Is an OData Gateway a thing?

[paule96]

I'm quite long using OData now (around 10 years) and I started lately to research a bit about GraphQl. So far both protocols are very similar from their usecases.

But one thing, what is quite nice in GraphQl is the possibility to build quite easy a gateway to other services with aggregation possibilities between them.

And I was just wondering if their is a way to do a similar thing with OData.

To have something like:

• People Service
  • odata/people
    • Name: string
    • CityId: string
• City Service
  • odata/city
    • Name: string
    • Id: string

And a gateway that define something like:

• People entity
  • Name: string
  • CityId: string
  • City: City
• City entity
  • Name: string
  • Id: string

And for the City property at the people entity their is some kind of resolver defined who sends a request to the City Service.

So you could do something at the gateway like:

/odata/people?$expand=City

What would result into:

sequenceDiagram
  User->>Gateway: `/odata/people?$expand=City`
  Gateway->>People Service: `/odata/people`
  People Service->>Gateway: Response for People
  Gateway->>City Service: `/odata/city('New York')`
  Gateway->>City Service: `/odata/city('Berlin')`
  Gateway->>City Service: `/odata/city('London')`
  City Service->>Gateway: Response for New York
  City Service->>Gateway: Response for Berlin
  City Service->>Gateway: Response for London
  Gateway->>User: Combine Result for people with city expanded

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[habbes]

Hello @paule96 this is a great questions. There are services which expose an OData gateway that can route requests to different backend services and combine the responses, but we don't have an official implementation for such a framework. So everyone does it their own way. However, there have been some explorations that could lead to such a gateway being much easier to build with OData. @corranrogue9 would your explorations on composability of OData services make such a gateway easier to define?

[paule96]

It would be nice to maybe try some open work to create a YARP extension for cases like that. :)

[corranrogue9]

As @habbes notes, this is definitely possible with OData. I am working on some new interfaces and implementations that should make this kind of work more straightforward, but this is work is a ways off. Beyond simply implementing the functionality, there are some interesting architectural questions which arise.

GET requests are generally pretty straightforward, especially if eventual consistency is a service paradigm. However, POST and PATCH requests end up with some well-known issues that occur in distributed systems (e.g. what happens when PATCHing a People entity and its City property and a failure occurs in one of the two updates?).