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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When we try to query the entire list, we get DataNodeNotFound exception because there is no data node with the xpath representing a list in the database. Ex: /bookstore/categories

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 "[" and any attribute identified in the query by special symbol "%"

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:

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 LIKE :escapedXpath||'[@%]' ESCAPE '\\' "
            + "AND xpath NOT LIKE :escapedXpath||'[@%[%' ESCAPE '\\'"

(xpath = '/bookstore/categories' OR xpath LIKE '/bookstore/categories[%')

And this would return 2 fragments as follows.

Impact on response body

The updated query returns child fragments when querying the entire list and it has the following impacts when compared to the existing response body.

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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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[
    {
        "stores:categories": {
            "name": "Test book",
            "price": 1000,
            "stock": false,
            "book-category": "SciFi"
        }
    },
    {
        "stores:categories": {
            "name": "Kids book updated",
            "price": 5000,
            "stock": true,
            "book-category": "Kids"
        }
    }
]

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[
    {
        "stores:categories": {
            "name": "Test book",
            "price": 1000,
            "stock": false,
            "book-category": "SciFi"
        }
    },
    {
        "stores:categories": {
            "name": "Kids book updated",
            "price": 5000,
            "stock": true,
            "book-category": "Kids"
        }
    }
]

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