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I've created a LEFT JOIN in LINQ. How do I get my query to return my nullable values?

+------+------+------+
| c1 | c2 | c3 |
|------+------+------|
| x1 | y1 | z1 |
| x2 | y2 | null |
| x3 | y3 | z1 |
+------+------+------+

Above is basically the SQL table returned after LEFT JOIN as expected

However using LINQ:

 var query = 
 ```
 into temp
 from t in temp.DefaultIfEmpty()
 select new
 
 ```,
 ```,
 Column3 = (int?)t.ColumnNo
 ;

Debugger barks at me for Column3 for:

Object reference not set to an instance of an object

c# linq

share|improve this question

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  t is null right? So you'd want to do (int?)t.?ColumnNo?
  
  – Brendan Green
  Mar 28 at 3:39
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It seems to me that you haven't posted valid C# code. Could you give us a minimal reproducible example? That would be your source as valid C# (rather than, or in addition to, the table of data) and then you could provide a query that is valid C#.
  
  – Enigmativity
  Mar 28 at 4:14
  

  
  
  
  

add a comment | 

0

I've created a LEFT JOIN in LINQ. How do I get my query to return my nullable values?

+------+------+------+
| c1 | c2 | c3 |
|------+------+------|
| x1 | y1 | z1 |
| x2 | y2 | null |
| x3 | y3 | z1 |
+------+------+------+

Above is basically the SQL table returned after LEFT JOIN as expected

However using LINQ:

 var query = 
 ```
 into temp
 from t in temp.DefaultIfEmpty()
 select new
 
 ```,
 ```,
 Column3 = (int?)t.ColumnNo
 ;

Debugger barks at me for Column3 for:

Object reference not set to an instance of an object

c# linq

share|improve this question

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  t is null right? So you'd want to do (int?)t.?ColumnNo?
  
  – Brendan Green
  Mar 28 at 3:39
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It seems to me that you haven't posted valid C# code. Could you give us a minimal reproducible example? That would be your source as valid C# (rather than, or in addition to, the table of data) and then you could provide a query that is valid C#.
  
  – Enigmativity
  Mar 28 at 4:14
  

  
  
  
  

add a comment | 

I've created a LEFT JOIN in LINQ. How do I get my query to return my nullable values?

+------+------+------+
| c1 | c2 | c3 |
|------+------+------|
| x1 | y1 | z1 |
| x2 | y2 | null |
| x3 | y3 | z1 |
+------+------+------+

Above is basically the SQL table returned after LEFT JOIN as expected

However using LINQ:

 var query = 
 ```
 into temp
 from t in temp.DefaultIfEmpty()
 select new
 
 ```,
 ```,
 Column3 = (int?)t.ColumnNo
 ;

Debugger barks at me for Column3 for:

Object reference not set to an instance of an object

c# linq

share|improve this question

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

+------+------+------+
| c1 | c2 | c3 |
|------+------+------|
| x1 | y1 | z1 |
| x2 | y2 | null |
| x3 | y3 | z1 |
+------+------+------+

 var query = 
 ```
 into temp
 from t in temp.DefaultIfEmpty()
 select new
 
 ```,
 ```,
 Column3 = (int?)t.ColumnNo
 ;

share|improve this question

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

share|improve this question

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

edited Mar 28 at 3:42

Brendan Green

9,45055 gold badges3434 silver badges6262 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

asked Mar 28 at 3:19

QmaQma

2144 bronze badges

3 Answers
3

active

oldest

votes

0

Because of your DefaultIfEmpty(), the resulting t can be null. And of course you can't get the ColumnNo from a null object.

The quick solution would be to use the null conditional operator::

Column3 = t?.ColumnNo; // assuming ColumnNo is already an int? otherwise cast to int?

Which has the same effect as:

Column3 = (t.ColumnNo != null) t.ColumnNo : null;

The null coalescing operator as others suggested won't work:

Column3 = (t.c3 ?? 0)

if t equals null, you can't get t.c3, and thus can't check if t.c3 equals null.

share|improve this answer

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you, this worked for me!
  
  – Qma
  Mar 28 at 12:22
  

  
  
  
  

add a comment | 

0

You can use ?? to set a default value if the column value is null:

 select new
 ```,
 ```,
 Column3 = (t.c3 ?? 0) // if null set its value to zero
 ;

share|improve this answer

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Isn't the issue that t is null, not that c3 is null?
  
  – Brendan Green
  Mar 29 at 2:39
  

  
  
  
  

add a comment | 

0

var list = (from PM in DataContext.table1
 join U in DataContext.table2 on PM.Id equals U.Id into obj1
 from U1 in obj1.DefaultIfEmpty()
 select new
 
 Professions = U1.ProfessionName // If null
 );

You can use DefaultIfEmpty and use that object to get the column so you can get null values in column.

share|improve this answer

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  They are already using DefaultIfEmpty(). As with the OP, wouldn't U1 be null?
  
  – Brendan Green
  Mar 29 at 2:39
  

  
  
  
  

add a comment | 

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0

Because of your DefaultIfEmpty(), the resulting t can be null. And of course you can't get the ColumnNo from a null object.

The quick solution would be to use the null conditional operator::

Column3 = t?.ColumnNo; // assuming ColumnNo is already an int? otherwise cast to int?

Which has the same effect as:

Column3 = (t.ColumnNo != null) t.ColumnNo : null;

The null coalescing operator as others suggested won't work:

Column3 = (t.c3 ?? 0)

if t equals null, you can't get t.c3, and thus can't check if t.c3 equals null.

share|improve this answer

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you, this worked for me!
  
  – Qma
  Mar 28 at 12:22
  

  
  
  
  

add a comment | 

0

Because of your DefaultIfEmpty(), the resulting t can be null. And of course you can't get the ColumnNo from a null object.

The quick solution would be to use the null conditional operator::

Column3 = t?.ColumnNo; // assuming ColumnNo is already an int? otherwise cast to int?

Which has the same effect as:

Column3 = (t.ColumnNo != null) t.ColumnNo : null;

The null coalescing operator as others suggested won't work:

Column3 = (t.c3 ?? 0)

if t equals null, you can't get t.c3, and thus can't check if t.c3 equals null.

share|improve this answer

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you, this worked for me!
  
  – Qma
  Mar 28 at 12:22
  

  
  
  
  

add a comment | 

Because of your DefaultIfEmpty(), the resulting t can be null. And of course you can't get the ColumnNo from a null object.

The quick solution would be to use the null conditional operator::

Column3 = t?.ColumnNo; // assuming ColumnNo is already an int? otherwise cast to int?

Which has the same effect as:

Column3 = (t.ColumnNo != null) t.ColumnNo : null;

The null coalescing operator as others suggested won't work:

Column3 = (t.c3 ?? 0)

if t equals null, you can't get t.c3, and thus can't check if t.c3 equals null.

share|improve this answer

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

Column3 = t?.ColumnNo; // assuming ColumnNo is already an int? otherwise cast to int?

Column3 = (t.ColumnNo != null) t.ColumnNo : null;

Column3 = (t.c3 ?? 0)

share|improve this answer

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

answered Mar 28 at 7:59

Harald CoppoolseHarald Coppoolse

14.3k33 gold badges3535 silver badges6969 bronze badges

0

You can use ?? to set a default value if the column value is null:

 select new
 ```,
 ```,
 Column3 = (t.c3 ?? 0) // if null set its value to zero
 ;

share|improve this answer

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Isn't the issue that t is null, not that c3 is null?
  
  – Brendan Green
  Mar 29 at 2:39
  

  
  
  
  

add a comment | 

0

You can use ?? to set a default value if the column value is null:

 select new
 ```,
 ```,
 Column3 = (t.c3 ?? 0) // if null set its value to zero
 ;

share|improve this answer

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Isn't the issue that t is null, not that c3 is null?
  
  – Brendan Green
  Mar 29 at 2:39
  

  
  
  
  

add a comment | 

You can use ?? to set a default value if the column value is null:

 select new
 ```,
 ```,
 Column3 = (t.c3 ?? 0) // if null set its value to zero
 ;

share|improve this answer

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

 select new
 ```,
 ```,
 Column3 = (t.c3 ?? 0) // if null set its value to zero
 ;

share|improve this answer

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

answered Mar 28 at 6:16

Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani

24.1k1919 gold badges7272 silver badges129129 bronze badges

0

var list = (from PM in DataContext.table1
 join U in DataContext.table2 on PM.Id equals U.Id into obj1
 from U1 in obj1.DefaultIfEmpty()
 select new
 
 Professions = U1.ProfessionName // If null
 );

You can use DefaultIfEmpty and use that object to get the column so you can get null values in column.

share|improve this answer

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  They are already using DefaultIfEmpty(). As with the OP, wouldn't U1 be null?
  
  – Brendan Green
  Mar 29 at 2:39
  

  
  
  
  

add a comment | 

0

var list = (from PM in DataContext.table1
 join U in DataContext.table2 on PM.Id equals U.Id into obj1
 from U1 in obj1.DefaultIfEmpty()
 select new
 
 Professions = U1.ProfessionName // If null
 );

You can use DefaultIfEmpty and use that object to get the column so you can get null values in column.

share|improve this answer

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  They are already using DefaultIfEmpty(). As with the OP, wouldn't U1 be null?
  
  – Brendan Green
  Mar 29 at 2:39
  

  
  
  
  

add a comment | 

var list = (from PM in DataContext.table1
 join U in DataContext.table2 on PM.Id equals U.Id into obj1
 from U1 in obj1.DefaultIfEmpty()
 select new
 
 Professions = U1.ProfessionName // If null
 );

You can use DefaultIfEmpty and use that object to get the column so you can get null values in column.

share|improve this answer

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges

var list = (from PM in DataContext.table1
 join U in DataContext.table2 on PM.Id equals U.Id into obj1
 from U1 in obj1.DefaultIfEmpty()
 select new
 
 Professions = U1.ProfessionName // If null
 );

share|improve this answer

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges

answered Mar 28 at 8:16

Nirav VasoyaNirav Vasoya

34433 silver badges1818 bronze badges