去除的LINQ查詢連接

Question

我有兩個實體是這樣的：

[Table("tblAccount")] 
public class Account 
{  
    [Key] 
    [Column("Creditor Registry ID", Order = 0)] 
    public int CreditRegistryId { get; set; } 

    [Key] 
    [Required] 
    [Column("Account No", Order = 1)] 
    public int AccountNo { get; set; } 

    [Column("Minimum Installment")] 
    public decimal MinimumInstallment { get; set; } 

    [Column("Account Status Date")] 
    public DateTime AccountStatusDate { get; set; } 

    [Required] 
    [Column("Account Type")] 
    public string AccountType { get; set; } 

    public virtual ICollection<AccountOwner> AccountOwners { get; set; } 
} 

和

[Table("tblAccountOwner")] 
public class AccountOwner 
{ 
    [Key] 
    [ForeignKey("Account")] 
    [Column("Creditor Registry ID", Order = 0)] 
    public int CreditorRegistryId { get; set; } 


    [Key] 
    [ForeignKey("Account")] 
    [Column("Account No", Order = 1)]   
    public int AccountNo { get; set; } 

    [Key] 
    [Column("Account Owner Registry ID", Order = 2)] 
    public long AccountOwnerRegistryId { get; set; } 

    public virtual Account Account { get; set; } 
} 

我想轉換下面的查詢工作，而加入作爲帳戶實體有accountOwners和accounOwner有帳戶導航財產（主鍵/外鍵關係）

var ownerRegId = 731752693037116688L; 
var excludeTypes = new[] { 'CA00', 'CA01', 'CA03', 'CA04', 'CA02', 'PA00', 'PA01', 'PA02', 'PA03', 'PA04' }; 
var maxStateChangeMonth = 4; 
var excludeStatusId = 999; 
var SumOfMonthlyPayments = 
    context.Accounts 
      .Join(context.AccountOwners, 
       a => new { CreditorRegistryId = a.CreditRegistryId, a.AccountNo }, 
       ao => new { ao.CreditorRegistryId, ao.AccountNo }, 
       (a, ao) => new { Account = a, AccountOwner = ao }) 
      .Where(x => x.AccountOwner.AccountOwnerRegistryID == ownerRegId 
        && !excludeTypes.Contains(x.Account.AccountType) 
        && (x.Account.StateChangeDate == null || x.Account.StateChangeDate.Month - DateTime.Now.Month <= maxStateChangeMonth) 
        && x.Account.AccountStatusID != excludeStatusId) 
      .Sum(x => Math.Abs(x.Account.MinimumInstallment)); 

由於Sergi建議我發起d這樣的：

var sum = (from account in context.Accounts 
      from owner in account.AccountOwners 
      where (owner.AccountOwnerRegistryId == ownerRegistryId 
       && !excludeTypes.Contains(account.AccountType) 
       && (account.StateChangeDate == null || 
        (account.StateChangeDate.Month - DateTime.Now.Month) 
         <= maxStateChangeMonth) 
       && account.AccountStatusId != excludeStatusId 
       && (includeMortgage.Contains(account.AccountType) || 
        account.AccountType.Contains("Mortgage"))) 
      select account.MinimumInstallment) 
       .Sum(minimumInstallment => Math.Abs(minimumInstallment)); 

我加了一個其他& &條款

&& (includeMortgage.Contains(account.AccountType) || 
    account.AccountType.Contains("Mortgage") 

，但現在我得到：

The cast to value type 'Decimal' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type.

感謝

Answer 1

至於你提到，你可以使用導航屬性代替連接，所以你可以嘗試這樣的：

var sum = (from account in context.Accounts 
      from owner in account.AccountOwners 
      where (owner.AccountOwnerRegistryID == ownerRegId 
       && !excludeTypes.Contains(account.AccountType) 
       && (account.StateChangeDate == null || 
        (account.StateChangeDate.Month - DateTime.Now.Month) 
         <= maxStateChangeMonth) 
       && account.AccountStatusID != excludeStatusId) 
      select account.MinimumInstallment) 
       .Sum(minimumInstallment => Math.Abs(minimumInstallment)); 

兩個「串聯」 from條款相當於Linq中的SelectMany方法。