Support custom types (#114)

[xcoulon]

This applies to:

• ID
• Attributes
• Relationships

Custom types need to be registered before usage, using the new
jsonapi.RegisterType() function which takes 3 arguments:

• the type to support (reflect.Type)
• the function to use when marshalling a response
• the function to use when unmarshalling a response

Example:

RegisterType(uuidType,
  func(value interface{}) (string, error) {
    result := value.(*UUID).String()
    return result, nil
  },
  func(value string) (interface{}, error) {
    return UUIDFromString(value)
  })

The custom type will be represented as a string in the JSON document
in the requests and responses.

Fixes #114

Signed-off-by: Xavier Coulon [email protected]

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[xcoulon]

I just signed the CLA.

[googlebot]

CLAs look good, thanks!

[bridgetlane]

+1

[shwoodard]

Please remove prints from tests so go test -v is clean

[shwoodard]

This should not marshal/unmarshal to/from string but rather interface{}. What if you want a number to go to a custom type? Input/output may not be a string.

Store state of return type by making type CustomType reflect.Type

Don't assume is custom type. Should be declared explicitly. IOW, add a comma separated value to struct tag, "custom", and add to constants.go.

[shwoodard]

Don't use init(), don't use make, use var in block, e.g.

var (
    customTypeMarshallingFuncs = map[reflect.Type]MarshallingFunc{}
    cutomTypeUnmarshallingFuncs = map[reflect.Type]UnmarshallingFunc{}
)

See,
https://play.golang.org/p/OnktgftaGQ

[shwoodard]

Follow pattern of net/http's http.Handle and http.HandleFunc, and don't rely on input/output being string e.g.

type TypeMarshaller interface {
    Marshal(interface{}) (interface{}, error)
}

type TypeUnmarshaller interface {
    UnMarshal(interface{}) (interface{}, error)
}

type TypeMarshalFunc func(interface{}) (interface{}, error)

func (tmf TypeMarshalFunc) func(thing interface{}) (interface{}, error) {
    return tmf(thing)
}

type TypeUnmarshalFunc func(interface{}) (interface{}, error)

func (tuf TypeUnmarshalFunc) func(thing interface{}) (interface{}, error) {
    return tuf(thing)
}

Then you can have RegisterCustomType(in, out reflect.Type, marshaller TypeMarshaller, unmarshaller TypeUnmarshaller) and RegisterCustomTypeFunc(in, out reflect.Type, marshallerFunc TypeMarshallerFunc, unmarshallerFunc TypeUnmarshallerFunc)`

[shwoodard]

I'm working on changing this. See wip @ https://github.com/shwoodard/jsonapi/blob/custom_types/custom_types.go

[xcoulon]

thanks for the review, @shwoodard ! I'm not sure I understood your last comment: do you mean I should abandon this PR since you're working on it, too ?

[mithmatt]

@shwoodard @xcoulon

I reviewed this pull request and also took a look at https://github.com/shwoodard/jsonapi/blob/custom_types/custom_types.go

Package encoding/json has Marshaler and Unmarshaler interfaces. Can we leverage these interfaces for custom types? This would avoid having users to call out custom types, the marshal and unmarshal functions explicitly through a register function.

There are numerous packages out there, which auto generates code to create MarshalJSON and UnmarshalJSON, such alvaroloes/enumer for enums.