Yup, stored the timestamps (still Date string) and the uuid in the tree. Works!
I have to ensure that the hierarchy is now of odd length in a way following
this scheme [root_id, (timestamp, descendant_id)*]
I am working with couchrest and made a view with a bit of wrapping to handle
the data correctly.
Here is the map function for the hierarchy and here the necessary code for
handling it when querying for a certain document.
When adding a document to another document you just simply take the parent's
'descends_from' value and push it's timestamp followed by it's uuid into and
set the result as the child's descends_from value. In the case of adding a
child to a toplevel post you just set 'descends_from' to a new array containing
only the parent's uuid.
It doesn't work with non-toplevel documents I think, but right now I don't need
that functionality, perhaps one could add that easily.
The whole code is taken from a small project of my building upon a fork of
scanty using couchdb as the backend. As soon as this is "kind of usable" I can
put it up to github.
Greetings
On Nov 24, 2009, at 11:06 PM, Patrick Barnes wrote:
> Why not just store timestamps in the tree? Use the unix time format to make
> comparison faster, and as long as no two posts are made at *exactly* the same
> time, no problem.
>
> Hmmm, guess the uuid would be needed to avoid that issue.
>
> [10:00:47, 123] : id:123
> ..[10:00:47, 123, 10:05:00, 126] : id:126
> ..[10:00:47, 123, 10:06:23, 127] : id:127
> [10:00:47, 124] : id:124
> ..[10:00:47, 124, 10:03:11, 125] : id:125
>
> A little bit cumbersome, true... but it should work.
> (Of course, 1259103826 is easier to sort by than "2009/11/25 09:04:12")
>
> ------
>
> The other option might simply be to use an incrementing number for your
> document key, rather than a UUID.
> * On creation of a document, pull the largest current key from _all_docs,
> increment it, and create the document.
> * If the document creation fails because another process has beaten it to the
> ID, reincrement and retry until an unclaimed ID is found.
>
> That should work as long as the write frequency isn't very high, and would
> give you a much neater tree.
>
> ------
>
> Let us know what you end up doing. :-)
> -Patrick
>
> Lennart Melzer wrote:
>> I'm having difficulties with your approach when trying to build a tree of
>> Documents.
>> I want to be able to represent some kind of threaded view upon documents,
>> where each branch is sorted by the creation date.
>> currently I am storing the hierarchy in the descends_from field of a
>> document. It contains the uuids of the posts this document descends from.
>> The problem (as you already pointed out) is that i cannot use these uuids as
>> keys for a view, since it will not order them correctly (by a timestamp),
>> but lexicographically by their id.
>> Right now I can either have those documents sorted by their creation date,
>> or hierarchically correct, but not both.
>> I don't want to use incrementing ids, since I'd like to stick with the uuids
>> ( or at least with ids, that do not tell anything about the ordering).
>> What I thought about is to use the uuids and the creation date of each
>> parent as the key (this is bloat, i know)
>> Something like
>> ["root_id","timestamp of the first level","first_level_id","timestamp of the
>> second level", "second_level_id"....]
>> So if C was created today and C descends from B and B has been created
>> yesterday and B descends from A, then the key in a view-row for A's children
>> should look like
>> [A,yesterday,B,today,C]
>> that way the resulting rows would be hierarchically correct and each branch
>> sorted by timestamps.
>> The problem would be to store the data for producing such complex keys
>> inside each document and still keep them in the correct order.
>> Any suggestions on how to solve this? Perhaps I really think way to complex,
>> or there's something wrong with the view logic I am thinking of.
>> Greetings,
>> Lennart
>> On Nov 18, 2009, at 12:23 PM, Patrick Barnes wrote:
>>> I would suggest that each comment has a 'hierarchy' attribute, like an
>>> OID...
>>> For instance: ('.'s for padding)
>>> [
>>> {"hierarchy":[1], "id":1, "data":"foo"}
>>> ...{"hierarchy":[1,2], "id":2, "data":"foo"}
>>> ...{"hierarchy":[1,3], "id":3, "data":"foo"}
>>> ......{"hierarchy":[1,3,5], "id":5, "data":"foo"}
>>> ......{"hierarchy":[1,3,16], "id":16, "data":"foo"}
>>> {"hierarchy":[4], "id":4, "data":"foo"}
>>> ...{"hierarchy":[4,6], "id":6, "data":"foo"}
>>> ......{"hierarchy":[4,6,8], "id":8, "data":"foo"}
>>> ...{"hierarchy":[4,7], "id":7, "data":"foo"}
>>> ......{"hierarchy":[4,7,9], "id":9, "data":"foo"}
>>> .........{"hierarchy":[4,7,9,10], "id":10, "data":"foo"}
>>>
>>> You needn't necessarily fill the hierarchy tree with ids, but the values
>>> should represent the order that you want the items to be displayed.
>>> (Perhaps a timestamp value?)
>>>
>>> To create a new comment under an existing one, take its "hierarchy" array
>>> value, and add a new ordering number to the end.
>>>
>>> To use this, write a view that uses hierarchy as a key - it will sort all
>>> the values into lexicographical order.
>>>
>>> To get all the items that a particular item is parent of...
>>> eg:
>>> All the children of comment {"hierarchy":[1,3], "id":3, "data":"foo"}
>>> can be found by querying the view with startkey:[1,3] and endkey:[1,3,{}]
>>>
>>> Write some display code to manage proper indentation, and you're done. :-)
>>>
>>>
>>>
>>> 7zark7 wrote:
>>>> Bit of a design question, hope you can provide some guidance:
>>>> I'm writing an internal wiki-like web application, and one of the
>>>> use-cases is to comment on a document.
>>>> Domain model is simple:
>>>> a Comment class with text, date, and a collection of child comments.
>>>> My first implementation stores the comment tree in a single document,
>>>> since it is very easy to serialize and deserialize, and the comment tree
>>>> itself can be thought of as a holistic "document".
>>>> This works great, but now running into an issue on how to best support
>>>> revision conflicts when multiple people are commenting at the same time.
>>>> If I were to keep the tree stored in a single document, I would have to
>>>> load the two conflicting versions in code, manually combine the trees, and
>>>> then save a new version, correct?
>>>> From a storage-perspective, it seems it would be simpler then to store
>>>> each comment as its own document, with a "foreign key" of sorts pointing
>>>> to a parent comment, which would be much less likely to have conflicts.
>>>> But then it seems I'm forcing a relational model into a document-based DB.
>>>> Any thoughts on this?
>>>> Thanks,
>>>> Z
