C#•9mo ago

Why does using `await` EF core execute command twice

I am using Blazor server app and add EF Core

public class UserAccountService(AppDBContext context) : ControllerBase, IUserAccountService
{
    private readonly AppDBContext _context = context;
    [HttpGet]
    public async Task<IEnumerable<UserAccountModel>> GetAccounts()
    {
        return await _context.Accounts.ToListAsync();
    }
}

public class UserAccountService(AppDBContext context) : ControllerBase, IUserAccountService
{
    private readonly AppDBContext _context = context;
    [HttpGet]
    public async Task<IEnumerable<UserAccountModel>> GetAccounts()
    {
        return await _context.Accounts.ToListAsync();
    }
}

Dependency

builder.Services.AddScoped<IUserAccountService, UserAccountService>();

builder.Services.AddScoped<IUserAccountService, UserAccountService>();

Here is the code where query executes twice

protected override async Task OnInitializedAsync()
{
    var response = await UserAccountService.GetAccounts();
    if (response != null)
    {
        accounts = response.ToList();
        Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(accounts, Newtonsoft.Json.Formatting.Indented));
    }
    else
    {
       
    }

}

protected override async Task OnInitializedAsync()
{
    var response = await UserAccountService.GetAccounts();
    if (response != null)
    {
        accounts = response.ToList();
        Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(accounts, Newtonsoft.Json.Formatting.Indented));
    }
    else
    {
       
    }

}

10 Replies

Jimmacle•9mo ago

how do you know that it's executing twice and that that's the reason?

xyrileOP•9mo ago

i see it in the console

Jimmacle•9mo ago

have you set a breakpoint on that call to make sure you aren't just calling it twice? also, i'd just make that service return a list to avoid the double ToList or just don't tolist it, i don't think that's a requirement for json serialization

xyrileOP•9mo ago

xyrileOP•9mo ago

this behaviour only occurs in OnInitializedAsync()

D.Mentia•9mo ago

https://stackoverflow.com/questions/58075628/why-are-blazor-lifecycle-methods-getting-executed-twice

Stack Overflow

Why are Blazor lifecycle methods getting executed twice?

So with a release of asp.net core 3.0 and blazor 1.0 I started doing some actual work with blazor. When splitting Blazor component code into code behind I am using the following public class Logout...

D.Mentia•9mo ago

tldr, prerendering, be careful about which methods you put your logic in

D.Mentia•9mo ago

https://learn.microsoft.com/en-us/aspnet/core/blazor/components/lifecycle?view=aspnetcore-8.0#component-initialization-oninitializedasync

ASP.NET Core Razor component lifecycle

Learn about the ASP.NET Core Razor component lifecycle and how to use lifecycle events.

D.Mentia•9mo ago

To prevent developer code in OnInitializedAsync from running twice when prerendering, see the Stateful reconnection after prerendering section. The content in the section focuses on Blazor Web Apps and stateful SignalR reconnection. To preserve state during the execution of initialization code while prerendering, see Prerender ASP.NET Core Razor components.

but tbh I thought it was that it renders once from the server, and then once for the client, even on blazor server

xyrileOP•9mo ago

yep this one fix my problem by changting this

<component type="typeof(App)" render-mode="ServerPrerendered" />

<component type="typeof(App)" render-mode="ServerPrerendered" />

to this

<component type="typeof(App)" render-mode="Server" />

<component type="typeof(App)" render-mode="Server" />

Gaming

Programming

Why does using `await` EF core execute command twice