What is the difference between Op.Data and Op.Doc ？

[cmfunc]

type Op struct {
	Id                interface{}            `json:"_id"`
	Operation         string                 `json:"operation"`
	Namespace         string                 `json:"namespace"`
	Data              map[string]interface{} `json:"data,omitempty"`
	Timestamp         primitive.Timestamp    `json:"timestamp"`
	Source            QuerySource            `json:"source"`
	Doc               interface{}            `json:"doc,omitempty"`
	UpdateDescription map[string]interface{} `json:"updateDescription,omitempty"`
	ResumeToken       OpResumeToken          `json:"-"`
}

I want to get latest document that have been change. for example, in "lessons" mongo collections, I update "$unset" the "room_id" filed of "lessons" collections , I need the doc data without "room_id" field.
I shouled select Op.Data and Op.Doc ? Op.Doc is value of Op.Data field "Doc" ?

[rwynn]

Op.Data was added first, it is your MongoDB data as a go map. Later, Op.Doc was added so that the type could be changed to interface{}. This allows one to do custom unmarshalling into your own struct.

https://github.com/rwynn/gtm#custom-unmarshalling

If you don't do any custom unmarshalling into your own struct, then both fields get the go map.