Mapping context values

[jmattheis]

Goverter should allow passing a mapping context through converter methods for custom conversions. This allows more customizability when the conversion requires other state. See also https://mapstruct.org/documentation/stable/api/org/mapstruct/Context.html

Example:

// goverter:converter
// goverter:extend LookupUser
type Converter interface {
    Convert(source Input, context UserContext) (Output, error)
}

type UserContext struct {
    UserNames map[int]string
}

func LookupUser(userID int, context UserContext) (User, error) {
    user := User{ID: userID}
    name, ok := context.UserNames[userID]
    if !ok {
        return user, fmt.Errorf("user with id %d not found", userID)
    }
    user.Name = name
    return user, nil
}

type Input struct {  UserIDs []int }
type Output struct { Users []User  }
type User struct {
    ID int
    Name string
}

Conversion contexts are additional parameters that are passed into the conversion methods (See Convert method from Converter), and they should be passed into custom methods (See LookupUser).

This feature is WIP, see https://github.com/jmattheis/goverter/issues/68#issuecomment-2349402479 for instructions to try it out.

Please :+1: this issue if you like this functionality. If you have a specific use-case in mind, feel free to comment it.

[pavelpatrin]

@jmattheis can I hope that this feature will be implemented once upon a time?

[jmattheis]

@pavelpatrin Yes, but it doesn't have a high priority on my to-do list.

[becash]

Hi, a made a beta version for that , it add "arguments", is a custom structure, that can be used in internal functions, say me a opinion, maybe some improvements, for me is all what i need

https://github.com/becash/goverter jmattheis

[jmattheis]

Hey @becash, it seems like the beta version has hardcoded the domain.Arguments type with a fixed position in the conversion method calls. I find this solution to inflexible, with the features https://github.com/jmattheis/goverter/issues/143 and https://github.com/jmattheis/goverter/issues/147 goverter needs a way to define arguments in a certain usage like source, target, and context.

If any of these tickets are implemented they should built the foundation to support this otherwise it probably has to be rewritten afterwards.

[becash]

of course is a beta, @jmattheis, i see problems that you mention, what you thing as idea? can be improved, or maybe replaced ?

about type name , is need to put in config? also need to indicate import path, maybe can you recomend a beter way also about "switch sig.Params().Len()" ... that im modify, i`m also thing it can me make better,
if you thing that my ideea can live, i can improve, to add in repository, but if you not agree, for me it work normal

[jmattheis]

Types that are context should be inferred from the conversion method signature.

// goverter:converter
type Converter interface {
	// goverter:arg:context ctxDB
	// goverter:arg:context ctxUsers
	// goverter:arg:source myInput
	Convert(ctxDB Database, myInput []Input, ctxUsers UserContext) []Output
}

Internally we can mark the Converter interface is context by default, to keep backwards compatibility.