英文:
Using and assign variables of other file (package) in go
问题
我有一个使用MongoDB作为后端数据库的HTTP服务器，我将数据库操作封装在一个单独的文件（package）中，并且不想每次都建立连接。所以我想创建一个全局会话，并像这样那样复制它可能是个好主意。到目前为止，我已经完成了以下工作：
在server.go文件中，我启动了HTTP服务器，并且我还想从这里初始化MongoDB连接，因为到目前为止，我不知道其他可以在整个HTTP服务器生命周期中保持连接的方法 
package main
import(
"./mylib"
"net/http"
)
...
func main(){
dbutil.MySession, err := dbutil.ConnectDb()
if err != nil {
panic(err)
}
// 为了方便起见，我将省略HTTP服务器配置代码
http.HandleFunc(...)
http.HandleFunc(...)
}
...
这里是dbutil.go文件，其中包含变量MySession。顺便说一下，它们的总目录结构应该是这样的：
.
├── mylib
│ └── dbutil.go
└── server.go
在dbutil.go中：
package dbutil
import (
...
)
var MySession *mgo.Session
func ConnectDb() (*mgo.Session, error){
session, err := mgo.Dial("127.0.0.1")
if err != nil {
return nil, err
}
return session, nil
}
但是当我编译并运行服务器时，它报错：
# command-line-arguments
./server.go:28: cannot declare name dbutil.MySession
我注意到，如果我将dbutil.MySession, err := dbutil.ConnectDb()更改为dbutil.MySession, err = dbutil.ConnectDb()，事情也不会起作用。
那么，在这种情况下，我该如何分配全局变量MySession？或者我一开始做错了什么（尝试使用其他文件的变量）？
英文:
I have a http server using mongodb as a backend db, I wrapped the db operations in a separate file (package), and I don't want to make a connection every time, So I think make a global session and copy it like this maybe a good idea. So this is so far I've got:
File server.go in which I start the http server, and I also want to init the mongodb connection from here, for I don't know other way to make a connection that could live through the whole life of the http server so far
package main
import(
"./mylib"
"net/http"
)
...
func main(){
dbutil.MySession, err := dbutil.ConnectDb()
if err != nil {
panic(err)
}
// I will just omit the http server config code for convenience
http.HandleFunc(...)
http.HandleFunc(...)
}
...
And here is the file dbutil.go which contains the variable MySession. By the way, the total dir structure of them is like this, should be fine:
.
├── mylib
│   └── dbutil.go
└── server.go
And in dbutil.go:
package dbutil
import (
...
)
var MySession *mgo.Session
func ConnectDb() (*mgo.Session, error){
session, err := mgo.Dial("127.0.0.1")
if err != nil {
return nil, err
}
return session, nil
}
But when I compile them and run the server, it complains that:
# command-line-arguments
./server.go:28: cannot declare name dbutil.MySession
I notice that if I change dbutil.MySession, err := dbutil.ConnectDb() to dbutil.MySession, err = dbutil.ConnectDb() things will not work either.
So How Can I assign the global Variable MySession in this case? Or did I do something wrong (try to use a variable of other file) at the first place?
答案1
得分: 4
短变量声明 := 创建新变量。新变量的名称不能包含包名，但你的代码中包含了包名：
dbutil.MySession, err := dbutil.ConnectDb()
只需不使用短变量声明即可：
var err error
dbutil.MySession, err = dbutil.ConnectDb()
// ...你的代码的其余部分
英文:
The Short variable declaration := creates new variables. The name of the new variables cannot contain package names, but yours does:
dbutil.MySession, err := dbutil.ConnectDb()
Just don't use the short variable declaration:
var err error
dbutil.MySession, err = dbutil.ConnectDb()
// ...rest of your code
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