Home EF Core async LINQ Where(predicate).ToListAsync() Error: CS1061 IEnumerable does not contain ToListAsync()

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EF Core async LINQ Where(predicate).ToListAsync() Error: CS1061 IEnumerable does not contain ToListAsync()

May 14, 2023

So I have a context class EFCoreMContext with defined property EFCore.DBSet<AccessTime> AccessTime

public class EFCoreMContext : Microsoft.EntityFrameworkCore.DbContext
{
    public Microsoft.EntityFrameworkCore.DbSet<User> Users { get; set; }
    public Microsoft.EntityFrameworkCore.DbSet<AccessTime> AccessTime { get; set; }
    ...
}

Then I have a repository class CAccessTimeRepository

public class CAccessTimeRepository : IRepository<AccessTime>
{
    private EFCoreMContext db;

    public CAccessTimeRepository(EFCoreMContext context)
    {
        this.db = context;
    }
    ...

with async functions:

    public async Task<IEnumerable<AccessTime>> FindAsync(Func<AccessTime, bool> predicate)
    {
        return await db.AccessTime.Where(predicate).ToListAsync();
    }
    ...
}

The trouble is when I try to use this ToListAsync() – Visual Studio highlights it with an error

CS1061 IEnumerable does not contain ToListAsync()

The thing is when I use .Where() with something like this

.Where(x => x.ID == 1)

it returns an IQueryable, so I can use ToListAsync(). But when I use this method with my predicate, it returns IEnumerable.

So deal with it I try to pass this code with an AsQueryable

public async Task<IEnumerable<AccessTime>> FindAsync(Func<AccessTime, bool> predicate)
{
    return await db.AccessTime
                   .Where(predicate)
                   .AsQueryable()
                   .ToListAsync();
}

While executing this code I get an error:

The source ‘IQueryable’ doesn’t implement ‘IAsyncEnumerable<_3TierApp.DAL.Entities.AccessTime>’. Only sources that implement ‘IAsyncEnumerable’ can be used for Entity Framework asynchronous operations.

I have no idea why .Where() with my predicate and with x => x.Id returns different types.

Can somebody explain? And also what will be the best working solution for this?

>Solution :

EF Core’s extensions like EntityFrameworkQueryableExtensions.ToListAsync work with IQueryable interface (check out the linked method signature), not an IEnumerable and IQueryable requires Expression<Func<...>> (Queryable.Where for example) not just Func<...> (which allows to analyze passed expression tree and generate SQL query), so change the signature accordingly:

public async Task<IEnumerable<AccessTime>> FindAsync(
     Expression<Func<AccessTime, bool>> predicate)
{
    return await db.AccessTime
         .Where(predicate)
         .ToListAsync();
}