Projects :

1. Wrapper
2. WebCLIPS
3. HLL
4. ODBC

An ODBC Interface for CLIPS

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- Table of Contents -

1. What does the ODBC Interface do?
2. How do I use the ODBC Interface
3. A simple example program
4. Download a more complete example
5. Notes and Caveats on using the interface
6. Technical Details
   

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What does the ODBC Interface do?

This function call allows a developer to issue a SQL query against an ODBC data source and have the resulting rows asserted as facts into a CLIPS program. It works with the CLIPS DLL and is meant for people who would like to embed CLIPS into a C++ program using the wrapper classes.

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How do I use the ODBC Interface

This is the function prototype for the ODBC interface :

int CCLIPSWrap::CLIPSODBCQuery(CString& strQuery,
                               CString& strCredentials,
                               CString& strDeftemplateName,
                               BOOL bImplode)

The parameters for the ODBC interface are :

• CString& strQuery - This is the SQL query

• CString& strCredentials - This is the ODBC connect string. This must contain DSN=ODBC data source name;. It may also contain UID and password information.

• CString& strDeftemplateName - Is the name of the deftemplate where the facts are to be asserted. All column names returned from the SQL query are forced to lower case. Code your deftemplate accordingly.

• BOOL bImplode - If this parameter is set to TRUE, then all data fields will be imploded before the fact is asserted.

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Notes and Caveats on using the interface

There are several details to keep in mind to use the CLIPS/ODBC interface properly :

• All ODBC administrivia must be in working order.
  (i.e. Drivers must be installed, ODBC data source must be registered etc.)
• All deleted records are skipped.
• If a record contains a data field with a NULL value, that field will NOT be included in the assert statement.
• A deftemplate containing all of the desired columns has to be loaded before the call to CCLIPSWRAP::CLIPSODBC() in order to 'catch' the rows returned from query.

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Technical Details

The solution was implemented by creating a new class, CVarRecordSet as an extension of CRecordset. Two functions were overridden to obtain the column names and actual data returned from a given query.

1. PreBindFields() - This function is called by the CRecordset::Open() function after the query has executed but before any data is fetched. By calling ::SQLDescribeCol() the column names are captured and stored for use as slot names in a deftemplate.
2. Move() - CRecordset::Move() is called initially to handle cursor movement, EOF/BOF processing etc. ::SQLGetData() is then invoked and the actual data is stored in CString format.

A fact is formatted, the function CCLIPSWRAP::CLIPSAssert() is invoked and the corresponding rules fire.

Information regarding CVarRecordset was obtained from book Visual C++ 4, Masterclass (chapter 7 by Ken Ramirez) available from Wrox Press. Note : The code provided provided in this book is compatible with VC++ 4.0. There is a version for VC++ 4.2/5.0 available in the CLIPS Wrapper Class

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Last modified : 9-Aug-2003
Michael Giordano