Pulp

The `fields` machinery works only with models before the switch to mongoengine.

When sending a criteria object to pymongo, the fields key restricts the fields of the dictionary that is returned. This doesn't work because Mongoengine objects are hydrated from those dictionaries, and instead of leaving them off at serialization time, they are simply set to null values.

$ http --json -a admin:admin --verify=no POST https://localhost/pulp/api/v2/repositories/search/ criteria:='{"filters": {"id": "zoo"}}'

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 296
Content-Type: application/json; charset=utf-8
Date: Thu, 22 Oct 2015 20:32:00 GMT
Keep-Alive: timeout=5, max=100
Server: Apache/2.4.16 (Fedora) OpenSSL/1.0.1k-fips mod_wsgi/4.4.8 Python/2.7.10

[
    {
        "_href": "/pulp/api/v2/repositories/zoo/", 
        "_id": {
            "$oid": "562946cfe779894f63353553"
        }, 
        "_ns": "repos", 
        "content_unit_counts": {}, 
        "description": null, 
        "display_name": null, 
        "id": "zoo", 
        "last_unit_added": null, 
        "last_unit_removed": null, 
        "notes": {
            "_repo-type": "rpm-repo"
        }, 
        "scratchpad": {}
    }
]

$ http --json -a admin:admin --verify=no POST https://localhost/pulp/api/v2/repositories/search/ criteria:='{"filters": {"id": "zoo"}, "fields": ["id"]}'

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 272
Content-Type: application/json; charset=utf-8
Date: Thu, 22 Oct 2015 20:32:11 GMT
Keep-Alive: timeout=5, max=100
Server: Apache/2.4.16 (Fedora) OpenSSL/1.0.1k-fips mod_wsgi/4.4.8 Python/2.7.10

[
    {
        "_href": "/pulp/api/v2/repositories/zoo/", 
        "_id": {
            "$oid": "562946cfe779894f63353553"
        }, 
        "_ns": "repos", 
        "content_unit_counts": {}, 
        "description": null, 
        "display_name": null, 
        "id": "zoo", 
        "last_unit_added": null, 
        "last_unit_removed": null, 
        "notes": {}, 
        "scratchpad": {}
    }
]