Table of Contents

BLAZMVVM0013: MvvmOwningComponentBase Usage Analyzer

Diagnostic Information

  • Diagnostic ID: BLAZMVVM0013
  • Category: Blazing.Mvvm
  • Severity: Warning
  • Title: Component should use MvvmOwningComponentBase for scoped services

Description

This analyzer detects when a Blazor component uses MvvmComponentBase<TViewModel> but the ViewModel depends on scoped services (such as Entity Framework DbContext). In such cases, the component should inherit from MvvmOwningComponentBase<TViewModel> instead to create a service scope and ensure proper lifetime management of scoped dependencies.

Problem

When a ViewModel injects scoped services like DbContext, using the standard MvvmComponentBase can lead to:

  1. Shared DbContext instances across multiple components
  2. Connection leaks and resource exhaustion
  3. Thread safety issues with concurrent database operations
  4. Stale data due to long-lived contexts

Solution

Use MvvmOwningComponentBase<TViewModel> which creates a dedicated service scope for the component and its ViewModel, ensuring:

  • Each component instance gets its own scoped service instances
  • Proper disposal of scoped services when the component is disposed
  • Thread-safe database operations
  • Fresh data for each component render

Examples

❌ Incorrect (Using MvvmComponentBase with scoped services)

// ViewModel with DbContext dependency
public class ProductsViewModel : ViewModelBase
{
    private readonly MyDbContext _context;

    public ProductsViewModel(MyDbContext context) // Scoped service
    {
        _context = context;
    }

    public async Task<List<Product>> GetProductsAsync()
    {
        return await _context.Products.ToListAsync();
    }
}

// View - INCORRECT: Should use MvvmOwningComponentBase
@page "/products"
@inherits MvvmComponentBase<ProductsViewModel> // ⚠️ Warning BLAZMVVM0013

<h3>Products</h3>

✅ Correct (Using MvvmOwningComponentBase)

// ViewModel with DbContext dependency
public class ProductsViewModel : ViewModelBase
{
    private readonly MyDbContext _context;

    public ProductsViewModel(MyDbContext context)
    {
        _context = context;
    }

    public async Task<List<Product>> GetProductsAsync()
    {
        return await _context.Products.ToListAsync();
    }
}

// View - CORRECT: Uses MvvmOwningComponentBase
@page "/products"
@inherits MvvmOwningComponentBase<ProductsViewModel> // ✅ Correct

<h3>Products</h3>

Common Scoped Services

The analyzer detects these common scoped service patterns:

  • Entity Framework Core: DbContext, Database, DbConnection
  • Database connections: IDbConnection, SqlConnection, MySqlConnection
  • Unit of Work pattern: Interfaces/classes containing "UnitOfWork", "Repository"
  • Custom scoped services: Services registered with ServiceLifetime.Scoped

When to Use Each Base Class

Scenario Base Class Reason
ViewModel uses only transient/singleton services MvvmComponentBase No service scope needed
ViewModel injects DbContext or database connections MvvmOwningComponentBase Creates owned scope for proper disposal
ViewModel uses scoped services MvvmOwningComponentBase Ensures proper service lifetime
No ViewModel ComponentBase Standard Blazor component

Service Registration Example

// Program.cs or Startup.cs
builder.Services.AddDbContext<MyDbContext>(options =>
    options.UseSqlServer(connectionString)); // Registered as SCOPED by default

// ViewModels
builder.Services.AddBlazingMvvm(options =>
{
    options.HostAssembly = typeof(Program).Assembly;
});

Benefits of MvvmOwningComponentBase

  1. Automatic scope management: Creates and disposes service scope automatically
  2. Thread safety: Each component gets its own DbContext instance
  3. Memory management: Scoped services are disposed when component is disposed
  4. Best practice compliance: Follows Microsoft's recommendations for scoped services in Blazor

Additional Resources

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