CFieldExchange Class

Supports the record field exchange (RFX) and bulk record field exchange (Bulk RFX) routines used by the database classes.

Syntax

class CFieldExchange

Members

Public Methods

Name	Description
CFieldExchange::IsFieldType	Returns nonzero if the current operation is appropriate for the type of field being updated.
CFieldExchange::SetFieldType	Specifies the type of recordset data member — column or parameter — represented by all following calls to RFX functions until the next call to SetFieldType.

Remarks

CFieldExchange does not have a base class.

Use this class if you are writing data exchange routines for custom data types or when you are implementing bulk row fetching; otherwise, you will not directly use this class. RFX and Bulk RFX exchanges data between the field data members of your recordset object and the corresponding fields of the current record on the data source.

Note

If you are working with the Data Access Objects (DAO) classes rather than the Open Database Connectivity (ODBC) classes, use class CDaoFieldExchange instead. For more information, see the article Overview:Database Programming.

A CFieldExchange object provides the context information needed for record field exchange or bulk record field exchange to take place. CFieldExchange objects support a number of operations, including binding parameters and field data members and setting various flags on the fields of the current record. RFX and Bulk RFX operations are performed on recordset-class data members of types defined by the enum FieldType in CFieldExchange. Possible FieldType values are:

• CFieldExchange::outputColumn for field data members.

• CFieldExchange::inputParam or CFieldExchange::param for input parameter data members.

• CFieldExchange::outputParam for output parameter data members.

• CFieldExchange::inoutParam for input/output parameter data members.

Most of the class's member functions and data members are provided for writing your own custom RFX routines. You will use SetFieldType frequently. For more information, see the articles Record Field Exchange (RFX) and Recordset (ODBC). For information about bulk row fetching, see the article Recordset: Fetching Records in Bulk (ODBC). For details about the RFX and Bulk RFX global functions, see Record Field Exchange Functions in the MFC Macros and Globals section of this reference.

Inheritance Hierarchy

CFieldExchange

Requirements

Header: afxdb.h

CFieldExchange::IsFieldType

If you write your own RFX function, call IsFieldType at the beginning of your function to determine whether the current operation can be performed on a particular field or parameter data member type (a CFieldExchange::outputColumn, CFieldExchange::inputParam, CFieldExchange::param, CFieldExchange::outputParam, or CFieldExchange::inoutParam).

BOOL IsFieldType(UINT* pnField);

Parameters

pnField
The sequential number of the field or parameter data member is returned in this parameter. This number corresponds to the data member's order in the CRecordset::DoFieldExchange or CRecordset::DoBulkFieldExchange function.

Return Value

Nonzero if the current operation can be performed on the current field or parameter type.

Remarks

Follow the model of the existing RFX functions.

CFieldExchange::SetFieldType

You need a call to SetFieldType in your recordset class's DoFieldExchange or DoBulkFieldExchange override.

void SetFieldType(UINT nFieldType);

Parameters

nFieldType
A value of the enum FieldType, declared in CFieldExchange, which can be one of the following:

• CFieldExchange::outputColumn

• CFieldExchange::inputParam

• CFieldExchange::param

• CFieldExchange::outputParam

• CFieldExchange::inoutParam

Remarks

For field data members, you must call SetFieldType with a parameter of CFieldExchange::outputColumn, followed by calls to the RFX or Bulk RFX functions. If you have not implemented bulk row fetching, then ClassWizard places this SetFieldType call for you in the field map section of DoFieldExchange.

If you parameterize your recordset class, you must call SetFieldType again, outside any field map section, followed by RFX calls for all the parameter data members. Each type of parameter data member must have its own SetFieldType call. The following table distinguishes the different values you can pass to SetFieldType to represent the parameter data members of your class:

SetFieldType parameter value	Type of parameter data member
CFieldExchange::inputParam	Input parameter. A value that is passed into the recordset's query or stored procedure.
CFieldExchange::param	same as CFieldExchange::inputParam.
CFieldExchange::outputParam	Output parameter. A return value of the recordset's stored procedure.
CFieldExchange::inoutParam	Input/output parameter. A value that is passed into and returned from the recordset's stored procedure.

In general, each group of RFX function calls associated with field data members or parameter data members must be preceded by a call to SetFieldType. The nFieldType parameter of each SetFieldType call identifies the type of the data members represented by the RFX function calls that follow the SetFieldType call.

For more information about handling output and input/output parameters, see the CRecordset member function FlushResultSet. For more information about the RFX and Bulk RFX functions, see the topic Record Field Exchange Functions. For related information about bulk row fetching, see the article Recordset: Fetching Records in Bulk (ODBC).

Example

This example shows several calls to RFX functions with accompanying calls to SetFieldType. Note that SetFieldType is called through the pFX pointer to a CFieldExchange object.

void CSections::DoFieldExchange(CFieldExchange *pFX)
{
   pFX->SetFieldType(CFieldExchange::outputColumn);
   RFX_Text(pFX, _T("[CourseID]"), m_CourseID);
   RFX_Text(pFX, _T("[InstructorID]"), m_InstructorID);
   RFX_Text(pFX, _T("[RoomNo]"), m_RoomNo);
   RFX_Text(pFX, _T("[Schedule]"), m_Schedule);

   // output parameter
   pFX->SetFieldType(CFieldExchange::outputParam);
   RFX_Long(pFX, _T("Instructor_Count"), m_nCountParam);

   // input parameter
   pFX->SetFieldType(CFieldExchange::inputParam);
   RFX_Text(pFX, _T("Department_Name"), m_strNameParam);
}

See also

Hierarchy Chart
CRecordset Class