Pulp

In pulp 2.7:

curl -k -u admin https://pulp27.example.com/pulp/api/v2/plugins/types/package_group/ | json_reformat
...
"unit_key": [
"id",
"repo_id"
],

In pulp 2.10:

curl -k -u admin https://pulp210.example.com/pulp/api/v2/plugins/types/package_group/ | json_reformat
...
"unit_key": [
"package_group_id",
"repo_id"
],

In both cases, querying for a package group via the API returns something along the lines of:

2016-12-16 10:03:54,568 - INFO - Response status : 200 

2016-12-16 10:03:54,568 - INFO - Response body :
 [
  {
    "updated": "2016-12-16T02:48:55Z", 
    "repo_id": "jamatt-test20160224-rpm-latest", 
    "created": "2016-12-15T22:32:58Z", 
    "unit_id": "42100971-88c3-49ee-86b5-5e95c6360843", 
    "unit_type_id": "package_group", 
    "_id": {
      "$oid": "58531a1ab351ba3cada3a5a0"
    }, 
    "metadata": {
      "mandatory_package_names": [
        "OnePM-test-package-minimum-fields", 
        "OnePM-test-package-destination-folder"
      ], 
      "repo_id": "jamatt-test20160224-rpm-latest", 
      "description": "YUM Group for OnePM testing", 
      "name": "onepm-test-yum-group", 
      "pulp_user_metadata": {}, 
      "default": false, 
      "_ns": "units_package_group", 
      "_last_updated": 1481840449, 
      "display_order": 1024, 
      "user_visible": true, 
      "translated_name": {}, 
      "translated_description": {}, 
      "optional_package_names": [], 
      "default_package_names": [], 
      "_content_type_id": "package_group", 
      "langonly": "en", 
      "_id": "42100971-88c3-49ee-86b5-5e95c6360843", 
      "id": "onepm-test-yum-group", 
      "conditional_package_names": []
    }
  }
]

Conditional Package Names: 
Default Package Names:     
Description:               YUM Group for OnePM testing
Id:                        onepm-test-yum-group
Mandatory Package Names:   OnePM-test-package-minimum-fields,
                           OnePM-test-package-destination-folder
Name:                      onepm-test-yum-group
Optional Package Names:    
User Visible:              True

Notice how in pulp 2.10 there is no package_group_id field in metadata, which my code was expecting.