Databases and the D Standard Library

[Jacob Carlborg via Digitalmars-d]

On 2017-01-03 18:13, Chris Wright wrote:

> The returned row data is mandatory, and its size can be much larger than
> the stack limit. (A MySQL MEDIUMBLOB field will likely break your stack
> limit.)
>
> I suppose you could have a streaming API for row data, one that has a
> stack-allocated buffer and returns slices of that:
>
>   string fieldName;
>   ubyte[] data;
>   ubyte[][string] fields;
>   db.query("SELECT * FROM USERS")
>     // have to revisit this if a db allows large names
>     .onFieldStart((fieldName) => field = fieldName)
>     .onFieldData((fragment) => data ~= fragment)
>     .onFieldEnd(() { fields[field] = data; data = null; })
>     .onRowEnd(() => process(fields))
>     .onResultsEnd!(() => writeln("done"))
>     .exec();
>
> This looks pretty terrible, to be honest. I get this sort of thing from
> nodejs because it doesn't want to potentially block and also doesn't want
> to delay letting me process things, but the worst I get there is usually
> two callbacks.
>
> This would also result in more GC use for the majority of people who use
> the GC.

Look, I didn't say that using the GC should be completely forbidden. I 
just said we should try to avoid it. For example, I've been using the 
ddb Postgres driver [1]. It uses classes for most of its types, even if 
it might not be necessary. Here's one example [2], unless there some 
intention to have some form of higher level, DB independent, API on top 
of this, I don't see a reason why that type needs to be a class.

>> 2. Buffers say nothing how they're allocated. With classes on the other
>> hand, you're basically forced to allocate with the GC
>
> You haven't looked at std.experimental.allocator, have you?

I know it's possible to allocate a class without the GC, hence the 
"basically". I'm not sure how other write their code but at least I make 
the assumption that all objects are allocated with the GC.

[1] https://github.com/pszturmaj/ddb
[2] https://github.com/pszturmaj/ddb/blob/master/source/ddb/postgres.d#L904

-- 
/Jacob Carlborg