Binding a Dropdown List in ASP.NET Core with EF Core and Azure Managed Identity

The Problem

Developers often need to populate dropdown lists dynamically from a database in ASP.NET Core applications. The challenge is to do this securely and efficiently, avoiding hardcoded connection strings and ensuring the solution is production-ready with Azure best practices.

Prerequisites

• .NET 8 SDK installed
• Azure CLI configured
• Azure SQL Database with Managed Identity enabled
• Visual Studio Code or IDE of choice

The Solution (Step-by-Step)

Step 1: Configure Azure Managed Identity and RBAC

Assign your App Service or Azure Function a System-Assigned Managed Identity. Then, grant the identity the Azure SQL Database Contributor role or a custom role with least privilege to access the database.

Step 2: Configure EF Core with DefaultAzureCredential

using Azure.Identity; // For DefaultAzureCredential
using Microsoft.EntityFrameworkCore;

var builder = WebApplication.CreateBuilder(args);

// Use DefaultAzureCredential for Managed Identity authentication
var credential = new DefaultAzureCredential();
var connectionString = builder.Configuration["AZURE_SQL_CONNECTION_STRING"];

builder.Services.AddDbContext<AppDbContext>(options =>
{
    options.UseSqlServer(connectionString, sqlOptions =>
    {
        sqlOptions.EnableRetryOnFailure(); // Resiliency for transient faults
    });
});

var app = builder.Build();
app.Run();

Explanation: We use DefaultAzureCredential to authenticate via Managed Identity, avoiding hardcoded secrets. The connection string should reference the server and database but omit credentials.

Step 3: Create the Model and DbContext

public class Category
{
    public int Id { get; set; }
    public string Name { get; set; } = string.Empty;
}

public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
{
    public DbSet<Category> Categories => Set<Category>();
}

Explanation: The Category entity represents the dropdown data source.

Step 4: Implement the Controller Action

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;

[ApiController]
[Route("api/[controller]")]
public class CategoriesController(AppDbContext context) : ControllerBase
{
    [HttpGet("dropdown")]
    public IActionResult GetDropdown()
    {
        // Fetch categories without tracking for performance
        var categories = context.Categories.AsNoTracking()
            .Select(c => new SelectListItem
            {
                Value = c.Id.ToString(),
                Text = c.Name
            }).ToList();

        return Ok(categories);
    }
}

Explanation: The action retrieves categories and maps them to SelectListItem for dropdown binding. AsNoTracking() improves performance for read-only queries.

Step 5: Bind in Razor View

@model YourViewModel

<select asp-for="SelectedCategoryId" asp-items="Model.Categories"></select>

Explanation: The Razor view uses asp-items to bind the dropdown list.

Best Practices & Security

• Use Managed Identity with DefaultAzureCredential instead of storing credentials in code or configuration files.
• Apply the Principle of Least Privilege by assigning only necessary RBAC roles like Azure SQL Database Contributor.
• Validate user input in controllers to prevent injection attacks.
• Use AsNoTracking() for read-only queries to improve performance.

Summary

• Bind dropdown lists using EF Core and strongly typed models.
• Secure database access with Azure Managed Identity and RBAC roles.
• Follow best practices for performance and security in production.