OOP, templates and macros in mql5, subtleties and uses

Igor Makanu 2020.08.30 09:39 #271

Maxim Kuznetsov:

I remember that in SQLite, field types are optional and you don't have to worry about specifying and casting types. It is "Lite" for a reason.

you can split a long query into 3-4-5 ones :-)

BEGIN TRANSACTION

INSERT INTO myTable VALUES (...); --- тут можно получить PrimaryKey

UPDATE myTable .... ; --- обновить по Primary

UPDATE myTable ... ; --- ещё...

COMMIT ; --- это если все запросы удачны.. иначе ROLLBACK

it's from the old memory, so you should check in the help

i would like to have a reproducible query code, it will take a long time to google, i've worked with a database occasionally - i have a problem, i googled it, i solved it - but i would like to see a failed database query

Maxim Kuznetsov 2020.08.30 09:39 #272

Vladimir Simakov:

Your particular problem should be solved like this:

string MakeRequest(string md5txt){
   static ENUM_STATISTICS intIndex[]={STAT_CONPROFITMAX_TRADES,
                                      STAT_MAX_CONPROFIT_TRADES,
                                      STAT_CONLOSSMAX_TRADES,
                                      STAT_MAX_CONLOSS_TRADES,
                                      STAT_DEALS,
                                      STAT_TRADES,
                                      STAT_PROFIT_TRADES,
                                      STAT_LOSS_TRADES,
                                      STAT_SHORT_TRADES,
                                      STAT_LONG_TRADES,
                                      STAT_PROFIT_SHORTTRADES,
                                      STAT_PROFIT_LONGTRADES,
                                      STAT_PROFITTRADES_AVGCON,
                                      STAT_LOSSTRADES_AVGCON};
   string ret="INSERT INTO \"TesterStatistics\" + StringFormat(" set md5= %d ,md5txt),
   for (int i=0,ii=0;i<=STAT_LOSSTRADES_AVGCON;++i){
      ret+=",";
      if (i==intIndex[ii]){
         ret+=StringFormat("%s = %d,",EnumToString((ENUM_STATISTICS)i),(int)TesterStatistics((ENUM_STATISTICS)i) ));
         ++ii;}
      else ret+=StringFormat("%s =%G",EnumToString((ENUM_STATISTICS),i),TesterStatistics((ENUM_STATISTICS)i));}
   return ret;}
   
DatabaseExecute(handleDB, MakeRequest("md5txt"));

a small fix, with more brackets to fix :-)
the main idea is not to use UPDATE x VALUES (), but UPDATE x SET name1=value1,name2=value2. To make the query work correctly when the database structure is changed and not depend on the order of the fields listed

FOREX - Trends, forecasts Is there something like Error: I get EMPTY_VALUE

Igor Makanu 2020.09.01 15:12 #273

there is approximately the following code (I read text fields from database and want to convert into enum)

class MyClass
{
public:
   enum A            {Aq, Aw, Ae, Ar, At, Ay};
   enum B            {Bq, Bw, Be};
   enum C            {Cq, Cw, Ce, Cr};

   static bool       txtToEnumA(const string txt, A &result);
   static bool       txtToEnumB(const string txt, B &result);
   static bool       txtToEnumC(const string txt, C &result);
};
//+------------------------------------------------------------------+
static bool MyClass::txtToEnumA(const string txt, A &result)
{
   for(int i = 0; i <= (int)A::Ay; i++)
   {
      if(StringCompare(EnumToString((A)i), txt) == 0)
      {
         result = (MyClass::A)i;
         return(true);
      }
   }
   return(false);
}
//+------------------------------------------------------------------+
static bool MyClass::txtToEnumB(const string txt, B &result)
{
   for(int i = 0; i <= (int)B::Be; i++)
   {
      if(StringCompare(EnumToString((B)i), txt) == 0)
      {
         result = (MyClass::B)i;
         return(true);
      }
   }
   return(false);
}
//+------------------------------------------------------------------+
static bool MyClass::txtToEnumC(const string txt, C &result)
{
   for(int i = 0; i <= (int)C::Cr; i++)
   {
      if(StringCompare(EnumToString((A)i), txt) == 0)
      {
         result = (MyClass::C)i;
         return(true);
      }
   }
   return(false);
}
//+------------------------------------------------------------------+
void OnStart()
{
   MyClass::A a;
   MyClass::B b;
   MyClass::C c;
   string txt[] = {"Aq", "Bw", "No"};

   if(MyClass::txtToEnumA(txt[0], a)) Print(txt[0], " in A = ", EnumToString(a));
   else Print("Error, ", txt[0], " not in A");

   if(MyClass::txtToEnumB(txt[1], b)) Print(txt[1], " in B = ", EnumToString(b));
   else Print("Error, ", txt[1], " not in B");

   if(MyClass::txtToEnumC(txt[2], c)) Print(txt[2], " in C = ", EnumToString(c));
   else Print("Error, ", txt[2], " not in C");
}
//+------------------------------------------------------------------+

2020.09.01 18:59:02.593 tst (EURUSD,M5) Aq in A = Aq

2020.09.01 18:59:02.593 tst (EURUSD,M5) Bw in B = Bw

2020.09.01 18:59:02.593 tst (EURUSD,M5) Error, No not in C

Everything works, but the question is again about the optimal code:

if any way to write instead of txtToEnumA() , txtToEnumB(), txtToEnumC()

template method ( template )

the problem is different number of elements in the enum

Any questions from newcomers Questions on OOP in Getting Deals Information -

Dmitry Fedoseev 2020.09.01 15:44 #274

What if there is an enum:

enum A            {Aq=10, Aw=9, Ae=8, Ar=7, At=6, Ay=5};

?

Igor Makanu 2020.09.01 16:27 #275

Dmitry Fedoseev:

What if there is an enum:

?

numbering the enum elements is not a problem, it's not clear what this would do

I have only 4 enumerations, not numbered

the problem is that I may want to add new elements to enumeration - in my code, I will add new elements to NOT the outermost ones - the code will work - I do not like the cumbersomeness of this code

but we are not talking about some universal code for all occasions, we need the current tasks in a template

SZY: i can't do without enumeration - it's convenient, i can equally read data both in source and in database, and in database maybe i want to correct some fields manually.... in general, everything suits me

Questions from Beginners MQL5 My indicator is shifting BrainSystem: Trading System Development

Maxim Kuznetsov 2020.09.01 17:49 #276

Igor Makanu:

numbering the elements of the enumeration is not a problem, it is not clear what this will do

I have only 4 enumerations, not numbered

the problem is that I may want to add new items to lists - in my code, I will add new items to NOT the outermost ones - the code will work - I do not like the unwieldiness of the code

but we are not talking about some universal code for all occasions, we need the current tasks in a template

SZY: i can't do without enumeration - it's convenient, i can equally read data both in source and in database, and in database maybe i want to correct some fields manually.... everything suits me fine

make a global array and fill it with pairs { EnumToString(x) , x }

struct StringID {

string str;

int id;

};

StringID IDS[];

and templates will be unnecessary.

Igor Makanu 2020.09.01 18:08 #277

Maxim Kuznetsov:

make a global array and fill it with pairs { EnumToString(x) , x }

struct StringID {

string str;

int id;

};

StringID IDS[];

and you won't need templates.

Your way of doing it is not much different from mine - it's cumbersome too, and if there will be any changes in the code, you'll have to edit the arrays too.

Checking time in Strategy OrdersTotal in a specif Requests & Ideas, the

Igor Makanu 2020.09.01 18:10 #278

solved my wish this way:

class MyClass
{
public:
   enum A            {Aq, Aw, Ae, Ar, At, Ay};
   enum B            {Bq, Bw, Be};
   enum C            {Cq, Cw, Ce, Cr};
   template<typename T>
   static bool       txtToEnum(const T LastElement, const string txt, T &result);
};
//+------------------------------------------------------------------+
template<typename T>
static bool MyClass::txtToEnum(const T LastElement, const string txt, T &result)
{
   for(int i = 0; i <= (int)LastElement; i++)
   {
      if(StringCompare(EnumToString((T)i), txt) == 0)
      {
         result = (T)i;
         return(true);
      }
   }
   return(false);
}
//+------------------------------------------------------------------+
void OnStart()
{
   MyClass::A a;
   MyClass::B b;
   MyClass::C c;
   string txt[] = {"Aq", "Bw", "No"};

   if(MyClass::txtToEnum(MyClass::Ay, txt[0], a)) Print(txt[0], " in A = ", EnumToString(a));
   else Print("Error, ", txt[0], " not in A");

   if(MyClass::txtToEnum(MyClass::Be, txt[1], b)) Print(txt[1], " in B = ", EnumToString(b));
   else Print("Error, ", txt[1], " not in B");

   if(MyClass::txtToEnum(MyClass::Cr, txt[2], c)) Print(txt[2], " in C = ", EnumToString(c));
   else Print("Error, ", txt[2], " not in C");

}
//+------------------------------------------------------------------+

2020.09.01 22:08:47.417 tst (EURUSD,M5) Aq in A = Aq

2020.09.01 22:08:47.417 tst (EURUSD,M5) Bw in B = Bw

2020.09.01 22:08:47.417 tst (EURUSD,M5) Error, No not in C

I need more defines not to enter LastElement, but on the whole this code is more compact

Any questions from newcomers MetaTrader 5 Strategy Tester: Questions on OOP in

bankova.elizabet 2020.09.27 15:54 #279

How much it takes to write all sorts of things

OOP, templates and macros in mql5, subtleties and uses - page 28