Re: HashMap and dynamic JDBC update

From:
Lew <noone@lewscanon.com>
Newsgroups:
comp.lang.java.programmer,comp.lang.java.help
Date:
Fri, 07 Aug 2009 09:04:36 -0400
Message-ID:
<h5h8p9$c0g$1@news.albasani.net>
Please *DO NOT* multipost.
(Reply cross-posted to rectify.)

Alessandro wrote:

I have an HashMap<String, Object> used to save names and values of
fields to be updated via JDBC update in a table. The type of data is
variable according to field name , so I'm using Object ... the idea to
produce update query is as follows but I believe there is a better
method to do it.

//START
public void updateQuery(Session session, String table,
HashMap<String,Object> updateH, String condition) throws Throwable{
                try{


Your indentation is far too wide for Usenet. Do not use TAB characters to
indent Usenet posts; use a maximum of four spaces per indent level.

                        String sQuery="UPDATE " + table + " SET ";
                        String keys="";

                        Iterator iterator = updateH.keySet().iterator
(); //key set
                        while(iterator.hasNext()) //got the key
and then remove first char,
ie ","
                                keys= keys + "," + iterator.next() +
"= ?";

                        PreparedStatement ps = session.connection
().prepareStatement(sQuery
+ keys.substring(1) + " WHERE " + condition);

                        while(iterator.hasNext()){
                                Object myObj=updateH.get(iterator.next
());
                                if(myObj instanceof String){


Anytime you are checking type with 'instanceof' to support varied behavior,
suspect that you've erred.

                                        ps.setString(....
                                }
                                else if (myObj.instanceof Date){
                                            ps.setDate(.....
                               }
                               //etc also for Double, Integer, ..
                        }
                        ps.executeUpdate();
                }
                catch(Throwable ex){
                        throw ex;
                }
        }

//END


I've built up queries and corresponding set logic, polymorphically, using tiny
little setters similar to

   interface ParmSetter <T>
   {
     void setValue( PreparedStatement ps, T value );
   }
   class StringSetter implements ParmSetter <String>
   {
     public void setValue( PreparedStatement ps, String value )
     {
       ps.setString( value );
     }
   }

Then you build up a list of SQL WHERE clause pieces and corresponding
ParmSetters as you receive criteria. Then you iterate through, calling

   nextSetter.setValue( ps, nextValue );

Yet another way is to skip 'PreparedStatement#setString()' and the rest and
just use 'setObject()'.

--
Lew

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