Adding HATEOAS support for data relation fields

[smeng9]

Hi,

I think it would be useful to add a reference sort of thing to the returned embedded field, if we want the user to navigate.

---

In https://eve-demo.herokuapp.com/ demo there are two domains -- works and people.
For now when we visit https://eve-demo.herokuapp.com/works, the embedded owner field in each of returned resource is just an objectid string with no href.

Expected Behavior

visit https://eve-demo.herokuapp.com/works

<resource href="works/5b89b1b091a5d0000495f56a" title="Work">
<_created>Fri, 31 Aug 2018 21:22:56 GMT</_created>
<_etag>9699888bc6e1d48fb52d3b573f302a24112802e8</_etag>
<_id>5b89b1b091a5d0000495f56a</_id>
<_updated>Fri, 31 Aug 2018 21:22:56 GMT</_updated>
<description>Description #25</description>
<owner href="people/5b89b1b091a5d0000495f54d">5b89b1b091a5d0000495f54d</owner>
<title>Book Title #25</title>
</resource>

visit https://eve-demo.herokuapp.com/works?embedded={%22owner%22:1}

<resource href="works/5b89b1b091a5d0000495f56a" title="Work">
<_created>Fri, 31 Aug 2018 21:22:56 GMT</_created>
<_etag>9699888bc6e1d48fb52d3b573f302a24112802e8</_etag>
<_id>5b89b1b091a5d0000495f56a</_id>
<_updated>Fri, 31 Aug 2018 21:22:56 GMT</_updated>
<description>Description #25</description>
<owner href="people/5b89b1b091a5d0000495f54d">
  <_created>Fri, 31 Aug 2018 21:22:56 GMT</_created>
  <_etag>103dab458e6e1cf1a70b74f770bb0cac9075a1c0</_etag>
  <_id>5b89b1b091a5d0000495f54d</_id>
  <_updated>Fri, 31 Aug 2018 21:22:56 GMT</_updated>
  <born>Wed, 25 Feb 1987 17:00:00 GMT</born>
  <firstname>Serena</firstname>
  <lastname>Love</lastname>
  <location>
  <address>363 Brannan St</address>
  <city>San Francisco</city>
  </location>
  <role>author</role>
</owner>
<title>Book Title #25</title>
</resource>

Actual Behavior

visit https://eve-demo.herokuapp.com/works

<resource href="works/5b89b1b091a5d0000495f56a" title="Work">
<_created>Fri, 31 Aug 2018 21:22:56 GMT</_created>
<_etag>9699888bc6e1d48fb52d3b573f302a24112802e8</_etag>
<_id>5b89b1b091a5d0000495f56a</_id>
<_updated>Fri, 31 Aug 2018 21:22:56 GMT</_updated>
<description>Description #25</description>
<owner>5b89b1b091a5d0000495f54d</owner>
<title>Book Title #25</title>
</resource>

visit https://eve-demo.herokuapp.com/works?embedded={%22owner%22:1}

<resource href="works/5b89b1b091a5d0000495f56a" title="Work">
<_created>Fri, 31 Aug 2018 21:22:56 GMT</_created>
<_etag>9699888bc6e1d48fb52d3b573f302a24112802e8</_etag>
<_id>5b89b1b091a5d0000495f56a</_id>
<_updated>Fri, 31 Aug 2018 21:22:56 GMT</_updated>
<description>Description #25</description>
<owner>
  <_created>Fri, 31 Aug 2018 21:22:56 GMT</_created>
  <_etag>103dab458e6e1cf1a70b74f770bb0cac9075a1c0</_etag>
  <_id>5b89b1b091a5d0000495f54d</_id>
  <_updated>Fri, 31 Aug 2018 21:22:56 GMT</_updated>
  <born>Wed, 25 Feb 1987 17:00:00 GMT</born>
  <firstname>Serena</firstname>
  <lastname>Love</lastname>
  <location>
  <address>363 Brannan St</address>
  <city>San Francisco</city>
  </location>
  <role>author</role>
</owner>
<title>Book Title #25</title>
</resource>

Environment

• Python version: eve live demo
• Eve version: eve live demo

[nicolaiarocci]

I like it. Feel free to provide a PR if you feel like doing it.

[smeng9]

I changed the title from "embedded fields" to "data relation fields" because some of the embedded fields are embedded 'strongly-typed' dictionaries. Besides, all the data relation fields defined in the schema will apply to the hateoas support, not just the fields in the query url's embedded argument. Hope this will make it more clear.

[nicolaiarocci]

Addressed by #1204

[s-eswar]

@nicolaiarocci I have used the field as 'id' for the referenced collection instead of default '_id'. What should be the end-point query like:
I have tried http://127.0.0.1:5000/works?embedded={"owner":1} But this doesn't work. Can you check this https://stackoverflow.com/questions/54669278/fetch-data-of-the-reference-table-using-id-in-python-eve

[einarhuseby]

@s-eswar your query is correct, however custom fields are not embeddable as of now. It will be fixed in 0.8.2, see #1225