我应该在哪里存储全局数据库实例？

Question

Where should I store the database instance after initializing it in go? I want to access them from the request handlers.

// server.go
storage, err := config.GetFileStorage(viper.GetViper())
if err != nil {
    log.Fatal(fmt.Sprintf("Failed to configure the file storage: %v
", err))
}

db, err := config.GetDatabase(viper.GetViper())
if err != nil {
    log.Fatal(fmt.Sprintf("Failed to configure the database: %v
", err))
}

This are just local variables in the main function. How could I expose them now to the go package with the handlers?

Answer 1

You can wrap the DB connection in a struct, and have it return your http handlers. Something like this:

package main

import (
    "database/sql"
    "log"
    "net/http"
)

type DBManager struct {
    db *sql.DB
}

func (m *DBManager) HelloHandler() http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        rows, err := m.db.Query("SELECT hello FROM world")
        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return
        }
        defer rows.Close()
        for rows.Next() {
            // do stuff
        }
    })
}

func main() {
    db, err := sql.Open("", "")
    if err != nil {
        panic(err)
    }
    m := DBManager{db: db}
    http.Handle("/", m.HelloHandler())
    log.Fatal(http.ListenAndServe(":8080", nil))
}

Also make sure your object can handle concurrent access like *sql.DB https://golang.org/pkg/database/sql/#DB

If you want/need to share more across the handlers you can take a look at the environment pattern: http://www.jerf.org/iri/post/2929