userB to user2's team, append userA, userB and userC to user3's team
db.Model(&users).Association("Team").Append(&userA, &userB, &[]User{userA, userB, userC})
// Reset user1's team to userA，reset user2's team to userB, reset user3's team to userA, userB and userC
db.Model(&users).Association("Team").Replace(&userA, &userB, &[]User{userA, userB, userC})

Delete Associations when deleting

You are allowed to delete selected has one/has many/many2many relations with Select when deleting records, for example:

// delete user's account when deleting user
db.Select("Account").Delete(&user)

// delete user's Orders, CreditCards relations when deleting user
db.Select("Orders", "CreditCards").Delete(&user)

// delete user's has one/many/many2many relations when deleting user
db.Select(clause.Associations).Delete(&user)

// delete user's account when deleting users
db.Select("Account").Delete(&users)

Критические изменения

We are trying to list big breaking changes or those changes can’t be caught by the compilers, please create an issue or pull request here if you found any unlisted breaking changes

Tags

• GORM V2 prefer write tag name in camelCase, tags in snake_case won’t works anymore, for example: auto_increment, unique_index, polymorphic_value, embedded_prefix, check out Model Tags
• Tags used to specify foreign keys changed to foreignKey, references, check out Associations Tags
• Not support sql tag

Table Name

TableName will not allow dynamic table name anymore, the result of TableName will be cached for future

func (User) TableName() string {
  return "t_user"
}

Please use Scopes for dynamic tables, for example:

func UserTable(u *User) func(*gorm.DB) *gorm.DB {
  return func(db *gorm.DB) *gorm.DB {
    return db.Table("user_" + u.Role)
  }
}

db.Scopes(UserTable(&user)).Create(&user)

Creating and Deleting Tables requires the use of the Migrator

Previously tables could be created and dropped as follows:

db.CreateTable(&MyTable{})
db.DropTable(&MyTable{})

Now you do the following:

db.Migrator().CreateTable(&MyTable{})
db.Migrator().DropTable(&MyTable{})

Foreign Keys

A way of adding foreign key constraints was;

db.Model(&MyTable{}).AddForeignKey("profile_id", "profiles(id)", "NO ACTION", "NO ACTION")

Now you add constraints as follows:

db.Migrator().CreateConstraint(&Users{}, "Profiles")
db.Migrator().CreateConstraint(&Users{}, "fk_users_profiles")

which translates to the following sql code for postgres:

ALTER TABLE `Profiles` ADD CONSTRAINT `fk_users_profiles` FORIEGN KEY (`useres_id`) REFRENCES `users`(`id`))

Method Chain Safety/Goroutine Safety

To reduce GC allocs, GORM V2 will share Statement when using method chains, and will only create new Statement instances for new initialized *gorm.DB or after a New Session Method, to reuse a *gorm.DB, you need to make sure it just after a New Session Method, for example:

db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})

// Safe for new initialized *gorm.DB
for i := 0; i < 100; i++ {
  go db.Where(...).First(&user)
}

tx := db.Where("name = ?", "jinzhu")
// NOT Safe as reusing Statement
for i := 0; i < 100; i++ {
  go tx.Where(...).First(&user)
}

ctxDB := db.WithContext(ctx)
// Safe after a `New Session Method`
for i := 0; i < 100; i++ {
  go ctxDB.Where(...).First(&user)
}

ctxDB := db.Where("name = ?", "jinzhu").WithContext(ctx)
// Safe after a `New Session Method`
for i := 0; i < 100; i++ {
  go ctxDB.Where(...).First(&user) // `name = 'jinzhu'` will apply to the query
}

tx := db.Where("name = ?", "jinzhu").Session(&gorm.Session{})
// Safe after a `New Session Method`
for i := 0; i < 100; i++ {
  go tx.Where(...).First(&user) // `name = 'jinzhu'` will apply to the query
}

Check out Method Chain for details

Default Value

GORM V2 won’t auto-reload default values created with database function after creating, checkout Default Values for details

Soft Delete

GORM V1 will enable soft delete if the model has a field named DeletedAt, in V2, you need to use gorm.DeletedAt for the model wants to enable the feature, e.g:

type User struct {
  ID        uint
  DeletedAt gorm.DeletedAt
}

type User struct {
  ID      uint
  // field with different name
  Deleted gorm.DeletedAt
}

NOTE: gorm.Model is using gorm.DeletedAt, if you are embedding it, nothing needs to change

BlockGlobalUpdate

GORM V2 enabled BlockGlobalUpdate mode by default, to trigger a global update/delete, you have to use some conditions or use raw SQL or enable AllowGlobalUpdate mode, for example:

db.Where("1 = 1").Delete(&User{})

db.Raw("delete from users")

db.Session(&gorm.Session{AllowGlobalUpdate: true}).Delete(&User{})

ErrRecordNotFound

GORM V2 only returns ErrRecordNotFound when you are querying with methods First, Last, Take which is expected to return some result, and we have also removed method RecordNotFound in V2, please use errors.Is to check the error, e.g:

err := db.First(&user).Error
errors.Is(err, gorm.ErrRecordNotFound)

Hooks Method

Before/After Create/Update/Save/Find/Delete must be defined as a method of type func(tx *gorm.DB) error in V2, which has unified interfaces like plugin callbacks, if defined as other types, a warning log will be printed and it won’t take effect, check out Hooks for details

func (user *User) BeforeCreate(tx *gorm.DB) error {
  // Modify current operation through tx.Statement, e.g:
  tx.Statement.Select("Name", "Age")
  tx.Statement.AddClause(clause.OnConflict{DoNothing: true})

  // Operations based on tx will runs inside same transaction without clauses of current one
  var role Role
  err := tx.First(&role, "name = ?", user.Role).Error
  // SELECT * FROM roles WHERE name = "admin"
  return err
}

Update Hooks support Changed to check fields changed or not

When updating with Update, Updates, You can use Changed method in Hooks BeforeUpdate, BeforeSave to check a field changed or not

func (user *User) BeforeUpdate(tx *gorm.DB) error {
  if tx.Statement.Changed("Name", "Admin") { // if Name or Admin changed
    tx.Statement.SetColumn("Age", 18)
  }

  if tx.Statement.Changed() { // if any fields changed
    tx.Statement.SetColumn("Age", 18)
  }
  return nil
}

db.Model(&user).Update("Name", "Jinzhu") // update field `Name` to `Jinzhu`
db.Model(&user).Updates(map[string]interface{}{"name": "Jinzhu", "admin": false}) // update field `Name` to `Jinzhu`, `Admin` to false
db.Model(&user).Updates(User{Name: "Jinzhu", Admin: false}) // Update none zero fields when using struct as argument, will only update `Name` to `Jinzhu`

db.Model(&user).Select("Name", "Admin").Updates(User{Name: "Jinzhu"}) // update selected fields `Name`, `Admin`，`Admin` will be updated to zero value (false)
db.Model(&user).Select("Name", "Admin").Updates(map[string]interface{}{"Name": "Jinzhu"}) // update selected fields exists in the map, will only update field `Name` to `Jinzhu`

// Attention: `Changed` will only check the field value of `Update` / `Updates` equals `Model`'s field value, it returns true if not equal and the field will be saved
db.Model(&User{ID: 1, Name: "jinzhu"}).Updates(map[string]interface{"name": "jinzhu2"}) // Changed("Name") => true
db.Model(&User{ID: 1, Name: "jinzhu"}).Updates(map[string]interface{"name": "jinzhu"}) // Changed("Name") => false, `Name` not changed
db.Model(&User{ID: 1, Name: "jinzhu"}).Select("Admin").Updates(map[string]interface{"name": "jinzhu2", "admin": false}) // Changed("Name") => false, `Name` not selected to update

db.Model(&User{ID: 1, Name: "jinzhu"}).Updates(User{Name: "jinzhu2"}) // Changed("Name") => true
db.Model(&User{ID: 1, Name: "jinzhu"}).Updates(User{Name: "jinzhu"})  // Changed("Name") => false, `Name` not changed
db.Model(&User{ID: 1, Name: "jinzhu"}).Select("Admin").Updates(User{Name: "jinzhu2"}) // Changed("Name") => false, `Name` not selected to update

Plugins

Plugin callbacks also need be defined as a method of type func(tx *gorm.DB) error, check out Write Plugins for details

Updating with struct

When updating with struct, GORM V2 allows to use Select to select zero-value fields to update them, for example:

db.Model(&user).Select("Role", "Age").Update(User{Name: "jinzhu", Role: "", Age: 0})

Associations

GORM V1 allows to use some settings to skip create/update associations, in V2, you can use Select to do the job, for example:

db.Omit(clause.Associations).Create(&user)
db.Omit(clause.Associations).Save(&user)

db.Select("Company").Save(&user)

and GORM V2 doesn’t allow preload with Set("gorm:auto_preload", true) anymore, you can use Preload with clause.Associations, e.g:

// preload all associations
db.Preload(clause.Associations).Find(&users)

Also, checkout field permissions, which can be used to skip creating/updating associations globally

GORM V2 will use upsert to save associations when creating/updating a record, won’t save full associations data anymore to protect your data from saving uncompleted data, for example:

user := User{
  Name:            "jinzhu",
  BillingAddress:  Address{Address1: "Billing Address - Address 1"},
  ShippingAddress: Address{Address1: "Shipping Address - Address 1"},
  Emails:          []Email{
    {Email: "jinzhu@example.com"},
    {Email: "jinzhu-2@example.com"},
  },
  Languages:       []Language{
    {Name: "ZH"},
    {Name: "EN"},
  },
}

db.Create(&user)
// BEGIN TRANSACTION;
// INSERT INTO "addresses" (address1) VALUES ("Billing Address - Address 1"), ("Shipping Address - Address 1") ON DUPLICATE KEY DO NOTHING;
// INSERT INTO "users" (name,billing_address_id,shipping_address_id) VALUES ("jinzhu", 1, 2);
// INSERT INTO "emails" (user_id,email) VALUES (111, "jinzhu@example.com"), (111, "jinzhu-2@example.com") ON DUPLICATE KEY DO NOTHING;
// INSERT INTO "languages" ("name") VALUES ('ZH'), ('EN') ON DUPLICATE KEY DO NOTHING;
// INSERT INTO "user_languages" ("user_id","language_id") VALUES (111, 1), (111, 2) ON DUPLICATE KEY DO NOTHING;
// COMMIT;

Join Table

In GORM V2, a JoinTable can be a full-featured model, with features like Soft Delete，Hooks, and define other fields, e.g:

type Person struct {
  ID        int
  Name      string
  Addresses []Address `gorm:"many2many:person_addresses;"`
}

type Address struct {
  ID   uint
  Name string
}

type PersonAddress struct {
  PersonID  int
  AddressID int
  CreatedAt time.Time
  DeletedAt gorm.DeletedAt
}

func (PersonAddress) BeforeCreate(db *gorm.DB) error {
  // ...
}

// PersonAddress must defined all required foreign keys, or it will raise error
err := db.SetupJoinTable(&Person{}, "Addresses", &PersonAddress{})

After that, you could use normal GORM methods to operate the join table data, for example:

var results []PersonAddress
db.Where("person_id = ?", person.ID).Find(&results)

db.Where("address_id = ?", address.ID).Delete(&PersonAddress{})

db.Create(&PersonAddress{PersonID: person.ID, AddressID: address.ID})

Count

Count only accepts *int64 as the argument

Transactions

some transaction methods like RollbackUnlessCommitted removed, prefer to use method Transaction to wrap your transactions

db.Transaction(func(tx *gorm.DB) error {
  // do some database operations in the transaction (use 'tx' from this point, not 'db')
  if err := tx.Create(&Animal{Name: "Giraffe"}).Error; err != nil {
    // return any error will rollback
    return err
  }

  if err := tx.Create(&Animal{Name: "Lion"}).Error; err != nil {
    return err
  }

  // return nil will commit the whole transaction
  return nil
})

Checkout Transactions for details

Migrator

• Migrator will create database foreign keys by default
• Migrator is more independent, many API renamed to provide better support for each database with unified API interfaces
• AutoMigrate will alter column’s type if its size, precision, nullable changed
• Support Checker through tag check
• Enhanced tag setting for index

Checkout Migration for details

type UserIndex struct {
  Name  string `gorm:"check:named_checker,(name <> 'jinzhu')"`
  Name2 string `gorm:"check:(age > 13)"`
  Name4 string `gorm:"index"`
  Name5 string `gorm:"index:idx_name,unique"`
  Name6 string `gorm:"index:,sort:desc,collate:utf8,type:btree,length:10,where:name3 != 'jinzhu'"`
}

Happy Hacking!