[GSOC] Database API draft proposal

[Daniel Gibson]

Am 03.04.2011 20:15, schrieb Fawzi Mohamed:
> On 3-apr-11, at 19:28, Piotr Szturmaj wrote:
> 
>> Fawzi Mohamed wrote:
>>> Looking more maybe I was a bit too harsh, if you define clearly the
>>> goals of your API then yes it might be a good project.
>>> The api doesn't have to be defined yet, but a more detailed definition
>>> of its goals should be there, maybe with code example of some usages.
>>> Questions that should be answered:
>>
>> I know your response is'nt to me, but please let me answer these questions
>> from my point of view, based on my recent work on ddb.
> 
> I think that your responses are very relevant, as it seems to me that your work
> is nice, and I find that if a GSoC is done in that direction it should
> definitely work together with the good work that is already done, let's don't
> create multiple competing projects if people are willing to work together.
> 
>>> * support for static and dynamic types.
>>> how access of dynamic and static types differs, should be as little as
>>> possible, and definitely the access one uses for dynamic types should
>>> work without changes on static types
>>
>> If you mean statically or dynamically typed data row then I can say my DBRow
>> support both.
> 
> yes but as I said I find the support for dynamic data rows weak.
> 
>>> * class or struct for row object
>>
>> I'm using struct, because I think row received from database is a value type
>> rather than reference. If one selects rows from one table then yes, it is
>> possible to do some referencing based on primary key, but anyway I think
>> updates should be done explicitly, because row could be deleted in the
>> meantime. In more complex queries, not all of selected rows are materialized,
>> i.e. they may be from computed columns, view columns, aggregate functions and
>> so on. Allocation overhead is also lower for structs.
>>
>>> * support for table specific classes?
>>
>> Table specific classes may be written by user and somehow wrap underlying row
>> type.
> 
> well with the current approach it is ugly because your calls would be another
> type, thus either you remove all typing or you can't have generic functions,
> accepting rows, everything has to be a template, looping on a table or a row you
> always need a template.
> 
>>> * reference to description of the table (to be able to get also dynamic
>>> types by column name, but avoid using too much memory for the structure)
>>
>> My PostgreSQL client already supports that. Class PGCommand has member
>> "fields", which contain information about returned columns. You can even check
>> what columns will be returned from a query, before actually executing it.
> 
> ok that is nice, and my point is that the type that the user sees by default
> should automatically take advantage of that
> 
>>> * Nice to define table structure, and what happens if the db has another
>>> structure.
>>
>> This is a problem for ORM, but at first, we need standard query API.
> 
> I am not so sure about this, yes these (also classes for tables) are part of the
> ORM, but the normal users will more often be at the ORM level I think, and how
> exactly we want the things look like that the object level can influence the
> choice of the best low level interface.
> 
>>> * you want to support only access or also db creation and modification?
>>
>> First, I'm preparing base "traditional" API. Then I want to write simple
>> object-relational mapping. I've already written some code that generated
>> CREATE TABLE for structs at compile time. Static typing of row fields is very
>> helpful here.
> 
> Very good I think that working on getting the API right there and having it nice
> to use is important.
> Maybe you are right and the current DBRow is indeed the best abstraction, but I
> am not yet 100% sure, to me it looks like it isn't the best end user abstraction
> (but it might be an excellent low level object)
> 

I'd hate not having a rows-and-tables view onto the database.
An Object-Relational-Mapper is nice to have of course, but I agree with Piotr
that a traditional view onto the DB is a good start to built an ORM on and I
think that the traditional view should also be available to the user (it'll be
there internally anyway, at least for traditional relational databases).

Also: How are you gonna write queries with only the ORM view? Parse your own
SQL-like-syntax that uses the Object type? Or have the SQL operators as methods?
And then generate the apropriate SQL string?
What about differences in SQL-syntax between different databases?
What about tweaks that may be possible when you write the SQL yourself and not
have it generated from your ORM?

No, being able to write the SQL-queries yourself and having a "low level" view
(tables and rows, like it's saved in the DB) is quite important.

However: Since Piotr already seems to have much work done, maybe Christian
Manning could polish Piotrs work (if necessary) and create a ORM on top of it?

Oh, and just an Idea: Maybe something like LINQ is feasible for ORM? So you can
write a query that includes local containers/ranges, remote Databases (=> part
of it will internally be translated to SQL) and maybe even XML (but that could
be added later once the std.xml replacement is ready)?

Cheers,
- Daniel