I was looking over the DynatableRF example and I was wondering why in SummaryWidget when you create a new Person instance the subfields like address and schedule are not auto-populated. Is there a better way than to manually instantiate a new instance of every non-primitive subfield down the tree?
The framework can't auto-populate subfields because it won't know if you want instances in those fields or you want them to be null. You want different things in different circumstances.
It sounds like what you are asking for is Dependency Injection in which case the GIN (GWT INjection) project can help.
Related
So I have run into a situation where I need to use the Entity Framework (DbContext) with databases whose columns are not known at compile time. Basically I don't have the luxury of hard coding a customTable class to put into the DbSet.
The only thing I can think of for solving this issue is using Reflection.Emit to create a customTable class at run-time based on information I glean by interrogating a database.
I was not able to find any information of solving this issue, but I am very new to working with the Entity Framework so maybe a solution would be more obvious to someone more experienced.
I feel like there should be a cleaner way than using Reflection.Emit to dynamically create a class to feed DbSet.
If I am way off base for the intended use of the Entity Framework that information would be useful as well.
Hi I'm investigating this problem too and I have found what seems like the solution.
http://romiller.com/2012/03/26/dynamically-building-a-model-with-code-first/
tells you how to make a DbContext into which you add a new DbSet using a type as a parameter. You can create this type using the Dynamic Linq Library:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
It has a method called CreateClass which will allow you to dynamically build a POCO class definition from a list of field names and load it, you can then create a DbSet using the new type you have created.
You can then get a non-generic DbSet from your updated DbContext using
db.Set(type)
where 'type' is a variable holding your new type. This can be worked on using the linq predicates in the dynamic linq library.
Incidentally, my application is for a CMS where new modules can add fields to the core data table for the CMS, and I don't want to use DI as its too inflexible as no given module will be able to provide a type which has all the fields it needs and all the other unknown modules might also need.
James
Say I want to populate a JPA entity using values supplied by a user through a web application form (Tapestry for that matter).
What is the best way to obtain the "blank" instance of the JPA entity that is going to be bound to the form fields?
As of now I just use the new operator as follows in my Tapestry class:
childminderAccount = new ChildminderAccount();
Is this not a somewhat a crude way of doing it? Is there a better way?
Nope, that's the best way to do it. One of the advantages of JPA (over old EJB Persistence) is that it is a "lighter" framework. One of it's lightnesses is the fact that it now works woth POJOs (or Java Beans). I would recommend however to take a look at Java's new validation API which is very lightweight as well, and it can insure that a JPA Bean is correctly populated from your form (like no non-nullable fields set to null, empty id field etc):
http://www.hibernate.org/subprojects/validator.html
I am struggling with how to understand the correct usage of models. Currently i use the inheritance of Db_Table directly and declare all the business logic there. I know it's not correct way to do this.
One solution would be to use Doctrine ORM, but this requires learning curve and all the current components what i use needs to be rewritten paginator and auth. Also Doctrine1 adds a another dozen classes which need to be loaded.
So the current cleanest implementation what i have seen is to use the Data Mapper classes between the so called model and DbTabel. I haven't yet implemented this as it seems to head writing another ORM. But example could be something this: SQL table User
create class with setters, getters, business logic here /model/User.php
data mapper /model/mapper/UserMapper.php, the funcionality is basically writing all the update, save actions in here.
the data source /model/DbTable/User.php extends the Db_Table_Abstract
Problems are with relationships between other models.
I have found it beneficial to not have my models extend Db_Table, but to use composition instead. That means my model 'has a' Db_Table rather than 'is a' Db_Table.
That way I find it much easier to reference multiple tables in the same model, which is a common requirement. This is enough for a simple project. I am currently developing a more complex application and have used the Data Mapper pattern and have found that it has simplified my code more than I would have believed.
Specifically, I have created a class which provides all access to the database and exposes methods such as getUser() etc.. That way, if the DB changes, or my client wants something daft like storing records in XML or we split the servers or something I only have to rewrite one class.
Again, my models do not extend this class, but have an instance of it assigned as a property during construction.
I would say the 'correct' way depends on the situation. Following the YAGNI and KISS principles, it is not good to over-complicate your model setup unless you really believe that it will benefit you in the long run.
What is the application you are developing? How is your current setup of extending Db_Table holding you back?
I have started developing my own web framework which has been coming along quite nicely. It simplifies and cators for all my specific needs. I have tried many frameworks like struts, struts 2, tapestry, spring and the list goes on. There are 2 big problems I find in all of these frameworks.
The ability to work with specific business logic/rules.
I am a bit of a perfectionist and the entire layout of these frameworks force you to scatter you validation, DAO logic and your form actions. I like to keep things grouped together and not do validation in my Hibernate Objects, Action classes and a separate XML files which causes a load unnecessary processing.
Ok back to my question. Does any one know of possible solutions to populating Objects from a HTTPRequest? I started looking into introspection and reflection, but I would like to see if there might be a better solution for something like this. Example: Object Student has 3 fields eg String Name, Integer age and Calendar DOB. What are the options in populating this object or any other Object from a HTTPrequest?
You could use a similar system to the way objects are sent in json by adding a __type__field that gets sent with each object. That way you know which object to create and introspect.
I'm using DataNucleus as a JPA implementation to store my classes in my web application. I use a set of converters which all have toDTO() and fromDTO().
My issue is, that I want to avoid the whole DB being sent over the wire:
If I lazy load, the converter will try to access ALL the fields, and load then (resulting in very eager loading).
If I don't lazy load, I'll get a huge part of the DB, since user contains groups, and groups contains users, and so on.
Is there a way to explicitly load some fields and leave the others as NULL in my loaded class?
I've tried the DataNucleus docs with no luck.
Your DTOs are probably too fine-grained. i.e. dont plan to have a DTO per JPA entity. If you have to use DTOs then make them more coarse grained and construct them manually.
Recently we have had the whole "to DTO or not to DTO, that is the question" discussion AGAIN. The requirement for them (especially in the context of a JPA app) is often no longer there, but one of the arguments FOR DTOs tends to be that the view has coarser data requirements.
To only load the data you really require, you would need to use a custom select clause containing only these elements that you are about to use for your DTOs. I know how painful this is, especially when it involves joins, which is why I created Blaze-Persistence Entity Views which will take care of making the query efficient.
You define your DTO as an interface with mappings to the entity, using the attribute name as default mapping, this looks very simple and a lot like a subset of an entity, though it doesn't have to. You can use any JPQL expression as mapping for your DTO attributes.