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From "Philip, Anil - Kansas City, MO" <anil.phi...@kcc.usda.gov>
Subject RE: Commons Dbutils: Request feedback for possible patch; handling nested beans.
Date Thu, 23 Jul 2009 17:06:23 GMT
I disagree. I see it as an enhancement. This limitation of dbutils is not mentioned in the
docs and the user stumbles upon it as a bug when he finds the member is unfilled. 
However this fix to BeanProcessor only covers bean(s) containing singly nested beans. IMHO
It would be good if we can figure out how to do bean(s) containing singly nested or a list
of nested beans; one-many.
thanks,
Anil Philip

-----Original Message-----
From: Dan Fabulich [mailto:dan@fabulich.com] 
Sent: Wednesday, July 22, 2009 7:03 PM
To: Commons Developers List
Subject: RE: Commons Dbutils: Request feedback for possible patch; handling nested beans.

I share Liam's intuition that I don't think we need this.

Now that you've written this processor for yourself, you can use it; it's 
easy to pass your own BeanProcessor to BasicRowProcessor, and you can 
always hand that BRP to any of our existing ResultSetHandlers.

Trying to provide perfectly general bean-mapping functionality may be 
over-engineering the problem.  The fact that you were able to pull this 
together in just a few lines of code is evidence that it may not be 
necessary to provide it in DBUtils.

-Dan

Philip, Anil - Kansas City, MO wrote:

> My fix was to create a NestedBeanProcessor that inherited from BeanProcessor and accepts
a mapping in the constructor.
> However, **in a patch, it would be better to simply modify the toBean() in BeanProcessor
and add a constructor that accepts a Hashtable**.
> Current fix:
> 1) For each nested bean, users will provide a mapping of property to nested object reference
so that the property can be found. In the above example, that would be: "bar"<---> ['activity',
Bar.class]
> 2) A new class, NestedBeanProcessor inherits from the BeanProcessor class in Dbutils.
It overrides the toBean() method.(Note: for a patch, We would add a constructor that accepts
a hashtable, and also modify toBean()) When this method is called to populate a bean from
a result set, it asks the superclass to fill in the data. Then it examines each mapping. Using
Java Reflection, it retrieves the nested reference. If this is null, it creates the nested
bean. Next, it retrieves the value of the field in the result set and calls the setter method
on the bean.
> 3) In the case where Foo contained a list of nested beans:
> for example
> ArrayList<Bar> bar;
> There is no way to specify this one-many relationship in Dbutils for automatic filling
of bar.activity from the top-level query. We would in this case, fill in the fields of Foo
and then use this instance to run a second query, using the BeanListHandler to fill in the
bar list and any nested fields of Bar.
>
> Hashtable<PropertyDescriptor, String> ht = new Hashtable<PropertyDescriptor,
String>();
> PropertyDescriptor prop = new PropertyDescriptor("activity", Bar.class);
> ht.put(prop, "bar");
> NestedBeanProcessor nbp = new NestedBeanProcessor(ht);
> QueryRunner runner = new QueryRunner();
> BasicRowProcessor burp = new BasicRowProcessor(nbp);
> BeanHandler bh = new BeanHandler(Foo.class, burp);
> Foo foo = (Foo) runner.query(connection,	"select face, activity from Mood", bh);
> System.out.println(foo.getFace() + " during this activity: " + foo.getBar().getActivity());
>
> Result:
> huffing during this activity: jog
> ----
> public class NestedBeanProcessor extends BeanProcessor {
>
> ...relevant methods shown...
>
> Hashtable<PropertyDescriptor, String> propertyForBeanMember;
>
> public NestedBeanProcessor(
> Hashtable<PropertyDescriptor, String> propertyForBeanMember) {
> 	super();
> 	this.propertyForBeanMember = propertyForBeanMember;
> }
> @Override
> public Object toBean(ResultSet rs, Class type) throws SQLException {
> 	Object bean = super.toBean(rs, type);
> 	Enumeration<PropertyDescriptor> keys = propertyForBeanMember.keys();
> 	while (keys.hasMoreElements()) {
> 		PropertyDescriptor property = keys.nextElement();
> 		Class<?> beanClass = bean.getClass();
> 		try {
> 			String fieldName = propertyForBeanMember.get(property);
> 			String fieldNameCapitalized = fieldName.substring(0, 1)
> 				.toUpperCase()
> 						+ fieldName.substring(1);
> 			String fieldGetterName = "get" + fieldNameCapitalized;
> 			String fieldSetterName = "set" + fieldNameCapitalized;
> 			Method fieldGetterMethod = beanClass
> 					.getDeclaredMethod(fieldGetterName);
> 			Method fieldSetterMethod = null;
> // we have to go thru all the methods because
> // PropertyDescriptor doesn't seem to provide a way to retrieve
> // the fieldClass
> // i.e. we would have liked to simply do
> // fieldSetterMethod = beanClass.getDeclaredMethod(fieldSetterName,  Bar.class);
> 			Method[] allMethods = beanClass.getDeclaredMethods();
> 			for (Method m : allMethods) {
> 				String mname = m.getName();
> 				if (mname.equals(fieldSetterName)) {
> 					fieldSetterMethod = m;
> 					break;
> 				}
> 			}
> 			Field beanField = beanClass.getDeclaredField(fieldName);
> 			Class<?> nestedBeanType = beanField.getType();
> 			Object nestedBeanValue = fieldGetterMethod.invoke(bean);
> 			// nestedBeanValue is the value in the reference
> 			if (nestedBeanValue == null) {
> 				// create
> 				nestedBeanValue = nestedBeanType.newInstance();
> 				// set value to new instance
> 				fieldSetterMethod.invoke(bean, nestedBeanValue);
> 			}
> 			System.out.println(" property :" + property
> 				+ " target nested Bean: " + nestedBeanValue);
> 			Class<?> propType = property.getPropertyType();
> 			Object targetValue = this.processColumn(rs, rs
> 				.findColumn(property.getName()), propType);
> 			if (propType != null && targetValue == null
> 				&& propType.isPrimitive()) {
> 				targetValue = primitiveDefaults.get(propType);
> 			}
> 			this.callSetter(nestedBeanValue, property, targetValue);
> 		} catch (Exception e) {
> 			e.printStackTrace();
> 			throw new SQLException(e.getMessage());
> 		}
> 	}
> 	return bean;
> }
>
>
> thanks,
> Anil Philip
>
> -----Original Message-----
> From: Liam Coughlin [mailto:lscoughlin@gmail.com]
> Sent: Wednesday, July 22, 2009 1:26 PM
> To: Commons Developers List
> Subject: Re: Commons Dbutils: Request feedback for possible patch; handling nested beans.
>
> The default BeanHandler is not a full mapping solution and I'm not sure you
> really want it to be -- that's a case where it might be in your best
> interest to implement a custom Handler.
>
> Cheers
> -L
>
> On Wed, Jul 22, 2009 at 12:59 PM, Philip, Anil - Kansas City, MO <
> anil.philip@kcc.usda.gov> wrote:
>
>>
>> Here is the example - I had an idea and implemented a possible fix that
>> works. I would like to know before I submit a patch, whether it really is a
>> solution or if there is a better way. In short, can I get feedback here?
>> --------
>> Problem:
>> Some of our beans contain object references to other beans. Those nested
>> beans may have properties that are intended to be filled in by one or more
>> fields from a query. However, since it is not on the surface, Dbutils cannot
>> find where the property is and so the nested property remains unfilled.
>>
>> Example:
>> Consider a table Moods to track our demeanor while we engage in an
>> activity. So it has two columns; face (demeanor) and activity.
>>
>> Face            Activity
>> -----       --------
>> huffing Jog
>> smile           Work
>> engrossed       movie
>> sad             Cry
>> distant distracted
>> bored           waiting
>>
>> Bean Foo contains an object reference to an instance - a bean- of class
>> Bar. Foo contains data field or property 'face', and Bar contains the
>> property 'activity', that we want to fill from this query:
>> "select face, activity from Mood"
>>
>> public class Foo {
>>        private String face;
>>        private Bar bar;
>>        public String getFace() {return face;}
>>        public void setFace(String face) {this.face = face;}
>>        public void setBar(Bar bar) {this.bar = bar;}
>>        public Bar getBar() {return bar;}
>> }
>> public class Bar {
>>        private String activity;
>>        public String getActivity() {return activity;}
>>        public void setActivity(String activity) {this.activity = activity;}
>> }
>>
>> Old way:
>> QueryRunner runner = new QueryRunner();
>> BeanHandler bh = new BeanHandler(Foo.class);
>> Foo foo = (Foo) runner.query(connection,
>>        "select face, activity from Mood", bh);
>>
>> Result:
>> Foo.bar is null and its fields are unpopulated.
>>
>> thanks,
>> Anil Philip
>>
>> -----Original Message-----
>> From: Dan Fabulich [mailto:dan@fabulich.com]
>> Sent: Tuesday, July 21, 2009 7:13 PM
>> To: Commons Developers List
>> Subject: Re: Commons Dbutils: Request feedback for possible patch; handling
>> nested beans.
>>
>> Philip, Anil - Kansas City, MO wrote:
>>
>>> We use dbutils in my team and found a problem when a bean has nested
>> object references.
>>> The properties in the nested bean are obviously not filled in.
>>
>> File a bug with an example?  I'm not sure I quite understand your
>> scenario.
>>
>> http://issues.apache.org/jira/browse/DBUTILS
>> (You need to login to file a bug.)
>>
>> -Dan
>>
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>>
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>>
>
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>


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