EAX_Mysql - MySQL library - MetaTrader 5용 라이브러리

Accidently I ran into MQL5 and was forced to pull a MySQL library together. As for any library I hope the examples show how the library can be used. As for any library actually the most important things are examples how to use it ;)

Examples:

Reading Data

#include <EAX\EAX_Mysql.mqh>

EAX_Mysql *db = new EAX_Mysql();

db.connect("myhost.mydomain.com", "myusername", "mypassword", "mydatabase", "mytable");

int iResults = db.read_rows("SELECT password, COUNT(*) as Hits FROM users GROUP BY password");
for (int i=0; i < iResults; i++) {
   string password = (string) db.get("password",i);
   int    hits     = (int) db.get("Hits", i);
}

Feeding Data

#include <EAX\EAX_Mysql.mqh>

// global
EAX_Mysql *db = new EAX_Mysql();

void OnInit() {
    db.connect("myhost.mydomain.com", "myusername", "mypassword", "metatrader", "Ticks";
}

void OnTick() {
    MqlTick tick;
    SymbolInfoTick(_Symbol,tick);
    // Add a new dataset for table Ticks
    db.AddNew("Ticks");
    // fill it with values..
    db.set("symbol", _Symbol);
    // You can send digits to digit DB fields if MySQL can convert
    db.set("ask", tick.ask);
    db.set("bid", tick.bid);
    db.set("last", tick.last);
    db.set("time", TimeToString(tick.time,TIME_DATE) + " " + TimeToString(tick.time,TIME_SECONDS));
    db.set("volume", tick.volume);
    db.write();

}

void OnDeinit() {
   // clean up memory
   delete db;
}

Interacting with Data

EAX_Mysql *db = new EAX_Mysql();

db.connect("myhost.mydomain.com", "myusername", "mypassword", "metatrader", "mytable")

// Select Table AgentsOnline (required to identify the correct Primary Key)
db.select("AgentsOnline");
// Read Dataset with Primary Key 5
db.read("5");
// modify any column,
db.set("lastupdate", (string) TimeLocal());
// write it back
db.write();

Installing:

• Identify your MQL5 Data Directory (MQL5).
  
• Download Connector/C (libmysql) for your MetaTrader environment (32 or 64bit) and put libymsql.dll into "MQL5\Libraries".
• create an folder EAX under Include.
• Put EAX_Mysql.mqh in "MQL5\Include\EAX".
  

Issues:

• As it uses internally a shared connection pointer the library can't handle more than one DB connection at a time (I had no need to add/migrate a connection pooling).
• no real error (mysql) handling, dropping db connection.
• no error handling/reconnection to the DB (=> db pooling).
• no support for multiple column primary keys.
  
• still beta - please drop me an email if you want to beta/test.
  
• DataTypes are not handled (internally just strings) must be on code/database.
• Database communication is ISO - too lazy to adjust the pointer/string arithmetic for UTF-8.
  

Credits:

• http://mqlmagazine.com/mql-programming/mql5-connecting-to-mysql/
• https://www.mql5.com/en/articles/364