Content Comparison

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Inconsistent response when retrieving data nodes.

When a get operation is performed on Root node xpath (/) it returns an array list containing all the data nodes under the root node xpath. But if the same operation is performed for a List Data node no array list is returned instead a 404 Not Found response is returned.

/v2/dataspaces/my-dataspace/anchors/multipleTop/node?xpath=/&descendants=3

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Inconsistent response when retrieving data nodes.

When a get operation is performed on Root node xpath (/) it returns an array list containing all the data nodes under the root node xpath. But if the same operation is performed for a List Data node no array list is returned instead a 404 Not Found response is returned.

/v2/dataspaces/my-dataspace/anchors/multipleTop/node?xpath=/&descendants=3

[
    {
        "stores:bookstore": {
            "store-name": "My Bookstore",
            "store-owner": "James",
            "categories": [
                {
                    "name": "Test book",
                    "price": 100,
                    "stock": false,
                    "book-category": "SciFi"
                }
            ]
        }
    },
    {
        "stores:electronics-store": {
            "store-name": "My Electronics store",
            "category": [
                {
                    "status": true,
                    "address": "India",
                    "store-type": "electronics"
                }
            ]
        }
    }
]

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WHERE anchor_id = :anchorId AND xpath = ANY (:xpaths)

So, from the above snapshot of the fragment table, it can be clearly seen that individual list items are stored in the CPS DB and there is no data node representing the entire list. And hence when the existing query is executed it looks for the fragment with the specific xpath. 

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 xpath = ANY (:xpaths)

So, from the above snapshot of the fragment table, it can be clearly seen that individual list items are stored in the CPS DB and there is no data node representing the entire list. And hence when the existing query is executed it looks for the fragment with the specific xpath. 

Now, the updated query does not look for a list data node for a given xpath (representing a list Ex: /bookstore/categories). Instead, it looks for all the fragments in the table which have a similar xpath starting with "[" and ending with ] using pattern matching.

To make it work we use a combination of LIKE and NOT LIKE keywords.

For this we make use of the LIKE keyword along with % wildcard to make use of pattern matching.

But the above query would also return fragments for xpaths like /bookstore/categories[@code='1']/books[@name="Hello"]

To avoid this scenario, we make use of NOT LIKE keyword along with the same % wildcard. and hence we have [%[% to exclude multiple opening brackets.

"SELECT * FROM fragment WHERE anchor_id = :anchorId "
+ "     AND (xpath = ANY (:xpaths) OR xpath LIKE ANY (array(SELECT concat(t, '[%') FROM unnest(:xpaths) as t)))

So as seen in the above segment of the query, we have "AND (xpath = ANY (:xpaths) OR xpath LIKE ANY (array(SELECT concat(t, '[%') FROM unnest(:xpaths) as t)))".

Any given xpath for a list (Ex: /bookstore/categories) would become like so:

(xpath = '/bookstore/categories' OR xpath LIKE '/bookstore/categories[%')       + "AND xpath LIKE :escapedXpath||'[@%]' ESCAPE '\\' "
            + "AND xpath NOT LIKE :escapedXpath||'[@%[%' ESCAPE '\\'"

And this would return 2 fragments as follows.

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[
    {
        "stores:bookstore": {
		 	"store-name": "My Bookstore",
   {         "stores:bookstorestore-owner": {"ABC",
            "categories": [
                {
                    "name": "Test book",
                    "price": 1000,
                    "stock": false,
                    "book-category": "SciFi"
                },
                {
                    "name": "Kids book",
                    "price": 5000,
                    "stock": true,
                    "book-category": "Kids"
                }
            ],
			"store-name": "My Bookstore",
            "store-owner": "ABC"
        }
    }
]

Here we can see that in the response we get a parent node bookstore and the list named "categories", as its child, and the list items identified by keys "SciFi" and "Kids" respectively. 

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