有条件的情况下加入

Question

我需要返回一个客户端列表，它们与使用LINQ的独立表中提供的标识字段相匹配。该SQL语句将如下所示，如果它是在一个存储过程：

Select client.* 
From ADLT_Clients as client 
    Inner Join ADLT_ClientIdentifiers as identifier 
     on client.ClientPIN = identifier.ClientPIN 
Where identifier.EmailAdrs = @EmailAddress 
    and identifier.FBINum = @FBINumber 
    (...) 

我试图用为此在LINQ如下：

Public Function FindByIndentifiers(adultClient As AdultClient) As List(Of AdultClient) 
     Dim adultClients As New List(Of AdultClient) 
     Dim clients = From client As ADLT_Client In _cmisiiEntities.ADLT_Clients 
         Join identifier In _cmisiiEntities.ADLT_ClientIdentifiers On client.ClientPIN Equals identifier.ClientPIN 
         Select client 

     If adultClient.AdultClientIdentifiers IsNot Nothing Then 
      With adultClient.AdultClientIdentifiers 
       If Not String.IsNullOrEmpty(.EmailAddress) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.EMailAdrs.Contains(.EmailAddress)) 
       If Not String.IsNullOrEmpty(.FBINumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.FBINum.Contains(.FBINumber)) 
       If Not String.IsNullOrEmpty(.ICOTSNumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.ICOTSNum.Contains(.ICOTSNumber)) 
       If Not String.IsNullOrEmpty(.InmateNumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.InmateNum.Contains(.InmateNumber)) 
       If Not String.IsNullOrEmpty(.LicenseNumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.LicenseNum.Contains(.LicenseNumber)) 
       If Not String.IsNullOrEmpty(.LicenseNumberState) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.LicenseNumState.Contains(.LicenseNumberState)) 
       If Not String.IsNullOrEmpty(.PassportNumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.PassportNum.Contains(.PassportNumber)) 
       If Not String.IsNullOrEmpty(.AlienRegistrationNumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.GreenCardNum.Contains(.AlienRegistrationNumber)) 
       If Not String.IsNullOrEmpty(.SocialSecurityNumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.SSN.Contains(.SocialSecurityNumber)) 
       If Not String.IsNullOrEmpty(.SPBINumber) Then clients = clients.Where(Function(f) f.ADLT_ClientIdentifiers.SPBINum.Contains(.SPBINumber)) 
      End With 
     End If 

     For Each client In clients.Take(100).ToList() 
      adultClients.Add(BuildAdultClient(client)) 
     Next 

     Return adultClients 
    End Function 

此代码时，没有有效的参数执行，没有任何where子句被添加并且clients.Take（100）.ToList（）语句执行正常。如果我包含任何有效的参数，因此添加一个where子句，则该语句会在ToList（）调用中提供NullReferenceException。

我的理论是，有一个别名问题，我试图添加where子句。当where子句是初始语句的一部分时，我使用join语句创建的标识符别名。如果我修改我的说法是：

  Dim clients = (From client As ADLT_Client In _cmisiiEntities.ADLT_Clients 
         Join identifier In _cmisiiEntities.ADLT_ClientIdentifiers On client.ClientPIN Equals identifier.ClientPIN) _ 
         .Where(Function(f) f.identifier.EMailAdrs.Contains(adultClient.EmailAddress)) _ 
         .Select(Function(f) f.client) 

代码也会执行。这里的区别是我正在通过定义的标识符别名。我不能在我的条件where语句中执行相同的f.identifier.EmailAdrs，因为标识符不是该上下文的一部分？

我在这里错过了什么，有没有更好的方法来正确地做到这一点，或者这是VB的限制吗？

Answer 1

如果我这样做是linqPad，与LINQ2SQL

Dim c as new Config with {.Category="Other"} 
Dim q =from c1 in Configs select c1 

if(c isnot nothing) then 
    if not string.isnullorempty(c.Category) then q=q.Where(Function(f) f.Category.Contains(c.Category)) 
end if 
q.Dump() 

它的工作原理，但如果我这样做

Dim c as new Config with {.Category="Other"} 
Dim q =from c1 in Configs select c1 

if(c isnot nothing) then 
    with c 
     if not string.isnullorempty(.Category) then q=q.Where(Function(f) f.Category.Contains(.Category)) 
    end with 
end if 
q.Dump() 

它抛出一个空引用异常。我认为这是你的子句与表达式冲突