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Struts & Hibernate
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| | | AW: How to realize extendable data objects? | AW: How to realize extendable data objects? 2003-09-24 - By Chester Chen
Back
There are two ways to add attributes to Material table in database.
1. Use Alter table to add additional column for each attribute you added
2. Use an generic "metadata table" for the attributes.
The metadata table contains metadata with columns Key and Value.
The key column contains the attribute name, the value column
contains the value.
you might have to add another column for data type to indicate the
type of the value. (Also you might replace value column
with String_Value, Number_Value, Date_Value, so you don't need to
worry about the data conversion).
In both ways, one can dynamically add, update, query the newly
added attributes.
One of my collegue used first approach in one of his project, and he
told me it works very well. And We have used the second approach in our
two different product lines (I am not sure Oracle DBA will likes the
first approach or not).
Hope this helps.
Udo Cirkel wrote:
>Hello all,
>
>thanks for your suggestions!
>
>Keely: Yes, your understanding of the scenario is correct...
>
>...and there is one more dimension of my problem to think about:
>
>The material data has to persist in a database. The initial
>database representation should be a table with a column
>for each attribute of Material. The sense of this requirement
>is to allow sql-queries about the attributes of Material.
>
>When deploying a new module how to achieve an appropriate
>extension of the database schema? Appropriate means, that the
>new database representation of Material and the added attributes
>can be queried, too (one goal is to provide an user-interface
>for auto generating sql-queries; these queries should possibly
>work about all - initial and new - attributes of Material).
>
>Which approach is appropriate to realize the access to all
>material data/attributes over a general access class?
>
>Please read this mail in conjunction with the first one.
>
>Thanks in advance, Udo
>
>
>
>-- --Ursprungliche Nachricht-- --
>Von: An interest list for Sun Java Center J2EE Pattern Catalog
>[mailto:J2EEPATTERNS-INTEREST@(protected)]Im Auftrag von PavanKumar
>Keely
>Gesendet: Dienstag, 23. September 2003 18:28
>An: J2EEPATTERNS-INTEREST@(protected)
>Betreff: Re: How to realize extendable data objects?
>
>
>If my understanding is correct,
>Existing scenario: If new module is installed then
>Material has to be changed according to the new module
>( adding attributes etc )
>Many modules in the application will use this Material
>object. Making this Material Object an instance of
>Hashtable/HashMap can solve your problem. Because you
>can just add one more attribute to this as simple as
>that and use that attribute in the new module. But one
>problem with this approach is we need to stick to the
>standard key names throughout the application. But
>avoid hardcoding the key name and use some
>initialization file, which will be initiated at the
>start of the server. This solution is on the lines of
>EJB Design pattern "DTO using HashMap".
>
>
>One more way of achieving extendibility is using XML
>data object. Whenever you create Material object that
>should form the data in the XML. But one problem with
>this approach is building XML and parsing the XML.
>
>
>if you have any queries or if you get a better
>solution than this please do let me know.
>
>
>thanks and best regards,
>
>Keely Pavan
>TATA Consultancy Services, Bangalore
>
>
>
>
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