我对Go还是陌生的，我正在尝试使用Ben Johnson网页的指导来创建结构化的应用程序。不幸的是，他的例子并不是一个完整的应用程序。

他的网页是https://medium.com/@benbjohnson/standard-package-layout-7cdbc8391fc1

我尝试使用他的方法，但不断收到“未定义：db”错误。它不会告诉我是哪一行引起了错误，只是文件“ MSSQL.go”

有人可以提供指导来帮助我解决此错误吗？

具有可接受解决方案的已编辑代码。

StatementPrinter.go

    package statementprinter

    type Statement struct {
      CustomerId   string
      CustomerName string
    }

    type StatementService interface {
      Statement(id string) (*Statement, error)
    }

main.go

            package main

            import (
              "fmt"
              "log"
              "github.com/ybenjolin/StatementPrinter"
              "github.com/ybenjolin/StatementPrinter/mssql"
              "database/sql"
              _ "github.com/alexbrainman/odbc"
            )

            const DB_INFO = "Driver={SQL Server};Server=cdc-edb2;Database=CostarReports;Trusted_Connection=yes;"

            var db *sql.DB

            func init() {
              var err error
              db, err = sql.Open("odbc", DB_INFO)
              if err != nil {
                log.Fatal("Error opening database connection.\n", err.Error())
              }
              err = db.Ping()
              if err != nil {
                log.Fatal("Error pinging database server.\n", err.Error())
              }
              fmt.Println("Database connection established.")
            }

            func main () {
              var err error
              defer db.Close()

              // Create services
              // Changes required here. Was ss := &statementprinter.Stat..
              ss := &mssql.StatementService{DB: db}

              // Use service
              var s *statementprinter.Statement
              s, err = ss.Statement("101583")
              if err != nil {
                log.Fatal("Query failed:", err.Error())
              }
              fmt.Printf("Statement: %+v\n", s)
            }

mssql.go

    package mssql  

    import (
      _ "github.com/alexbrainman/odbc"
      "database/sql"
      "github.com/ybenjolin/StatementPrinter"
    )

    // StatementService represents a MSSQL implementation of statemenetprinter.StatementService.
    type StatementService struct {
      DB *sql.DB
    }

    // Statement returns a statement for a given customer.
    func (s *StatementService) Statement(customer string) (*statementprinter.Statement, error) {
      var err error
      var t statementprinter.Statement
      // Changes required here. Was row := db.Query......
      row := s.DB.QueryRow(`Select Customer, CustomerName From AccountsReceivable.rptfARStatementHeader(?)`, customer)
      if row.Scan(&t.CustomerId, &t.CustomerName); err != nil {
        return nil, err
      }
      return &t, nil