Filtering records with IEnumerable.Select

Annie picture Annie · Apr 26, 2013 · Viewed 56.1k times · Source

In ASP.NET MVC 4 project, I have a model for join (with payload):

public class LeagueMember
{
    [Key, Column(Order = 0)]
    public int MemberId { get; set; }

    [Key, Column(Order = 1)]
    public int LeagueId { get; set; }

    public bool? IsActive { get; set; }

    [Required]
    public virtual League League { get; set; }

    [Required]
    public virtual Member Member { get; set; }

}

I am trying to pull all the active members of the league. So, in League model, I created a property like this:

public virtual ICollection<LeagueMember> LeagueMembers { get; set; }

public IEnumerable<Member> GetActiveMembers
{
    get
    {
        return LeagueMembers.Select(a => a.IsActive == true ? a.Member : null);
    }
}

But it looks like it returns a collection with size equals to that of all Members (with null values for the inactive members).

Is there a better way to apply filter in anonymous method to avoid nulls?

Answer

von v. picture von v. · Apr 26, 2013

But it looks like it returns a collection with size equals to that of all Members (with null values for the inactive members).

Because you are specifically telling it do so. In your code you are telling the query to return a Member instance is the member is active OR a null if the member is NOT active.

return LeagueMembers.Select(a => a.IsActive == true ? a.Member : null);

You can go away with the ? expression and simply do a:

return LeagueMembers
    .Where(a => a.IsActive.GetValueOrDefault(false))
    .Select(o=>o.Member);