Can plsql return table of object type

Question

Dear All,
I am trying to return a set of data using object type.
But i am able to return only a single row but I want to return multiple rows.
I am trying to create the procedure which will return the table of object type but I am not able to assign value to table of object type.
Any ideas will be appreciated.
Regards
Abhishek

Answer 1

ArchitectView wrote:
The intention is to create a tree structure of data.Is this structure stored in the database? If so, then what data model is used? Relational? Hierachical? Object?
Each of these have pros and cons. The object model has many when persisted in a database as it nowhere near as flexible and robust as relational. Simple example, you can define an object class called Address. You can define a collection class called addressList. You can make that collection class a column in the Customers table. This allows you to store multiple addresses for a customer - as part of the same row for a customer.
However, there is a data modeling issue here. How do you index the region code in the address to do region based sales and marketing queries? There is a performance issue here - every time a customer row is read, the Addresses column is also read and this column contains a collection of addresses... Expensive I/O wise.
If relational data model was used, there would have been an Addresses table. It would have had a region index. And every time you read a customer row, all the addresses of that customer is not automatically read into memory too.
This Pl/SQL is to be called by another program which will accept the tree structure.So PL/SQL is to deliver a tree structure class?
You have mentioned about the design being not optimal, please elaborate.
I am doing these steps to improve performance.
i already have a java code which creates the data in the tree form {common data model -  XML} .
I am thinking that if I create the structure in database , it will be better for performance.What makes sense to me (performance, usability and data modeling wise) is to use a relational design to store the tree data in Oracle. Each tree item will have a unique identifier and an optional parent identifier. The latter will be a foreign key constraint to the unique identifier.
The PL/SQL procedure can use a hierachical SQL to select the relevant root nodes from the tree table (i.e. start with tree items that have null parent identifiers) and transform this into a XML and supply XML output.
This allows Java to call this PL/SQL procedure, and get XML in response.
An alternative would be to not use XML, but instead define the tree structure as Java expects it, using SQL advance data types (i.e. classes). But instead of using that for store of the tree's data, the PL/SQL proc uses it to transform the tree data (selected via a hierarchical query) into this class object structure.
The Java client then needs to have wrapper classes for these SQL classes - and when it calls the PL/SQL proc, it gets a class structure returned that it can natively use on its side.
This a tad more complex to do than the XML interface - but could be faster as the Java layer does not need to transform the XML into a local data structure... it gets an equivalent data structure directly from PL/SQL.
The only issue ito performance I can see, is attempting to use such an object structure also as data storage (Oracle table) structure. This is usually less than optimal. Fair to say, that relational data modeling still reigns supreme ito usability, integrity and performance. (at least within RDBMS products, like Oracle)