基于列表中的字符串选择C＃LINQ

Question

So I have a class named event which contains a List ListofInvites, It has email addresses of different user(another class which has a emailid property), now I want to select all the events based on whether the listofinvites string contains that specific email

I have tried this but i'm getting an error

var userEmailID = this.User.Identity.GetUserName();


var events = this.dataBase.Events
       .OrderBy(e => e.DateAndTime)
       .Where(e => e.listOfInvites.Contains(userEmailID))
       .Select(EventViewModel.ViewModel);

Yeah sorry I was in a hurry last night when i posted this

So I have this event class

public class Event
{
    public Event()
    {
        this.IsPublic = true;
        this.DateAndTime = DateTime.Now;
    }
    [Key]
    public int EventID { get; set; }

    [Required]
    [MaxLength(200)]
    public string Title { get; set; }

    [Required]
    public DateTime DateAndTime { get; set; }

    public string AuthorId { get; set; }
    public int Duration { get; set; }
    public string Description { get; set; }
    public string OtherDetails { get; set; }
    [MaxLength(200)]
    public string Location { get; set; }
    public bool IsPublic { get; set; }
    public IEnumerable<string> listOfInvites { get; set; }

    public string  InviteList { get; set; }
}
}

the error i'm getting is

System.NotSupportedException: 'The specified type member 'listOfInvites' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.'

Answer 1

Hope the below code will solve your issue.

var events = dataBase.Events.Where(p => p.listOfInvites.Contains(userEmailID)).ToList();

Answer 2

It would help to see your classes, but I'm guessing you have a list of some class named Event in your database, each of which has a List<Invite> property, and then an EmailId string property on each one of those Invite instances. If that's the case, since your EmailId is not a property in the Event itself, you'll have to iterate through each event's List<Invite> to get the EmailId associated with it. The relations I'm guessing are: Many events in your database; many invites on each Event ; and one EmailID on each Invite .

Following this assumptions, I would do this:

var events = this.database.Events.Where(e => e.ListOfInvites.Any(i => i.EmailId.Contains(userEmailId))).ToList();

So, from each of the events on the (assummed) List<Event> on your database, we'll search through every invite in it's ListOfInvites property (that's the e => e.ListOfInvites part), looking for any invite where it's EmailId matches the one we passed, ie: i => i.EmailId.Contains(userEmailId) . This var will then become a List<Event> representing all the events to which our user is invited.

Answer 3

In the Event entity, you are declaring a IEnumerable<string> property ( listOfInvites ) while list of primitive types is not supported in Entity Framework and since this property is not mapped to a database column you cannot use it in a where expression.
You need to create another entity (therefore table) for ListOfInvites with a foreign key to the Event entity.