Advanced Usage

Error Handling

After perform any operations, if there are any error happened, GORM will set it to *DB's Error field

if err := db.Where("name = ?", "jinzhu").First(&user).Error; err != nil {
    // error handling...
}

// If there are more than one error happened, get all of them with `GetErrors`, it returns `[]error`
db.First(&user).Limit(10).Find(&users).GetErrors()

// Check if returns RecordNotFound error
db.Where("name = ?", "hello world").First(&user).RecordNotFound()

if db.Model(&user).Related(&credit_card).RecordNotFound() {
    // no credit card found handling
}

Transactions

To perform a set of operations within a transaction, the general flow is as below.

// begin a transaction
tx := db.Begin()

// do some database operations in the transaction (use 'tx' from this point, not 'db')
tx.Create(...)

// ...

// rollback the transaction in case of error
tx.Rollback()

// Or commit the transaction
tx.Commit()

A Specific Example

func CreateAnimals(db *gorm.DB) err {
  tx := db.Begin()
  // Note the use of tx as the database handle once you are within a transaction

  if tx.Error != nil {
    return err
  }

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

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

  return tx.Commit().Error
}

SQL Builder

Run Raw SQL

Run Raw SQL

db.Exec("DROP TABLE users;")
db.Exec("UPDATE orders SET shipped_at=? WHERE id IN (?)", time.Now(), []int64{11,22,33})

// Scan
type Result struct {
    Name string
    Age  int
}

var result Result
db.Raw("SELECT name, age FROM users WHERE name = ?", 3).Scan(&result)

sql.Row & sql.Rows

Get query result as *sql.Row or *sql.Rows

row := db.Table("users").Where("name = ?", "jinzhu").Select("name, age").Row() // (*sql.Row)
row.Scan(&name, &age)

rows, err := db.Model(&User{}).Where("name = ?", "jinzhu").Select("name, age, email").Rows() // (*sql.Rows, error)
defer rows.Close()
for rows.Next() {
    ...
    rows.Scan(&name, &age, &email)
    ...
}

// Raw SQL
rows, err := db.Raw("select name, age, email from users where name = ?", "jinzhu").Rows() // (*sql.Rows, error)
defer rows.Close()
for rows.Next() {
    ...
    rows.Scan(&name, &age, &email)
    ...
}

Scan sql.Rows In Iteration

rows, err := db.Model(&User{}).Where("name = ?", "jinzhu").Select("name, age, email").Rows() // (*sql.Rows, error)
defer rows.Close()

for rows.Next() {
  var user User
  db.ScanRows(rows, &user)
  // do something
}

Generic database interface sql.DB

Get generic database interface *sql.DB from *gorm.DB connection

// Get generic database object `*sql.DB` to use its functions
db.DB()

// Ping
db.DB().Ping()

Connection Pool

db.DB().SetMaxIdleConns(10)
db.DB().SetMaxOpenConns(100)

Composite Primary Key

Set multiple fields as primary key to enable composite primary key

type Product struct {
    ID           string `gorm:"primary_key"`
    LanguageCode string `gorm:"primary_key"`
}

Logger

Gorm has built-in logger support, by default, it will print happened errors

// Enable Logger, show detailed log
db.LogMode(true)

// Disable Logger, don't show any log
db.LogMode(false)

// Debug a single operation, show detailed log for this operation
db.Debug().Where("name = ?", "jinzhu").First(&User{})

Customize Logger

Refer GORM's default logger for how to customize it https://github.com/jinzhu/gorm/blob/master/logger.go

db.SetLogger(gorm.Logger{revel.TRACE})
db.SetLogger(log.New(os.Stdout, "\r\n", 0))

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