Hey all, wondering if there's an existing best practice for this so I'm not
reinventing the wheel.
It's frustratingly common to have APIs where the response JSON can be one
of several distinct objects, and the indicator of which object has been
returned is itself a property of the object.
So you might get a `{ "type": "aType", "aField" : ."..." }` or a `{ "type":
"bType", "bField": "..." }` response from the same API.
What's the best way to deserialize in these situations?
Ideas I've tried so far:
- Unmarhsal twice, once into a struct that just defines the `Type`
property and ignores all other fields, then again based on the type set the
first time.
Works, but for large objects it's extremely wasteful.
- Unmarshal into a large struct that defines all possible subtypes as
anonymous struct fields so their declarations are treated as being on the
outer struct, then cast to the appropriate type after unmarshaling to mask
all the unfilled fields.
Again, works, but feels awful. It also presents a real issue when you
need to verify that no fields other than the expected fields for the given
type were present, which you can usually do with
Decoder.DisallowUnknownFields, but silently succeeds if one of the fields
is valid for a different object type.
I'm trying to do this as much with stdlib as possible. I've looked into
some other libraries that make heavy use of JSON decoding and have seen
both my above ideas, as well as just entirely custom Unmarshaller
implementations. Hopefully it doesn't come to that.
Cheers,
Andrew
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