Bwfc Data Migration

Session State Migration

Use SessionShim (Default — Works Everywhere)

Pages inheriting WebFormsPageBase get a Session property backed by SessionShim. SessionShim works in BOTH SSR and interactive modes:

• SSR: Reads/writes to ASP.NET Core ISession (cookie-backed)
• Interactive: Uses in-memory ConcurrentDictionary scoped per circuit

Original Web Forms:

Session["CartId"] = Guid.NewGuid().ToString();
var cartId = Session["CartId"].ToString();
Session["payment_amt"] = 99.99m;

Migrated Blazor (IDENTICAL):

Session["CartId"] = Guid.NewGuid().ToString();
var cartId = Session["CartId"].ToString();
Session["payment_amt"] = 99.99m;

No IHttpContextAccessor. No Minimal API. No cookies. Just Session["key"].

For non-page components, inject SessionShim directly:

@inject SessionShim Session

@code {
    protected override void OnInitialized()
    {
        var userId = Session["UserId"]?.ToString() ?? "guest";
    }
}

When to Upgrade Beyond SessionShim

Only consider alternatives when you need cross-tab or cross-server persistence:

ProtectedBrowserStorage — For data that must survive page refreshes:

@inject ProtectedSessionStorage SessionStorage

protected override async Task OnAfterRenderAsync(bool firstRender)
{
    if (firstRender)
    {
        var result = await SessionStorage.GetAsync<ShoppingCart>("cart");
        cart = result.Success ? result.Value! : new ShoppingCart();
    }
}

Database-backed — For shopping carts that persist across sessions:

public class CartService(IDbContextFactory<AppDbContext> factory)
{
    public async Task<Cart> GetCartAsync(string userId)
    {
        using var db = factory.CreateDbContext();
        return await db.Carts
            .Include(c => c.Items)
            .FirstOrDefaultAsync(c => c.UserId == userId) ?? new Cart();
    }
}

Scoped services — When the pattern doesn't fit key-value storage:

public class WizardStateService
{
    public int CurrentStep { get; set; }
    public FormData Data { get; set; } = new();
    public bool IsComplete => CurrentStep == 5 && Data.IsValid();
}

// Program.cs
builder.Services.AddScoped<WizardStateService>();

Progression model:

1. Start with SessionShim (zero migration cost)
2. Move to scoped services if you need typed, structured state
3. Move to database if you need persistence across circuits/sessions

1. Entity Framework 6 → EF Core

Web Forms: EF6 with DbContext instantiated directly in code-behind or via SelectMethod string binding. Blazor: EF Core 10.0.3 (latest .NET 10) with IDbContextFactory registered in DI.

Step 1: Detect the provider. The L1 script's Find-DatabaseProvider function reads Web.config <connectionStrings> and scaffolds the correct EF Core package. Check the L1 output's [DatabaseProvider] review item for the detected provider and connection string. Use these values in your Program.cs configuration — do not guess or substitute.

CRITICAL: Preserve the original database provider. Examine the Web Forms project's Web.config connection strings and EF configuration to identify the database provider (SQL Server, PostgreSQL, MySQL, SQLite, Oracle, etc.). The migrated Blazor application MUST use the same database provider — do NOT switch providers unless explicitly requested by the user.

⚠️ NEVER default to SQLite. The most common Web Forms database is SQL Server (often LocalDB for dev). If you see System.Data.SqlClient or (LocalDB) in connection strings, use Microsoft.EntityFrameworkCore.SqlServer — NOT Microsoft.EntityFrameworkCore.Sqlite. SQLite is ONLY appropriate if the original application specifically used System.Data.SQLite.

Database Provider Detection & Migration

Step 1: Identify the original provider from the Web Forms project:

Step 2: Install the matching EF Core provider package in the Blazor project:

# Example for SQL Server
dotnet add package Microsoft.EntityFrameworkCore.SqlServer --version 10.0.3

# Example for PostgreSQL
dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL --version 10.0.3

# Example for MySQL (Pomelo)
dotnet add package Pomelo.EntityFrameworkCore.MySql --version 10.0.3

Step 3: Configure the matching provider in Program.cs:

// SQL Server — matches System.Data.SqlClient
options.UseSqlServer(connectionString)

// PostgreSQL — matches Npgsql
options.UseNpgsql(connectionString)

// MySQL — matches MySql.Data.MySqlClient
options.UseMySql(connectionString, ServerVersion.AutoDetect(connectionString))

// SQLite — matches System.Data.SQLite
options.UseSqlite(connectionString)

Install matching EF Core packages for .NET 10: Microsoft.EntityFrameworkCore, the provider-specific package (see table above), .Tools, and .Design.

// Web Forms — direct DbContext in code-behind
public IQueryable<Product> GetProducts()
{
    var db = new ProductContext();
    return db.Products;
}

// Blazor — Program.cs (use the provider that matches the original Web Forms database)
builder.Services.AddDbContextFactory<ProductContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
    // ↑ Replace with UseNpgsql(), UseMySql(), UseSqlite(), etc. to match original provider

// Blazor — Service layer
public class ProductService(IDbContextFactory<ProductContext> factory)
{
    public async Task<List<Product>> GetProductsAsync()
    {
        using var db = factory.CreateDbContext();
        return await db.Products.ToListAsync();
    }

    public async Task<Product?> GetProductAsync(int id)
    {
        using var db = factory.CreateDbContext();
        return await db.Products.FindAsync(id);
    }
}

Critical: Use IDbContextFactory, NOT AddDbContext, for Blazor Server. Blazor circuits are long-lived — a single DbContext accumulates stale data and tracking issues.

EF6 → EF Core API Changes

Connection String Migration

<!-- Web Forms — Web.config -->
<connectionStrings>
  <add name="DefaultConnection"
       connectionString="Data Source=(LocalDb)\MSSQLLocalDB;Initial Catalog=MyApp;Integrated Security=True"
       providerName="System.Data.SqlClient" />
</connectionStrings>

// Blazor — appsettings.json
{
  "ConnectionStrings": {
    "DefaultConnection": "Data Source=(LocalDb)\\MSSQLLocalDB;Initial Catalog=MyApp;Integrated Security=True"
  }
}

2. DataSource Controls → Service Injection

Web Forms DataSource controls have no BWFC equivalent. Replace with injected services.

<!-- Web Forms — declarative data binding -->
<asp:SqlDataSource ID="ProductsDS" runat="server"
    ConnectionString="<%$ ConnectionStrings:DefaultConnection %>"
    SelectCommand="SELECT * FROM Products" />
<asp:GridView DataSourceID="ProductsDS" runat="server" />

@* Blazor — service injection *@
@inject IProductService ProductService

<GridView Items="products" ItemType="Product" AutoGenerateColumns="true" />

@code {
    private List<Product> products = new();

    protected override async Task OnInitializedAsync()
    {
        products = await ProductService.GetProductsAsync();
    }
}

Service Registration Pattern

// Program.cs — use the provider that matches the original Web Forms database
builder.Services.AddRazorComponents().AddInteractiveServerComponents();
builder.Services.AddBlazorWebFormsComponents(); // ⚠️ REQUIRED — registers BWFC services
builder.Services.AddDbContextFactory<ProductContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection")));
    // ↑ Match the original provider: UseNpgsql(), UseMySql(), UseSqlite(), etc.

builder.Services.AddScoped<IProductService, ProductService>();
builder.Services.AddScoped<ICategoryService, CategoryService>();
builder.Services.AddScoped<IOrderService, OrderService>();

// ... after builder.Build() ...
app.UseBlazorWebFormsComponents(); // ⚠️ REQUIRED — .aspx URL rewriting middleware. BEFORE MapRazorComponents.
app.MapRazorComponents<App>().AddInteractiveServerRenderMode();

SelectMethod String → SelectHandler Delegate Conversion

BWFC's DataBoundComponent<ItemType> has a native SelectMethod parameter of type SelectHandler<ItemType> — a delegate with signature (int maxRows, int startRowIndex, string sortByExpression, out int totalRowCount) → IQueryable<ItemType>. When set, OnAfterRenderAsync automatically calls it to populate Items. This is the native BWFC data-binding pattern that mirrors how Web Forms did it.

Option A — Preserve SelectMethod as delegate (recommended):

Option B — Items binding (ONLY when original used DataSource, NOT SelectMethod):

⚠️ Use Option B ONLY when the original Web Forms markup used DataSource/DataBind(), NOT when it used SelectMethod. If the original had SelectMethod="GetProducts", you MUST use Option A above.

CRUD methods (no BWFC parameter equivalent — wire to service calls in event handlers):

3. Session, ViewState, and Application State Migration

Web Forms: Session["key"], ViewState["key"], Application["key"] dictionaries. Blazor: SessionShim (auto-registered by AddBlazorWebFormsComponents()), component fields, and singleton services.

Session["key"] → SessionShim (Zero-Change Migration)

No code changes needed. WebFormsPageBase.Session delegates to SessionShim automatically:

// Web Forms — works IDENTICALLY in Blazor via SessionShim
Session["ShoppingCart"] = cart;
var cart = (ShoppingCart)Session["ShoppingCart"];

// SessionShim also supports typed access:
var cart = Session.Get<ShoppingCart>("ShoppingCart");
Session.Set("ShoppingCart", cart);

How SessionShim works:

• SSR mode: Backed by ASP.NET Core ISession (cookie-persisted)
• Interactive mode: In-memory ConcurrentDictionary scoped per circuit
• Seamless: Automatically switches based on render mode

For non-page components:

@inject SessionShim Session

@code {
    private string GetUserId() => Session["UserId"]?.ToString() ?? "guest";
}

ViewState["key"] → Component Fields

ViewState is component-instance state. Use normal C# fields/properties:

// Web Forms
ViewState["CurrentPage"] = pageIndex;
var page = (int)ViewState["CurrentPage"];

// Blazor
private int currentPage;

Application["key"] → Singleton Services

Application-wide state becomes singleton services:

// AppStateService.cs
public class AppStateService
{
    private readonly ConcurrentDictionary<string, object> _state = new();
    public void Set(string key, object value) => _state[key] = value;
    public T? Get<T>(string key) => _state.TryGetValue(key, out var val) ? (T)val : default;
}

// Program.cs
builder.Services.AddSingleton<AppStateService>();

State Storage Options

ProtectedSessionStorage Example

@inject ProtectedSessionStorage SessionStorage

@code {
    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            var result = await SessionStorage.GetAsync<ShoppingCart>("cart");
            cart = result.Success ? result.Value! : new ShoppingCart();
        }
    }

    private async Task SaveCart()
    {
        await SessionStorage.SetAsync("cart", cart);
    }
}

Note: ProtectedSessionStorage only works after the first render (it requires JS interop). Always check in OnAfterRenderAsync, not OnInitializedAsync.

Reference Documents

Architecture migration patterns (Global.asax, Web.config, routes, handlers, enhanced navigation) are in the child document:

• ARCHITECTURE-TRANSFORMS.md Global.asax → Program.cs, Web.config → appsettings.json, route table → @page directives, HTTP handlers/modules → middleware, third-party integrations → HttpClient, files to create during migration, and Blazor enhanced navigation workarounds.

Common Data Migration Gotchas

DbContext Lifetime — CRITICAL

Blazor Server circuits are long-lived. Always use IDbContextFactory and create short-lived DbContext instances per operation.

WRONG — IQueryable returned from disposed context:

private IQueryable<Product> GetProducts(int categoryId)
{
    using var db = DbFactory.CreateDbContext();
    return db.Products.Where(p => p.CategoryId == categoryId); // Context disposed before query executes!
}

RIGHT — materialize inside using block:

private IQueryable<Product> GetProducts(int categoryId)
{
    using var db = DbFactory.CreateDbContext();
    var results = db.Products
        .Where(p => p.CategoryId == categoryId)
        .ToList(); // Execute query NOW while context is alive
    return results.AsQueryable(); // Return materialized data as IQueryable
}

For SelectHandler delegates, the delegate is invoked by BWFC infrastructure AFTER your method returns. You MUST materialize:

// BWFC SelectHandler delegate — MUST materialize
private IQueryable<Product> SelectProducts(int maxRows, int startRowIndex, 
    string sortByExpression, out int totalRowCount)
{
    using var db = DbFactory.CreateDbContext();
    totalRowCount = db.Products.Count();
    
    var results = db.Products
        .OrderBy(p => p.Name)
        .Skip(startRowIndex)
        .Take(maxRows)
        .ToList(); // CRITICAL — materialize NOW
        
    return results.AsQueryable();
}

No Page-Level Transaction Scope

Web Forms SelectMethod runs inside a page lifecycle. Blazor doesn't have this. Use explicit transaction scopes in services if needed:

using var db = factory.CreateDbContext();
using var transaction = await db.Database.BeginTransactionAsync();
// ... operations
await transaction.CommitAsync();

Async All the Way

Web Forms SelectMethod returns IQueryable synchronously. Blazor services should be async:

// WRONG: return db.Products.ToList();
// RIGHT: return await db.Products.ToListAsync();

ConfigurationManager Shim Available

ConfigurationManager.AppSettings["key"] works via BWFC's ConfigurationManager shim. Call app.UseConfigurationManagerShim() in Program.cs to bind it to IConfiguration. For new code, prefer injecting IConfiguration or using the Options pattern.

Static Helpers with HttpContext

Web Forms often has static helper classes that access HttpContext.Current. These must be refactored to accept dependencies via constructor injection.

ThreadAbortException Dead Code Warning

Web Forms throws ThreadAbortException when Response.Redirect(url, true) is called with endResponse=true. Blazor does not throw this exception — ResponseShim.Redirect() silently ignores the endResponse parameter. Any catch (ThreadAbortException) blocks become dead code after migration. Review and remove them. Code that runs AFTER Response.Redirect(url, true) will execute in Blazor (unlike Web Forms where execution stopped).

❌ Common Anti-Patterns to Avoid

DO NOT Create Minimal API Endpoints for Page Actions

Minimal APIs are for real HTTP endpoints (REST APIs, webhooks), NOT for migrating Web Forms page actions.

WRONG:

// Program.cs — creating API endpoint for a page action
app.MapPost("/api/cart/add", async (CartItem item, CartService cart) =>
{
    cart.Add(item);
    return Results.Ok();
});

// Cart.razor — calling the API
await Http.PostAsJsonAsync("/api/cart/add", item);

RIGHT:

// Cart.razor — just call the service directly
@inject CartService CartService

<button @onclick="() => CartService.Add(item)">Add to Cart</button>

When Minimal APIs ARE appropriate:

• External REST API consumed by mobile apps, SPAs, or third parties
• Webhooks from payment processors, GitHub, etc.
• Form POST endpoints for authentication (login/logout/register) — these need HTTP context for cookies

When they are NOT appropriate:

• Replacing button click handlers in migrated Web Forms pages
• Working around Session["key"] access — use SessionShim instead
• "Because HttpContext is null" — you don't need HttpContext for most operations

DO NOT Use IHttpContextAccessor to Access Session

You already have Session via WebFormsPageBase or @inject SessionShim.

WRONG:

@inject IHttpContextAccessor HttpContextAccessor

var session = HttpContextAccessor.HttpContext?.Session;
var cartId = session?.GetString("CartId");

RIGHT:

@inherits WebFormsPageBase

var cartId = Session["CartId"]?.ToString();

DO NOT Replace Session with Cookies

If the original Web Forms code used Session["key"], use SessionShim. Don't invent cookie-based workarounds.

WRONG:

// Creating cookie-based cart ID because "Session doesn't work in Blazor"
Response.Cookies.Append("CartId", Guid.NewGuid().ToString());
var cartId = Request.Cookies["CartId"];

RIGHT:

// SessionShim handles the storage — just use Session
Session["CartId"] = Guid.NewGuid().ToString();
var cartId = Session["CartId"]?.ToString();

DO NOT Use HttpContext.Current.Session

There is no HttpContext.Current in ASP.NET Core. Use the Session property.

WRONG:

HttpContext.Current.Session["UserId"] = userId;

RIGHT:

Session["UserId"] = userId; // From WebFormsPageBase or injected SessionShim