digitalmars.D - std.database design suggestion
- bls <bizprac orange.fr> Oct 10 2011
- bls <bizprac orange.fr> Oct 10 2011
- Johann MacDonagh <johann.macdonagh.no spam.gmail.com> Oct 10 2011
- bls <bizprac orange.fr> Oct 11 2011
- Kagamin <spam here.lot> Oct 11 2011
- bls <bizprac orange.fr> Oct 11 2011
- Daniel Gibson <metalcaedes gmail.com> Oct 11 2011
-- Sorry for posting on D.announce --
Hi, what do you people think about using the GoF
Factory (design) pattern ?
F.I.
abstract class Database {
//common database stuff
public abstract void connect(string user, string pw);
// execSql(); prepare() etc...
}
abstract class DatabaseFactory {
public abstract Database GetDatabase();
}
class PostgreSQL:Database {
// common
public override void connect(string user, string pw) {
}
//PostgreSQL specific
public void funkyPGstuff() {}
}
class PostreSQLFactory:DatabaseFactory {
public override Database GetDatabase() {
return new PostgreSQL();
}
}
class MySQL:Database {
// common
public override void connect(string user, string pw) {
}
//MySQL specific
public void funkyMySQLstuff() {}
}
class MySQLFactory:DatabaseFactory {
public override Database GetDatabase() {
return new MySQL();
}
}
Oct 10 2011
well, the previous code was half baked, this should explain what I want
to archive...
int main(string[] args)
{
DatabaseFactory factory;
if(args[0] == "MySQL")
factory = new MySQLFactory();
else
factory = new PostreSQLFactory();
updatePricelist(factory);
return 0;
}
abstract class Database {
//common database stuff
public abstract void connect(string user, string pw);
// execSql(); prepare() etc...
}
abstract class DatabaseFactory {
public abstract Database GetDatabase();
}
final class PostgreSQL:Database {
// common
public override void connect(string user, string pw) {
}
//PostgreSQL specif
public void funkyPGstuff() {}
}
final class PostreSQLFactory:DatabaseFactory {
public override Database GetDatabase() {
return new PostgreSQL();
}
}
final class MySQL:Database {
// common
public override void connect(string user, string pw) {
}
//MySQL specif
public void funkyMySQLstuff() {}
}
final class MySQLFactory:DatabaseFactory {
public override Database GetDatabase() {
return new MySQL();
}
}
// Update PriceList without knowing the concrete database
void updatePricelist(DatabaseFactory factory) {
Database db = factory.GetDatabase();
//db.execSQL("UPDATE ...");
}
Oct 10 2011
On 10/10/2011 7:19 AM, bls wrote:if(args[0] == "MySQL") factory = new MySQLFactory(); else factory = new PostreSQLFactory();
Perhaps my design pattern knowledge is a bit shaky (it is), but isn't the point of a factory to give it hints about what you want to create, and it decides how to do it? Something like: Database d = Factory.gimmeAConnection("MySql", "server", "username", "pwd");
Oct 10 2011
bls <bizprac orange.fr> Am 11.10.2011 05:14, schrieb Johann MacDonagh:Perhaps my design pattern knowledge is a bit shaky (it is), but isn't the point of a factory to give it hints about what you want to create, and it decides how to do it? Something like: Database d = Factory.gimmeAConnection("MySql", "server", "username", "pwd");
I guess you describe the "Factory method" pattern. def : Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses. My snippet is based on the "Abstract Factory" pattern. Also called "Factory design" pattern or simply "Factory" pattern . Indeed a bit confusing. def : Provide an interface for creating families of related or dependent objects without specifying their concrete classes. see also > http://www.dofactory.com/Patterns/Patterns.aspx
Oct 11 2011
bls Wrote:abstract class DatabaseFactory { public abstract Database GetDatabase(); }
the method is usually called CreateInstance.
Oct 11 2011
Am 11.10.2011 13:37, schrieb Kagamin:bls Wrote:abstract class DatabaseFactory { public abstract Database GetDatabase(); }
the method is usually called CreateInstance.
I think this is true for the Factory _method_ pattern. I am using the _Abstract_ Factory pattern. See http://en.wikipedia.org/wiki/Abstract_factory_pattern Though createDatabaseInstance () seems to be reasonable/ (follows common coding conventions) -- slightly modified snippet-- import std.stdio; int main(string[] args) { IDatabaseFactory factory; if(args[0] == "MySQL") factory = new MySQLFactory(); else factory = new PostreSQLFactory(); updatePricelist(factory); return 0; } public interface IDatabase { //common database stuff alias open connect; public void open(const string[string] params); //alias close disconnect; //public void close(); // exec(); prepare() etc... } public interface IDatabaseFactory { public IDatabase createDatabaseInstance(); } final class PostgreSQL : IDatabase { // common public void open(const string[string] params) { } //PostgreSQL specific public void funkyPGstuff() {} } final class PostreSQLFactory : IDatabaseFactory { public IDatabase createDatabaseInstance() { return new PostgreSQL(); } } final class MySQL : IDatabase { // common public void open(const string[string] params) { } //MySQL specific public void funkyMySQLstuff() {} } final class MySQLFactory : IDatabaseFactory { public IDatabase createDatabaseInstance() { return new MySQL(); } } // Update PriceList without knowing the db backend void updatePricelist(IDatabaseFactory factory) { IDatabase db = factory.createDatabaseInstance(); db.connect([ "host" : "localhost", "database" : "test", "user" : "bls", "password" : "secret" ]); //db.exec("UPDATE ..."); }
Oct 11 2011
Am 10.10.2011 12:04, schrieb bls:-- Sorry for posting on D.announce -- Hi, what do you people think about using the GoF Factory (design) pattern ? F.I. abstract class Database { //common database stuff public abstract void connect(string user, string pw); // execSql(); prepare() etc... } abstract class DatabaseFactory { public abstract Database GetDatabase(); } class PostgreSQL:Database { // common public override void connect(string user, string pw) { } //PostgreSQL specific public void funkyPGstuff() {} } class PostreSQLFactory:DatabaseFactory { public override Database GetDatabase() { return new PostgreSQL(); } } class MySQL:Database { // common public override void connect(string user, string pw) { } //MySQL specific public void funkyMySQLstuff() {} } class MySQLFactory:DatabaseFactory { public override Database GetDatabase() { return new MySQL(); } }
I think this would make sense and JDBC does something similar, if I recall correctly. Cheers, - Daniel
Oct 11 2011