Solved

Mapping Suggestion needed

Posted on 2011-03-16
11
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Last Modified: 2012-05-11
I have a table which contains 3 columns id,key,value. The data in the table looks like this :-

1)1,userId,test
2)1,firstName,foo
3)1, lastName, foo Test

Now when i query the table  :-

List<Property> values = hibernateDao.findById("xx");

I get list of values as i mentioned above. I can do this :-

User user = new User();
foreach(Property prop : values ) {
if(prop.getKey().equalsIgnoreCase("userId") {
user.setUserId(prop.getValue()):
}
if(prop.getKey().equalsIgnoreCase("firstName") {
user.setFirstName(prop.getValue());
}
.
.
}
return user;

This works fine but i am trying to find more efficient way of doing it instead of using nested if statements.
0
Comment
Question by:Micheal_Male
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11 Comments
 
LVL 47

Expert Comment

by:for_yan
Comment Utility
And what is Property ?
Is it a type defined by Hibernate ?
0
 

Author Comment

by:Micheal_Male
Comment Utility
Its an entity class
0
 
LVL 47

Expert Comment

by:for_yan
Comment Utility
But who defines it? Does it implement Comparable?
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Author Comment

by:Micheal_Male
Comment Utility
It's just a class itself which holds field names id,key and value. It does not implement comparable.
0
 

Author Comment

by:Micheal_Male
Comment Utility

@Entity
@Table(name="property")
public class Property {

@OneToMany(mappedBy="property")
@JoinColumn("id")
private String id;
@Column(name="key")
private String key;
@Column(name="value")
private String value;

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LVL 47

Expert Comment

by:for_yan
Comment Utility

If you defined it in your code, then you can implement Comparable
and define compareTo method
in such a way that Collections.sort(values) will produce the known order of keys,
then you would not need to check with if's but could know that fiirst element corresponds
say to userid, second to first name, etc

0
 

Author Comment

by:Micheal_Male
Comment Utility
hmm that sounds a little dangerous if someone else adds a new key or it might break by putting the wrong key value in user pojo.
0
 
LVL 47

Expert Comment

by:for_yan
Comment Utility
That is true.
If I were you, I would go for if's, as you mentioned in your original post; don't see any problems with those.
I just suggested, as you were looking for possible alternatives.  
0
 
LVL 5

Expert Comment

by:josephtsang
Comment Utility
what about refactoring your code with the Visitor design pattern?
0
 
LVL 5

Accepted Solution

by:
josephtsang earned 250 total points
Comment Utility
Work in this way:

1. Replace all lines inside the for-loop by these 2 lines


Setter<User> setter = setterMap.get(prop.getKey());
setter.set(user, prop.getValue())

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2. Before entering the for-loop, prepare a setter map as follows


Map<String,Setter<User>> setterMap = new HashMap<String,Setter<User>>();
setterMap.put( "userId", new Setter<User> { 
	public void set(User user, String value) { user.setUserId(value); } });
setterMap.put( "firstName", new Setter<User> { 
	public void set(User user, String value) { user.setFirstName(value); } });
setterMap.put( "lastName", new Setter<User> { 
	public void set(User user, String value) { user.setLastId(value); } });

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3. Define a private inner interface Setter in your class


private interface Setter<T> { 
	public void set(T t, String value); 
}

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So if you have defined any new key-value pairs for the records, you just need to put a new entry into the map in Step 2. Others just keep the same. Less code change for the enhancement.
0
 

Author Comment

by:Micheal_Male
Comment Utility
Great. However I just found a mapping framework also. Hopefully that will suffix my needs.
0

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