LOBs in the Object Cache

Consider these object cache issues for internal and external LOB attributes:

• Internal LOB attributes: Creating an object in object cache, sets the LOB attribute to empty. When you create an object in the object cache that contains an internal LOB attribute, the LOB attribute is implicitly set to empty. You may not use this empty LOB locator to write data to the LOB. You must first flush the object, thereby inserting a row into the table and creating an empty LOB -- that is, a LOB with 0 length. Once the object is refreshed in the object cache (use OCI_PIN_LATEST), the real LOB locator is read into the attribute, and you can then call the OCI LOB API to write data to the LOB.

• External LOB attributes: Creating an object in object cache, sets the BFILE attribute to NULL. When creating an object with an external LOB (BFILE) attribute, the BFILE is set to NULL. It must be updated with a valid directory alias and filename before reading from the file.

When you copy one object to another in the object cache with a LOB locator attribute, only the LOB locator is copied. This means that the LOB attribute in these two different objects contain exactly the same locator which refers to one and the same LOB value. Only when the target object is flushed is a separate, physical copy of the LOB value made, which is distinct from the source LOB value.

See Also: "Example of an Update Using Read Consistent Locators" for a description of what version of the LOB value will be seen by each object if a write is performed through one of the locators.

Therefore, in cases where you want to modify the LOB that was the target of the copy, you must flush the target object, refresh the target object, and then write to the LOB through the locator attribute.