Golang示例

MemFire Cloud 提供Python、Java、spring、golang、nodejs、小程序开发示例，讲述如何编译执行程序，帮助用户如何采用多种语言来使用连接MemFire Cloud的云数据库。

示例下载地址
Golang示例下载地址：https://gitee.com/memfiredb/memfiredb-example-golang

环境描述
• Go version 1.8 , or later
• Go PostgreSQL driver 已经安装
go get github.com/lib/pq

创建示例应用
1、加密连接
• 在MemFire Cloud平台上完成注册操作，并创建证书认证的数据库test
• 点击数据库test的连接信息，下载访问证书，需要包括memfiredb.crt memfiredb.key root.crt，并拷贝到运行go程序的环境下；
创建源码文件main.go，文件内容如下:

/**
Copyright (c) 2020, Nimblex Co .,Ltd.
Created on 2020-07-21 19:35
**/
package main

import (
    "database/sql"
    _ "github.com/lib/pq"
    "log"
)

func main() {
    db, err := sql.Open("postgres", "user=test password=test dbname=test host=192.168.80.161 port=5433 sslmode=require sslcert=./memfiredb.crt sslkey=./memfiredb.key sslrootcert=./ca.crt")
    if err != nil {
        log.Fatal("数据库连接失败" + err.Error())
    }

    defer db.Close()
    rows, err := db.Query("SELECT * FROM table_name WHERE id = 1")
    if err != nil {
        log.Fatal(err.Error())
    }
    println(rows)
}

2、无加密连接
• 在MemFire Cloud平台上完成注册操作，并创建数据库非证书认证dbname数据库
创建源码文件main.go，文件内容如下:

  **
Copyright (c) 2020, Nimblex Co .,Ltd.
Created on 2020-12-10 11:59
**/

package main

import (
    "context"
    "flag"
    "fmt"
    "github.com/go-pg/pg/v10"
    "github.com/go-pg/pg/v10/orm"
    "strings"
    "sync"
)

var (
    addr   = flag.String("addr", "192.168.80.161:5433", "memfire address to connect")
    user   = flag.String("user", "test", "memfire user")
    passwd = flag.String("passwd", "test", "memfire password")
    dbname = flag.String("db", "dbname", "memfire database name to connect")
)

func panicIf(err error) {
    if err != nil {
        panic(err)
    }
}

func test_transaction_try_again(db *pg.DB) {
    incrInTx := func(db *pg.DB) error {
        // Transaction is automatically rolled back on error.
        return db.RunInTransaction(db.Context(), func(tx *pg.Tx) error {
            var counter int
            _, err := tx.QueryOne(
                pg.Scan(&counter), `SELECT counter FROM counters FOR UPDATE`)
            if err != nil {
                return err
            }

            counter++

            _, err = tx.Exec(`UPDATE counters SET counter = ?`, counter)
            return err
        })
    }

    var wg sync.WaitGroup
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            for {
                err := incrInTx(db)
                if err != nil {
                    if strings.Contains(err.Error(), "40001") ||
                        strings.Contains(err.Error(), "Try again") ||
                        strings.Contains(err.Error(), "Restart read required") {
                        fmt.Println("Try again")
                        continue
                    }
                    panic(err)
                }
                break
            }

        }()
    }
    wg.Wait()
}

type Counter struct {
    Counter int64
}

type User struct {
    Id     int64
    Name   string
    Emails []string
}

// createSchema creates database schema for Counter/ User
func createSchema(db *pg.DB) error {
    models := []interface{}{
        (*Counter)(nil),
        (*User)(nil),
    }

    for _, model := range models {
        err := db.Model(model).CreateTable(&orm.CreateTableOptions{
            Temp:        false,
            IfNotExists: true,
        })
        if err != nil {
            return err
        }
    }
    return nil
}

func main() {
    flag.Parse()

    opt := pg.Options{
        Addr:     *addr,
        User:     *user,
        Password: *passwd,
        Database: *dbname,
        OnConnect: func(ctx context.Context, cn *pg.Conn) error {
            println("new connection created")
            return nil
        },
    }

    db := pg.Connect(&opt)
    defer db.Close()

    err := createSchema(db)
    panicIf(err)

    _, err = db.Exec("delete from counters")
    panicIf(err)

    cnt := &Counter{
        Counter: 1,
    }
    _, err = db.Model(cnt).Insert()
    panicIf(err)

    test_transaction_try_again(db)
}

3、编译执行
go run main.go