I have weird problem that I cannot solve. I have an ASP.NET MVC Core 2 application using EF Core. I have a button that triggers an action method. I click the button, it redirects me to the view where I click another button, that makes some database operations and brings me back to the original page.
And inside that method I simply use my ApplicationDbContext:
MyEntry myEntry = _db.MyEntries.FirstOrDefault(e => e.MyProperty == myValue);
The thing is that when I go that path several times, it works. And it stops working on the eighth call, it's always the same line (executing database) that suddenly starts taking about half a minute.
When I modify my code (e.g. move some database code outside loop, create collection and then use it inside loop) it stops working at the other moment - always the same line of code, after the same number of executions, but in a different place.
Any ideas what could be wrong?
I simply use the database in my controller:
private readonly ApplicationDbContext _database;
public MyController(ApplicationDbContext database)
{
_database = database;
}
And ApplicationDbContext is:
public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
Thanks!
It feels like the MyEntry entity needs a key:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<MyEntry>()
.HasKey(b => new { b.Id, b.MyProperty});
}
Related
I have 2 questions.
First=> How can i pass value between 2 ViewModels ?
For example, I m adding data and showing it into the MainPAGE, and simultaneously I want to show the same data ( Observable Collection ) in the ChildPAGE too. Inside the ChildPAGE Xaml I assigned the BindingContext to ViewModel and I assigned listview’s data source to that Observable Collection .But I couldn’t make it work . I tried some examples, but I couldn’t manage it to work. If the data load in the ChildPAGE’s constructor then it works else doesn’t work. I thought , I would improve the performance with using one ObservableCollection, but I think, the mechanism in MVVM is different.
So how can I use one ObservableCollection in 2 pages.
Second => How can I pass data between ViewModels without using the constructor.
Example: I Have 2 Pages ( MainPage and ChidPage) and 2 ViewModels ( MainVM and ChildVM ) .
Situation => If I would pass data from MainPage to ChildPage , I would send data within the constructor .But I want to get data from Childpage to MainPage . So PopAsync doesn’t have a constructor. I also tried EventHandler but it doesn’t work.
Is the only solution is Messaging center? Or what do you advice for better performance? Also does the MessagingCenter reduces the performance because of high usage of RAM?
NOTE: ( I want to learn the mvvm architecture, so I don’t want to use other MVVM Frameworks. I want to get the idea of MVVM and C# comprehensively.)
Thanks in advance
You could create a model class that both view models depend on. The model itself would hold the observable collection, while the view models reference the observable collection. This is a good way to share data across various view models throughout the life of your app. Usually you will want to make the model a singleton to ensure that it really is the same data.
If you don't want to use messaging center, you can use an MVVM framework which comes with other benefits. I use Prism to simplify navigation and you can pass navigation parameters along.
Finally, and this is not the best option usually, you may maintain data in the App object. You can set values in the Properties collection. This is not advisable for complex objects.
EDIT
First you would have some data transfer object which the ObservableCollection would contain, unless you're just holding integers or something.
public class MyDTO
{
//fields for Data Transfer Object
}
DTO's are often among your models, but sometimes you need a composite class to hold DTO's and collections of DTO's
Here is a simple Model that would contain your ObservableCollection
public class MyCollectionModel
{
#region Singleton Pattern
private MyCollectionModel()
{
}
public static MyCollectionModel Instance { get; } = new MyCollectionModel();
#endregion
private ObservableCollection<MyDTO> _dtos;
public ObservableCollection<MyDTO> MyObservableCollection
{
get { return _dtos; }
set { _dtos = value; }
}
}
Note that this implements the Singleton pattern. It could even implment INotifyPropertyChanged as well.
Next your view models, imagine a MyVM1 and MyVM2, would reference the ObservableCollection in your Model with something like this.
public class MyVM1 : INotifyPropertyChanged // Do the same with MyVM2, which would be the binding context for view 2
{
private MyCollectionModel _model;
public MyVM1 ()
{
_model = MyCollectionModel.Instance;
}
private ObservableCollection<MyDTO> myVar;
public ObservableCollection<MyDTO> MyProperty //Bind to this in your View1
{
get
{
return _model.MyObservableCollection;
}
set
{
myVar = value;
NotifyPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
I'm leaving quite a few things out here, and don't really have time to build an entire project just to test. I hope this helps.
You normally use await navService.PushAsync(new MyPage2(dataToShare)); to pass data between pages/VMs. This involves using constructors. Here is a simple example of it: https://stackoverflow.com/a/47873920/1508398
Since you don't want to use constructors, you may load the data on your child page from your service. Alternatively, you may cache the data on the local storage (client-side) and simply load it from there in your child/main page.
In my edmx model are 2 related tables: Challenge and ChallengeNote (has FK back to ChallengeID)
I can do this in breeze all day long
var qry = dataservice.getQuery("Challenges");
However, this fails every time:
var qry = dataservice.getQuery("Challenges").expand("ChallengeNotes");
The searchFailed is called and is the only error information in the console.
return dataservice.execute(qry.inlineCount(true))
.then(seachSucceeded)
.fail(searchFailed);
Does Breeze support relational data like this?
Does one need to write some custom code to support?
What am I missing?
Here's related answered question, but I was already following (unless I missed something) the answer's solution (and why I have the 2 context.Configuration settings in my ContextProvider).
breezejs-error-when-loading-an-entity-with-related-data
Here's another similar question that's been unanswered breeze-expand-query-fails-with-object-object-has-no-method-getproperty
Here's my provider code (want to use the BeforeSaveEntity override further on in the project):
public class ModelProvider : EFContextProvider<ModelEntities>
{
public ModelProvider()
: base()
{
this.Context.Configuration.LazyLoadingEnabled = false;
this.Context.Configuration.ProxyCreationEnabled = false;
}
}
Here's my controller code:
[BreezeController]
public class DataController : ApiController
{
readonly ModelProvider _contextProvider = new ModelProvider();
[HttpGet]
public string Metadata()
{
return _contextProvider.Metadata();
}
[Queryable(AllowedQueryOptions = AllowedQueryOptions.All)]
[HttpGet]
public IQueryable<Challenge> Challenges()
{
return _contextProvider.Context.Challenges.Include(x => x.ChallengeNotes);
}
[HttpPost]
public SaveResult SaveChanges(JObject saveBundle)
{
return _contextProvider.SaveChanges(saveBundle);
}
[HttpGet]
public IQueryable<ChallengeNote> ChallengeNotes()
{
return _contextProvider.Context.ChallengeNotes;
}
}
When I browse to the URL, it's including the related entity:
http://localhost:53644/breeze/data/Challenges?$filter=Active%20eq%20true&$top=10&$expand=ChallengeNotes&$inlinecount=allpages
Here is the data coming from the Controller
At this point all things, imo, are pointing to Breeze configuration on either the Server or Client.
TIA
Breeze absolutely does support this, but you do need to make sure that your Entity Framework model is set up correctly. Take a look at the DocCode sample in the Breeze zip for a number of examples of using both expand (client side) or EF include (server side) clauses.
One guess about your problem is that you are using the Breeze camelCasing naming convention and therefore your "expand" clause should be
var qry = dataservice.getQuery("Challenges").expand("challengeNotes");
i.e. "challengeNotes" (note the casing) is the name of the client side property that corresponds to a server side property of "ChallengeNotes". To clarify, "expand" clauses take the names of client side "properties" as parameters and property names are what are transformed as a result of the Breeze.NamingConvention.
In contrast, a query resource name i.e. "Challenges" in your example is the name of the server side resource ( as a result of marking your "Challenges" method with the [HttpGet] annotation. This name is NOT affected by the NamingConvention.
Side notes: Your example has both an expand and an Include clause. Either of these is sufficient all by itself. You do not need both. In general you can either include an "expand" clause in your client side query OR have an Entity Framework "Include" clause on the server. The advantage of the first is that you can control the expand on the client, the advantage of the second is that you can insure that every query for a specified resource always fetches some related entities.
Hope this helps!
Ok!
I have to say both technology are great. Although there seems that something I do not get it.
You have a data in you database (and let say you want to show data from a table that has references to other tables).
I have a model with List or IEnumerable or IQueryable or whatever...
So in my view I want do foreach through the list of object and take advantage of cool feature of references to other tables. No problem in controller while you are in
using (var datatabse = new MyEntity)
{
}
But when you get out of using db has disposed and you get common error The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
So i do not see other options as creating in memory copies of entity objects...but you loose all cool EF4 references and you have to manually load data first in your model and then with foreach show it on the view.
So instead of List<(EF4Type)> or IEnumerable<(EF4Type)> or IQueryable<(EF4Type)>
you have to do List<(MyCustomHelperClass)> where MyCustomHelperClass represents a class with properties similiar to entity objects and probably some additional beacuse you do not have access to properties of referenced tables Then you have to do foreach and Load data into this List and the another #foreach on the view with Razor to show all.
Twice as much work and if project is big...you can see a bigger picture of how manny those helperClasses you need. Was all this cool new technology really meant to be used in that way?....or am I missing something.
You are probably getting that error when you reference a lazy loaded property in your view. You should eager load everything you need in the Controller before passing it to the View.
See Loading Related Objects (Entity Framework).
The following example will cause all courses to be retrieved with the departments in the same query. This is eager loading.
// Load all departments and related courses
var departments1 = context.Departments
.Include(d => d.Courses)
.ToList();
Without the Include() part, courses could be retrieved later (possibly after your context has been disposed in the view). This is called lazy loading.
Along with eager loading as remembered by jrummell, there's also another way of loading related entries, it's explicit loading. Let's suppose you have a User entity, with many Groups entities related to it. You can explicitly load them:
var user = context.Users.Find(id); // Load the user.
context.Entry(user)
.Collection(u => u.Groups)
.Load();
This way you don't have to use the .Include(), and you can even filter the Groups:
context.Entry(user)
.Collection(u => u.Groups)
.Query()
.Where(g => g.SomeProperty.Contains("something"))
.Load();
TheMentor,
Depending on whether you have a repository or a db context, this object should only live for the duration of the controller action (Request), so you should be able to do everything required within the confines of the action.
Maybe i've misunderstood, but based on your question, this is what your issue appears to be. If I have misunderstood, then I'd still suggest that the db repository or db context should be referenced across the controller, rather then invoking it inside the action each time.
so you should see something like this in your controller:
public class TasksController : BaseController
{
private readonly TaskService _serviceTasks;
public TasksController(IRepository repository)
{
_serviceTasks = new TaskService(repository);
}
//
// GET: /Tasks/
public ActionResult Index()
{
var viewModel = _serviceTasks.All<Task>();
return View(viewModel);
}
public ActionResult Details(int id)
{
var domainModel = _serviceTasks.GetById<Task>(id);
var viewModel = PopulateDetailsViewModel(domainModel);
return View(viewModel);
}
//.. rest of actions cut
}
I can't post my code at the moment as I am on the road and out of office. Here is my code greatly simplified. I don't think I have a syntax issue as such - I think I need a clarification or, a pointer.
Model:
[Validaton attribute]
class Data
{
[Required]
int xx
..
}
ViewModel:
class VM
{
SelectItem Items;
int ItemID;
Data dt = new Data();
public VM
{
Items =... Load from db...
}
}
View
#Textbox xx (etc)
#DropDownFor(VM.ItemID, VM.Items
Controller
void Index
{
VM vm = new VM();
//I also default some items here works well - I get a nice form all loaded.
return View(vm);
}
[POST]
void Index(VM stuffPosted)
{
If ModelState.OK)(
{
All good. We direct to another page with Redirect To Action
}
else
{
return View(stuffPosted)
//This is the problem case where I need an efficiency
}
PROBLEM
The form loads fine with the Index method. On postback submit, the ID comes back correctly in ItemID. If there is an error - the ModelState sends back the view...and all the selection list(s) are in place, with selections. Oh joy! BUT, in the Postback method, the VM stuffposted instance class invokes the constructor and there is another (expensive) db call....to reload the collections..then the 'ViewState' seems to load the selected IDs over the top of it...
If I refactor the code so as there is no expensive reload of the collections...then I get the classic error along the lines of
int32 but expecting IEnumerable and my original form does not show ...
I am missing something, clearly..how to reload the collection from 'ViewState' (page) for reuse in an error situation, and not need a db call.
You could use SessionState to avoid the database trip to repopulate the dropdown. Populate the SessionState on the first GET request, and then load from it when you need to repopulate the dropdown (on error) on POST. However be wary of the size of the collection you are storing in SessionState - you may be better going to the database after all to re-load the data.
I'm using logical delete in my system and would like to have every call made to the database filtered automatically.
Let say that I'm loading data from the database in the following way :
product.Regions
How could I filter every request made since Regions is an EntitySet<Region> and not a custom method thus not allowing me to add isDeleted = 0
So far I found AssociateWith but I'd hate to have to write a line of code for each Table -> Association of the current project...
I'm looking into either building generic lambda Expressions or.. something else?
You could create an extension method that implements your filter and use that as your convention.
public static class RegionQuery
{
public static IQueryable<Region> GetAll(this IQueryable<Region> query, bool excludeDeleted=true)
{
if (excludeDeleted)
return query.Regions.Where(r => !r.isDeleted);
return query.Regions;
}
}
So whenever you want to query for regions you can make the following call to get only the live regions still providing an opportunity to get at the deleted ones as well.
context.Regions.GetAll();
It my be a little wonky for access the Products property, but still doable. Only issue is you would have to conform to the convention. Or extend the containing class.
someProduct.Regions.GetAll();
I hope that helps. That is what I ended up settling on because I haven't been able to find a solution to this either outside of creating more indirection. Let me know if you or anyone else comes up with a solution to this one. I'm very interested.
It looks to me like you're using a relationship between your Product and Region classes. If so, then somewhere, (the .dbml file for auto-generated LINQ-to-SQL), there exists a mapping that defines the relationship:
[Table(Name = "Product")]
public partial class Product
{
...
private EntitySet<Region> _Regions;
[Association(Storage = "_Regions")]
public EntitySet<Region> Regions
{
get { return this._Regions; }
set { this._Regions.Assign(value); }
}
...
}
You could put some logic in the accessor here, for example:
public IEnumerable<Region> Regions
{
get { return this._Regions.Where(r => !r.isDeleted); }
set { this._Regions.Assign(value); }
}
This way every access through product.Regions will return your filtered Enumerable.