Hi,
Another weekend on hacking code to get the Tyrannt project off the ground. Again I am concentrating on the middle OData web service tier. One of the rules I set myself was to not allow this tier to update the database. These update requests are only meant to be done on the back end tier via messages passed along the Azure Service Bus (ASB).
After an initial hiccup which resulted in my WCF service request falling over with “Not enough memory” (These are hosted in Azure extra small compute instances). I managed to get a working service in the cloud that exposed all my current tables.
Next I wanted to split the tables over multiple data services. I initially achieved this by creating multiple database contexts. This also allowed me to intercept the SaveChanges call in the database context when someone did a Post or Put (Below is my current thinking of how to do this, although this may change when I find it doesn’t work
)
But when it came to trying to actually run this, I kept getting an error saying:
Anyway I still needed to expose different tables in different services. And as a nice surprise this time, it was very easy to do.
Here is my DB Context class:
And this is my service code (For now I only want to expose the NewsArticles one) :
And it worked 
For those curious, here is the service URI:
https://tyranntrpg.org:8443/OData/Codex.svc/
I cannot guarantee this service will always work or still exist in future but it’ll be there while I test client side code.
Another weekend on hacking code to get the Tyrannt project off the ground. Again I am concentrating on the middle OData web service tier. One of the rules I set myself was to not allow this tier to update the database. These update requests are only meant to be done on the back end tier via messages passed along the Azure Service Bus (ASB).
After an initial hiccup which resulted in my WCF service request falling over with “Not enough memory” (These are hosted in Azure extra small compute instances). I managed to get a working service in the cloud that exposed all my current tables.
Next I wanted to split the tables over multiple data services. I initially achieved this by creating multiple database contexts. This also allowed me to intercept the SaveChanges call in the database context when someone did a Post or Put (Below is my current thinking of how to do this, although this may change when I find it doesn’t work
)
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| Public Overrides Function SaveChanges() As Integer For Each change In ChangeTracker.Entries Dim job As tJob Dim entity = change.Entity Dim entityType = change.Entity.GetType.Name Select Case entityType Case "NewsArticle" job = New tjUpdateNewsArticle Dim na As NewsArticle = CType(entity, NewsArticle) '.... Etc End Select Next Return MyBase.SaveChanges()End Function |
The model backing the 'TyranntSubsetContext' context has changed since the database was created.After a lot of searching it seemed like some people said this was possible and other said it was not. I decided to change tack and use a single database context that had all my tables in it, but make a duplicate one in my service project which I can use to intercept the saves. (The Back end tier will need normal database access as this will be doing the writes)
Anyway I still needed to expose different tables in different services. And as a nice surprise this time, it was very easy to do.
Here is my DB Context class:
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| Imports System.Data.EntityImports Tyrannt.Model.EmailImports Tyrannt.Model.NewsImports Tyrannt.Model.ErrorsImports Tyrannt.Model.MembershipImports Tyrannt.Infrastructure.JobsImports Tyrannt.Infrastructure.Jobs.NewsPublic Class GlobalDbContext Inherits DbContext Public Property NewsArticles As DbSet(Of NewsArticle) Public Property EmailMessages As DbSet(Of EmailMessage) Public Property ErrorMessages As DbSet(Of ErrorMessage) Public Property Members As DbSet(Of Member) Public Property MemberTypes As DbSet(Of MemberType) 'Public Overrides Function SaveChanges() As Integer ' For Each change In ChangeTracker.Entries ' Dim job As tJob ' Dim entity = change.Entity ' Dim entityType = change.Entity.GetType.Name ' Select Case entityType ' Case "NewsArticle" ' job = New tjUpdateNewsArticle ' Dim na As NewsArticle = CType(entity, NewsArticle) ' End Select ' Next ' Return MyBase.SaveChanges() 'End FunctionEnd Class |
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| Imports System.Data.ServicesImports System.Data.Services.CommonImports System.LinqImports System.ServiceModel.WebPublic Class News Inherits DataService(Of GlobalDbContext) ' This method is called only once to initialize service-wide policies. Public Shared Sub InitializeService(ByVal config As DataServiceConfiguration) ' Expose only the required tables with the relevant access rights config.SetEntitySetAccessRule("NewsArticles", EntitySetRights.All) ' General settings config.UseVerboseErrors = True config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V3 End SubEnd Class |
For those curious, here is the service URI:
https://tyranntrpg.org:8443/OData/Codex.svc/
I cannot guarantee this service will always work or still exist in future but it’ll be there while I test client side code.
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