Im quite new to backbone and thinking of collections vs model. Lets say i have to do a json-call to an endpoint wich only returns 2-3 properties in one single object. Is it then really necessary to use a collection for that one single model?
Or can i just do the call directly from a model and then use it in my view. I mean, does the model have the same functionallity as a collection? i.e you can load, fetch, parse etc.
Yes, you can populate model from a server with a model.fetch call. To do this you'll have to set url for your model.
In Backbone, Models represent entities for your application domain while Collections are a way to group models by type.
Collections are basically helpers when dealing with multiple instances of a given Model. They've got functions to sort, filter or iterate (and some more from Underscore.js) and also have several functions to deal with Model creation such as fetch, create, etc.
Since they're helping you deal with multiple models, Collections have an url attribute which is used by its models to build urls when communicating with server individually.
So, if you just have info for an entity you will use a Model (i.e: http://host.com/entity/3). If you have an URL for several entities, you may use a Collection (i.e: http://host.com/entities). However, keep in mind that you may use Collections just for grouping and easier use, even when you don't have any URL for it.
Related
When modeling a CouchDB object in Backbone, should there be a 1-1 relationship between a backbone model and a CouchDB database?
Currently, my models are around database documents and not a whole database. I am also using PouchDB to communicate witch CouchDB.
CouchDB dev here. Would not make them match 1:1. put all docs that belong to an app into a single database and give them a type field. Use a view to get all docs per type (or put the type as the prefix of the _id and use _all_docs/allDocs()) and have all docs of a type match the backbone model 1:1).
After a bunch of research and experimentation I came to the following conclusions.
You should use collections to model your database if your database holds related documents OR if you are using PouchDB.
Here is why:
1) A collection that holds related models is analogous to a a database that holds related documents.
2) Most importantly, if you are using PouchDB, you should use a collection to model your database. By doing so you can tie a collection to a PouchDB object and take advantage of backbone's events when the database or collection changes.
The alternative is to pass a reference to a PouchDB instance to each model.
In my WPF application I'm using the MVVM pattern and the repository pattern. I have a repository that provides a list of aircraft objects. From a user perspective, I want to display these aircrafts in several different ways (e.g. on a map, in lists, in textual form, etc..), and also allow the user to filter the objects. To achieve this I have built views and viewmodels for each of the different ways of representing the data.
My problem now is that I'm not sure what the best practice is for making the list of aircraft objects available for all the different viewmodels. Here's some of the alternatives I've considered:
1.Inject the repository into each viewmodel, and then get all the objects from the repo.
2.Inject the repository into a MainViewModel that retrieves all the objects from the repo, and then inject the object collection into all other viewmodels that needs it.
So in sum: I have a set of viewmodels that all make use of the same collection of model objects. What is the best practice for sharing this collection between the viewmodels when using the repository pattern?
In a WPF application I'll typically create service objects which encapsulate repositories which in turn contain a session object each, but I use dependency injection to inject the actual implementations. One of the major benefits of doing this is that everything can be easily mocked for unit testing, but another one is that you now have total control over the scope of these objects. If you're pulling your data from a database then you'll have different strategies for session management depending on whether you're developing a windows app vs a web site (say) and in enterprise applications this requirement will change even within the same code base. There's a good article on Germán Schuager's blog discussing the pros and cons of various session management strategies but for WPF applications using one session per form seems to be a good one. If you're using something like Ninject then you simply scope your ISession object to the view model for your top-level "page" and then all the objects within the logical hierarchy for that page can create their own repositories without needing to know about each other. Since they're all sharing the same session object they're also sharing the same entities in the repository cache and thus the model is now being shared by multiple view models. The only thing that remains is to add property notification to the entity classes in your domain layer so that changes made by one view model propagate through to the others, but that's a topic for another post (hint: your DB layer should provide some mechanism for injecting your own wrapper proxies to add property change notification automatically using things like Castle DynamicProxy etc).
The general rule of thumb is that EACH view should have it's own ViewModel, you can reuse ViewModels via inheritance or adding properties but again a view "DESERVES" it's own ViewModel.
You can have your views leverage interfaces, your viewmodels can implement interfaces.
We have a complex composite financial application where we needed to share various model objects across viewmodels, So we took an approach: we created a high level Model Object which holds collections of other model entities. This high level model is returned/populated in servicelayer. We share this high level model object in many viewmodels and with many PRISM modules using event aggregator .
So in your case you may have a AircarftsData Model, which can maintain collection of aircrafts. you can populate this model using your repository. Then You can pass this AircarftsData in various viewmodels.
We have shipped our application in production with this design and faced no issues as such. One thing you might want to be careful of Memory leakage of this Model object. If somehow any child object of this Model is leaked in memory then whole high level model may remain in memory.
Your data should be located in some place... (Service, Database, File, Etc...).
In that case, you should have a class which manage yours client requests:
GetAllAircrafts, Create, Update, Etc...
This class somtimes called XXXService.
I think that this is where you should expose your collection of models.
This service can be injected to the view models and share the collection of models through a get property (Maybe as a read only collection...?)
Good luck !
I provide a form for users to upload their own data. I use ajax-form-submit and then parse the data to create numerous models (one per row in uploaded csv).
Now, I want to create models into a predefined collection.
I can use add which takes an array of models but unfortunately, it does not send PUSH at server side. I know I can iterate and create .create for each model but let's say I have 10k models, it would create 10k calls. Sounds unreasonable. Did I miss anything?
The other way is to accept multiple models at server and use .ajax calls and then add manually to the collection for UI rendering.
Looking for the best route. Thanks.
Backbone and REST simply do not cover all real-world use cases such as your bulk create example. Nor do they have an official pattern for bulk delete, which is also extremely common. I am baffled as to why they refuse to address these extremely common use cases, but in any case, you're left to your own good judgement here. So I would suggest adding a bulkSave or import method to your collection. That should send an AJAX POST request with your CSV form data to the server, the server should save the info and if all goes well, return a JSON array of the newly-created models. You collection should take that JSON array in the POST response and pass it to reset (and parse as well if you need special parsing).
Definitely don't do a POST request for each model (row in your CSV), especially if you plan on having 10K models. However, to be clear, it wouldn't be completely terrible to do that pattern for a few dozen models if your UI shows real-time progress and error handling on a per-record basis (23 of 65 saved, for example).
I like the pragmatic approach of #PeterLyons but another idea could be trying to transform your not REST functionality to a REST functionality.
What you want is to create a bunch of Models at once. REST doesn't allow create multiple resources at one. What REST likes is to create one resource at a time.
No problem, we create a new resource call Bulk with its own url and its own POST verb. The attributes of this Model are the array of Models you want to create.
With this approach you can also solve future functionalities like modify and remove multiple Models at once.
Now you just need to figure out how to associate the array of Models to this new Model and how to make the Bulk.toJSON method responses properly.
I've been wondering what lives in the community for quite some time now;
I'm talking about big, business-oriented WPF/Silverlight enterprise applications.
Theoretically, there are different models at play:
Data Model (typically, linked to your db tables, Edmx/NHibarnate/.. mapped entities)
Business Model (classes containing actual business logic)
Transfer Model (classes (dto's) exposed to the outside world/client)
View Model (classes to which your actual views bind)
It's crystal clear that this separation has it's obvious advantages;
But does it work in real life? Is it a maintenance nightmare?
So what do you do?
In practice, do you use different class models for all of these models?
I've seen a lot of variations on this, for instance:
Data Model = Business Model: Data Model implemented code first (as POCO's), and used as business model with business logic on it as well
Business Model = Transfer Model = View Model: the business model is exposed as such to the client; No mapping to DTO's, .. takes place. The view binds directly to this Business Model
Silverlight RIA Services, out of the box, with Data Model exposed: Data Model = Business Model = Transfer Model. And sometimes even Transfer Model = View Model.
..
I know that the "it depends" answer is in place here;
But on what does it depend then;
Which approaches have you used, and how do you look back on it?
Thanks for sharing,
Regards,
Koen
Good question. I've never coded anything truly enterprisey so my experience is limited but I'll kick off.
My current (WPF/WCF) project uses Data Model = Business Model = Transfer Model = View Model!
There is no DB backend, so the "data model" is effectively business objects serialised to XML.
I played with DTO's but rapidly found the housekeeping arduous in the extreme, and the ever present premature optimiser in me disliked the unnecessary copying involved. This may yet come back to bite me (for instance comms serialisation sometimes has different needs than persistence serialisation), but so far it's not been much of a problem.
Both my business objects and view objects required push notification of value changes, so it made sense to implement them using the same method (INotifyPropertyChanged). This has the nice side effect that my business objects can be directly bound to within WPF views, although using MVVM means the ViewModel can easily provide wrappers if needs be.
So far I haven't hit any major snags, and having one set of objects to maintain keeps things nice and simple. I dread to think how big this project would be if I split out all four "models".
I can certainly see the benefits of having separate objects, but to me until it actually becomes a problem it seems wasted effort and complication.
As I said though, this is all fairly small scale, designed to run on a few 10's of PCs. I'd be interested to read other responses from genuine enterprise developers.
The seperation isnt a nightmare at all, infact since using MVVM as a design pattern I hugely support its use. I recently was part of a team where I wrote the UI component of a rather large product using MVVM which interacted with a server application that handled all the database calls etc and can honestly say it was one of the best projects I have worked on.
This project had a
Data Model (Basic Classes without support for InotifyPropertyChanged),
View Model (Supports INPC, All business logic for associated view),
View (XAML only),
Transfer Model(Methods to call database only)
I have classed the Transfer model as one thing but in reality it was built as several layers.
I also had a series of ViewModel classes that were wrappers around Model classes to either add additional functionality or to change the way the data was presented. These all supported INPC and were the ones that my UI bound to.
I found the MVVM approach very helpfull and in all honesty it kept the code simple, each view had a corresponding view model which handled the business logic for that view, then there were various underlying classes which would be considered the Model.
I think by seperating out the code like this it keeps things easier to understand, each View Model doesnt have the risk of being cluttered because it only contains things related to its view, anything we had that was common between the viewmodels was handled by inheritance to cut down on repeated code.
The benefit of this of course is that the code becomes instantly more maintainable, because the calls to the database was handled in my application by a call to a service it meant that the workings of the service method could be changed, as long as the data returned and the parameters required stay the same the UI never needs to know about this. The same goes for the UI, having the UI with no codebehind means the UI can be adjusted quite easily.
The disadvantage is that sadly some things you just have to do in code behind for whatever reason, unless you really want to stick to MVVM and figure some overcomplicated solution so in some situations it can be hard or impossible to stick to a true MVVM implementation(in our company we considered this to be no code behind).
In conclusion I think that if you make use of inheritance properly, stick to the design pattern and enforce coding standards this approach works very well, if you start to deviate however things start to get messy.
Several layers doesn't lead to maintenance nightmare, moreover the less layers you have - the easier to maintain them. And I'll try to explain why.
1) Transfer Model shouldn't be the same as Data Model
For example, you have the following entity in your ADO.Net Entity Data Model:
Customer
{
int Id
Region Region
EntitySet<Order> Orders
}
And you want to return it from a WCF service, so you write the code like this:
dc.Customers.Include("Region").Include("Orders").FirstOrDefault();
And there is the problem: how consumers of the service will be assured that the Region and Orders properties are not null or empty? And if the Order entity has a collection of OrderDetail entities, will they be serialized too? And sometimes you can forget to switch off lazy loading and the entire object graph will be serialized.
And some other situations:
you need to combine two entities and return them as a single object.
you want to return only a part of an entity, for example all information from a File table except the column FileContent of binary array type.
you want to add or remove some columns from a table but you don't want to expose the new data to existing applications.
So I think you are convinced that auto generated entities are not suitable for web services.
That's why we should create a transfer model like this:
class CustomerModel
{
public int Id { get; set; }
public string Country { get; set; }
public List<OrderModel> Orders { get; set; }
}
And you can freely change tables in the database without affecting existing consumers of the web service, as well as you can change service models without making changes in the database.
To make the process of models transformation easier, you can use the AutoMapper library.
2) It is recommended that View Model shouldn't be the same as Transfer Model
Although you can bind a transfer model object directly to a view, it will be only a "OneTime" relation: changes of a model will not be reflected in a view and vice versa.
A view model class in most cases adds the following features to a model class:
Notification about property changes using the INotifyPropertyChanged interface
Notification about collection changes using the ObservableCollection class
Validation of properties
Reaction to events of the view (using commands or the combination of data binding and property setters)
Conversion of properties, similar to {Binding Converter...}, but on the side of view model
And again, sometimes you will need to combine several models to display them in a single view. And it would be better not to be dependent on service objects but rather define own properties so that if the structure of the model is changed the view model will be the same.
I allways use the above described 3 layers for building applications and it works fine, so I recommend everyone to use the same approach.
We use an approach similar to what Purplegoldfish posted with a few extra layers. Our application communicates primarily with web services so our data objects are not bound to any specific database. This means that database schema changes do not necessarily have to affect the UI.
We have a user interface layer comprising of the following sub-layers:
Data Models: This includes plain data objects that support change notification. These are data models used exclusively on the UI so we have the flexibility of designing these to suit the needs of the UI. Or course some of these objects are not plain as they contain logic that manipulate their state. Also, because we use a lot of data grids, each data model is responsible for providing its list of properties that can be bound to a grid.
Views: Our XAML definitions of the views. To accommodate for some complex requirements we had to resort to code behind in certain cases as sticking to a XAML only approach was too tedious.
ViewModels: This is where we define business logic for our views. These guys also have access to interfaces that are implemented by entities in our data access layer described below.
Module Presenter: This is typically a class that is responsible for initializing a module. Its task also includes registering the views and other entities associated with this module.
Then we have a Data Access layer which contains the following:
Transfer Objects: These are usually data entities exposed by the webservices. Most of these are autogenerated.
Data Adapters such as WCF client proxies and proxies to any other remote data source: These proxies typically implement one or more interfaces exposed to the ViewModels and are responsible for making all calls to the remote data source asynchronously, translating all responses to UI equivalent data models as required. In some cases we use AutoMapper for translation but all of this is done exclusively in this layer.
Our layering approach is a little complex so is the application. It has to deal with different types of data sources including webservices, direct data base access and other types of data sources such as OGC webservices.
Not sure how to structure this. Model inheritance seems sensible, but it looks like Django will add a one-to-one link between the related models, which I don't need. Here's my situation: I have two models, for a Game and a Turn within a game. What I'd like to do is provide a "demo" version of these on my website for potential users to play around with. I want them to function just like the real models, but to populate different tables (eg say "demo_game" and "demo_turn") so I can clean them periodically and not "pollute" the real game/turn tables.
What's the best way to structure this? I could just copy the models to new versions, but would rather have a more elegant way to keep them in sync in case I modified one, but there is no need for any db relationship between a model and its demo version.
Create abstract base classes for each type, then derive concrete children.