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).

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.