...

{
  "cps-cavsta-onap-internal:ran-coverage-area": {
    "pLMNIdList": [
      {
        "mcc": "310",
        "mnc": "410",
    }
  ],
  "coverage-area": [
          {
            "coverageArea": "Washington",
            "coverageAreaTAList": [
              {
                "nRTAC": 234,
                "taCellsList": [
                  {
                    "cellLocalId": 15709
            }
      }
    ]
        }
      ]
    }
          }
            ]
          }
        ]
      }
    ]
  }
}

So although the key-value for the coverageAreaTAList is known the key for the parent list is NOT known. so this requires a more advanced query:

It could be done with either query #3 or #5 #4 described in CPS-235: Overview of (early) CPS Query and Update Scenarios assuming it wil ahve have an option to also retreive all retrieve all descendants

#21 List tracking area (coverageAreaTAList) for the specified coverage area#21

I think this is a simple 'get with children' xpath e.g. :  \/ran-coverage-area[@mcc=310 and @mnc=410]\coverare/coverage-area[@coverageArea="Wahington"]'Washington']

Note: Compound key fields need to be in alphabetical order. The key is matched as a string literal so incorrect order or spacing issues will result in the key not being found in the database

3. Field Mapping Between ConfigDB Schema and Yang Model

...