Doing Callbacks

An external procedure executing on the Oracle8i server can call the access function OCIExtProcGetEnv to obtain OCI environment and service handles. With the OCI, you can use callbacks to execute SQL statements and PL/SQL subprograms, fetch data, and manipulate LOBs. Moreover, callbacks and external procedures operate in the same user session and transaction context, so they have the same user privileges.

The following example is a version of c_findmin that is simplified to illustrate callbacks. The complete listing is available on the disk that is included with this kit.

Static  OCIEnv   *envhp;
Static  OCISvcCtx  *svchp;
Static OCIError   *errhp;
Int   c_findmin (OCIExtProcContext *ctx, OCILobLocator  *lobl) {
sword  retval;
retval = OCIExtProcGetEnv (ctx, &envhp, &svchp, &errhp);
if ((retval != OCI_SUCCESS) && (retval !=  OCI_SUCCESS_WITH_INFO))
   exit(-1);
   /* Use lobl to read the CLOB, compute the minimum, and store the value
       in retval. */
return retval;
}

Restrictions on Callbacks

With callbacks, the following SQL statements and OCI routines are not supported:

• Transaction control statements such as COMMIT

• Data definition statements such as CREATE

• Object-oriented OCI routines such as OCIRefClear

• Polling-mode OCI routines such as OCIGetPieceInfo

• All these OCI routines:

  OCIEnvInit 
  OCIInitialize 
  OCIPasswordChange 
  OCIServerAttach 
  OCIServerDetach 
  OCISessionBegin 
  OCISessionEnd 
  OCISvcCtxToLda 
  OCITransCommit 
  OCITransDetach 
  OCITransRollback 
  OCITransStart
  
  

• Also, with OCI routine OCIHandleAlloc, the following handle types are not supported:

  OCI_HTYPE_SERVER 
  OCI_HTYPE_SESSION 
  OCI_HTYPE_SVCCTX 
  OCI_HTYPE_TRANS