The scenario where I need to use HTML 5 Database storage requires
storing a tree of data. Each item has a unique id, generated by the
database. Child nodes have a "parentId" field which points to their
parent ID. Creating the records for a new tree in the database
requires multiple transactions. First, the root item must be created.
When the callback returns, the children of the root item can be
created, because the id of the root item is now known. For each
child, when the appropriate callback returns, the children of the
child can be created, because their parent IDs are now known, and so
forth.
Minimizing the number of transactions (and thus the overall time to
create a database) requires there be multiple transactions outstanding
at any given time. Thus, when a callback function is called, it
needs to determine _which_ transaction has completed. The current
version of the HTML 5 Database storage spec does not make this easy.
It is straightforward for my app to generate a unique ID for each
transaction, but the spec provides no way to pass this to the
callbacks. In JavaScript, I can add an "id" field to the transaction
object, but then the _same_ id gets passed to each statement callback,
and the transaction object is not passed _at all_ to the transaction
success callback.
I'm sure there are other scenarios where it would be useful for a
statement callback to know which statement has completed, and for a
transaction callback to know which transaction has just completed.
Thank you.
- HTML 5 Database Storage Does Not Enable Chaining Transactions Doug Reeder
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