I am creating my first Blazor web application for self education purposes. There is a simple database with data. Dataset is currently rather small. However while clicking on page link it takes some 1-2 seconds to load. Just wondering that how long it would take if dataset would consist of larger amount of items. Is there a way to load page first and then populate the data?
public class EmployeesBase : ComponentBase:
[Inject]
protected IRepository Repository { get; set; }
protected List<BlazorCompanyManager.Data.Employee> employees;
protected override void OnInitialized()
{
this.employees = this.Repository.GetEmployees();
}
public interface IRepository:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace BlazorCompanyManager.Data
{
public interface IRepository
{
public List<Employee> GetEmployees();
public Employee GetEmployee(Guid id);
public bool UpdateEmployee(Employee employee);
public void AddEmployee(Employee employee);
public void DeleteEmployee(Guid id);
}
}
public class Repository : IRepository:
protected readonly ApplicationDbContext dbContext;
public Repository(ApplicationDbContext db)
{
this.dbContext = db;
}
public List<Employee> GetEmployees()
{
return this.dbContext.EmployeeTable.ToList();
}
I have tried to make it work with OnInitializedAsync and other override methods, but got no success so far. Could anyone give some idea on how it can be done?
You''re running an async code block synchronously, thus blocking the UI thread.
this.dbContext.EmployeeTable.ToList()
should look like this:
public async ValueTask<List<Employee>> GetEmployeesAsync()
{
using var dbContext = this.DBContext.CreateDbContext();
var list = await dbContext
.EmployeeeTable
.ToListAsync()
?? new List<TRecord>();
return list;
}
To do this you also need to move to an IDbContextFactory in your Repository. You can no longer rely on a single DbContext.
protected virtual IDbContextFactory<MyDbContext> DBContext { get; set; } = null;
public xxxxxRepository(IConfiguration configuration, IDbContextFactory<MyDbContext> dbContext)
=> this.DBContext = dbContext;
Startup/Program
var dbContext = configuration.GetValue<string>("Configuration:DBContext");
services.AddDbContextFactory<MyDbContext>(options => options.UseSqlServer(dbContext), ServiceLifetime.Singleton);
You component initialization then looks like this.
protected async override void OnInitializedAsyc()
{
this.employees = await this.Repository.GetEmployeesAsync();
}
Data loading will be dependant on your data server, but the UI will be responsive. You may need to consider paging as the data set grows - you can only display so many rows at once so why fetch them all at once!
Related
I'm following Gerald Versluis's videos https://www.youtube.com/watch?v=uxqQqyuZ3Qo https://www.youtube.com/watch?v=8_cqUvriwM8
All good (and great teaching), but uses code behind and I'm trying to be a good boy and learn mvvm and binding - and wishing I perhaps hadn't ;)
So I can get the data from my database and convert to a List and then cycle through the list to add to an observable collection which is referenced in the Xaml's CollectionView ItemsSource=.
This seems pretty longwinded and not "reactive" (is that the right word?)
So my question is how do I link the CollectionView in the Xaml directly to the SQLite database (through the Database.cs)?
I'm using CommunityToolkit.Mvvm.ComponentModel; and I know how to use [ObservableProperty] and now how to setup a class to be reactive - see .net maui Cannot get updated fields in an Observable collection to update in bound collection view
Do I apply these to the Classes.Friend.cs class and does sqlite understand all that?
Ok here's some code snippets
MainPage.xaml
<CollectionView ItemsSource="{Binding FriendsOC}"
...
MainPage.xaml.cs --note the BindingContext here and not in xaml (refer .net Maui databinding to shell flyout item IsVisible property )
public MainPage()
{
InitializeComponent();
BindingContext = new CensusViewModel();
}
ViewModels.CensusViewModel.cs
public partial class CensusViewModel : ObservableObject
{
[ObservableProperty]
public ObservableCollection<Friend> friendsOC = new();
public CensusViewModel()
{
Console.WriteLine("heyupski G");
LoadData();
}
public async void LoadData() {
List<Friend> l = await App.Database.GetFriendsAsync();
foreach (Friend f in l)
{
FriendsOC.Add(f);
}
}
....
Database.Database.cs
public class Database
{
private readonly SQLiteAsyncConnection _database;
public Database(string dbPath)
{
_database = new SQLiteAsyncConnection(dbPath);
_database.CreateTableAsync<Friend>();
_database.CreateTableAsync<FSGroup>();
}
public Task<List<Friend>> GetFriendsAsync()
{
return _database.Table<Friend>().ToListAsync();
}
public Task<int> SaveFriendAsync(Friend friend)
{
return _database.InsertAsync(friend);
}
public Task<int> DeleteFriendAsync(Friend friend)
{
return _database.DeleteAsync(friend);
}
public Task<int> UpdateFriendAsync(Friend friend)
{
return _database.UpdateAsync(friend);
}
public Task<int> DeleteAllFriendsAsync() => _database.DeleteAllAsync<Friend>();
...
}
Classes.Friend.cs
public class Friend
{
[PrimaryKey, AutoIncrement]
public int Id { get; set; }
public string LName { get; set; }
public string FName { get; set; }
I think that's it.
Yet again I also ask the question: is there a definitive tutorial/explanation on binding and mvvm, because this is like climbing a slippery pole and I'm just hacking...
I'm working on a new project that uses CosmosDB and Entity Framework Core (via the Microsoft.EntityFrameworkCore.Cosmos NuGet package, version 5.0.7; the project itself is .NET Core 5). I'm new to both, and running into an issue I can't sort out.
In short, I need to save a complex object to the database. It's a big model that will have multiple collections of classes underneath it, each with their own properties and some with collections underneath them as well. I'm trying to configure EF with OwnsOne and OwnsMany to store these child objects underneath the top-level one. The code compiles, and will save to the database so long as all the owned objects are left empty. But whenever I put anything into an owned object, either with OwnsOne or OwnsMany, I get a pair of NullReferenceExceptions.
I've tried to strip my code down to the very basics. Here's how it currently looks.
Owner and owned classes:
public class Questionnaire
{
// Constructors
private Questionnaire() { }
public Questionnaire(Guid id)
{
Test = "Test property.";
TV = new TestQ();
Id = id;
}
public Guid Id { get; set; }
public string Test { get; set; }
public TestQ TV { get; set; }
// Public Methods
public void AddForm(Form f)
{
// not currently using this method
//Forms.Add(f);
}
}
public class TestQ
{
public TestQ()
{
TestValue = "test ownsone value";
}
public string TestValue { get; set; }
}
DbContext:
public class QuestionnaireDbContext : DbContext
{
public DbSet<Questionnaire> Questionnaires { get; set; }
public QuestionnaireDbContext(DbContextOptions<QuestionnaireDbContext> options) : base(options) { }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.HasDefaultContainer(nameof(Questionnaires));
modelBuilder.Entity<Questionnaire>().HasKey(q => q.Id);
modelBuilder.Entity<Questionnaire>().OwnsOne(q => q.TV);
}
}
And the code from the service that calls the dbContext (note that this is based on a generic service that I didn't set up originally). The actual exceptions are thrown here.
public virtual TEntity Add(TEntity entity)
{
_context.Entry(entity).State = EntityState.Added;
_context.SaveChanges();
return entity;
}
Ultimately I need this to work with OwnsMany and a collection, but I figured it might be simpler to get it working with OwnsOne first. The key thing to note here is that if I comment out the line
TV = new TestQ();
in the Questionnaire class, the model persists correctly into CosmosDB. It's only when I actually instantiate an owned entity that I get the NullReferenceExceptions.
Any advice would be much appreciated! Thank you!
Well, I'm not sure why this is the case, but the issue turned out to be with how we were adding the document. Using this generic code:
public virtual async Task<TEntity> Add(TEntity entity)
{
_context.Entry(entity).State = EntityState.Added;
await _context.SaveChanges();
return entity;
}
was the issue. It works just fine if I use the actual QuestionnaireDbContext class like so:
context.Add(questionnaire);
await context.SaveChangesAsync();
Im using asp.net core. Here is the basic way to use model with controller.
public class BookController : Controller
{
private readonly ApplicationDbContext _context { get; set; }
public BookController(ApplicationDbContext context)
{
_context = context;
}
public IActionResult Create(Book model)
{
// adding new model
}
public IActionResult Edit(Book model)
{
// modifying the model
}
public IActionResult Delete(Book model)
{
// removing the model
}
}
My question: when shall/should I implement the code inside the controller? When shall/should I implement it in another class?
Something like this:
public interface IBook
{
int Add(Book book);
int Update(Book book);
int Remove(Book book);
}
public class BookData : IBook
{
private readonly ApplicationDbContext _context { get; set; }
BookData(ApplicationDbContext context)
{
_context = context
}
public int Add(Book model)
{
// ...
return _context.SaveChanges();
}
// other implements...
}
Then, calling it inside controller:
public IActionResult Create(Book model)
{
var bookData = new BookData(_context);
int result = bookData.Add(model);
// ...
}
For the interface, I think it may be useful for the case: I have many controllers that require same action/method names.
Example: MessageController requires 3 actions/methods at least (Create/Add, Edit/Update, Delete/Remove). It's same to NotificationController class, CommentController class...
So, the interface can be improved to:
public interface IMyService<T> where T : class
{
int Add(T model);
int Update(T model);
int Remove(T model);
}
public class MyService<T> : IMyService<T> where T : class
{
private readonly ApplicationDbContext _context { get; set; }
public MyService(ApplicationDbContext context)
{
_context = context;
}
public int Add(T model)
{
Type type = typeof(model);
if (type == typeof(Book))
{
// adding new book model
}
else if (type == typeof(Comment))
{
// adding new comment model
}
// ...
return -1;
}
// other implements...
}
Do I misunderstand something?
If I read it correctly with data classes you actually means repository (which is an abstraction over the persistence layer). You should always encapsulate persistence logic behind a class (be it via repository pattern, command/query pattern or request handler) and use it instead of directly using the context in your service classes.
That being said, you can directly inject your BookData to your controller instead of the ApplicationDbContext. One thing you should consider you lose in your current implementation is the Unit of Work pattern. Right now, every add will instantly persist the data.
This may not be what you want, so you should move the _context.SaveChanges(); outside of the Add/Remove/Update methods and call it explicitly. This allows you to insert i.e. 10 records and if one of them fails, nothing will be persisted to the database.
But if you call _context.SaveChanges(); after each insert and you get an error in the 8th (of 10) records, then 7 get persisted and 3 will be missing and you get inconsistent data.
Controller shouldn't contain any logic at all, only do short validation of the input model (ModelState.IsValid check) and if its okay, call the services which do all the logic and report the result back to the user. Only in very simple tutorials and guides logic is put into the controller action for reasons of simplicity. In real world applications you should never do that. Controllers are much harder to unit test than service classes.
Rather simple question regarding entity framework and how to consume the objectcontext.
In a asp.net webform application I am implementing most of data getters in a data class and trying to determine if its better (in a generic sense of better) to have a private context for the entire class or declare a context in each of the methods.
Example 1:
public class Data
{
private MyEntity context = new MyEntity();
public Customer GetCustomer()
{
return context.Customer.Single();
}
public Order GetOrder()
{
return context.Order.Single();
}
}
Or Example 2:
public class Data
{
public Customer GetCustomer()
{
using (MyEntity ctx = new MyEntity())
{
return context.Customer.Single();
}
}
public Order GetOrder()
{
using (MyEntity ctx = new MyEntity())
{
return context.Order.Single();
}
}
}
Personally im a big fan of using a shared context across your whole post back, however neither of these scenarios really achieve this. My personal preference is to use a dependency injection container such as ninject to manage the lifecycle of your EF context. This means that you can make your whole postback transactional.
in terms of implementation I would go for soemthing like the following:
public class Data
{
private MyContext _context;
public Data(MyContext context)
{
_context = context;
}
public Customer GetCustomer()
{
return _context.Customer.Single();
}
public Order GetOrder()
{
return _context.Order.Single();
}
}
with a binding similar to:
Bind<MyContext>().ToSelf().InRequestScope();
I am going though the Apress ASP.NET MVC 3 book and trying to ensure I create Unit Tests for everything possible but after spending a good part of a day trying to work out why edit's wouldn't save (see this SO question) I wanted to create a unit test for this.
I have worked out that I need to create a unit test for the following class:
public class EFProductRepository : IProductRepository {
private EFDbContext context = new EFDbContext();
public IQueryable<Product> Products {
get { return context.Products; }
}
public void SaveProduct(Product product) {
if (product.ProductID == 0) {
context.Products.Add(product);
}
context.SaveChanges();
}
public void DeleteProduct(Product product) {
context.Products.Remove(product);
context.SaveChanges();
}
}
public class EFDbContext : DbContext {
public DbSet<Product> Products { get; set; }
}
I am using Ninject.MVC3 and Moq and have created several unit tests before (while working though the previously mentioned book) so am slowly getting my head around it. I have already (hopefully correctly) created a constructor method to enable me to pass in _context:
public class EFProductRepository : IProductRepository {
private EFDbContext _context;
// constructor
public EFProductRepository(EFDbContext context) {
_context = context;
}
public IQueryable<Product> Products {
get { return _context.Products; }
}
public void SaveProduct(Product product) {
if (product.ProductID == 0) {
_context.Products.Add(product);
} else {
_context.Entry(product).State = EntityState.Modified;
}
_context.SaveChanges();
}
public void DeleteProduct(Product product) {
_context.Products.Remove(product);
_context.SaveChanges();
}
}
BUT this is where I start to have trouble... I believe I need to create an Interface for EFDbContext (see below) so I can replace it with a mock repo for the tests BUT it is built on the class DbContext:
public class EFDbContext : DbContext {
public DbSet<Product> Products { get; set; }
}
from System.Data.Entity and I can't for the life of me work out how to create an interface for it... If I create the following interface I get errors due to lack of the method .SaveChanges() which is from the DbContext class and I can't build the interface using "DbContext" like the `EFDbContext is as it's a class not an interface...
using System;
using System.Data.Entity;
using SportsStore.Domain.Entities;
namespace SportsStore.Domain.Concrete {
interface IEFDbContext {
DbSet<Product> Products { get; set; }
}
}
The original Source can be got from the "Source Code/Downloads" on this page encase I have missed something in the above code fragments (or just ask and I will add it).
I have hit the limit of what I understand and no mater what I search for or read I can't seem to work out how I get past this. Please help!
The problem here is that you have not abstracted enough. The point of abstractions/interfaces is to define a contract that exposes behavior in a technology-agnostic way.
In other words, it is a good first step that you created an interface for the EFDbContext, but that interface is still tied to the concrete implementation - DbSet (DbSet).
The quick fix for this is to expose this property as IDbSet instead of DbSet. Ideally you expose something even more abstract like IQueryable (though this doesn't give you the Add() methods, etc.). The more abstract, the easier it is to mock.
Then, you're left with fulfilling the rest of the "contract" that you rely on - namely the SaveChanges() method.
Your updated code would look like this:
public class EFProductRepository : IProductRepository {
private IEFDbContext context;
public EFProductRepository(IEFDbContext context) {
this.context = context;
}
...
}
public interface IEFDbContext {
IDbSet<Product> Products { get; set; }
void SaveChanges();
}
BUT... the main question you have to ask is: what are you trying to test (conversely, what are you trying to mock out/avoid testing)? In other words: are you trying to validate how your application works when something is saved, or are you testing the actual saving.
If you're just testing how your application works and don't care about actually saving to the database, I'd consider mocking at a higher level - the IProductRepository. Then you're not hitting the database at all.
If you want to make sure that your objects actually get persisted to the database, then you should be hitting the DbContext and don't want to mock that part after all.
Personally, I consider both of those scenarios to be different - and equally important - and I write separate tests for each of them: one to test that my application does what it's supposed to do, and another to test that the database interaction works.
I guess your current code looks something like this (I put in the interface):
public class EFProductRepository : IProductRepository {
private IEFDbContext _context;
// constructor
public EFProductRepository(IEFDbContext context) {
_context = context;
}
public IQueryable<Product> Products {
get { return _context.Products; }
}
public void SaveProduct(Product product) {
if (product.ProductID == 0) {
_context.Products.Add(product);
} else {
_context.Entry(product).State = EntityState.Modified;
}
**_context.SaveChanges();**
}
public void DeleteProduct(Product product) {
_context.Products.Remove(product);
**_context.SaveChanges();**
}
}
public class EFDbContext : DbContext, IEFDbContext {
public DbSet<Product> Products { get; set; }
}
public interface IEFDbContext {
DbSet<Product> Products { get; set; }
}
The problem is EFProductRepository now expects an object implementing the IEFDbContext interface, but this interface does not define the SaveChanges method used at the lines I put between the asteriskes so the compiler starts complaining.
Defining the SaveChanges method on the IEFDbContext interface solves your problem:
public interface IEFDbContext {
DbSet<Product> Products { get; set; }
void SaveChanges();
}