CODEWITHSUNDEEP
c#repository-pattern
sarin
sarin

Reputation: 5307

Can't convert from Type ICollection to List with async

I have the following code in a service:

var countriesTask = countryIds != null && countryIds.Any()
                                    ? this.dataContext.Countries.Where(c => countryIds.Contains(c.CountryId)).ToListAsync()
                                    : Task.FromResult(new List<Country>());
        var countries = await countriesTask;

I wanted to refactor out the dependency Datacontext by creating a RepositoryBase class:

IRepositoryBase:
    Task<ICollection<T>> FindAllAsync(Expression<Func<T, bool>> match);

RepositoryBase:
    public virtual async Task<ICollection<T>> FindAllAsync(Expression<Func<T, bool>> match)
    {
        return await this.DbContext.Set<T>().Where(match).ToListAsync();
    }

And then refactoring the above to:

   var countriesTask = countryIds != null && countryIds.Any()
                                ? this.countryRepository.FindAllAsync(c => countryIds.Contains(c.CountryId))
                                : Task.FromResult(new List<Country>());
   var countries = await countriesTask;

I'm getting a type conversion error (Can't convert from Type ICollection Country to Type List Country and my brain isn't working this morning. I know there is a ToListAsync that's probably causing the problem, but each time I change something, something else breaks! What do I do

Upvotes: 2

Views: 2542

Answers (1)

Enigmativity
Enigmativity

Reputation: 117084

It seems to me that you just need to do this:

var countriesTask =
    countryIds != null && countryIds.Any()
    ? this.countryRepository.FindAllAsync(c => countryIds.Contains(c.CountryId))
    : Task.FromResult<ICollection<Country>>(new List<Country>());

Basically both sides of the ?: operator need to return the same type. Your code was trying to return Task<ICollection<Country>> & Task<List<Country>>. By making both return Task<ICollection<Country>> it should work fine.

Upvotes: 4

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