1. APIs and Business Functions Guide
  2. Example: JDECACHE Internal Index Definition Structure

Example: JDECACHE Internal Index Definition Structure

In this example, assume that the user is looking for a record that matches these index key values:

  • 1

  • c

  • i

JDECACHE accesses the values that you pass in the structure at the byte offsets that were defined in the call to jdeCacheInit or jdeCacheInitEx.

JDECACHE compares the values 1, c, and i that it retrieves from the passed structure to the corresponding values in each of the cache records at the corresponding byte offset. The cache records are stored as the structures that were inserted into the cache by jdeCacheAdd, which is the same structure as the one you pass first. The structure that matches the passed key is the second structure to which HCUR1 points.

You should never create a smaller structure that contains just the key to access the cache. Unlike most indexing systems, JDECACHE does not store a cache record's index separately from the actual cache record. This is because JDECACHE deals with memory-resident data and is designed to be as memory-conservative as possible. Therefore, JDECACHE does not waste memory by storing an extra structure for the sole purpose of indexing. Instead, a JDECACHE record has a dual purpose of index storage and data storage. This means that, when you retrieve a record from JDECACHE using a key, the key should be contained in a structure that is of the same type as the structure that is used to store the record in the cache.

Do not use any key structure to access the cache other than the one for which offsets that were defined in the index passed to jdeCacheInit or jdeCacheInitEx. The structure that contains the keys when accessing a cache should be the same structure that is used to store the cache records.

If jdeCacheInit or jdeCacheInitEx is called twice with the same cache name and the same user handle without an intermediate call to jdeCacheTerminate, the cache that was initialized using the first jdeCacheInit or jdeCacheInitEx will be retained. Always call jdeCacheInit or jdeCacheInitEx with the same index each time that you call it with the same cache name. If you call jdeCacheInit or jdeCacheInitEx for the same cache with a different index, none of the JDECACHE APIs will work.

The key for searches must always use the same structure type that stores cache records.