如何使用Web api2在ASP.NET MVC中制作异步和等待方法

Question

I'm newly to the ASP.NET MVC with Web API 2 and I created async and await method by using asp.net MVC with Web API 2 which is going to be store into the SQL DB. When I try to call my repository method in the API Controller I got an error cannot await ”system.collections.generic.list”. If anybody has idea about it kindly let me know.

 Model: namespace AsyncMVCWEBAPI.Models { public class Product { public string Name { get; set; } public double Price { get; set; } public string Category { get; set; } } } API Controller: public static async Task<Product> GetProduct() { return await GetAllProduct(); // Here i'm getting an error can not await "system.collections.generic.list" } Repository: public static IEnumerable<Product> GetAllProduct() { using (SqlConnection con = new SqlConnection(connectionString)) { if (con.State == ConnectionState.Closed) con.Open(); List<Product> students = new List<Product>(); SqlCommand cmd = new SqlCommand("spGetAllStudentDetails", con); cmd.CommandType = CommandType.StoredProcedure; SqlDataReader rdr = cmd.ExecuteReader(); while (rdr.Read()) { Product product = new Product(); product.Price = Convert.ToInt32(rdr["Price"]); product.Name = rdr["Name"].ToString(); product.Category = rdr["Category"].ToString(); students.Add(product); } return students; } } 

Answer 1

The main problem is that you can't await a method that is not async. You should rewrite your GetAllProduct method to make it async with the following signature:

public static async Task<IEnumerable<Product>> GetAllProduct()

Also don't forget to use Async methods to get your data from database:

    ...
    await con.OpenAsync();
    ...
    SqlDataReader rdr = await cmd.ExecuteReaderAsync();
    while (await rdr.ReadAsync())
    {
        ...
        students.Add(product);
    }
    return students;

Answer 2

As the previous answer said you have to change your signature to:

public static async Task<IEnumerable<Product>> GetAllProduct()

If you want to skip the ADO.NET boilerplate stuff, you can instead use Dapper ( https://github.com/StackExchange/dapper-dot-net ) to simplify the code:

public static async Task<IEnumerable<Product>> GetAllProduct()
{
    using (var con = new SqlConnection(connectionString))
    {
        await con.OpenAsync();
        return await con.QueryAsync<Product>("spGetAllStudentDetails", commandType: CommandType.StoredProcedure);
    }
}