实体框架 - Linq to Entities中的数据库视图或连接

Question

I have a database table with many lookup tables:

OrderType  
ShippingType  
etc.

My Order table is referencing each one of these tables:

Order
  OrderID
  OrderTypeID
  ShippingTypeID

I am using the Entity Framework as my data access layer. I have a page that needs to display information for an Order. I am struggling to figure out the best/right way to use these entities.

My page should be displaying the data like:

Order #1000000
Shipping Type: UPS
Order Type: Online
Etc Type: Etc.

Is it better to create a view in the database that brings back the data I need and then add it to my entity model, and just use that directly so I don't have to write joins in my queries? Or is it better to create an intermediate class like so:

class OrderView
{
    public int OrderNumber { get; set; }
    public string OrderType { get; set; }
    public string ShippingType { get; set; }
}

var order = from o in db.Orders
            join ot in db.OrderTypes on o.OrderTypeID equals ot.OrderTypeID
            join st in db.ShippingTypes on o.ShippingTypeID equals st.ShippingTypeID
            select new OrderView 
            { 
                OrderNumber = o.OrderNumber, 
                ShippingType = st.Description, 
                OrderType = ot.Description 
            };

What is the better way here?

Answer 1

You don't need join , per se. What you can do is use Navigation Properties for OrderType and ShippingType in order to access them without the need for joins. You'll have something like:

var order = from o in db.Orders
            select new OrderView 
            { 
                OrderNumber = o.OrderNumber, 
                ShippingType = o.ShippingType.Description, 
                OrderType = o.OrderType.Description 
            };

I don't see any advantage to doing this in a view.

Answer 2

You can use Linq-to-entities. I usually switch to SQL or View when I have something which I can't write in L2E (like Common table expression and hiearchical queries) or when L2E performance is bad. If you do not have these problems you should be happy with L2E.

Btw. your query can be rewritten without joins - damn @Craig was faster.

Answer 3

Views can be good for several reasons:

1. They can insulate you from changes in the underlying table structure
2. They can abstract away normalisation details (the joins)
3. Yoi can revoke all permissions on tables, and provide restricted access through views.

Do whatever leads to more understandable code.

Answer 4

using a database view can hinder the SQL optimizer's ability to get you the best execution plan. so if the EF-generated query is not a horror (use SQL Profiler to make sure!) i`d go for EF.