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Learn more about: CFieldExchange Class |
CFieldExchange Class |
11/04/2016 |
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24c5c0b3-06a6-430e-9b6f-005a2c65e29f |
Supports the record field exchange (RFX) and bulk record field exchange (Bulk RFX) routines used by the database classes.
class CFieldExchange
| 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. |
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::outputColumnfor field data members. -
CFieldExchange::inputParamorCFieldExchange::paramfor input parameter data members. -
CFieldExchange::outputParamfor output parameter data members. -
CFieldExchange::inoutParamfor 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.
CFieldExchange
Header: afxdb.h
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);
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.
Nonzero if the current operation can be performed on the current field or parameter type.
Follow the model of the existing RFX functions.
You need a call to SetFieldType in your recordset class's DoFieldExchange or DoBulkFieldExchange override.
void SetFieldType(UINT nFieldType);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
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).
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.
[!code-cppNVC_MFCDatabase#33]