数据库技术在BREW中的应用

lingfeng

数据库技术在BREW中的应用
数据库技术作为一种对信息管理的高效方式，逐渐在业界占据了重要的地位，可以说目前任何类型的IT产品，都或多或少的采用了数据库技术，数据库产品无所不入。
BREW作为无线开发环境也提供了数据库技术。那么下面我就对数据库技术作一下分析：
BREW数据库是一种简单的关系型数据库，无多任务，无多用户，多记录。它提供给开发者三个接口：IDBMgr，IDatabase，IDBRecord。
IDBMgr接口用于创建、打开、和删除数据库。IDatabase接口用户创建和访问数据库中的记录。IDBRecord接口用户访问、更新数据库记录中的域。
下面是一些常用的数据库操作：
1、创建新数据库
代码：
IDBMgr *    pIDBMgr = NULL;
IDatabase * pIDatabase = NULL;
boolean     bCreate = TRUE;
ISHELL_CreateInstance(pIShell, AEECLSID_DBMGR, (void **)&pIDBMgr);
if (pIDBMgr == NULL)
return;
if ((pIDatabase = IDBMGR_OpenDatabase (pIDBMgr, pszFile, bCreate)) == NULL)
{
// Opened an already existing database.
}
else
{
// Create an database.
}

2、打开数据库
代码：
IDBMgr *    pIDBMgr = NULL;
IDatabase * pIDatabase = NULL;
boolean     bCreate = FALSE;
ISHELL_CreateInstance(pIShell, AEECLSID_DBMGR, (void **)&(*pIDBMgr));
if (pIDBMgr == NULL)
return;
if (((*pIDatabase) = IDBMGR_OpenDatabase ((*pIDBMgr), pszFile, bCreate)) == NULL)
{
// Opened an already existing database.
}
else
{
// Opened an database.
}

3、关闭数据库
代码：
// IDATABASE_Release closes the open database files, and frees
// any memory associated with the database.
if (pIDatabase)
{
IDATABASE_Release (pIDatabase);
}
// Release IDBMgr object. This step needs to be done
// only if no further use of the IDBMgr object is needed.
if (pIDBMgr)
{
IDBMGR_Release (pIDBMgr);
}

4、创建一条记录
代码：
boolean CreateOneRecord(IDatabase * pIDatabase, AEEDBField * dbField, int nNumfields)
{
IDBRecord * pIDBRecord = NULL;
            
// IDATABASE_CreateRecord: creates a new database record with the fields
// specified by pDBFields.
if ((pIDBRecord = IDATABASE_CreateRecord (pIDatabase, dbField, nNumfields)) != NULL)
{
  // Successfully created a database record.
  // Release record
  IDBRECORD_Release (pIDBRecord);
  return TRUE;
}
else
{
  //Create DB Record Failed
}
return FALSE;
}
dbField指向数据库记录域，nNumfields是域的个数。可以创建一个这样的记录：
代码：
{
AEEDBField dbField[3];
int nNumfields = 3;
const char firstName [] = "John";
const char lastName  [] =  "Smith";
const char address   [] = "123 First Street, USA";
AEEDBFieldType fieldType;
AEEDBFieldName fieldName;
// Data fill values used to create a database record.
// The parameter dbField is a three item array of type
// AEEDBField. Each array item corresponds to three fields
// of the record.
dbField[0].fName = AEEDBFIELD_FIRSTNAME;
dbField[0].fType = AEEDB_FT_STRING;
dbField[0].pBuffer = (void *)firstName;
dbField[0].wDataLen = STRLEN (firstName);
dbField[1].fName = AEEDBFIELD_LASTNAME;
dbField[1].fType = AEEDB_FT_STRING;
dbField[1].pBuffer = (void *)lastName;
dbField[1].wDataLen = STRLEN (lastName);
dbField[2].fName = AEEDBFIELD_ADDRESS;
dbField[2].fType = AEEDB_FT_STRING;
dbField[2].pBuffer = (void *)address;
dbField[2].wDataLen = STRLEN (address);

return CreateOneRecord(pIDatabase, dbField, 3);
}

5、获取记录个数
代码：
uint32 GetRecordCount(IDatabase * pIDatabase)
{
// IDATABASE_GetRecordCount: returns the number of records in the
// database specified. This gives the number of records in the
// database prior to creating any records in the database.
return IDATABASE_GetRecordCount (pIDatabase);
}

6、读取记录域
代码：
boolean GetRecordByID(IDatabase * pIDatabase, uint16 u16RecID)
{
IDBRecord * pIDBRec1 = NULL;
AEEDBFieldType fType;
AEEDBFieldName fName;
uint16 fLen;
byte * data = NULL;;
// This will reset the record Index to 0.
IDATABASE_Reset (pIDatabase);
// IDATABASE_GetRecordByID: returns a pointer to the record whose
// record ID is specified.
pIDBRec1 = IDATABASE_GetRecordByID (pIDatabase, u16RecID);
// Get the raw data of the field
for(;;)
{
  // Get record 1 first field and display it
  fType = IDBRECORD_NextField (pIDBRec1, &fName, &fLen);
  data = IDBRECORD_GetField (pIDBRec1, &fName, &fType, &fLen);
  if (data != NULL)
  {
   switch(fName)
   {
   case AEEDBFIELD_FIRSTNAME;
    break;
   case AEEDBFIELD_LASTNAME;
    break;
   case AEEDBFIELD_ADDRESS;
    break;
   default:
    break;
   }
  }
  else
  {
   break; //break for
  }
}
// Now remove record 1.
IDBRECORD_Release(pIDBRec1);
return TRUE;
}