ObjectContext 实例已被释放 - Winforms Entity Framework

I am trying to solve this problem and did read content regarding this error but was unable to figure out a solution. I am building a winforms application using Entity framework for a simple Products Categories scenario. Here is a snapshot of my model.

ProductService 类中检索所有产品的代码是

public static List<Product> GetAllProducts()
{
    List<Product> products = new List<Product>();
    using (var entity = new SUIMSEntities1())
    {
        products = (from p in entity.Products
                    select p).ToList();
        return products;
    }            
}

产品代码后面的代码是

List<Product> prods=ProductServices.GetAllProducts();
dgvProducts.DataSource = prods;

When I try to load the Products in datagridview, the following error is shown:

您能告诉我是什么原因导致了这个问题吗？

Edit:Include 成功了，在这个特定场景中，我更改了 GetAllProducts() 如下

        public static List<Product> GetAllProducts()
        {
            using (var entity = new SUIMSEntities1())
            {
                List<Product> products = entity.Products.Include("Category").ToList();
                return products;                
            }            
        }

默认情况下，实体框架 (EF) 将延迟加载您的类别对象集。由于您的 Category 对象集是延迟加载的，因此当其他代码稍后引用 Category 时，EF 将尝试加载该集。但是，此时您的上下文已被处理，导致您看到错误。

您需要做的是强制上下文急切地加载您的类别实体集，如下所示：

public static List<Product> GetAllProducts()
{
    List<Product> products = new List<Product>();
    using (var entity = new SUIMSEntities1())
    {
        entity.Include("Category");  //force eager loading of Category
        products = (from p in entity.Products
                    select p).ToList();
        return products;
    }            
}