I can't quite decide how to go about separating my view models from my DB models.
I'm using an ActiveRecord pattern for my DB access. Meaning I get a User class instance for each User row in the database.
In WebForms I'm used to use these as my model objects, implementing most of the business logic directly on my ActiveRecords.
I realize this isn't exactly 3-tiered design, and I'd really like to improve upon it, especially in MVC, where separation of concerns is empathized.
So I'd think the Controller shouldn't have access to my DB models, but how do I then go about storing/loading data from the DB ?
It's not my impression you should place a huge amount of business logic in your view models either, so somehow I think I'm missing a central piece of the puzzle.
What I'm looking for is some best-practice advice I guess :-)
I hope all this made sense, otherwise please ask.
I strongly suggest creating one view model per view and using AutoMapper to map properties from your active records to your view models. I don't believe that there's a problem with your controller having access to your DB models; the controller should be responsible for translating them into view models.
As for translating view models (really post data models) back into active records, you can use AutoMapper for this as well in simple cases and custom code for the rest.
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I have programmed in Rails, Django, Zend, and CakePHP. Also, Wordpress and Drupal.
Now, I am "catching up to speed" in as fairly large application in CodeIgniter.
Typically, my experience with MVC frameworks, has led me to believe that Models represent business logic in reference to actual database tables. In the CodeIgniter docs and in the code base I'm dissecting I see models created that represent something as vague as a page. A lot of the business logic is written directly into those models and they incorporate other actual data models. I'm not sure this is ideal and following MVC.
Should models be created beyond data models?
Also, lets say I have a data model representing a user (user table in DB). In that user table there is a column called gender of the type enum('male', 'female'). Now I want to populate a dropdown with the gender options from the enum column.
Where is it most appropriate to put this logic?
The user model is an object used to represent a single user or row in the db... right? So it doesn't seem fitting to include a function in the user model/class called "get_gender_options", because, while the function is related to the user table, it is NOT relevant to a single user object. In Zend this kind of logic could be built into the form object itself.
There is not "right" answer, just one we can consider the most appropriate...
I would probably just put the "get_gender_options" in the model, rather than sticking it in the view for the form. To keep it DRY but not put it in the model, I would create a helper to hold this.
I am working on a project that has a large database with all the data already in it. So now, I don't see the mvc project model being used very much, since the views are being strongly typed to a database model.
I am very new to this stuff, so is database simply taking place of the model "space" ?
since the views are being strongly typed to a database model
That's wrong. You shouldn't pass any domain models to the views. You should be using view models which are classes specifically designed for the requirements of a given view. A controller action should query your data access layer which will return some domain models and then map those domain models to view models and then pass this view model to the view. A view model is a representation of the database for a specific view.
I am wondering how the models in code ignitor are suposed to be used.
Lets say I have a couple of tables in menu items database, and I want to query information for each table in different controllers. Do I make different model classes for each of the tables and layout the functions within them?
Thanks!
Models should contain all the functionality for retrieving and inserting data into your database. A controller will load a model:
$this->load->model('model_name');
The controller then fetches any data needed by the view through the abstract functions defined in your model.
It would be best to create a different model for each table although its is not essential.
You should read up about the MVC design pattern, it is used by codeigniter and many other frameworks because it is efficient and allows code reuse. More info about models can be found in the Codeigniter docs:
http://codeigniter.com/user_guide/general/models.html
CodeIgniter is flexible, and leaves this decision up to you. The user's guide does not say one way or the other how you should organize your code.
That said, to keep your code clean and easy to maintain I would recommend an approach where you try to limit each model to dealing with an individual table, or at least a single database entity. You certainly want to avoid having a single model to handle all of your database tables.
For my taste, CodeIgniter is too flexible here - I'd rather call it vague. A CI "model" has no spec, no interface, it can be things as different as:
An entity domain object, where each instance represents basically a record of a table. Sometimes it's an "anemic" domain object, each property maps directly to a DB column, little behaviour and little or no understanding of objects relationships and "graphs" (say, foreign keys in the DB are just integer ids in PHP). Or it can also be a "rich (or true) domain object", with all the business intelligence, and also knows about relations: say instead of $person->getAccountId() (returns int) we have $person->getAccount(); perhaps also knows how to persist itself (and perhaps also the full graph or related object - perhaps some notion of "dirtiness").
A service object, related to objects persistence and/or general DB querying: be a DataMapper, a DAO, etc. In this case we have typically one single instance (singleton) of the object (little or no state), typically one per DB table or per domain class.
When you read, in CI docs or forums, about , say, the Person model you can never know what kind of patter we are dealing with. Worse: frequently it's a ungly mix of those fundamentally different patterns.
This informality/vagueness is not specific to CI, rather to PHP frameworks, in my experience.
I have a web application built on an MVC design.
I have a database which contains a large number of objects (forum threads) which I can't load into memory at once. I now want to display (part of) this collection with different filters in effect (kinda like what stackoverflow does with questions sorted by date, votes, tags etc).
Where do I implement the filtering logic? It seems to me that this must go into the model part of the application, as only models interact with the database (in my implementation). If I make the filtering a part of the view, then the view must access the database directly to get the list of filtered objects, right? I'd like to avoid this, because it exposes the database layout to the view. But at the same time, displaying different views of the same data should be implemented in the view part of the application, as they are just that -- different views of the same data.
So how do I resolve this? Do I create an additional model, say, FilteredThreadsList, and have it remember the filter to use, and then use a FilteredView to display the list of threads that FilteredThreadsList spits out?
Or do I have to build a ThreadQueryier that allows views to query the database for certain thread objects, so I can have the filtering logic in a view without exposing the database backend?
You should never query data from the view. I don't know what framework you are using in particular but as for Ruby on Rails (should be the same for other frameworks) we always pull the necessary data from the controller and store all that information into a variable. The variable will be accessed by the view which can help you avoid querying your database directly from the view.If the code to query the database gets too lengthy in the controller, insert that code into the model instead so it's more maintainable for your project in the future. Additionally, you can call this model method from multiple places in your application if needed. Good luck!
From an architectural point of view, the model should be having the code for filtering. This is so, because in many applications the code for filtering is not trivial and has a good amount of domain logic in it. (Think of filtering top gainers from a list of stocks). From your example as well, it looks the same since you might want to filter by vote or by date or by tags and then by answered or unanswered etc.
In some very simple applications that deal with search/list of entities and allows Create/Read/Update/Delete of an entity, the pagination, sorting and filtering logic is usually very generic and can be implemented in a controller base class that is inherited by all entity-specific controller classes.
The bottom line is this: if your filtering logic is generic put it in the controller else put it in the model.
Model, that's only bunch of entities.
View provides a visual representation of the data from model - use as much of views as you want. If your application is web based, you can fetch data into browser just once (AJAX) using and re-use them for different UI components rendered in the browser.
As for what entities and what view to use for their representation, I think it's work of Controller. If you need some support for it on "model layer", add it but avoid tight coupling.
I am just getting started with MVC, and it seems like it will be a great way to go, once I manage to switch my thinking to it.
Most of the material I have come across seems to have a 1-1 relationship between models, views, and tables - ie each model represents a table and allows CRUD, plus more complex functions.
What if I have an Account Model, which would allow account creation and updating.
I would want to use a /signup view and controller to create() the account, but would want to use a /members/account view and controller to update, change pw, etc.
Would it be better to have a Signup Model, or am I ok with just using whatever model I need from multiple locations?
Also, say an account can have many users, but I want to create the first user at signup. I would like to run the account setup and user creation as a transaction. Should I have an Account Model and User Model, and work with both, or just have the signup create() function for Account create the default user?
I am using PHP with CodeIgniter
In general, what you want to do is most likely to consider your tables to be an additional "layer" below your model; the MVC concept generally doesn't deal too much with the implementation of backing issues; i.e. whether or not you're using DB tables or flat file storage or in-memory data representations.
What I would suggest is to look at the problem as one of having one layer that does interaction between your tables and your application; your "data objects" layer. Think of this as pure serialization. If you're using an object model, this will be your ORM layer.
Then you want to have another layer that defines the "business logic"; i.e. the interaction of your data with your data. This has to do with things such as how the Account interacts with the User, etc. The encapsulation here basically takes care of your high-level interactions. In this way, you can define the abstractions that make the most sense for your business requirements without needing to depend on implementation; for example, you can define a "UserAccount" Model, that will do all the things that you need to do to handle User Accounts; define all the things that you want that abstraction to do. Then, once you've got that abstraction down, that is your Model; you can then define, in the internal workings of that model, how the interactions occur with your persistence code.
In this way, you abstract out the persistence and implementation of your Model from the actual Model interface. So you can define your model as doing the things you want it to do without concern for the underlying implementation. The benefits of this are significant; the process of thinking about what you want your Model to do, in isolation from the way in which it will be doing it, can be very instructional; as well, if your backing data layer changes, your Model doesn't need to change; so you can prototype with a flat file, for example.