[Springframework-developer] TR : [springframework - Help] Spring JDBC object usage - multiple queries

[JP P. <jp....@ti...>]

-----Message d'origine-----
De=A0: JP Pawlak [mailto:jp....@ti...]=20
Envoy=E9=A0: lundi 11 ao=FBt 2003 19:51
=C0=A0: 'SourceForge.net'
Objet=A0: RE : [springframework - Help] Spring JDBC object usage -
multiple queries

Hi Jim,

This is a common situation. Rod was using a technique approaching this
done below. But in fact no of the two application demos uses it. In such
case, we generally create a first abstract class subclassing the mapRow
method which contains the common code and an incomplete constructor.
Something like this:

	abstract class MyObjectSqlQuery extends MappingSqlQuery{
       =20
		protected MyObjectSqlQuery (DataSource ds, String sql) {
			super(ds, sql);
			// No compile in this class
		}
=20
		protected Object mapRow(ResultSet rs, int rownum) throws
SQLException {
			MyObject myObject =3D ...
			// Here creating the object from the resultset
			// Assuming all the SQL orders calling for the
needed fields.
			return myObject;
		}
	}

And after all concrete Query objects will subclass it.

	class AllMyObjectSqlQuery extends MyObjectSqlQuery {
		protected AllMyObjectSqlQuery (DataSource ds) {
			super(ds, SQL_SELECT_ALL);
			compile();
		}
	}

	class SomeMyObjectSqlQuery extends MyObjectSqlQuery {
		protected SomeMyObjectSqlQuery (DataSource ds) {
			super(ds, SQL_SELECT_SOME);
			// Related to the WHERE statement
			declareParameter(new
SqlParameter(Types.INTEGER));
			declareParameter(new SqlParameter(Types.CHAR));
			declareParameter(new SqlParameter(Types.CHAR));
			...
			compile();
		}
	}

For these two classes you generally will use one of the execute()
methods or  add a method using them internally.

For a single retrieval :

	class FindMyObjectSqlQuery extends MyObjectSqlQuery {
		protected FindMyObjectSqlQuery (DataSource ds) {
			super(ds, SQL_SELECT_ONE);
			// Generally just the id as integer or long like
here
			declareParameter(new
SqlParameter(Types.BIGINT));
			compile();
		}
	=09
		public MyObject getMyObject(long id) {
			return (MyObject) this.findObject(id);
		}
	}

Nevertheless, you must have a specific class for each SQL Select with a
different parameters signature with this design. Otherwise, you will
make tricky SQL select for optional elements in the WHERE Clause [(name
=3D ? or isnull(?))].

Hope this answer to your question,
Regards,
Jean-Pierre

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queries


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By: jnemesh

Hi!  I'm exploring the Spring framework a bit, and I have a question:

I typically do 2 modes of queries for selects:
Find a single object
Range

So, for example, the API might allow for someone to find a single
datatype,
or a list of all available datatypes.

I'd like to bundle those 2 calls under the same object, so I can avoid
repetition
of code (for mapping the results.)  What I'd like to do is be able to
register
multiple sql querries for the object, and call the correct one via
methods with
strong typing that internally call execute(<params>).

One of the problems I'm running into with this is that different queries
on
the same object wind up having different parameters, and I can't
undeclare params
before I compile.  Because of this, if methods are run in the wrong
order it
causes problems.

If I were to subclass one of the classes so that the mapping code was
reused,
wouldn't I be exposing the other class's methods and causing this same
problem?

What's a good way to handle this?  Or should I just implement a new
class for
each query, and re-use the mapping code?  I guess I could implement a
super
class that just has the mapping code, and each subclass could extend it
- but
that leaves me with even more classes to deal with.  And the API for a
thousand
classes with 1 method each is difficult to read.

Any advice greatly appreciated.

-Jim

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