我该如何解决这个错误。无法将对象从dbnull转换为其他类型 [英] How do I solve this error. Object cannot be cast from dbnull to orther types

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问题描述

我有一个问题，我想得到每个** BusType **的小计。我现在的问题是我收到此错误`对象无法从DBNull转换为其他类型`。当我试图继续显示错误`对象不能从DBNull转换为其他类型`时，我将断点放在`return ds`上时，我确实得到了DataTable的结果。我该如何解决这个问题。

需要的输出 



 BusType | BusName | BusL | BusInterest | BusAdmin | BusPenalty | TotalBusCollected 
  1   - 会计| HIGHVELD | -23。 91  |  0  | -22。 84  |  0  | -46。 75  
  1   - 会计|必和必拓| -50。 81  | -79。 21  | -76 |  - 20.  02  | -226。 04  
  -    ------------------------ + ------- +  - ---------- + -------- + ----------- + -----------------  
小计| -74。 72  | -79。 21  | -98。  84  | -20。 02  | -272。 79  
   -    ----------------- ------- ------- + + ----------- + -------- + ----------- +  - ----------------  
  2   -  FOOD | SAB | -14。 18  | -435。 97  | -2。 57  | -67。 55  | -520。 27  
  2   -  FOOD | DISTIL | -43。 05  | 0 | -66， 59  | 0 | -109。 64  
   -    ---------------- -------- ------- + + ----------- + -------- + ----------- + -----------------  
小计| -57。 23  | -435。< span class =code-digit> 97  | -69。 16  | -67。 55  | -629。 91  
   -    ------------------------ + ------- + ----------- + ---- ---- + ----------- + -----------------  
  3   -  MINING | ANGLOGOLD | -4。 43  | 0 | -72 | 0 | -76。 43  
   -    ------------------------ + ----- -  + ----------- + -------- + ----------- -------------- + ---  
小计| -4。 43  | 0 | -72 | 0 | -76。 43





Code 



  var  query =（ from  _transaction  in  _entities.Transactions 
  join  _cd   _entities.Organisations on _transaction.Refno equals _cd.Refno 
  join  _b   _entities.BusinessType on _transaction.BusinessTypeCode equals _b.BusinessTypeCode 
  group   new  
 {
 _trans = _transaction，
 cd = _cd，
} 
 by  new  {_transaction.BusinessTypeCode，_ transaction.Refno，_cd.BusinessName，_b.Description}  into  _group 
  orderby  _group.Key.BusinessTypeCode 
 选择  new  
 {
 BusinessTypeCode = _group.Key.BusinessTypeCode，
 BusType = _group.Key.BusinessTypeCode +    -  + _group.Key.Description，
 BusName = _group.Key.BusinessName，
 BusL = _group.Sum（X =&安培; GT; x._trans.Bu sL），
 BusInterrest = _group.Sum（x =& gt; x._trans.BusInterrest），
 BusAdmin = _group.Sum（x =& gt; x._trans.BusAdmin），
 BusPenalty = _group.Sum（x =& gt; x._trans。 BusPenalty），
 TotalBusCollected = _group.Sum（x =& gt; x._trans.TotalBusCollected）
}）; 
 DataTable dt =  new  DataTable（）; 
 DataSet ds =  new  DataSet（）; 
 ds.Tables.Add（query.CopyToDataTable（））; 
 ds.Tables [ 0 ]。TableName =  表1; 
  double  BusL =  0 ;  double  BusInterrest =  0 ;  double  BusAdmin =  0 ; 
  double  BusPenalty =  0 ;  double  TotalBusCollected =  0 ;  string  Title =  string  .Empty; 
  for （ int  I =  0 ; I& lt; = dt.Rows.Count  -   1 ; i ++）
 {
  if （i& gt;  0 ）
 {
  if （dt.Rows [i] [  BusType]。ToString（）。ToLower（） ！= dt.Rows [i]] [  BusType]。ToString（）。ToLower（） ）
 {
 dt.Rows.InsertAt（dt.NewRow（），i）; 
 dt.Rows [i] [  BusType] =标题，
 Title =  string  .Empty; 
 dt.Rows [i] [  BusL] = BusL; 
 BusL =  0 ; 
 dt.Rows [i] [  BusInterrest] = BusInterrest; 
 BusInterrest =  0 ; 
 dt.Rows [i] [  BusAdmin] = BusAdmin; 
 BusAdmin =  0 ; 
 dt.Rows [i] [  BusPenalty] = BusPenalty; 
 BusPenalty =  0 ; 
 dt.Rows [i] [  TotalBusCollected] = TotaBusCollected; 
 TotalBusCollected =  0 ; 
 i ++; 
} 
} 
 Title =  小计 + dt .Rows [i] [  BusType]; 
 BusL + = Convert.ToDouble（dt.Rows [i] [  BusL] ）; 
 BusInterrest + = Convert.ToDouble（dt.Rows [i] [  BusInterrest]） ; 
 BusAdmin + = Convert.ToDouble（dt.Rows [i] [  BusAdmin]） ; 
 BusPenalty + = Convert.ToDouble（dt.Rows [i] [  BusPenalty]） ; 
 TotalBusCollected + = Convert.ToDouble（dt.Rows [i] [  TotalBusCollected]） 
} 
 返回 ds;





< b>我的尝试：



double BusL = 0; double BusInterrest = 0; double BusAdmin = 0;

double BusPenalty = 0; double TotalBusCollected = 0; string Title = string.Empty;

for（int I = 0; I< = dt.Rows.Count - 1; i ++）

{

if（i> 0）

{

if（dt.Rows [i] [BusType]。ToString（）。ToLower（）！= dt .Rows [i]] [BusType]。ToString（）。ToLower（））

{

dt.Rows.InsertAt（dt.NewRow（），i ）;

dt.Rows [i] [BusType] =标题，

Title = string.Empty;

dt.Rows [i] [BusL] = BusL;

BusL = 0;

dt.Rows [i] [ BusInterrest] = BusInterrest;

BusInterrest = 0;

dt.Rows [i] [BusAdmin] = BusAdmin;

BusAdmin = 0;

dt.Rows [i] [BusPenalty] = BusPenalty;

BusPenalty = 0;

dt.Rows [i] [TotalBusCollected] = TotaBusCollected;

TotalBusCollected = 0;

i ++;

}

}

Title =小计为+ dt.Rows [i] [BusType];

BusL + = Convert.ToDouble（dt.Rows [i] [BusL ]）;

BusInterrest + = Convert.ToDouble（dt.Rows [i] [BusInterrest]）;

BusAdmin + = Convert.ToDouble（dt.Rows [i] [BusAdmin]）;

BusPenalty + = Convert.ToDouble（dt.Rows [i] [BusPenalty]）;

TotalBusCollected + = Convert.ToDouble（dt。行[i] [TotalBusCollected]）

}

返回ds;

解决方案

DataRow-cell（通常，在这里，显然）包含 DBNull 而不是 null 。 （确切地说，它包含类DBNull的单个实例。）



如果你没想到这种可能性，你可能会遇到数据完整性问题而你可能想要检查是否要使某些列不可为空并插入0（零）而不是空（null）。



如果要允许空值，你必须照顾这种可能性。最好的方法，也取代你的Convert.ToDouble（..） - 调用是使用通用字段< T>（列） -method DataRow ：

  double  busL = dt.Rows [i ] .Field< double>（  BusL）;



如果行单元格包含DBNull，则返回 double 的默认值（即0），否则返回包含的double值。


@Sacha Lefevre我仍在犯同样的错误



 Title =  小计 + dt.Rows [i] .Field< string>（   BusType）; 
 BusL + = dt.Rows [i] .Field< double>（  BusL ）; 
 BusInterrest + = dt.Rows [i] .Field< double>（  BusInterrest） ; 
 BusAdmin + = dt.Rows [i] .Field< double>（  BusAdmin） ; 
 BusPenalty + = dt.Rows [i] .Field< double>（  BusPenalty） ; 
 TotalBusCollected + = dt.Rows [i] .Field< double>（  TotalBusCollected） ;


I have a problem here i want to get the subtotal of each **BusType**. My problem now is that i am getting this error `Object cannot be cast from DBNull to orther types`. I do get the result on DataTable when i put the Breakpoint on `return ds` when i am trying to proceed it display that error `Object cannot be cast from DBNull to orther types` . How can i solve this.
Needed Output

BusType        |BusName   | BusL  |BusInterest|BusAdmin| BusPenalty|TotalBusCollected
1 - ACCOUNTING |HIGHVELD  |-23.91 | 0         |-22.84  | 0         |-46.75
1 - ACCOUNTING |BHP       |-50.81 |-79.21     |-76     |-20.02     |-226.04
--------------------------+-------+-----------+--------+-----------+-----------------
Subtotal                  |-74.72 |-79.21     |-98.84  |-20.02     |-272.79
--------------------------+-------+-----------+--------+-----------+-----------------
2 - FOOD         |SAB       |-14.18 |-435.97    |-2.57   |-67.55     |-520.27
2 - FOOD         |DISTIL    |-43.05 |0          |-66,59  |0          |-109.64
--------------------------+-------+-----------+--------+-----------+-----------------
Subtotal                     |-57.23 |-435.97    |-69.16  |-67.55     |-629.91
--------------------------+-------+-----------+--------+-----------+-----------------
3 - MINING     |ANGLOGOLD |-4.43  |0          |-72     |0          |-76.43
--------------------------+-------+-----------+--------+-----------+-----------------
Subtotal                 |-4.43  |0          |-72     |0          |-76.43



Code

var query = (from _transaction in _entities.Transactions
    join _cd in _entities.Organisations on _transaction.Refno equals _cd.Refno
    join _b in _entities.BusinessType on _transaction.BusinessTypeCode equals _b.BusinessTypeCode
              group new
              {
                  _trans = _transaction,
                   cd = _cd,
               }
               by new { _transaction.BusinessTypeCode,_transaction.Refno, _cd.BusinessName, _b.Description } into _group
               orderby _group.Key.BusinessTypeCode
               select new
                       {
                          BusinessTypeCode = _group.Key.BusinessTypeCode,
                          BusType = _group.Key.BusinessTypeCode + " - " +_group.Key.Description,
                          BusName = _group.Key.BusinessName,
                          BusL = _group.Sum(x=&gt;x._trans.BusL),
                          BusInterrest = _group.Sum(x =&gt; x._trans.BusInterrest),
                          BusAdmin = _group.Sum(x =&gt; x._trans.BusAdmin),
                          BusPenalty = _group.Sum(x =&gt; x._trans.BusPenalty),
                          TotalBusCollected =_group.Sum(x=&gt;x._trans.TotalBusCollected)
                       });
                DataTable dt=new DataTable();
                DataSet ds = new DataSet();
                ds.Tables.Add(query.CopyToDataTable());
                ds.Tables[0].TableName = "Table1";
    double BusL=0; double BusInterrest=0; double BusAdmin=0;
    double BusPenalty=0; double TotalBusCollected=0; string Title = string.Empty;
for(int I=0; I&lt;=dt.Rows.Count - 1; i++)
{
  if(i &gt; 0)
  {
     if(dt.Rows[i]["BusType"].ToString().ToLower() != dt.Rows[i]]["BusType"].ToString().ToLower())
     {
        dt.Rows.InsertAt(dt.NewRow(),i);
        dt.Rows[i]["BusType"]=Title,
        Title = string.Empty;        
        dt.Rows[i]["BusL"]=BusL;
        BusL=0;
        dt.Rows[i]["BusInterrest"]=BusInterrest;
        BusInterrest=0;
        dt.Rows[i]["BusAdmin"]=BusAdmin;
        BusAdmin=0;
        dt.Rows[i]["BusPenalty"]=BusPenalty;
        BusPenalty=0;
        dt.Rows[i]["TotalBusCollected"]=TotaBusCollected;
        TotalBusCollected=0;
        i++;
     }
   }
   Title = "Subtotal for "+dt.Rows[i]["BusType"];
   BusL +=Convert.ToDouble(dt.Rows[i]["BusL"]);
   BusInterrest+=Convert.ToDouble(dt.Rows[i]["BusInterrest"]);
   BusAdmin+=Convert.ToDouble(dt.Rows[i]["BusAdmin"]);
   BusPenalty+=Convert.ToDouble(dt.Rows[i]["BusPenalty"]);
   TotalBusCollected+=Convert.ToDouble(dt.Rows[i]["TotalBusCollected"])
}
return ds;



What I have tried:

double BusL=0; double BusInterrest=0; double BusAdmin=0;
double BusPenalty=0; double TotalBusCollected=0; string Title = string.Empty;
for(int I=0; I<=dt.Rows.Count - 1; i++)
{
if(i > 0)
{
if(dt.Rows[i]["BusType"].ToString().ToLower() != dt.Rows[i]]["BusType"].ToString().ToLower())
{
dt.Rows.InsertAt(dt.NewRow(),i);
dt.Rows[i]["BusType"]=Title,
Title = string.Empty;
dt.Rows[i]["BusL"]=BusL;
BusL=0;
dt.Rows[i]["BusInterrest"]=BusInterrest;
BusInterrest=0;
dt.Rows[i]["BusAdmin"]=BusAdmin;
BusAdmin=0;
dt.Rows[i]["BusPenalty"]=BusPenalty;
BusPenalty=0;
dt.Rows[i]["TotalBusCollected"]=TotaBusCollected;
TotalBusCollected=0;
i++;
}
}
Title = "Subtotal for "+dt.Rows[i]["BusType"];
BusL +=Convert.ToDouble(dt.Rows[i]["BusL"]);
BusInterrest+=Convert.ToDouble(dt.Rows[i]["BusInterrest"]);
BusAdmin+=Convert.ToDouble(dt.Rows[i]["BusAdmin"]);
BusPenalty+=Convert.ToDouble(dt.Rows[i]["BusPenalty"]);
TotalBusCollected+=Convert.ToDouble(dt.Rows[i]["TotalBusCollected"])
}
return ds;

解决方案

A DataRow-cell (usually, and here, apparently) contains DBNull instead of null. (To be exact, it contains the single instance of the class DBNull.)

If you didn't expect this possibility, you might have a data integrity problem and you might want to check if you want to make some columns non-nullable and insert 0's (zeroes) instead of nothing (null).

If you want to allow nulls, you have to take care for that possibility. The best way for that, which also replaces your Convert.ToDouble(..)-calls is to use the generic Field<T>(column)-method of DataRow:

double busL = dt.Rows[i].Field<double>("BusL");


This will return the default value for double (which is 0) in case the row-cell contains DBNull and the contained double-value otherwise.


@Sacha Lefevre I am still geting the same error

Title = "Subtotal for "+dt.Rows[i].Field<string>("BusType");
BusL +=dt.Rows[i].Field<double>("BusL");
BusInterrest+=dt.Rows[i].Field<double>("BusInterrest");
BusAdmin+=dt.Rows[i].Field<double>("BusAdmin");
BusPenalty+=dt.Rows[i].Field<double>("BusPenalty");
TotalBusCollected+=dt.Rows[i].Field<double>("TotalBusCollected");


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