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Struts & Hibernate
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| | | Subject: Object Synchronization in DAO | Subject: Object Synchronization in DAO 2005-08-02 - By Jerry Osme?a
Back
I would assume that the User is a data transfer object(DTO), is that correct?
The way I will do this is I will modify the DTO to be sensitive to the changes
of any of its attributes. This can be done by adding a changes attribute of
type hashmap of Name/value pair to your dto. Then when an attribute of this
dto changes, add the name/value pair of this attribute in the hashmap. Then
during the implementation of your DAO, you pull this list of changes and use
the name and value to generate the sql accordingly.
for e.g.
Class User {
String name;
String userId;
HashMap changes;
Public User () {
changes = new HasMap();
}
setUserId(String userId)
{
this.userId = userId;
fireChanges("userId", userId); <-- you can also make a condition such that
if the value is Null or the same as the old value do not trigger the change.
}
fireChanges(String name, String value)
{
changes.put(name, value);
}
}
In your DAO implementation get the changes map and loop thru it. Based on its
name, generate the corresponding sql and bind the corresponding value.
Hope this helps.
Regards,
Jerry
Maciej Gawinecki <d299052@(protected)> wrote:
Imagine the situation from client side of DAO Design Pattern
class User {
String name;
int userID;
...
}
...
User user = UserDAO.findUser(UserID);
user.setName("Johny");
UserDAO.updateUser(user);
...
In what a way UserDAO could guess which record in DB should be updated, if
information contained in 'user' class are ambiguous, e.g. supposing there
doesn't exist any unique primary key like userID?
Any help would be appreciated,
Maciej
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<DIV>I would assume that the User is a data transfer object(DTO), is that
correct?</DIV>
<DIV> </DIV>
<DIV>The way I will do this is I will modify the DTO to be sensitive to the
changes of any of its attributes. This can be done by adding a changes
attribute of type hashmap of Name/value pair to your dto. Then when an
attribute of this dto changes, add the name/value pair of this attribute in the
hashmap. Then during the implementation of your DAO, you pull this list of
changes and use the name and value to generate the sql accordingly.</DIV>
<DIV> </DIV>
<DIV>for e.g.</DIV>
<DIV> </DIV>
<DIV>Class User {</DIV>
<DIV>String name;</DIV>
<DIV>String userId;</DIV>
<DIV>HashMap changes;</DIV>
<DIV> </DIV>
<DIV>Public User () {</DIV>
<DIV> changes = new HasMap();</DIV>
<DIV>}</DIV>
<DIV> </DIV>
<DIV>setUserId(String userId)</DIV>
<DIV>{</DIV>
<DIV> this.userId = userId; </DIV>
<DIV> fireChanges("userId", userId); <-- you can also make
a condition such that if the value is Null or the same as the old value do not
trigger the change.</DIV>
<DIV>}</DIV>
<DIV> </DIV>
<DIV>fireChanges(String name, String value)</DIV>
<DIV>{</DIV>
<DIV> changes.put(name, value); </DIV>
<DIV>}</DIV>
<DIV> </DIV>
<DIV>}</DIV>
<DIV> </DIV>
<DIV>In your DAO implementation get the changes map and loop thru it. Based on
its name, generate the corresponding sql and bind the corresponding value.</DIV
>
<DIV> </DIV>
<DIV>Hope this helps.</DIV>
<DIV> </DIV>
<DIV>Regards,</DIV>
<DIV> </DIV>
<DIV>Jerry<BR><B><I>Maciej Gawinecki <d299052@(protected)></I></B>
wrote:</DIV>
<BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER
-LEFT: #1010ff 2px solid">Imagine the situation from client side of DAO Design
Pattern<BR><BR>class User {<BR>String name;<BR>int userID;<BR>...<BR>}<BR><BR>
<BR>...<BR>User user = UserDAO.findUser(UserID);<BR>user.setName("Johny");<BR
>UserDAO.updateUser(user);<BR>...<BR><BR>In what a way UserDAO could guess which
record in DB should be updated, if<BR>information contained in 'user' class are
ambiguous, e.g. supposing there<BR>doesn't exist any unique primary key like
userID?<BR><BR>Any help would be appreciated,<BR><BR>Maciej<BR><BR>============
========================================================<BR>Companion Site: http
://www.corej2eepatterns.com<BR>J2EE BluePrints: http://java.sun.com/blueprints
/corej2eepatterns<BR>List Archive: http://archives.java.sun.com/archives
/j2eepatterns-interest.html<BR>Unsubscribing: email "signoff J2EEPATTERNS
-INTEREST" to listserv@(protected)<BR></BLOCKQUOTE><p>
<hr size=1> <a href="http://us.rd.yahoo.com/evt=34442/*http:/
/www.yahoo.com/r/hs">Start your day with Yahoo! - make it your home page </a>
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