H1 2015 - db access support in Phobos

[Vadim Lopatin via Digitalmars-d]

On Tuesday, 3 February 2015 at 15:30:42 UTC, Daniel Kozák wrote:
> V Tue, 03 Feb 2015 15:20:40 +0000
> Vadim Lopatin via Digitalmars-d <digitalmars-d at puremagic.com> 
> napsáno:
>
>> On Tuesday, 3 February 2015 at 14:41:02 UTC, Vadim Lopatin 
>> wrote:
>> > On Tuesday, 3 February 2015 at 10:49:07 UTC, Robert burner
>> >> IMO writing:
>> >>
>> >> foreach(it; db.select<User>("...")) {
>> >> }
>> >>
>> >> is epic. you have entered std.(range|algorithm) land.
>> >
>> > Implemented in v0.2.17 for select.
>> >
>> > test:
>> >
>> >     auto ds = new ConnectionPoolDataSourceImpl(new 
>> > SQLITEDriver(), "ddbctest.sqlite");
>> >     auto conn = ds.getConnection();
>> >     scope(exit) conn.close();
>> >     Statement stmt = conn.createStatement();
>> >     scope(exit) stmt.close();
>> >     // test data preparation
>> >     stmt.executeUpdate("DROP TABLE IF EXISTS user");
>> >     stmt.executeUpdate("CREATE TABLE user (id INTEGER 
>> > PRIMARY KEY, name VARCHAR(255) NOT NULL, flags int null)");
>> >     stmt.executeUpdate(`INSERT INTO user (id, name, flags) 
>> > VALUES (1, "John", 5), (2, "Andrei", 2), (3, "Walter", 2), 
>> > (4, "Rikki", 3), (5, "Iain", 0), (6, "Robert", 1)`);
>> >
>> >     // our POD struct
>> >     struct User {
>> >         long id;
>> >         string name;
>> >         int flags;
>> >     }
>> >
>> >     // let's execute select and nump query result
>> >     foreach(user; stmt.select!User.where("id < 
>> > 6").orderBy("name desc")) {
>> >         writeln("id:", user.id, " name:", user.name, " 
>> > flags:", user.flags);
>> >     }
>> >
>> > Output is:
>> > ------------------
>> > id:3 name:Walter flags:2
>> > id:4 name:Rikki flags:3
>> > id:1 name:John flags:5
>> > id:5 name:Iain flags:0
>> > id:2 name:Andrei flags:2
>> > ------------------
>> > Where and orderBy are optional - without them always reads 
>> > all rows in default order.
>> >
>> > Possible improvements: ability to specify field list to read 
>> > only necessary fields.
>> 
>> Update in v0.2.19: you can specify field list for select
>> 
>>      writeln("reading all user table rows, but fetching only 
>> id and name (you will see default value 0 in flags field)");
>>      foreach(ref e; stmt.select!(User, "id", "name")) {
>>          writeln("id:", e.id, " name:", e.name, " flags:", 
>> e.flags);
>>      }
>> 
>> output:
>> 
>> reading all user table rows, but fetching only id and name 
>> (you will see default value 0 in flags field)
>> id:1 name:John flags:0
>> id:2 name:Andrei flags:0
>> id:3 name:Walter flags:0
>> id:4 name:Rikki flags:0
>> id:5 name:Iain flags:0
>> id:6 name:Robert flags:0
>> 
> This is dangerous zone, you shoud not do this ;-). In my work I 
> have
> writen our ORM-like db layer which has this funcionality (mainly
> performance reasons) but if I can go back in time. I will be 
> against
> such a misfeature.

It's not considered as a main API. It's not madatory to import 
this module.
It's a set of helpers to simplify getting field values from 
ResultSet into struct or tuple, or write to prepared statement 
parameters, a kind of syntax sugar.

For ORM purposes, real ORM must be used.