Hello again,
I've noticed some inconsistencies with regard to the initial document in an
empty database. I understand that it is often treated as an indication that the
database is "empty". I.e., if the database has only one node and it's a
document at the first pre value, then Data.empty() returns true. The problem
arises because the database isn't actually empty - it contains one empty
document - and some commands/methods view it as an empty database while others
treat it as a database with one empty document. Several examples:
- The method Data.doc(name) will return -1 (indicating the document doesn't
exist) while Data.docs() will return an array of size 1 with the first value a
0 (indicating there is one document at pre value 0). This is actually my own
problem because the API I'm writing relies on these two methods being
internally consistent - I can't have one telling me there is one document
called "XYZ" but then have the other refuse to give me a pre value for the
"XYZ" document I was just told exists.
- The GUI shows a single doc node in the tree view but issuing the command
"list [database name]" shows the database as having no resources.
- I can evaluate the query "insert node 'text' into doc('[initial document
name]')" and it executes. I can see the new text node under the initial
document in the GUI tree view. Now when I issue the command "list [database
name]" I see 1 resource. Having the list command report different numbers of
resources before and after a XQuery insertion seems odd.
- If I issue the command "ADD TO newdoc <xyz/>", I can see the new
doc("newdoc") node with the child <xyz> element in the GUI but the previously
empty document is now gone. This also seems odd - I'm not sure how I feel about
an ADD command removing data from the database (even if it was just intended to
be a placeholder).
In the end, I think BaseX should support the notion of a database with one
empty document as being valid - there are probably cases where one might want
to start their session in that state. I'm not sure what the solution is or
should be (or if it's even something that is worth or needs solving). My own
preference would be for the internal indication of an empty database to use a
different node kind dedicated for that purpose so there is no confusion whether
the single node at pre 0 is an empty initial document or an indication of an
empty database.
At the very least, I think the inconsistencies above should be corrected - if a
single empty document node is intended to signify an empty database and is not
actually intended to be part of the database, then you should not see it in the
GUI, not be allowed to insert content to it, etc.
Dave
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