用動態LINQ查詢子表到sql？

Question

我有一個相當複雜的查詢，我需要寫。如果可能，我希望使用Linq to Sql來完成它。該數據庫是這樣的：

客戶（第一，最後，ID，性別）
訂單（日期，數量，重量，ITEMNAME，價格）
地址（城市，州，郵編）

該查詢將讓用戶通過任何這些字段進行搜索，並且在數字字段的情況下，按照他們的期望搜索<，=，或>。

像這樣的事情將是我需要實現簡單的查詢：

查詢1： 選擇客戶，其中第一名稱=「約翰」，並至少有一個訂單與（重量> 40或數量> 10或價格> 5）和郵政編碼= 12345

問題2： 選擇客戶其中第一名稱=「約翰」和具有至少一個以便與重量< 20和ITEMNAME =「插件」和數量= 10）和zipcode = 12345.

我可以得到搜索的基本部分f或客戶，但我堅持搜索訂單表，用戶可以用OR方式指定<> =。

 

query = Context.Customers.AsQueryable(); 
if (searchingFirstName) query = query.Where(cust => cust.First == firstName); 
if (searchingLastName) query = query.Where(cust => cust.Last == lastName); 
if (searchingZip) query = query.Where(cust => cust.Address.Zip == zip); 

// using dynamic Linq 
if (searchingGender) query = query.Where("Gender == @0", gender); 

// how do I search the Orders? The dynamic linq functions appear 
// to only work on the top level table 
 

Answer 1

你可以從LinqKit使用PredicateBuilder。它增加了一些新的擴展方法，lambda表達式斷言：

var predicate = PredicateBuilder.True<Customer>(); 

if (searchingFirstName) 
{ 
    predicate = predicate.And(cust => cust.First == firstName); 
} 

if (searchingOrders) 
{ 
    // Some code to unify the .And() and .Or() cases 
    Expression<Func<Order, bool>> subpredicate; 
    Func<Expression<Func<Order, bool>>, Expression<Func<Order, bool>>, Expression<Func<Order, bool>>> joiner; 
    if (orderMethodAny) 
    { 
     subpredicate = PredicateBuilder.True<Order>(); 
     joiner = PredicateBuilder.And; 
    } 
    else 
    { 
     subpredicate = PredicateBuilder.False<Order>(); 
     joiner = PredicateBuilder.Or; 
    } 

    if (searchingOrderDate) 
    { 
     // ... 
    } 

    if (searchingOrderWeight) 
    { 
     switch (orderOp) 
     { 
      case Op.Less: 
       subpredicate = joiner(subpredicate, ord => ord.Weight < orderWeight); 
       break; 
      case Op.LessEqual: 
       subpredicate = joiner(subpredicate, ord => ord.Weight <= orderWeight); 
       break; 
      case Op.Equal: 
       subpredicate = joiner(subpredicate, ord => ord.Weight == orderWeight); 
       break; 
      case Op.GreaterEqual: 
       subpredicate = joiner(subpredicate, ord => ord.Weight >= orderWeight); 
       break; 
      case Op.Greater: 
       subpredicate = joiner(subpredicate, ord => ord.Weight > orderWeight); 
       break; 
      case Op.NotEqual: 
       subpredicate = joiner(subpredicate, ord => ord.Weight != orderWeight); 
       break; 
     } 
    } 

    if (searchingOrderQuantity) 
    { 
     // ... 
    } 

    if (searchingOrderItemName) 
    { 
     // ... 
    } 

    if (searchingOrderPrice) 
    { 
     // ... 
    } 

    predicate = predicate.And(cust => cust.Orders.Any(subpredicate)); 
} 

if (searchingZipCode) 
{ 
    predicate = predicate.And(cust => cust.ZipCode == zipCode); 
} 

var query = Context.Customers.Where(predicate); 

您可能需要將它們作爲參數，或.AsExpandable()上可查詢前呼籲謂詞.Expand()，如果您使用的是實體框架。