There is a better IDbContextFactory interface: ASP.NET Core Blazor Server with Entity Framework Core (EFCore)

Prerequisites: normal configuration for ASP.NET Core to connect a database.

Models > ToDo.cs

public class ToDo
{
    [Key]
    public int Id { get; set; }

    [Required]
    public string Content { get; set; }
    public bool IsDone { get; set; }
}

 Interfaces > IToDoService.cs

public interface IToDoService
{
    public Task<List<ToDo>> GetAsync();
    public Task<ToDo> GetAsync(int id);
    public Task CreateAsync(ToDo todo);
    public Task DeleteAsync(int id);
}

Services > ToDoService.cs

public class ToDoService : IToDoService
{
    public ToDoService(ApplicationDbContext context)
    {
        _context = context;
    }

    private ApplicationDbContext _context { get; }

    public async Task<List<ToDo>> GetAsync()
    {
        var todos = await _context.ToDos
            .OrderBy(x => x.Id)
            .ToListAsync();

        return todos;
    }

    public async Task<ToDo> GetAsync(int id)
    {
        var todo = await _context.ToDos.FindAsync(id);

        if (todo is null)
        {
            return null;
        }
        else
        {
            return todo;
        }
    }

    public async Task CreateAsync(ToDo todo)
    {
        await _context.ToDos.AddAsync(todo);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(int id)
    {
        var todo = await _context.ToDos.FindAsync(id);
        if (todo is not null)
        {
            _context.ToDos.Remove(todo);
            await _context.SaveChangesAsync();
        }
    }
}

Program.cs

builder.Services.AddScoped<IToDoService, ToDoService>();

Pages > ToDo.razor

@page "/todo"
@inject IToDoService ToDoService

<h3>ToDo</h3>

@if (todos is null)
{
    <p>Loading...</p>
}
else
{
<ul class="list-group">
    @foreach (var todo in todos)
    {
        <li class="list-group-item" @key="todo.Id">
            <span>@todo.Content</span>
            <button class="btn btn-outline-danger btn-sm" @onclick="@(() => Delete(todo.Id))">Delete</button>
        </li>
    }
</ul>
}

<div class="input-group mt-3">
    <input type="text" class="form-control" placeholder="New todo" @bind="nextTodo">
    <button class="btn btn-outline-primary" type="button" @onclick="Add" disabled="@adding">@(adding ? "adding..." : "Add New")</button>
</div>


@code {
    List<blazorserver.Models.ToDo> todos;
    string nextTodo;
    bool adding;

    protected override async Task OnInitializedAsync()
    {
        await Get();
    }

    async Task Get()
    {
        todos = await ToDoService.GetAsync();
    }

    async Task Add()
    {
        if (!string.IsNullOrWhiteSpace(nextTodo.Trim()))
        {
            var next = new blazorserver.Models.ToDo
            {
                Content = nextTodo.Trim(),
            };

            adding = true;
            await ToDoService.CreateAsync(next);
            nextTodo = string.Empty;
            adding = false;
            await Get();
        }
    }

    async Task Delete(int id)
    {
        await ToDoService.DeleteAsync(id);
        await Get();
    }
}