将资源从命令传递到 urfave/cli/v2 中的子命令

Question

Is is possible, and if so how, to let a Command initialize a resource and pass it down to its Subcommands . Image an application that takes its arguments like

$ mycmd db --connect <...> create <...>
$ mycmd db --connect <...> update <...>

This may not be a great example but it illustrates the concept. Here db is some resource that all the subcommands depend on. I would like a single function to be responsible for the initialization of the db resource and then pass the initialized resource down to the subcommands. I can't figure out how to do this with urfave/cli/v2 .

You could do it by creating two separate cli.App s, one that parses the db part of the arguments just to create a context.Context with context.WithValue and then use that context to create the second cli.App which would parse the remainder of the arguments. I'm sure there's a better way to do it.

I'm grateful for any help!

Answer 1

Maybe you can achieve this with context values. You set the value in the Before callback. Below code is copied and modified from the subcommands example:

package main

import (
  "fmt"
  "log"
  "os"

  "github.com/urfave/cli/v2"
)

func main() {
  app := &cli.App{
    Commands: []*cli.Command{
      {
        Name:   "db",
        Before: func(c *cli.Context) error {
            db := initDB()
            c.Context = context.WithValue(c.Context, "db", db)
            return nil
        }
        Subcommands: []*cli.Command{
          {
            Name:  "connect",
            Action: func(c *cli.Context) error {
                db := c.Context.Value("db").(*MyDB) // remember to assert to original type
                //use db
                return nil
            },
          },
        },
      },
    },
  }

  err := app.Run(os.Args)
  if err != nil {
    log.Fatal(err)
  }
}