The problem is simple yet complicated. I have Created a data model in silverlight and its services. Now I've changed the Database. Added a field in one of the table, and updated the data model. Now I've to update the services that i'd created before. I don't want to delete the previous service. Is there any way through which i can update the service?
If you mean a WCF RIA Services Domain Context, then your best bet is to keep your modifications in a separate partial class file.
That way you can recreate the Domain Context when you make data changes (such as your adding of a new field) and not have to do so much reworking to fit it back in.
Related
in odata (.net core) it is possible to generate delta results in a delta feedback,
like this https://learn.microsoft.com/en-us/odata/webapi/DeltaFeed_support.
As I see in the example, they create manually the delta response. This can occur in very large result a long-running task before it will be sent back to the client.
I wonder if there is possible, to get an automated way of doing this and how?
So I use entity framework for this.
I thought a little bit about it, but I don't see another change to implement a "log" table to hold every action on all entities, or I must use an event sourcing pattern. The second one was not a choice for already implemented solutions I think.
Maybe there exists another way for this?
Any Ideas?
I have a dbml file (linq to sql) to connect to my database. I have a manager that uses a generic repository (for each entity) to talk to the dbml. A manager uses the Repo to do work (CRUD operations). A WCF wraps the manager and exposes the it to the outside world (so my application can use it).
DB <--> IRepository< Entity, DataContext> <--> IManager(IRepo, IRepo...) <--> WCFService(IManager)
I've tested the manager, it works fine every time. The problem is the WCF. I'll read data (e.g. GetAllLocations), update the data (e.g. change a Location name), but then at some random point later, I'll read dirty data. E.g. if I've been changing a location name to from "BC 1", to "BC 2", to "BC 3", sometimes I'll read it and get older values. Like after I've changed it to "BC 3" and I am expecting to read "BC 3", I get "BC 1" (which doesn't make sense since the value before the update was "BC 2" anyway). WCF does not have caching by default, so why is this happening on my WCF and NOT on my manager? All the WCF does is pass values to the manager and get values from the manager, it's a very basic wrapper class.
NOTE: I am using StructureMap to automatically resolve DependencyInjection and IoC stuff.
Problem methods: anything that's reading (e.g. GetLocationById and GetAllLocations). They just don't always return the latest data from the database. I know it's not the manager because I created a simple project to test both the Manager and WCF independently, and only the WCF had dirty reads after updating data (specifically the Location). I have not testing all the other entities yet.
One final note: I kept getting the "System.Data.Linq.ChangeConflictException: Row not found or changed." exception. I changed the DBML designer Location Entity's properties (except the PK) to Update Check: Never. The dirty reads were happening before this change anyway and the manager works fine (and it uses the DBML). So I have no reason to believe this is causing the dirty reads.
Also, the Location Entity has a trigger in the database, but I'm eliminated this as the cause because I disabled it and that didn't help, and once again, the manager works fine.
There are a couple of things that could be causing this:
The Isolational level of the ambient transaction scope, could be different
One difference going over WCF is that going through IIS could cause things to run concurrently
The things that you could try are:
Set the isolation level of the transaction scope
make sure that your connection string enables MARS - Multiple Active Result Sets
Turns out this was a caching issue caused by using WCF and Structure Map. I'd changed the default structure map caching when registering my data contexts in the data registry.
For<MyDataContext>()
//.HybridHttpOrThreadLocalScoped()
.Use(() => new MyDataContext());
The default was per call which is what I needed.
I've been developing several iOS applications using Core Data and it has been an excellent framework to work with. However, I've encountered an issue whereby we more or less have distributed objects (synced) across multiple platforms. A web/database server backend and mobile devices.
Although it hasn't been a problem until now, the static nature of the data model used by Core Data has me a little stuck. Basically what is being requested is a dynamic forms system whereby forms can be created on a server and propagated to the devices. I'm aware of the technique for performing this with a set number of tables with something like:
Forms table
Fields table
Instance of Forms table
Instance Values table
and just linking everything together. What I'm wondering however is if there is an alternative system to Core Data (something above talking to an SQLite database directly) that will allow for a more dynamic object graph. Even a standard ORM would be good if there are options for modifying the schema at runtime. The main reason I want to go down this route is for performance in the sense that I don't want the instance values table exploding with entries (on the local device or server).
My other option is to have the static schema (object-graph) on the iOS devices but have a conversion layer on the server's side which fetches the correct object, populates the properties and saves it to the correct table. Then when the devices comes to sync, it does the reverse and breaks it down into instances. While this saves the server from having a bloated instance value table, it could still be a problem on the device.
Any suggestions are appreciated.
Using specific tables/entities for forms and fields, and entities for instances of each, is probably what I would recommend. Trying to manipulate the ORM schema on the fly if it's going to be happening frequently doesn't seem like a good idea in general.
However, if the schema is only going to change infrequently, you can probably do it with Core Data. You can programatically create and/or manipulate the NSManagedObjectModel prior to creating a NSManagedObjectContext. You can also create migration logic so data stored in an old model can be preserved when you update the model and need to recreate the context and stores.
These other SO posts may be helpful:
Customize core data model at runtime?
Handling Core Data Model Changes
You need to think carefully about what you are actually modeling.
Are you modeling: (1) the actual "forms" i.e. UI elements, (2) data that might be presented in any number of UI versions e.g. firstName or (3) both?
A data model designed to model forms would have entities like:
Form{
name:string
fields<-->Field.form
}
Field{
width:number
height:number
xPos:number
yPos:number
label:sting
nextTab<-->Field.priorTab
priorTab<-->Field.nextTab
form<<-->Form.fields
}
You would use this to store data about form as displayed in the user interface. Then you would have a separate entities and probably a separate model to store the actual data that would populate the UI elements that are configured by the first data model.
You can use Core Data to modeling anything you just need to know what you are really modeling.
I'm working on creating a WCF Domain Service which at the moment provides access to a database. I created the Entity Model, added the DomainService (LinqToEntitiesDomainService) and everything works so far.
But there are cases when my data doesn't come from the DB but somewhere else (for instance an uploaded file). Are there any best practices out there how to handle this different data sources properly without resorting to writing two completely different data providers? It would be great to access both types with one interface. Is there already something I can use?
I'm fairly new to this so any advice apart from that is highly appreciated.
How many cases where the data comes from a file? How many files? How will you know if a file is there? Are you going to poll the directory? what format are the files? (XML support is possible)
Microsoft's documentation suggests that you can create a custom host endpoint, but I don't know what limitations there are.
I am using NHibernate for a project, and I am absolutely beginner. I am fetching some objects from a table and showing it to a form, where they can be edited. If an user inserts a new object into the table from some other window, I want to show this newly inserted object into the edit window. My application uses tabbed window interface, so user can simultaneously open insert window and edit window at the same time.
So basically what I need is a way to determine if a newly created object exists in the database which is not fetched before by ISession, and if not, then fetch that new object from the database. In other words, I need to synchronize my session with the database, just like flush method, but in the reverse way.
Can anyone help me?
Publish/Subscription method works well for this. Check out the Publishing Events part of Ayende's sample desktop application. Basically after you've added a new item, you publish that information and other parts of your application that subscribed can update their lists accordingly.
You are taking the path to NHibernate Hell.
Be sure to work your infrastructure (ie defining interfaces, defining session management patterns and notification pattern) and isolate these non-business utilies from the rest of your code before using NHibernate to implement them.
Good luck.