c# - Entity Framework : Unable to create a constant value of type **. 此上下文仅支持原始类型或枚举类型

Question

我有这个问题:

     public override IEnumerable<Order> ExecuteQuery(MovieRentalContext database)
    {

        return from order in database.Orders
            where (customer == null || customer.Id == order.CustomerId)
            select order;
    }

客户是类中的字段。有订单类

   public class Order: Entity
{
    [Required]
    public Copy Copy { get; set; }

    public Customer Customer { get; set; }
    public DateTime OrderDate { get; set; }
    public DateTime EstimatedReturnDate { get; set; }
    public Salesman Salesman { get; set; }

    public DateTime? ActualReturnDate { get; set; }
    public decimal Price { get; set; }

    [ForeignKey("Customer")]
    public long CustomerId { get; set; }
}

实体包含 Id。我想获取客户的订单，但在执行查询期间抛出异常:

Unable to create a constant value of type >'MovieRental.DataAccess.Models.Customer'. Only primitive types or enumeration >types are supported in this context.

我尝试了我发现的一切，但它仍然不起作用。有什么问题？

Answer 1

我会说你的 customer == null 代码导致了这个。 EF 正在尝试将其转换为 SQL，但客户不在该上下文中。尝试将该条件置于查询之外。

即

public override IEnumerable<Order> ExecuteQuery(MovieRentalContext database)
{
    if (customer != null)
    {
        return from order in database.Orders
            where order.CustomerId == customer.Id
            select order;
    }
    else
    {
        return from order in database.Orders
            select order;
    }

}