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Passing an argument to a repository
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alindzon View Drop Down
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Joined: 28-Jul-2010
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Posts: 31 		Post Options Post Options   Quote alindzon Quote  Post ReplyReply Direct Link To This Post Topic: Passing an argument to a repository
    Posted: 18-Oct-2010 at 9:20am
I am stuck on something which shows how green I am at MVVM and even C#.
 
I have setup a repository to query a table and return a subset based on a parameter that comes from the current selection of the parent datagrid.  i.e. when I select a manufacturer I want to populate related links and addresses in a child grid.
 
I cannot for the life of me figure out how to pass in the current manufacturer ID.
 
This is what I have in the repository, where do I add an argument so it can be passed in, and how does it get passed?  right now it just loads the data for the first manufacturer and I have no idea how to get it to update, or to pass the currentid.

public interface ManufacturerLinkRepository

{EntityQueryOperation<ManufacturerLink> LoadManufacturerLinks(ICollection<ManufacturerLink> results, Action success);}

public class ManufacturerLinkProductionRepository : ManufacturerLinkRepository

{public EntityQueryOperation<ManufacturerLink> LoadManufacturerLinks(ICollection<ManufacturerLink> results, Action success)

{etc...

and in the viewmodel when it first loads the data
ManufacturerLinks = new ObservableCollection<ManufacturerLink>();
and later
private ManufacturerLinkRepository _linkrepository;

private ManufacturerLinkRepository GetLinkRepository(){

LinkRepo = IsInDesignMode ? (ManufacturerLinkRepository)

new ManufacturerLinkDesignRepository() :

new ManufacturerLinkProductionRepository();

return LinkRepo;}

private ManufacturerLinkRepository LinkRepo{

get { return _linkrepository ?? GetLinkRepository(); }

set { _linkrepository = value; }}
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WardBell View Drop Down
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Posts: 338 		Post Options Post Options   Quote WardBell Quote  Post ReplyReply Direct Link To This Post Posted: 19-Oct-2010 at 10:32pm

I don't understand the question in relation to the code that defines the Repository.

Why doesn't your "LoadManufacturersLinks" method take a Manufacturer ID parameter. I must be missing something.
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alindzon View Drop Down
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Posts: 31 		Post Options Post Options   Quote alindzon Quote  Post ReplyReply Direct Link To This Post Posted: 25-Oct-2010 at 5:08pm

I cannot figure out how to add a parameter.  Where do you put it?
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WardBell View Drop Down
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Posts: 338 		Post Options Post Options   Quote WardBell Quote  Post ReplyReply Direct Link To This Post Posted: 25-Oct-2010 at 7:42pm
I might define as follows
 
public interface ManufacturerLinkRepository {
  EntityQueryOperation<ManufacturerLink> LoadManufacturerLinks(
      int mfgID,
    Action<ICollection<ManufacturerLink>> OnSuccess,
    Action<EntityQueriedEventArgs<ManufacturerLink>> OnFail);
}
 
or perhaps, if you didn't want to leave the operation result backdoor available, ...
 
public interface ManufacturerLinkRepository {
  void LoadManufacturerLinks(
      int mfgID,
    Action<ICollection<ManufacturerLink>> OnSuccess,
    Action<EntityQueriedEventArgs<ManufacturerLink>> OnFail);
}


Edited by WardBell - 25-Oct-2010 at 7:53pm
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alindzon View Drop Down
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Posts: 31 		Post Options Post Options   Quote alindzon Quote  Post ReplyReply Direct Link To This Post Posted: 25-Oct-2010 at 9:00pm

Sorry to be so dense, but I am not clear how the design and production structure would look.

I am happy to give up on repositories unless someone can produce one clear example of how a devforce repository should look in the MVVM light world and how the viewmodel needs to interact with it.  All this abstraction is giving me a headache.
 
I have been using the way you organized the repository in your mvvm light example, which defines the interface, then each class for production and design, and finally the entiryqueryoperation for each.
 
 
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WardBell View Drop Down
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Posts: 338 		Post Options Post Options   Quote WardBell Quote  Post ReplyReply Direct Link To This Post Posted: 22-Dec-2010 at 4:33pm
@alindzon Don't give up. But also cast your net wider. There are many examples out there to study.
 
It is important to avoid blindly following any one example shown in demo code ... any demo code. There is no one way. And the author is not trying to account for every circumstance and often cuts corners in one area while concentrating on another.
 
I would say that the Repository in MVVM Lite1 is only one example and, as it happens, not typical of the way I would write one today (which may be different from the way I'll write it tomorrow). You must look to these demos for inspiration ... not prescription.
 
MVVM Lite is almost the simplest MVVM Light example we could write. The next step in the learning progression might be BookShelfDF; see http://links.ideablade.com/drc-bookshelf
 
BookShelf has a repository that better refects current thinking. You will notice that query methods return void rather than operation coordination objects (e.g, EntityQueryOperation<T>); I now recommend against returning the operation object. 
 
The query signature now sports both success and fail callbacks as final parameters. The signarture doesn't include a collection to receive the results; it expects you to do what you will with the results returned to the success callback. I'm not against a collection parameter for everyone; I personally find it troublesome because, as a repository author, I don't know if I should clear the list first, create it, fill it, filter it further, turn off events while I'm filling, etc. etc.  Better to leave those decisions to the caller (typically a VM). But you are welcome to think differently about all these points.
 
MVVM Lite didn't have any parameterized queryies. You don't write a query method that you don't need.
 
BookShelf DOES have parameterized queryies; see GetBooksByCategory. In my earlier reply I showed you an example that was similar in this respect. Did you have trouble with that? You didn't say in your subsequent posts.
 
BookShelf is also a richer exploration of an application that combines design-time and runtime modalities. The accompanying document walks you through how that works and the tour video will provide clues too.
 
Hope this helps.
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WardBell View Drop Down
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Posts: 338 		Post Options Post Options   Quote WardBell Quote  Post ReplyReply Direct Link To This Post Posted: 24-Dec-2010 at 10:15am
Updated MVVM Lite1 solution repositories and ViewModel to better reflect our current recommendations for repository interfaces.
 
Retained the design repository for simplicity of this example. We recommend that you only have one version of a repository and switch between production, design, test, and development environments by swapping the EntityManager that is provided in the constructor parameter as we do in BookShelfDF; see http://links.ideablade.com/drc-bookshelf
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