Managing Collections

Topics:

Obtaining a Member Count
Resequencing a Collection
Verifying Whether a Collection Exists
Adjusting a Member Sequence ID
Sorting Collection Members
Clearing Collection Session State

Obtaining a Member Count

Use COLLECTION_MEMBER_COUNT to return the total count of all members in a collection. Note that this count does not indicate the highest sequence in the collection.

See Also:

"COLLECTION_MEMBER_COUNT Function"

Resequencing a Collection

Use RESEQUENCE_COLLECTION to resequence a collection to remove any gaps in sequence IDs while maintaining the same element order.

See Also:

"RESEQUENCE_COLLECTION Procedure"

Verifying Whether a Collection Exists

Use COLLECTION_EXISTS to determine if a collection exists.

See Also:

"COLLECTION_EXISTS Function"

Adjusting a Member Sequence ID

You can adjust the sequence ID of a specific member within a collection by moving the ID up or down. When you adjust a sequence ID, the specified ID is exchanged with another ID. For example, if you were to move the ID 2 up, 2 becomes 3, and 3 would become 2.

Use MOVE_MEMBER_UP to adjust a member sequence ID up by one. Alternately, use MOVE_MEMBER_DOWN to adjust a member sequence ID down by one.

Sorting Collection Members

Use the SORT_MEMBERS method to reorder members of a collection by the column number. This method sorts the collection by a particular column number and also reassigns the sequence IDs for each member to remove gaps.

See Also:

"SORT_MEMBERS Procedure"

Clearing Collection Session State

Clearing the session state of a collection removes the collection members. A shopping cart is a good example of when you might need to clear collection session state. When a user requests to empty the shopping cart and start again, you must clear the session state for a collection. You can remove session state of a collection by calling the TRUNCATE_COLLECTION method or by using f?p syntax.

Calling the TRUNCATE_COLLECTION method deletes the existing collection and then recreates it, for example:

APEX_COLLECTION.TRUNCATE_COLLECTION(
    p_collection_name => collection name);

You can also use the sixth f?p syntax argument to clear session state, for example:

f?p=App:Page:Session::NO:collection name

See Also:

"TRUNCATE_COLLECTION Procedure"

Determining Collection Status

The p_generate_md5 parameter determines if the MD5 message digests are computed for each member of a collection. The collection status flag is set to FALSE immediately after you create a collection. If any operations are performed on the collection (such as add, update, truncate, and so on), this flag is set to TRUE.

You can reset this flag manually by calling RESET_COLLECTION_CHANGED.

Once this flag has been reset, you can determine if a collection has changed by calling COLLECTION_HAS_CHANGED.

When you add a new member to a collection, an MD5 message digest is computed against all 50 attributes and the CLOB attribute if the p_generated_md5 parameter is set to YES. You can access this value from the MD5_ORIGINAL column of the view APEX_COLLECTION. You can access the MD5 message digest for the current value of a specified collection member by using the function GET_MEMBER_MD5.