On Sunday, 13 September 2015 at 03:03:44 UTC, Andrei Alexandrescu
wrote:
On 09/12/2015 04:08 PM, Martin Nowak wrote:
On Friday, 11 September 2015 at 23:47:42 UTC, Andrei
Alexandrescu wrote:
1. Use lambdas, which seem to already do what you want:
db.get!Person.filter!(p => p.age > 21 && p.name == "Peter")
The way this'd go, the db.get!Person() call returns an input
range of
Person. Presumably introspection is being used to bind fields
in the
query such as "age" and "name" to static field names in
struct Person.
Then good old std.algorithm.filter takes care of the rest.
I'm instantiating the lambda with a fake p to capture the
expression so
I can translate it to whatever SQL, MongoDB, columnar db is
used.
Yah, understood. Problem here is the approach is bound to run
into walls at every few steps. Say you fix the comparisons to
work. Then you have operators such as LIKE that are necessary
yet not representable in D. So more tricks are in order. This
is what I've seen with ET in C++ - an endless collection of
tricks to achieve modest outcomes at enormous costs.
Once gain, that says more about C++ than anything else. C# have
such mechnism and users seems very happy with it.
2. If you want to embed real SQL into D, use string-based
DSLs.
Strings don't capture context, aren't typechecked, and require
a complex
CTFE parser.
db.get!Person.where!"age > 21 & name = ?"(name);
Understood as well. I figure from the example you have binding
in mind, which is good. At some point you need to bite the
bullet and write a parser for the relational query language you
want there.
That sounds like a bigger problem than whatever you mentioned
before.
