实体框架-过滤子实体

Question

I used entity framework with my example. I wanted to filter child entity but it break program at run time with error: "The entity or complex type 'CodeFirstNamespace.Customer' cannot be constructed in a LINQ to Entities query." Can anyone help me? Thanks.

public class Customer
    {
        public int CustomerID { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Email { get; set; }
        //public virtual ICollection<Address> Addresses
        public List<User> Users { get; set; }
        public List<Address> Addresses { get; set; }
        public List<Order> Orders { get; set; }
        public List<CheckProduct> CheckProducts { get; set; }
    }

public Customer GetCustomerCheckProduct(string email, Byte checkType)
    {
        IQueryable<Customer> customers = context.Set<Customer>().Include("CheckProducts").Where(c => c.Email == email);
        if (checkType != 0)
        {
            var cus = customers.Select(customer => new Customer { CheckProducts = customer.CheckProducts.Where(s => s.CheckType == checkType).ToList() }).SingleOrDefault();
            return cus;
        }

        return null;
    }

Answer 1

假设您要查找具有给定类型的CheckProducts的第一个（如果有的话）客户，为什么不简单地使用它呢？

var cus = customers.FirstOrDefault(c => c.CheckProducts.Any(cp => cp.Checktype == checkType));

Answer 2

To filter a collection navigation property you can do the following:

var customer = <get customer entity>;

var filteredCheckProducts = context.Entry( customer )
    .Collection( c => c.CheckProducts )
    .Query()
    .Where( cp => cp.CheckType == checkType )
    .ToArray();