[v2] Adding a vars map to a groupBy query changes the shape of the results

[Jackamus29]

Tweaking a groupBy query to include a vars map changes the shape of the results from an object with the groupBy values as keys to an array of two-tuples where the first element is the groupBy value.

Without vars map

{
	"selectDistinct": [
		"?studentName",
		"?studentId"
	],
	"where": [
		["?profile", "profile/name", "?studentName"],
		["?profile", "profile/student_id", "?studentId"],
		["?assertion", "assertion/recipient", "?profile"],
        ["?assertion", "assertion/source", "?source"],
        ["?source", "profile/name", "?sourceName"]
	],
	"opts": {
		"compact": true,
        "groupBy": "?sourceName"
	}
}

=>

{
  "Institution A": [
    [
      "Lenny",
      "leonard2"
    ],
    [
      "Freddy",
      "fred25"
    ]
  ],
  "Institution B": [
    [
      "Freddy",
      "fred25"
    ]
  ]
}

With vars map

{
	"selectDistinct": [
		"?studentName",
		"?studentId"
	],
	"where": [
		["?profile", "profile/name", "?studentName"],
		["?profile", "profile/student_id", "?studentId"],
		["?assertion", "assertion/recipient", "?profile"],
        ["?assertion", "assertion/source", "?source"],
        ["?source", "profile/name", "?sourceName"]
	],
	"vars": {
		"?achievementType": ["Degree"]
	},
	"opts": {
		"compact": true,
        "groupBy": "?sourceName"
	}
}

=>

[
  [
    "Institution A",
    [
      [
        "Lenny",
        "leonard2"
      ],
      [
        "Freddy",
        "fred25"
      ]
    ]
  ],
  [
    "Institution B",
    [
      [
        "Freddy",
        "fred25"
      ]
    ]
  ]
]

[Jackamus29]

Note, this may be related to #499

[Jackamus29]

Another oddity about this query is that if you add additional items to the vars map, it seems to duplicate the results.

vars map with a binding of length 1

{
	"selectDistinct": [
		"?studentName",
		"?studentId"
	],
	"where": [
		["?profile", "profile/name", "?studentName"],
		["?profile", "profile/student_id", "?studentId"],
		["?assertion", "assertion/recipient", "?profile"],
        ["?assertion", "assertion/source", "?source"],
        ["?source", "profile/name", "?sourceName"]
	],
	"vars": {
		"?achievementType": ["Degree"]
	},
	"opts": {
		"compact": true,
        "groupBy": "?sourceName"
	}
}

=

[
 [
   "Institution A",
   [
     [
       "Lenny",
       "leonard2"
     ],
     [
       "Freddy",
       "fred25"
     ]
   ]
 ],
 [
   "Institution B",
   [
     [
       "Freddy",
       "fred25"
     ]
   ]
 ]
]

vars map with an item of length 2

{
   "selectDistinct": [
   	"?studentName",
   	"?studentId"
   ],
   "where": [
   	["?profile", "profile/name", "?studentName"],
   	["?profile", "profile/student_id", "?studentId"],
   	["?assertion", "assertion/recipient", "?profile"],
       ["?assertion", "assertion/source", "?source"],
       ["?source", "profile/name", "?sourceName"]
   ],
   "vars": {
   	"?achievementType": ["Degree", "Test"]
   },
   "opts": {
   	"compact": true,
       "groupBy": "?sourceName"
   }
}

=>

[
 [
   "Institution A",
   [
     [
       "Lenny",
       "leonard2"
     ],
     [
       "Freddy",
       "fred25"
     ]
   ]
 ],
 [
   "Institution B",
   [
     [
       "Freddy",
       "fred25"
     ]
   ]
 ],
 [
   "Institution A",
   [
     [
       "Lenny",
       "leonard2"
     ],
     [
       "Freddy",
       "fred25"
     ]
   ]
 ],
 [
   "Institution B",
   [
     [
       "Freddy",
       "fred25"
     ]
   ]
 ]
]

[aaj3f]

@zonotope @Jackamus29 not to tack on here, but I'm also seeing an odd NullPointerException with vars that can be reproduced here:

Transaction 1

[{
    "_id": "_predicate",
    "type": "string",
    "name": "_user/awards",
    "multi": true
}]

Transaction 2

[{
    "_id": "_user",
    "username": "jack",
    "awards": ["HS Degree", "College Degree"]
},
{
    "_id": "_user",
    "username": "kate",
    "awards": ["HS Degree", "College Degree", "Grad School Degree"]
}]

Query without vars

{
  "selectDistinct": [
      "?user",
      "?username",
      "?award",
      "(count ?award)"
      ],
  "where": [
      ["?user", "_user/awards", "?award"],
      ["?user", "_user/username", "?username"]
      ]
}

// =>

[
  [
    87960930223082,
    "kate",
    "College Degree",
    5
  ],
  [
    87960930223082,
    "kate",
    "Grad School Degree",
    5
  ],
  [
    87960930223082,
    "kate",
    "HS Degree",
    5
  ],
  [
    87960930223081,
    "jack",
    "College Degree",
    5
  ],
  [
    87960930223081,
    "jack",
    "HS Degree",
    5
  ]
]

Query with vars [broken; NullPointerException]

{
  "selectDistinct": [
      "?user",
      "?username",
      "?award",
      "(count ?award)"
      ],
  "where": [
      ["?user", "_user/awards", "?award"],
      ["?user", "_user/username", "?username"]
      ],
   "vars": {
      "?award": ["HS Degree"]
    }
}

// =>

2023-06-13 11:46:17,344 ERROR fluree.db.server - Uncaught exception on "async-dispatch-7" - java.lang.NullPointerException: null\n

[bplatz]

That was marked as done in #514