如何在异步中使用FirstOrDefaultAsync（）等待Web API

Question

I have created one .NET Core API , where my all methods are asynchronous but there is one requirement like GetBalance() which just return one entity (record) only.

I am not able to using SingleOrDefaultAsync() , getting error like does not contain a definition for this.

I am using simple basic EF Code First approach with no Repository pattern.

Here is my code example.

public async Task<ResponseBalanceModel> GetBalanceFor(int accountNumber)
{
    var result = await _dbContext.Accounts.Where(x => 
             x.AccountNumber == accountNumber)
             .SingleOrDefaultAsync(); // this is not working.

    /*Below tried code are not working. 
    var result1 = await _dbContext.Accounts.Where(x => x.AccountNumber == accountNumber).SingleOrDefaultAsync();

    var result2 = await _dbContext.Accounts.FirstOrDefaultAsync(x => x.AccountNumber == accountNumber);
    */
 }

For more clarification

Reference of Entityframework in my project. (.NET Core)

Answer 1

Got the solution just installed!

Install-Package Microsoft.EntityFrameworkCore.Tools in my .net core project and it start working... Thank you all guys for your comments.

Reason :

1. System.Linq namespace does support ToListAsync(), ToAsyncEnumerable(), and FindAsync() and SaveChangesAsync()

2. To work with FirstOrDefaultAsync() and SingleOrDefaultAsync() method we have to install this package.

Thanks again.

Answer 2

The EF Core async extension methods are defined in the Microsoft.EntityFrameworkCore namespace. This namespace must be imported for the methods to be available.