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Writing a database application for PDAs

• Tags:
• SQL,
• Database,
• PDA,
• Windows CE

Khalid Shaikh. Builder.com Builder.com

Published: 30 Aug 2002 15:47 BST

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The CeWriteRecordProps function adds a record to the database, as shown in the following code snippet:

CEOID CeWriteRecordProps(
HANDLE hDbase,
CEOID oidRecord,
WORD cPropID,
CEPROPVAL * rgPropVal );

You need to fill the CEPROPVAL structure with the properties that its table is going to contain. This is akin to assigning data types to columns in a standard Access or SQL database. Table A outlines the legal data types.

Value Description CEVT_BLOB A CEBLOB structure CEVT_BOOL A Boolean value CEVT_FILETIME A FILETIME structure CEVT_12 A 16-bit signed integer CEVT_14 A 32-bit signed integer CEVT_LPWSTR A null-terminated string CEVT_R8 A 64-bit signed integer CEVT_UI2 A 16-bit unsigned integer CEVT_UI4 A 32-bit unsigned integer

Our application stores the following properties in the CEDB database as shown in the following list:

• strTitle--256-character Unicode string
• nHour--short int
• nMinute--short int
• nRating--float
• strDescription--1,024-character Unicode string

Reading from the database

You must take care to set the "Seek" of the database to the right position before reading. The Overview tab enumerates all the records in the database from start to finish whenever that Overview property page receives focus.

The CeReadRecordPropsEx requires a handle to the database and a buffer to dump all the contents of the record into. CeReadRecordPropsEx can even allocate an appropriate amount of RAM on the heap, which you have to free after the function call. There is no need to respecify the CEPROPVAL.

CEOID CeReadRecordPropsEx (
HANDLE hDbase,
DWORD dwFlags,
LPWORD lpcPropID,
CEPROPID * rgPropID,
LPBYTE * lplpBuffer,
LPDWORD lpcbBuffer,
HANDLE hHeap );

Closing the database

You close the database by unmounting the volume that the database is located on. The function CeUnmountDBVol helps accomplish that, as shown in the following code:

BOOL CeUnmountDBVol (
PCEGUID pceguid );

Conclusion

You now have the foundation and code to write a simple, quick database application using Windows CE. In the next installment, I will cover an ADOCE client application that hits SQL Server via a wireless connection located on a corporate backbone.

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