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十进制的?with Left outer join在LINQ中获取空引用

ef-core-2.1 asp.net-core-2.1 linq

0

Ramesh · 技术社区 · 6 年前

我想在林肯做两个左外联 var 但是在选择所需的颜色时,我得到 Object reference not set to an instance of an object 在我想要的地方出错 Nullable decimal .

    var FLS = (from ee in SumTillFYEnd 
                        join es in SumTillFYStart on ee.Account equals es.Account into temp
                        from t in temp.DefaultIfEmpty()                             
                        select new
                        {  
                            Account = ee.Account, // As of here it works
                            BeginDr = (t.DrStartCF == 0) ? (decimal?) null : t.DrStartCF // Here I get error Object reference not set to an instance of an object.
                        });

有时SumTillFYEnd,有时sumtillfyest变为空。我想加入应该使用默认值,以防任何一个或两者都为空。

1 回复 | 直到 6 年前

1

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Chris Pratt 6 年前

问题是试图转换 null 到 decimal? . 你不能直接投 无效的 到另一个类型,是否可以为空。这总是会导致 NullReferenceException . 你想要的是 default . 换言之,替换:

(decimal?)null

与

default(decimal?)

2

0

hiFI 5 年前

我用默认类解决了这个问题。

我看到的原因是decimal不能为空,所以它也需要为默认值设置 0 或 decimal.MinValue

所以,您需要为 SumTillFYStart 喜欢

var defaultSumTillFYStart = new SumTillFYStart { Account = string.Empty, DrStartCF =0};

在上面的上下文中,然后在您的代码片段中替换

from t in temp.DefaultIfEmpty()

带着这个

from t in temp.DefaultIfEmpty(defaultSumTillFYStart)

我有一个linqPad,写在下面,但为不同的子集;我认为它将帮助某些人:

void Main()
{
    List<Debtor> debtors = new List<Debtor>();
    List<SecurityHolding> holdings = new List<SecurityHolding>();

    //Initialize Debtor
    debtors.Add(new Debtor(){
        AccountId = "J1",
        OutstandingValue = 501.95M
    });

    debtors.Add(new Debtor(){
        AccountId = "J2",
        OutstandingValue = 75.68M
    });

    debtors.Add(new Debtor(){
        AccountId = "J3",
        OutstandingValue = 100.01M
    });

    //Initialize Security Holding
    holdings.Add(new SecurityHolding(){
        AccountId = "J2",
        SecurityHoldingValue = 100M
    });

    holdings.Add(new SecurityHolding(){
        AccountId = "J3",
        SecurityHoldingValue = 200M
    });


    var defaultHolding = new SecurityHolding { AccountId= string.Empty, SecurityHoldingValue = 0};

    var result = (from d in debtors
                   join p in holdings
                   on d.AccountId equals p.AccountId into temp
                   from t in temp.DefaultIfEmpty(defaultHolding)
                   select new
                   {
                        AccountId = d.AccountId,
                        OutstandingValue = d.OutstandingValue,
                        HoldingValue = (decimal?)t.SecurityHoldingValue
                   });

    result.Dump();
}

// Define other methods and classes here
public class Debtor
{
    public string AccountId {get;set;}
    public decimal OutstandingValue {get;set;}
}

public class SecurityHolding
{
    public string AccountId {get;set;}
    public decimal SecurityHoldingValue {get;set;}
}

这里是输出: