NHibernate的多個子集在lambda表達式查詢*

Question

我找一模一樣的

How to efficiently query with filter on children at different levels?

而是「lambda表達式」語法。

我真的需要這個，任何人都可以幫忙嗎？謝謝！

Answer 1

下面是從後的代碼片段，你在這兩種查詢語法和lambda語法引用：https://stackoverflow.com/a/12324116/670028：

LINQ查詢語法：

var listOfString = new List<string>() { "String1", "String2" }; 

var customers = 
(
    from a in session.Query<A>() 
    from b in a.B 
    from c in b.C 
    where a.Status == "Active" 
      && listOfStrings.Contains(b.SomeField) 
      && listOfStrings.Contains(c.someOtherField) 
    select a) 
    .ToList(); 

LINQ lambda語法：

var listOfString = new List<string>() { "String1", "String2" }; 

var customers = 
    (
     session.Query<A>() 
      .SelectMany(a => a.B, (a, b) => new { a, b }) 
      .SelectMany(@t => b.C, (@t, c) => new { @t, c }) 
      .Where(@t => a.Status == "Active" 
          && listOfStrings.Contains(b.SomeField) 
          && listOfStrings.Contains(c.someOtherField)). 
      Select 
      (@t => a)) 
     .ToList(); 

正如您所看到的，它不像LINQ查詢語法那樣「乾淨」，因爲每次使用.SelectMany時都必須繼續投影到新的匿名類型中（） 方法。它也可能與所有這些變量名稱有點混淆，這就是爲什麼當我需要執行像這樣的查詢時，我傾向於使用LINQ查詢語法而不是lambda表達式。

而只是爲了好玩，這裏是用.SelectMany（），看起來通過給匿名類型更有意義的名稱更好一點，更現實的例子：

public void Get_StarPowerCorporations_PendingShipment_Orders_Shipping_To_NewYork_Or_Chicago() 
{ 
    var session = UnitOfWork.Current.GetSession(); 

    var listOfCities = new List<string> { "New York", "Chicago" }; 

    var customerAndOrders = session.Query<Customer>() 
     .SelectMany(c => c.Orders, (Customer, Orders) => new { Customer, Orders }) 
     .SelectMany(CustomerAndOrders => CustomerAndOrders.Orders.OrderDetails, (CustomerAndOrders, OrderDetails) => new { CustomerAndOrders, OrderDetails }) 
     .Where(x => x.CustomerAndOrders.Customer.CompanyName == "StarPower Corporatation" 
         && x.CustomerAndOrders.Orders.Status == "Pending Shipment" 
         && listOfCities.Contains(x.OrderDetails.City)) 
     .Select(x => x.CustomerAndOrders.Customer) 
     .Fetch(x => x.Orders) 
     .ToList(); 
} 

public class Customer 
{ 
    public int CustomerId { get; set; } 
    public string CompanyName { get; set; } 
    public IList<Address> Addresses { get; set; } 
    public IList<Order> Orders { get; set; } 
} 

public class Address 
{ 
    public int AddressId { get; set; } 
} 

public class Order 
{ 
    public int OrderId { get; set; } 
    public string Status { get; set; } 
    public IList<OrderDetail> OrderDetails { get; set; } 
} 

public class OrderDetail 
{ 
    public int OrderDetailId { get; set; } 
    public string City { get; set; } 
}