Bug 15434 - [IndexedDB] Detail steps for assigning a key to a value
[IndexedDB] Detail steps for assigning a key to a value
Status: RESOLVED FIXED
Product: WebAppsWG
Classification: Unclassified
Component: Indexed Database API
unspecified
All All
: P2 minor
: ---
Assigned To: Eliot Graff
public-webapps-bugzilla
:
Depends on:
Blocks:
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Reported: 2012-01-05 21:44 UTC by Joshua Bell
Modified: 2012-02-29 17:47 UTC (History)
4 users (show)

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Description Joshua Bell 2012-01-05 21:44:12 UTC
In section 5.1 "Object Store Storage Operation", step 2: when a key generator is used with store with in line keys, the spec says: "set the property in value pointed to by store's key path to the new value for key"

The "steps for extracting a key from a value using a key path" are called out explicitly under Algorithms in 4.7. Should the steps for assigning a key to a value using a key path be similarly documented? 

Cribbing from the spec, this could read as:

4.X Steps for assigning a key to a value using a key path

When taking the steps for assigning a key to a value using a key path, the implementation must run the following algorithm. The algorithm takes a key path named /keyPath/, a key named /key/, and a value named /value/ which may be modified by the steps of the algorithm.

1. If /keyPath/ is the empty string, skip the remaining steps and /value/ is not modified.
2. Let /remainingKeypath/ be /keyPath/ and /object/ be /value/.
3. If /remainingKeypath/ has a period in it, assign /remainingKeypath/ to be everything after the first period and assign /attribute/ to be everything before that first period. Otherwise, go to step 7.
4. If /object/ does not have an attribute named /attribute/, then skip the rest of these steps and /value/ is not modified.
5. Assign /object/ to be the /value/ of the attribute named /attribute/ on /object/.
6. Go to step 3.
7. NOTE: The steps leading here ensure that /remainingKeyPath/ is a single attribute name (i.e. string without periods) by this step.
8. Let /attribute/ be /remainingKeyPath/
9. If /object/ has an attribute named /attribute/ which is not modifiable, then skip the remaining steps and /value/ is not modified.
10. Set an attribute named /attribute/ on /object/ with the value /key/.

Notes: 

The above talks in terms of a mutable value. It could be amended to have an initial step which produces a clone of the value, which is later returned, but given how this algorithm is used the difference is not observable, since the value stored should already be a clone that doesn't have any other references.

Step 9 is present in case the key path refers to a "special" property, e.g. a String/Array length, Blob/File properties, etc.
Comment 1 Jonas Sicking 2012-01-25 01:08:38 UTC
This is the set of steps people seemed to agree on after the thread in the mailing list:

1. Let /remainingKeypath/ be /keyPath/ and /object/ be /value/.
2. if /object/ is not an Object object or an Array object (see structured clone algorithm), then throw a DOMException of type DataError.
3. If /remainingKeypath/ has a period in it, assign /remainingKeypath/ to be everything after the first period and assign /attribute/ to be everything before that first period. Otherwise, go to step 7.
4. If /object/ does not have an attribute named /attribute/, then create the attribute and assign it an empty object.
5. Assign /object/ to be the value of the attribute named /attribute/ on /object/.
6. Go to step 2.
7. NOTE: The steps leading here ensure that /remainingKeyPath/ is a single attribute name (i.e. string without periods) by this step. They also ensure that /object/ is an Object or an Array, and not a Date, RegExp, Blob etc.
8. Let /attribute/ be /remainingKeyPath/
9. Set an attribute named /attribute/ on /object/ with the value /key/.

Note that the intent is that these steps are only executed if evaluating the keyPath did not yield a value. I.e. every time before we run these steps we evaluate the keyPath against /value/ and only if that does not yield a value (where 'undefined' does count as a value) do we generate a key and use the above steps to modify /value/ to contain the generated key.

Because of this we know that at step 10 the object does not have an attribute with name /attribute/.
Comment 2 Eliot Graff 2012-02-29 17:47:55 UTC
Changes live in the Editor's draft of 29 February.