Slide 10.5: Palm OS databases (cont.)   Slide 10.7: Palm OS databases (cont.)   Home

Palm OS Databases (Cont.)

---

Using the Data Manager
Using the Data Manager is similar to using a traditional file manager, except that the data is broken down into multiple records instead of being stored in one contiguous chunk.

1. To create or delete a database, call DmCreateDatabase and DmDeleteDatabase.


2. To open a database for reading or writing, you must first get the database ID. Calling DmFindDatabase searches a particular memory card for a database by name and returns the local ID of the database header. Alternatively, calling DmGetDatabase returns the database ID for each database on a card by index.


3. After determining the database ID, you can open the database for read-only or read/write access. When you open a database, the system locks down the database header and returns a reference to a database access structure. Call DmDatabaseInfo, DmSetDatabaseInfo, and DmDatabaseSize to query or set information about a database, such as its name, size, creation and modification dates, attributes, type, and creator.


4. Call the following functions when viewing or updating a database:
   • DmGetRecord takes a record index as a parameter, marks the record busy, and returns a handle to the record. If a record is already busy when DmGetRecord is called, an error is returned.
   
   
   • DmQueryRecord is faster if the application only needs to view the record; it does not check or set the busy bit, so it is not necessary to call DmReleaseRecord when finished viewing the record.
   
   
   • DmReleaseRecord clears the busy bit, and updates the modification number of the database and marks the record dirty if the dirty parameter is true.