Form "Complex" Model (nested entities): MVC, SWF

[emilio.remogna]

Hello,

I have some problems to understand if there are some differences in how form/model binding works in Spring MVC / Spring Web Flow; in particular when I use "complex" models (nested entities).

I'm so sorry, but I wasn't able to find relevant documentation about possible differences, so let me explain through a very simple example.

First, MVC case; then Web Flow case.

Environment: SWF 2.3.1.RELEASE + Spring 3.1.0.RELEASE

*** MVC case ***

I have two objects: Bogus and NestedBogus

First object: Bogus

package org.sbibiz.mvcjpa.bogus;

import java.io.Serializable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Bogus implements Serializable {

	private static final long serialVersionUID = 1L;

	private static final Logger logger = LoggerFactory.getLogger(Bogus.class);

	public Bogus() {
		
		// NOTICE THE LOGGER HERE!
		
		logger.info("Bogus Constructor called");
	}

	private String id;

	private String name;

	private NestedBogus nestedBogus;

	public String getId() {

		return id;
	}

	public void setId(String id) {

		this.id = id;
	}

	public String getName() {

		return name;
	}

	public void setName(String name) {

		this.name = name;
	}

	public NestedBogus getNestedBogus() {

		return nestedBogus;
	}

	public void setNestedBogus(NestedBogus nestedBogus) {

		this.nestedBogus = nestedBogus;
	}
}

Second object: NestedBogus

package org.sbibiz.mvcjpa.bogus;

import java.io.Serializable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class NestedBogus implements Serializable {
	
	private static final long serialVersionUID = 1L;

	private static final Logger logger = LoggerFactory
			.getLogger(NestedBogus.class);

	public NestedBogus() {
		
		// NOTICE THE LOGGER HERE!
		
		logger.info("Nested Bogus Constructor called");
	}

	private String id;

	private String name;

	public String getId() {

		return id;
	}

	public void setId(String id) {

		this.id = id;
	}

	public String getName() {

		return name;
	}

	public void setName(String name) {

		this.name = name;
	}
}

I have this controller (GET snippet):

@RequestMapping(value = "/bogus", method = RequestMethod.GET)
public String ordering_GET(Locale locale, Model model) {

	model.addAttribute("myBogus", new Bogus());

	return "bogus";
}

And the view (FORM snippet):

<sf:form action="${myURL}" method="post" modelAttribute="myBogus">
	bogus.id: <sf:input path="id"/><br/>
	bogus.name: <sf:input path="name"/><br/>
	bogus.nestedBogus.id: <sf:input path="nestedBogus.id"/><br/>
	bogus.nestedBogus.name: <sf:input path="nestedBogus.name"/>
	<input type="submit" value="Go, Bogus! Go!" />
</sf:form>

EVERYTHING WORKS FINE!

And the logger says to me:

INFO : org.sbibiz.mvcjpa.bogus.Bogus - Bogus Constructor called
INFO : org.sbibiz.mvcjpa.bogus.NestedBogus - Nested Bogus Constructor called

*** SWF case ***

In a flow, now, I have this view state (conf snippet):

<var name="myBogus" class="org.sbibiz.mvcjpa.bogus.Bogus" />
...
<view-state id="start" view="bogus" model="myBogus">
...
</view-state>

When I request the flow... EVERYTHING STOPS WORKING... :-(

And I get:

INFO : org.sbibiz.mvcjpa.bogus.Bogus - Bogus Constructor called
ERROR: org.springframework.web.servlet.tags.form.InputTag - An ELException occurred getting the value type for expression 'nestedBogus.id' on context [class org.sbibiz.mvcjpa.bogus.Bogus]
org.springframework.binding.expression.EvaluationException: An ELException occurred getting the value type for expression 'nestedBogus.id' on context [class org.sbibiz.mvcjpa.bogus.Bogus]
	at org.springframework.binding.expression.spel.SpringELExpression.getValueType(SpringELExpression.java:105)
	at org.springframework.webflow.mvc.view.BindingModel.getFormattedValue(BindingModel.java:228)
	at org.springframework.webflow.mvc.view.BindingModel.getFieldValue(BindingModel.java:142)
	at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:120)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:178)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:198)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:164)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:151)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:142)
	at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:126)
[...]
Caused by: org.springframework.expression.spel.SpelEvaluationException: EL1007E:(pos 12): Field or property 'id' cannot be found on null
	at org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:205)
	at org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:72)
	at org.springframework.expression.spel.ast.CompoundExpression.getValueInternal(CompoundExpression.java:57)
	at org.springframework.expression.spel.standard.SpelExpression.getValueType(SpelExpression.java:117)
	at org.springframework.binding.expression.spel.SpringELExpression.getValueType(SpringELExpression.java:100)
	... 71 more
[...]

It seems to me that in the first case Spring "takes care" to set up the model properly.

In the second one, I'm able to make it work only if I modify Bogus.java a little: private NestedBogus nestedBogus = new NestedBogus(); But that's not what I'd like...

Am I wrong? Have I forgot something? Or what am I ignoring?

Thank you very much!

Regards.

[goldman]

You should always be setting up your model properly yourself. Apparently Spring MVC does it for you in the first example, but I would consider this a bug - or at least a design pattern that should not be used. Dont rely on Spring to initialize your model, do it yourself always!

[emilio.remogna]

Thank you for your reply and your suggestion, goldman.

I think you're right when you say that it's better to set up models without relying on framework.
This way offers greater control.

I have to admit, then, that I've never noticed before this MVC's behaviour (usually I do all the stuff to initialize my models).

Regards

e.