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NeoJSON: parsing mapped nil fields

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Skip Lentz-2

NeoJSON: parsing mapped nil fields

Hi all,

When parsing with NeoJSON, I’m experiencing some problems.

If I parse a JSON representation using NeoJSONReader>>next (i.e. not according to a schema), it parses nil fields just fine.

But when I explicitly set a value schema, it won’t parse it in the case it is nil (or “null” in JSON). Is there a way to let it return nil in the case the parser encounters “null”, and otherwise serialize it as a value schema (e.g. a Point class).

Taking the example from the paper (https://github.com/svenvc/docs/blob/master/neo/neo-json-paper.md):

(NeoJSONReader on: ’null' readStream)
    mapInstVarsFor: Point;
    nextAs: Point.

Is there a way to adapt the above snippet so that it evaluates to ‘nil’ instead of resulting in an error? I ask because I am parsing an API response which sometimes contains a “null” field, and sometimes a JSON object for that field.

Thanks.

Sven Van Caekenberghe-2

Re: NeoJSON: parsing mapped nil fields

Hi,

> On 22 Dec 2015, at 17:40, Skip Lentz <[hidden email]> wrote:
>
> Hi all,
>
> When parsing with NeoJSON, I’m experiencing some problems.
>
> If I parse a JSON representation using NeoJSONReader>>next (i.e. not according to a schema), it parses nil fields just fine.
> But when I explicitly set a value schema, it won’t parse it in the case it is nil (or “null” in JSON). Is there a way to let it return nil in the case the parser encounters “null”, and otherwise serialize it as a value schema (e.g. a Point class).
>
> Taking the example from the paper (https://github.com/svenvc/docs/blob/master/neo/neo-json-paper.md):
> (NeoJSONReader on: ’null' readStream)
> mapInstVarsFor: Point;
> nextAs: Point.
>
> Is there a way to adapt the above snippet so that it evaluates to ‘nil’ instead of resulting in an error? I ask because I am parsing an API response which sometimes contains a “null” field, and sometimes a JSON object for that field.
>
> Thanks.

NeoJSON does have a bit of a split personality.

When using #next it parses whatever is there and returns it as either primitives, a map or a list, nested to any depth.

When you use mappings and #nextAs: it tries to map a static type structure on what is coming in. As such it is not really prepared for dynamic surprises like objects being replaced by null. Do also note that the typing info is totally absent from the JSON itself, unlike STON for example. NeoJSON also tries (and succeeds) in maintaining a stream based parser that does not generate intermediate structures except your own domain models.

But your request does make sense and I will think about it. It might be possible. It has been a while that I really thought about the implementation.

Sven