如何使异步方法返回任务<ienumerable<t> >? </ienumerable<t>

Question

I am currently refactoring a method that has the async keyword but does not use await, thus running synchronously.

private async Task<IEnumerable<Obj>> SearchObj(string value)
    {
        if (string.IsNullOrEmpty(value))
            return _db.Objects;

        return _db.Objects.AsEnumerable().Where(x => x.SomeProperty.Contains(value, StringComparison.InvariantCultureIgnoreCase));
    }

How do I modify this method so that it runs asynchronously? Is it even necessary to run this asynchronously given a large dataset?

I have tried using the AsAsyncEnumerable() method but am not sure how to execute the Where() filter on an IAsyncEnumerable object.

Answer 1

Don't use AsEnumerable . Use one of the *Async() Methods:

private async Task<IEnumerable<Obj>> SearchObj(string value)
{
    if (string.IsNullOrEmpty(value))
        return await _db.Objects.ToListAsync();

    return await _db.Objects.Where(x => x.SomeProperty.Contains(value, StringComparison.InvariantCultureIgnoreCase)).ToListAsync();
}

Answer 2

AsEnumerable is not async method and it is needed to use ToListAsync , ToArrayAsync before returning IEnumerable . Also note that .Contains(value, StringComparison.InvariantCultureIgnoreCase) overload translation is not supported. Just use .Contains(value) , if default collation in database is case insensitive, it will work by default.

private Task<IEnumerable<Obj>> SearchObj(string value)
{
    var query = _db.Objects.AsQueryable();

    if (!string.IsNullOrEmpty(value))
        query = query.Where(x => x.SomeProperty.Contains(value));

    return query.ToListAsync();
}

If dtabase/column collation is not case insitive, you have to upper/lower case string values:

private Task<IEnumerable<Obj>> SearchObj(string value)
{
    var query = _db.Objects.AsQueryable();

    if (!string.IsNullOrEmpty(value))
    {
        value = value.ToUpper();
        query = query.Where(x => x.SomeProperty.ToUpper().Contains(value));
    }

    return query.ToListAsync();
}