如何验证EF中的父实体是否不是子实体

Question

Let's say I have one to many relationship table ( Ex User - Rent )

public class User 
{
        public string UserName { get; set; }
        public string Email { get; set; }
        public string Password { get; set; }
        public virtual ICollection<Rent> Rents { get; set; }  
}

public class Rent 
{
        public Int64 VideoId { get; set; }
        public Int64 UserId { get; set; }
        public virtual User User{get; set;}
        public int RentingLength { get; set; }
        public int RentingCost { get; set; }
}

I want to delete a User record. Before that, I want to check whether User has references to Rent or not.

What I have is :

context.Users.Include("Rents").ToList();

then check Rent list is null or not.

Is there any better way to do that?

Thanks.

Answer 1

context.Users.Include("Rents").ToList(); will materialize your query, getting all users. Best way should be context.Rent.Where(r => r.userId == DesiredUserId).Any() . If true then user has rents.

Answer 2

Use Any like this to check if record exits

public bool Exists(int YourUserId)
{
    dbcontext.Rent.Any(e => e.UserId == YourUserId);
}

Answer 3

You are using Virtual keyword in navigational properties which means Rents will automatically be included in your query of Users. So you don't need the Include Explicitly.

So you can just do

context.Users.Find(Id)

And it will include Rent as well for the user with primary key id