command object vs modelobject

[lasher169]

Hi,

I understand command objects and form objects are really the same thing. What I would like to know is when using spring mvc is there a necessity to maintain command object/form objects or can I just use the model objects to collect data from the form as if it was a command/form object.

Under struts you would collect the data into a form bean(Form object) and then copy it into your model objects before applying data manipulation. Please let me know which is the best approach.

Thanks

Chris

[Jörg Heinicke]

I do not really know what you are after ...

Spring manages the command or form-backing object for you. If you don't break it (usually by instantiating ModelAndView instance yourself) it gets added correctly and automatically to the model. On a submit request Spring does the binding of request parameter values to the command object for you. So actually you need nothing to do yourself, just provide a command object - and avoid breaking the default method flow.

Joerg

[lasher169]

what is the difference between a domain object, form object?

what I want to know do I need a form object can I use a domain object to be a form object as well.

Thanks

[Marten Deinum]

You can use your DomainObject as a command object. However make sure that you know what you are doing, especially in managed environments like Hibernate and/or JPA backed objects.

[TrevorIngs]

what is the difference between a domain object, form object?

what I want to know do I need a form object can I use a domain object to be a form object as well.

Thanks

I dont think there is an exact answer to your question, it really depends on what your doing IMHO. For example, if you need to display a single property from serveral "domain" objects then would you expose each to the UI layer?

Generally speaking, what has "worked best" for myself has been to create a composite command object to the UI. The command object may have domain objects, or simple property values (coming from a range of sources), example


public class EditMovieCommand {

//domain object
private Movie movie;
//some view related data
private boolean editView;
//id of domain object
private Long storeId;

//getters and setters
...
}


I treat the command as a container for the "stuff" (love that word), that I would only load once (from a domain perspective) - formBackingObject or createFormObject.

I feel this has quite a few advantages and makes adding additional "once off" values at later stages to your UI easier without introducing DTOs.

[Jörg Heinicke]

what I want to know do I need a form object can I use a domain object to be a form object as well.

You get into architectural discussions here, there have been a few threads in the architecture forum about using DTOs or domain objects in the web layer. Unfortunately, you can't search (http://forum.springframework.org/showthread.php?t=22782) for "dto" with this forum.

Joerg

[lasher169]

thanks for the reply...

I am striving to see what is the right and wrong way of doing things. Been coding for so long and all these new things coming out I tend to get lost with all the conventions.

Chris

[lumpynose]

thanks for the reply...

I am striving to see what is the right and wrong way of doing things. Been coding for so long and all these new things coming out I tend to get lost with all the conventions.

Chris

Hee hee! Welcome to the club.

In addition to your question I also have problems figuring out where to put my classes; i.e., in what package. For example, I had to make a simple data transfer object for adding the user's password to the db, containing just the user's id and their password. Where do I put that dto, in the dao packages or the service layer packages? I ended up making a package in the dao tree named dto but I don't know if that's right or not.

[lumpynose]

Also, in one of the first chapters in the book Expert Spring MVC and Web Flow by Seth Ladd he gives a nice explanation of how to slice and dice and think about the different layers.