GORM

go get -u gorm.io/gorm

# 基于 cgo 的 sqlite
go get -u gorm.io/driver/sqlite

# 不需要 cgo
go get -u github.com/glebarez/sqlite
go get -u github.com/glebarez/go-sqlite

go get -u gorm.io/driver/postgres

const (
	PrimaryKey   string = "~~~py~~~" // primary key
	CurrentTable string = "~~~ct~~~" // current table
	Associations string = "~~~as~~~" // associations
)

import (
  "gorm.io/driver/sqlite"
  _ "github.com/glebarez/sqlite"
  "gorm.io/gorm"
)

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

// 直接调用 processor
func TestPreloadOnly(t *testing.T){
  // 模型只包含主键
  var m models.User
  m.ID = 1
  // 通常逻辑 - 但构造出来的 stmt 包含基础信息
  stmt := db.Model(&m).Preload("Profile")
  // 填充需要的信息 - 正常逻辑这些字段会被填充
  stmt.Statement.Dest = stmt.Statement.Model
  stmt.Statement.ReflectValue = reflect.ValueOf(stmt.Statement.Dest).Elem()
  assert.NoError(t, stmt.Statement.Parse(stmt.Statement.Model))

  // 直接调用 preload
  callbacks.Preload(stmt)
  assert.NoError(t, stmt.Error)

  // 字段被成功 preload
  fmt.Println(m.Profile)
}

// 查询条件与数据不同但可以一次操作
db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrCreate(&user)

import (
  "github.com/google/uuid"
  "github.com/lib/pq"
)

type Post struct {
  ID     uuid.UUID `gorm:"type:uuid;default:uuid_generate_v4()"`
  Title  string
  Tags   pq.StringArray `gorm:"type:text[]"` // 需要指定类型
}

// 操作当前的 Statement 可修改语句
func (u *User) BeforeCreate(tx *gorm.DB) error {
  // 通过 tx.Statement 修改当前操作，例如：
  tx.Statement.Select("Name", "Age")
  tx.Statement.AddClause(clause.OnConflict{DoNothing: true})

  // tx 是带有 `NewDB` 选项的新会话模式
  // 基于 tx 的操作会在同一个事务中，但不会带上任何当前的条件
  err := tx.First(&role, "name = ?", user.Role).Error
  // SELECT * FROM roles WHERE name = "admin"
  // ...
  return err
}

// 更新部分字段
db.Clauses(clause.OnConflict{
  Columns:   []clause.Column{{Name: "id"}},
  DoUpdates: clause.AssignmentColumns([]string{"name", "age"}),
}).Create(&users)

// 从新映射
db.Clauses(clause.OnConflict{
  Columns:   []clause.Column{{Name: "id"}},
  DoUpdates: clause.Assignments(map[string]interface{}{
    "role": "user"，
    "count": gorm.Expr("GREATEST(count, VALUES(count))"),
  }),
}).Create(&users)

// 更新所有
db.Clauses(clause.OnConflict{
  Columns:   []clause.Column{{Name: "id"}},
  UpdateAll: true,
}).Create(&users)

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

// 可生成完整 SQL - 不要用于查询，有 SQL 注入风险
db.Dialector.Explain(stmt.SQL.String(), stmt.Vars...)

db.Session(&gorm.Session{SkipHooks: true}).Create(&user)

type Cat struct {
  ID    int
  Name  string
  Toy   Toy `gorm:"polymorphic:Owner;"`
}

type Dog struct {
  ID   int
  Name string
  Toy  Toy `gorm:"polymorphic:Owner;"`
}

type Toy struct {
  ID        int
  Name      string
  OwnerID   int
  OwnerType string
}

type Model struct {
  ID    int
  UID   string // uuid
}
type Cat struct {
  Model
  Name  string
  Toy   Toy `gorm:"polymorphic:Owner;"`
}

type Dog struct {
  Model
  Name string
  Toy  Toy `gorm:"polymorphic:Owner;"`
}

type Toy struct {
  ID        int
  Name      string
  OwnerID   int
  OwnerType string
  OwnerUID string
}

type User struct {
    ID          int       `sql:"DEFAULT:myfunction"`
    XID         int       `sql:"type:bigint; DEFAULT:id_generator()"`
    CreatedAt   time.Time `sql:"DEFAULT:current_timestamp"`
}

type User struct {
    gorm.Model
    Email  string    `gorm:"unique;not null;type:varchar(100);default:null"`
}