I agree with Hubert. My impression is that instead of making an equivalent JSON representation of the CSDL, we are making something more complicated and harder to read so that we adhere to another spec. And in some cases, I think we are losing some of
the OData information. For example, in section 4.1.2.4 in the JSON CSDL document, there is an example of an Edm.Decimal property, Price. Nowhere in the example JSON does it actually say that the OData type of the property is Edm.Decimal. Yet if you were
to access that property directly (i.e. ~/Entity(key)/Price), the context URL in the payload would contain Edm.Decimal.
Another thing to consider is that in the current CSDL document we have the section about Metadata Service Schema. The JSON payloads that are returned when accessing this service is quite different than the proposed JSON CSDL format based on JSON schema,
yet it is intended to represent the same information. That seems like a huge inconsistency in our spec.
I think our highest priority has to be clearly and concisely describing the OData metadata of a service in a JSON document that is consistent with the rest of the OData spec. As Hubert mentions, JSON schema does not appear to be a natural fit.
Matt
-----Original Message-----
From: odata@lists.oasis-open.org [
mailto:odata@lists.oasis-open.org] On Behalf Of Hubert Heijkers
Sent: Friday, December 12, 2014 6:00 AM
To: Handl, Ralf
Cc: odata@lists.oasis-open.org
Subject: Re: [odata] JSON CSDL: Representing property facets
Hi Ralf, et.al.,
It's been bothering me for a bit, and I don't think I can express very well
what exactly it is, but I more and more am getting the feeling, especially
when I see things like you are proposing, that we are creating something
pretty ugly just because we are trying to adhere to something that is not
likely the best natural fit for what we are trying to convey, which, after
all, is the schema of our service.
Now don't get me wrong, I do see value in having a JSON schema, but for
those cases were we'd want to validate our payloads, for which we need less
then what we are trying to put in currently. As you say, there are clients
that are not interested in validating payloads, and I wonder, aren't we
making it to hard on them because we are trying to make the JSON CSDL a
JSON Schema too?
So here is a crazy idea, why wouldn't we have a nice clean JSON CSDL and,
separately, allow services to provide a JSON Schema as well put purely for
validation, meaning that it wouldn't have to convey any of the OData
specifics?
Any thoughts anybody? Tell me if you think I'm nuts too, wouldn't be the
first time, I can take it;-).
Happy holidays,
-H
Hubert Heijkers
STSM, Chief Architect TM1 Server
Business Analytics
Phone: +31-20-513-9456
Mobile: +31-621-394123
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Date: 11/28/2014 11:29 AM
Subject: [odata] JSON CSDL: Representing property facets
I’ve received feedback that the current translation of primitive type
facets into JSON Schema makes the JSON CSDL hard to understand for clients
that are not interested in validating payloads but just want to get the
OData metadata.
For example a simple
<Property Type="Edm.Decimal" Name="Price" Precision="15" Scale="3" />
Becomes (as Nullable="true" is the default):
"anyOf":[{"type":"number", "multipleOf":0.001, "minimum":-999999999999.999,
"maximum":999999999999.999}, {"type":"null"}]
One way to make this more digestible would be to redundantly add the OData
facets to the JSON Schema representation:
"anyOf":[{"type":"number", "multipleOf":0.001, "minimum":-999999999999.999,
"maximum":999999999999.999}, {"type":"null"}], "precision":15, "scale":3
And redundantly add "nullable":false so clients don’t have to check for the
anyOf" or "type":["number","null"] constructs.
What do you think?
Thanks in advance!
--Ralf
In preparing for battle
I have always found that plans are useless,
but planning is indispensable.
- Dwight D. Eisenhower