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Oracle Tips by Burleson 


A collection is a way to work with a set of data without committing it to the base database tables.  The concept is very much like a shopping cart.  The data is collected, then, when all the necessary data has been collected, it can be inserted into a table, or tables, from the collection.  Another way to put it is a collection works like persistent session state for a multi-dimensional array of data.

The data in a collection can only be seen by the session that created it.  Also, a session can have many collections.  For example, there may be one collection for books and another collection for music CDs.

If you have downloaded and installed the EASY Samples application from the code depot, you will be able reference it with the explanations that follow.  The collections page ID is 1132.

The explanation provided here will be a departure from the way things have been done so far.  The normal process walks through the steps to create all the components, but since collections are an intermediate to advanced topic, it is assumed you already know how to create the components necessary.

A collection stores data in a character format.  It can store up to 50 elements plus a CLOB.  The 50 columns are of data type varchar2(4000).

Working with Collections

The use of collections utilizes some of the HTML DB API.  The package for this process is htmldb_collection.  This package has several procedures and functions.

Creating a Collection

The collection being created here is a subset of the CONFERENCE_RSVP table.  The code is in the Create Collection process on page 1132 of the EASY Samples application.

if htmldb_collection.collection_exists( 'CONF') = TRUE then 

  htmldb_collection.delete_collection( 'CONF' );

end if; 

  p_collection_name => 'CONF',
  p_query       => 'select id, last_name, first_name, rsvp_date,
                     company, ''O''
                from  conference_rsvp
                where  payment = ''Check''',
  p_generate_md5  => 'YES'); 

htmldb_collection.reset_collection_changed( 'CONF' );

While creating the collection above, the first step is to check to see if the collection exists.  If it does, it is deleted.  Then, the CONF collection can be created using a query to populate it.

The above book excerpt is from:

Easy HTML-DB Oracle Application Express

Create Dynamic Web Pages with OAE

ISBN 0-9761573-1-4   

Michael Cunningham & Kent Crotty


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