gojsj2025/backend/docs/gorm/Connecting to a Database.md

Connecting to a Database GORM officially supports the databases MySQL, PostgreSQL, SQLite, SQL Server, and TiDB

MySQL import ( "gorm.io/driver/mysql" "gorm.io/gorm" )

func main() { // refer https://github.com/go-sql-driver/mysql#dsn-data-source-name for details dsn := "user:pass@tcp(127.0.0.1:3306)/dbname?charset=utf8mb4&parseTime=True&loc=Local" db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{}) } NOTE: To handle time.Time correctly, you need to include parseTime as a parameter. (more parameters) To fully support UTF-8 encoding, you need to change charset=utf8 to charset=utf8mb4. See this article for a detailed explanation

MySQL Driver provides a few advanced configurations which can be used during initialization, for example:

db, err := gorm.Open(mysql.New(mysql.Config{ DSN: "gorm:gorm@tcp(127.0.0.1:3306)/gorm?charset=utf8&parseTime=True&loc=Local", // data source name DefaultStringSize: 256, // default size for string fields DisableDatetimePrecision: true, // disable datetime precision, which not supported before MySQL 5.6 DontSupportRenameIndex: true, // drop & create when rename index, rename index not supported before MySQL 5.7, MariaDB DontSupportRenameColumn: true, // change when rename column, rename column not supported before MySQL 8, MariaDB SkipInitializeWithVersion: false, // auto configure based on currently MySQL version }), &gorm.Config{}) Customize Driver GORM allows to customize the MySQL driver with the DriverName option, for example:

import ( _ "example.com/my_mysql_driver" "gorm.io/driver/mysql" "gorm.io/gorm" )

db, err := gorm.Open(mysql.New(mysql.Config{ DriverName: "my_mysql_driver", DSN: "gorm:gorm@tcp(localhost:9910)/gorm?charset=utf8&parseTime=True&loc=Local", // data source name, refer https://github.com/go-sql-driver/mysql#dsn-data-source-name }), &gorm.Config{}) Existing database connection GORM allows to initialize *gorm.DB with an existing database connection

import ( "database/sql" "gorm.io/driver/mysql" "gorm.io/gorm" )

sqlDB, err := sql.Open("mysql", "mydb_dsn") gormDB, err := gorm.Open(mysql.New(mysql.Config{ Conn: sqlDB, }), &gorm.Config{}) PostgreSQL import ( "gorm.io/driver/postgres" "gorm.io/gorm" )

dsn := "host=localhost user=gorm password=gorm dbname=gorm port=9920 sslmode=disable TimeZone=Asia/Shanghai" db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{}) We are using pgx as postgres’s database/sql driver, it enables prepared statement cache by default, to disable it:

// https://github.com/go-gorm/postgres db, err := gorm.Open(postgres.New(postgres.Config{ DSN: "user=gorm password=gorm dbname=gorm port=9920 sslmode=disable TimeZone=Asia/Shanghai", PreferSimpleProtocol: true, // disables implicit prepared statement usage }), &gorm.Config{}) Customize Driver GORM allows to customize the PostgreSQL driver with the DriverName option, for example:

import ( _ "github.com/GoogleCloudPlatform/cloudsql-proxy/proxy/dialers/postgres" "gorm.io/gorm" )

db, err := gorm.Open(postgres.New(postgres.Config{ DriverName: "cloudsqlpostgres", DSN: "host=project:region:instance user=postgres dbname=postgres password=password sslmode=disable", }) Existing database connection GORM allows to initialize *gorm.DB with an existing database connection

import ( "database/sql" "gorm.io/driver/postgres" "gorm.io/gorm" )

sqlDB, err := sql.Open("pgx", "mydb_dsn") gormDB, err := gorm.Open(postgres.New(postgres.Config{ Conn: sqlDB, }), &gorm.Config{}) GaussDB import ( "gorm.io/driver/gaussdb" "gorm.io/gorm" )

dsn := "host=localhost user=gorm password=gorm dbname=gorm port=8000 sslmode=disable TimeZone=Asia/Shanghai" db, err := gorm.Open(gaussdb.Open(dsn), &gorm.Config{}) We are using gaussdb-go as gaussdb’s database/sql driver, it enables prepared statement cache by default, to disable it:

// https://github.com/go-gorm/gaussdb db, err := gorm.Open(gaussdb.New(gaussdb.Config{ DSN: "user=gorm password=gorm dbname=gorm port=8000 sslmode=disable TimeZone=Asia/Shanghai", PreferSimpleProtocol: true, // disables implicit prepared statement usage }), &gorm.Config{}) Customize Driver GORM allows to customize the GaussDB driver with the DriverName option, for example:

import ( _ "github.com/GoogleCloudPlatform/cloudsql-proxy/proxy/dialers/gaussdb" "gorm.io/gorm" )

db, err := gorm.Open(gaussdb.New(gaussdb.Config{ DriverName: "cloudsqlgaussdb", DSN: "host=project:region:instance user=gaussdb dbname=gaussdb password=password sslmode=disable", }) Existing database connection GORM allows to initialize *gorm.DB with an existing database connection

import ( "database/sql" "gorm.io/driver/gaussdb" "gorm.io/gorm" )

sqlDB, err := sql.Open("gaussdbgo", "mydb_dsn") gormDB, err := gorm.Open(gaussdb.New(gaussdb.Config{ Conn: sqlDB, }), &gorm.Config{}) SQLite import ( "gorm.io/driver/sqlite" // Sqlite driver based on CGO // "github.com/glebarez/sqlite" // Pure go SQLite driver, checkout https://github.com/glebarez/sqlite for details "gorm.io/gorm" )

// github.com/mattn/go-sqlite3 db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{}) NOTE: You can also use file::memory:?cache=shared instead of a path to a file. This will tell SQLite to use a temporary database in system memory. (See SQLite docs for this)

SQL Server import ( "gorm.io/driver/sqlserver" "gorm.io/gorm" )

// github.com/denisenkom/go-mssqldb dsn := "sqlserver://gorm:LoremIpsum86@localhost:9930?database=gorm" db, err := gorm.Open(sqlserver.Open(dsn), &gorm.Config{}) TiDB TiDB is compatible with MySQL protocol. You can follow the MySQL part to create a connection to TiDB.

There are some points noteworthy for TiDB:

You can use gorm:"primaryKey;default:auto_random()" tag to use AUTO_RANDOM feature for TiDB. TiDB supported SAVEPOINT from v6.2.0, please notice the version of TiDB when you use this feature. TiDB supported FOREIGN KEY from v6.6.0, please notice the version of TiDB when you use this feature. import ( "fmt" "gorm.io/driver/mysql" "gorm.io/gorm" )

type Product struct { ID uint gorm:"primaryKey;default:auto_random()" Code string Price uint }

func main() { db, err := gorm.Open(mysql.Open("root:@tcp(127.0.0.1:4000)/test"), &gorm.Config{}) if err != nil { panic("failed to connect database") }

db.AutoMigrate(&Product{})

insertProduct := &Product{Code: "D42", Price: 100}

db.Create(insertProduct) fmt.Printf("insert ID: %d, Code: %s, Price: %d\n", insertProduct.ID, insertProduct.Code, insertProduct.Price)

readProduct := &Product{} db.First(&readProduct, "code = ?", "D42") // find product with code D42

fmt.Printf("read ID: %d, Code: %s, Price: %d\n", readProduct.ID, readProduct.Code, readProduct.Price) } Clickhouse https://github.com/go-gorm/clickhouse

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

func main() { dsn := "tcp://localhost:9000?database=gorm&username=gorm&password=gorm&read_timeout=10&write_timeout=20" db, err := gorm.Open(clickhouse.Open(dsn), &gorm.Config{})

// Auto Migrate db.AutoMigrate(&User{}) // Set table options db.Set("gorm:table_options", "ENGINE=Distributed(cluster, default, hits)").AutoMigrate(&User{})

// Insert db.Create(&user)

// Select db.Find(&user, "id = ?", 10)

// Batch Insert var users = []User{user1, user2, user3} db.Create(&users) // ... } Connection Pool GORM using database/sql to maintain connection pool

sqlDB, err := db.DB()

// SetMaxIdleConns sets the maximum number of connections in the idle connection pool. sqlDB.SetMaxIdleConns(10)

// SetMaxOpenConns sets the maximum number of open connections to the database. sqlDB.SetMaxOpenConns(100)

// SetConnMaxLifetime sets the maximum amount of time a connection may be reused. sqlDB.SetConnMaxLifetime(time.Hour) Refer Generic Interface for details

Unsupported Databases Some databases may be compatible with the mysql or postgres dialect, in which case you could just use the dialect for those databases.