如何从Go lang中的数据库中获取数据

Question

package main

import (
    "encoding/json"
    "gorilla/mux"
    "log"
    "net/http"
    "database/sql"
    _ "go-sql-driver/mysql"
    )

func GetPeople(w http.ResponseWriter, r *http.Request, db *sql.DB) {
    json.NewEncoder(w).Encode(db.QueryRow("SELECT * from test.animal"))
}

func main() {

db, err := sql.Open("mysql", "root:mariadb@tcp(127.0.0.1:3306)/test")
if err != nil {
    panic(err.Error())
}
defer db.Close()
router := mux.NewRouter()

router.HandleFunc("/people", GetPeople).Methods("GET")

log.Fatal(http.ListenAndServe(":8000", router))
}

I need to make my db recognized inside the GetPeople function but giving the function a third parameter (db *sql.DB) is impossible.

How can I solve it? Thank you

Answer 1

Another way to do this is using closures, this prevents global use of variables:

func GetPeopleHandler(db *sql.DB) func (w http.ResponseWriter, r *http.Request) {
    return func (w http.ResponseWriter, r *http.Request) {
        json.NewEncoder(w).Encode(db.QueryRow("SELECT * from test.animal"))
    }
}

func main() {
    var err error
    db, err = sql.Open("mysql", "root:mariadb@tcp(127.0.0.1:3306)/test")
    if err != nil {
        panic(err.Error())
    }
    defer db.Close()
    router := mux.NewRouter()

    router.HandleFunc("/people", GetPeopleHandler(db)).Methods("GET")

    log.Fatal(http.ListenAndServe(":8000", router))
}

Answer 2

Simply make your db variable global, not local in main() :

var db *sql.DB

func GetPeople(w http.ResponseWriter, r *http.Request) {
    json.NewEncoder(w).Encode(db.QueryRow("SELECT * from test.animal"))
}

func main() {
    var err error
    db, err = sql.Open("mysql", "root:mariadb@tcp(127.0.0.1:3306)/test")
    if err != nil {
        panic(err.Error())
    }
    defer db.Close()

    router := mux.NewRouter()
    router.HandleFunc("/people", GetPeople).Methods("GET")
    log.Fatal(http.ListenAndServe(":8000", router))
}

See related questions:

How to use global var across files in a package?

Performance difference between global database connection and opening connection everytime on Golang