DatabaseReset
重置请求，比如调用DatabasePrepare()之后。
int DatabaseReset(
int request //在DatabasePrepare中接收的请求句柄
);参数
request
[in] DatabasePrepare()中获得的请求句柄。
返回值
如果成功返回true，否则返回false。要获得错误代码，请使用GetLastError()，可能回应：
- ERR_DATABASE_INVALID_HANDLE (5121) - 无效数据库句柄；
- 以ERR_DATABASE_ERROR(5601)开始的SQLite错误代码。
注意
DatabaseReset()函数用于通过不同的参数值多次执行请求。例如，当使用INSERT命令将数据批量添加到表格中时，应该为每个条目形成一组自定义的字段值。
与DatabasePrepare()不同，DatabaseReset() 调用不会通过SQL命令将字符串编译到新请求中，因此DatabaseReset()的执行速度要比DatabasePrepare()快得多。
如果在执行DatabaseRead()之后应该更改请求参数值，则DatabaseReset()与DatabaseBind()函数和/或DatabaseBindArray()一起使用。这意味着在设置新请求参数值之前（阻止DatabaseBind/DatabaseBindArray调用之前），应该调用DatabaseReset()进行重置。参数化请求本身应该使用DatabasePrepare()来创建。
与atabasePrepare()一样，DatabaseReset()不会发出数据库请求。当调用DatabaseRead()或DatabaseReadBind()时，进行直接请求执行。
如果通过调用DatabaseBind()/DatabaseBindArray()来设置参数值，则DatabaseReset()调用不会导致重置请求中的参数值，即参数保留其值。因此，只能更改单个参数值。调用DatabaseReset()后不需要重新设置所有请求参数。
使用DatabaseFinalize()移除的请求句柄不能传递给DatabaseReset()。这将导致错误。
例如：
//+------------------------------------------------------------------+
//| 脚本程序起始函数 |
//+------------------------------------------------------------------+
void OnStart()
{
//--- 创建或打开数据库
string filename="symbols.sqlite";
int db=DatabaseOpen(filename, DATABASE_OPEN_READWRITE | DATABASE_OPEN_CREATE);
if(db==INVALID_HANDLE)
{
Print("DB: ", filename, " open failed with code ", GetLastError());
return;
}
else
Print("Database: ", filename, " opened successfully");
//--- 如果SYMBOLS表格已存在，请将其删除
if(DatabaseTableExists(db, "SYMBOLS"))
{
//--- 删除表格
if(!DatabaseExecute(db, "DROP TABLE SYMBOLS"))
{
Print("Failed to drop table SYMBOLS with code ", GetLastError());
DatabaseClose(db);
return;
}
}
//--- 创建SYMBOLS表格
if(!DatabaseExecute(db, "CREATE TABLE SYMBOLS("
"NAME TEXT NOT NULL,"
"DESCRIPTION TEXT ,"
"PATH TEXT ,"
"SPREAD INT ,"
"POINT REAL NOT NULL,"
"DIGITS INT NOT NULL,"
"JSON BLOB );"))
{
Print("DB: ", filename, " create table failed with code ", GetLastError());
DatabaseClose(db);
return;
}
//--- 显示SYMBOLS表格中所有字段列表
if(DatabasePrint(db, "PRAGMA TABLE_INFO(SYMBOLS)", 0)<0)
{
PrintFormat("DatabasePrint(\"PRAGMA TABLE_INFO(SYMBOLS)\") failed, error code=%d at line %d", GetLastError(), __LINE__);
DatabaseClose(db);
return;
}
//--- 创建参数化请求，将交易品种添加到SYMBOLS表格中
string sql="INSERT INTO SYMBOLS (NAME,DESCRIPTION,PATH,SPREAD,POINT,DIGITS,JSON)"
" VALUES (?1,?2,?3,?4,?5,?6,?7);"; // 请求参数
int request=DatabasePrepare(db, sql);
if(request==INVALID_HANDLE)
{
PrintFormat("DatabasePrepare() failed with code=%d", GetLastError());
Print("SQL request: ", sql);
DatabaseClose(db);
return;
}
//--- 检查所有交易品种并将其添加到SYMBOLS表格中
int symbols=SymbolsTotal(false);
bool request_error=false;
DatabaseTransactionBegin(db);
for(int i=0; i<symbols; i++)
{
//--- 在添加交易品种之前设置参数值
ResetLastError();
string symbol=SymbolName(i, false);
if(!DatabaseBind(request, 0, symbol))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
//--- 如果之前的DatabaseBind()调用成功，则设置下一个参数
if(!DatabaseBind(request, 1, SymbolInfoString(symbol, SYMBOL_DESCRIPTION)))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
if(!DatabaseBind(request, 2, SymbolInfoString(symbol, SYMBOL_PATH)))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
if(!DatabaseBind(request, 3, SymbolInfoInteger(symbol, SYMBOL_SPREAD)))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
if(!DatabaseBind(request, 4, SymbolInfoDouble(symbol, SYMBOL_POINT)))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
if(!DatabaseBind(request, 5, SymbolInfoInteger(symbol, SYMBOL_DIGITS)))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
if(!DatabaseBind(request, 6, GetSymBolAsJson(symbol)))
{
PrintFormat("DatabaseBind() failed at line %d with code=%d", __LINE__, GetLastError());
request_error=true;
break;
}
//--- 执行插入条目的请求并检查错误
if(!DatabaseRead(request)&&(GetLastError()!=ERR_DATABASE_NO_MORE_DATA))
{
PrintFormat("DatabaseRead() failed with code=%d", GetLastError());
DatabaseFinalize(request);
request_error=true;
break;
}
else
PrintFormat("%d: added %s", i+1, symbol);
//--- 在下一次参数更新之前重置请求
if(!DatabaseReset(request))
{
PrintFormat("DatabaseReset() failed with code=%d", GetLastError());
DatabaseFinalize(request);
request_error=true;
break;
}
} //--- 完成所有交易品种的检查
//--- 交易事务状态
if(request_error)
{
PrintFormat("Table SYMBOLS: failed to add %d symbols", symbols);
DatabaseTransactionRollback(db);
DatabaseClose(db);
return;
}
else
{
DatabaseTransactionCommit(db);
PrintFormat("Table SYMBOLS: added %d symbols",symbols);
}
//--- 将SYMBOLS表格保存为CSV文件。
string csv_filename="symbols.csv";
if(DatabaseExport(db, "SELECT * FROM SYMBOLS", csv_filename,
DATABASE_EXPORT_HEADER|DATABASE_EXPORT_INDEX|DATABASE_EXPORT_QUOTED_STRINGS, ";"))
Print("Database: table SYMBOLS saved in ", csv_filename);
else
Print("Database: DatabaseExport(\"SELECT * FROM SYMBOLS\") failed with code", GetLastError());
//--- 关闭数据库文件并告知
DatabaseClose(db);
PrintFormat("Database: %s created and closed", filename);
}
//+------------------------------------------------------------------+
//| 交易品种规格返回为JSON |
//+------------------------------------------------------------------+
string GetSymBolAsJson(string symbol)
{
//--- 缩进
string indent1=Indent(1);
string indent2=Indent(2);
string indent3=Indent(3);
//---
int digits=(int)SymbolInfoInteger(symbol, SYMBOL_DIGITS);
string json="{"+
"\n"+indent1+"\"ConfigSymbols\":["+
"\n"+indent2+"{"+
"\n"+indent3+"\"Symbol\":\""+symbol+"\","+
"\n"+indent3+"\"Path\":\""+SymbolInfoString(symbol, SYMBOL_PATH)+"\","+
"\n"+indent3+"\"CurrencyBase\":\""+SymbolInfoString(symbol, SYMBOL_CURRENCY_BASE)+"\","+
"\n"+indent3+"\"CurrencyProfit\":\""+SymbolInfoString(symbol, SYMBOL_CURRENCY_PROFIT)+"\","+
"\n"+indent3+"\"CurrencyMargin\":\""+SymbolInfoString(symbol, SYMBOL_CURRENCY_MARGIN)+"\","+
"\n"+indent3+"\"ColorBackground\":\""+ColorToString((color)SymbolInfoInteger(symbol, SYMBOL_BACKGROUND_COLOR))+"\","+
"\n"+indent3+"\"Digits\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_DIGITS))+"\","+
"\n"+indent3+"\"Point\":\""+DoubleToString(SymbolInfoDouble(symbol, SYMBOL_POINT), digits)+"\","+
"\n"+indent3+"\"TickBookDepth\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_TICKS_BOOKDEPTH))+"\","+
"\n"+indent3+"\"ChartMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_CHART_MODE))+"\","+
"\n"+indent3+"\"TradeMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_TRADE_EXEMODE))+"\","+
"\n"+indent3+"\"TradeCalcMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_TRADE_CALC_MODE))+"\","+
"\n"+indent3+"\"OrderMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_ORDER_MODE))+"\","+
"\n"+indent3+"\"CalculationMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_TRADE_CALC_MODE))+"\","+
"\n"+indent3+"\"ExecutionMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_TRADE_EXEMODE))+"\","+
"\n"+indent3+"\"ExpirationMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_EXPIRATION_MODE))+"\","+
"\n"+indent3+"\"FillFlags\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_FILLING_MODE))+"\","+
"\n"+indent3+"\"ExpirFlags\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_EXPIRATION_MODE))+"\","+
"\n"+indent3+"\"Spread\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_SPREAD))+"\","+
"\n"+indent3+"\"TickValue\":\""+StringFormat("%G", (SymbolInfoDouble(symbol, SYMBOL_TRADE_TICK_VALUE)))+"\","+
"\n"+indent3+"\"TickSize\":\""+StringFormat("%G", (SymbolInfoDouble(symbol, SYMBOL_TRADE_TICK_SIZE)))+"\","+
"\n"+indent3+"\"ContractSize\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_TRADE_CONTRACT_SIZE)))+"\","+
"\n"+indent3+"\"StopsLevel\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_TRADE_STOPS_LEVEL))+"\","+
"\n"+indent3+"\"VolumeMin\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_VOLUME_MIN)))+"\","+
"\n"+indent3+"\"VolumeMax\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_VOLUME_MAX)))+"\","+
"\n"+indent3+"\"VolumeStep\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_VOLUME_STEP)))+"\","+
"\n"+indent3+"\"VolumeLimit\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_VOLUME_STEP)))+"\","+
"\n"+indent3+"\"SwapMode\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_SWAP_MODE))+"\","+
"\n"+indent3+"\"SwapLong\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_SWAP_LONG)))+"\","+
"\n"+indent3+"\"SwapShort\":\""+StringFormat("%G",(SymbolInfoDouble(symbol, SYMBOL_SWAP_SHORT)))+"\","+
"\n"+indent3+"\"Swap3Day\":\""+IntegerToString(SymbolInfoInteger(symbol, SYMBOL_SWAP_ROLLOVER3DAYS))+"\""+
"\n"+indent2+"}"+
"\n"+indent1+"]"+
"\n}";
return(json);
}
//+------------------------------------------------------------------+
//| 形成空格缩进 |
//+------------------------------------------------------------------+
string Indent(const int number, const int characters=3)
{
int length=number*characters;
string indent=NULL;
StringInit(indent, length, ' ');
return indent;
}
/*
结果：
Database: symbols.sqlite opened successfully
#| cid name type notnull dflt_value pk
-+-------------------------------------------
1| 0 NAME TEXT 1 0
2| 1 DESCRIPTION TEXT 0 0
3| 2 PATH TEXT 0 0
4| 3 SPREAD INT 0 0
5| 4 POINT REAL 1 0
6| 5 DIGITS INT 1 0
7| 6 JSON BLOB 0 0
1: added EURUSD
2: added GBPUSD
3: added USDCHF
...
82: added USDCOP
83: added USDARS
84: added USDCLP
Table SYMBOLS: added 84 symbols
Database: table SYMBOLS saved in symbols.csv
Database: symbols.sqlite created and closed
*/
另见
DatabasePrepare、DatabaseBind、 DatabaseBindArray、DatabaseFinalize