Page History

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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

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)

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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 to that of the list followed by opening square bracket starting with "[" and any attribute identified in the query by special symbol "%"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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Currently in order to retrieve the entire list data node we have to query the Parent data node. So, in the above example for the list named "categories" we have to query the parent node that is "bookstore". Hence the xpath in the query would become "/bookstore" and we would get the following response:

[
    {
        "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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