How Entity framework works with lambda-expressions in ASP.NET MVC

Question

I'm working with EF code first. There are two classes which define my many to many association tables:

public class UserProfile
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int UserId { get; set; }
    public string Email { get; set; }

    public virtual ICollection<Habit> Habits { get; set; }
}



public class Habit
{
    [Key]
    public int HabitId { get; set; }

    public virtual ICollection<UserProfile> Users { get; set; }
}

I need to select from my database all habits for current user. I'm very new to c#, and the problem is that I can't understand how to work with complex lambda-expressions. I tried that:

context.Habits.Where(habit => habit.Users
                .Where(user=>user.Email==User.Identity.Name)).ToList()

But it's wrong. Could you please correct my lambda-based query. Thanks.

user.Email==User.Identity.Name ?

octref
– octref

2013-07-12 17:29:26 +00:00
Commented Jul 12, 2013 at 17:29 — octref
– octref, Commented Jul 12, 2013 at 17:29

Tallmaris · Accepted Answer · 2013-07-12 17:52:53Z

2

Why not add a DbSet<UserProfile> to your context and then do:

context.Users.Include("Habits")
       .First(user => user.Email == User.Identity.Name)
       .Habits;

If you want to avoid the above and rather fix the query you should do:

context.Habits.Where(habit =>                   
           habit.Users.Any(user=>user.Email==User.Identity.Name)).ToList();

Any returns true if any item in the IEnumerable satisfies the condition.

edited Jul 12, 2013 at 17:52

answered Jul 12, 2013 at 17:45

Tallmaris

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Comments

Omada · Accepted Answer · 2013-07-12 17:37:09Z

0

Try using Select (or SelectMany if you want a single flattened list) for the first lambda expression:

context.Habits.Select(habit =>
    habit.Users.Where(user => user.Email == User.Identity.Name)
    ).ToList()

The problem is that Where requires that the lambda expression return a boolean, and it was returning an IEnumerable<UserProfile>.

answered Jul 12, 2013 at 17:37

Omada

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Slauma · Accepted Answer · 2013-07-12 20:08:00Z

0

Because you want to select a specific property (Habits) from the UserProfile entity the most straight-forward way would be to use Select in my opinion:

var habits = context.UserProfiles
    .Where(user => user.Email == User.Identity.Name)
    .Select(user => user.Habits)
    .SingleOrDefault(); // I assume here that the Email is unique

answered Jul 12, 2013 at 20:08

Slauma

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