Returning different types of objects in a column in a dataset

[Myron Marston]

For a WebService I am developing, I return a DataSet that contains a
table listing Field Names and Field Values. The FieldValue column is
given the type object becuase it can potentially contain any of the
primative value types (date, int, decimal, string, bool, etc).
However, when my client consumes the webservice, it is always a string,
even if the value wasn't a string when it was put into the dataset.
How do I return different types of objects in the same column of a
dataset, and get a client to recognize it?

Thanks!

[Chad Z. Hower aka Kudzu]

"Myron Marston" <gu***********@hotmail.com> wrote in
news:11*********************@o13g2000cwo.googlegro ups.com:

For a WebService I am developing, I return a DataSet that contains a
table listing Field Names and Field Values. The FieldValue column is
given the type object becuase it can potentially contain any of the
primative value types (date, int, decimal, string, bool, etc).
However, when my client consumes the webservice, it is always a string,
even if the value wasn't a string when it was put into the dataset.
How do I return different types of objects in the same column of a
dataset, and get a client to recognize it?

Web services cannot return objects. Objects are not "portable". So whats
happening is its serializing it, and for the object that you are searlizing
thats whats happening.

You can convert each one to a string (ToString or so) and then reparse on the
other side.
--
Chad Z. Hower (a.k.a. Kudzu) - http://www.hower.org/Kudzu/
"Programming is an art form that fights back"

Blog: http://blogs.atozed.com/kudzu

[Myron Marston]

It appears that Web services can return objects. I wrote a test
webservice that returns an object based on the parameter, and my client
recognized it correctly. Here is the code that works:

<WebMethod()> _
Public Function GetObject(ByVal ObjectType As String) As Object
Select Case ObjectType
Case "Date"
Return Date.Today
Case "Int"
Return 23
Case "Decimal"
Return 23.34534D
Case "Bool"
Return False
Case Else
Return New Object
End Select
End Function

However, when I try to stuff an object in a column in a datatable and
return the dataset, this fails. Here is some test code for that:

<WebMethod()> _
Public Function GetDataSet(ByVal ObjectType As String) As DataSet
Dim ds As New DataSet
Dim dt As DataTable = ds.Tables.Add("Test")
dt.Columns.Add("Object", GetType(Object))
Dim dr As DataRow = dt.NewRow
dr("Object") = GetObject(ObjectType)
dt.Rows.Add(dr)
Return ds
End Function

So, is this only a problem with datasets?

[Chad Z. Hower aka Kudzu]

"Myron Marston" <gu***********@hotmail.com> wrote in
news:11**********************@g14g2000cwa.googlegr oups.com:

It appears that Web services can return objects. I wrote a test
No, it cant. Webservcies can return VALUE types, or objects that can
convert themselves to strings. That is very different.
<WebMethod()> _
Public Function GetObject(ByVal ObjectType As String) As Object
Select Case ObjectType
Case "Date"
Return Date.Today
Case "Int"
Return 23
Case "Decimal"
Return 23.34534D
Case "Bool"
Return False
Case Else
Return New Object
End Select
End Function
Thats not returning an object.
However, when I try to stuff an object in a column in a datatable and
return the dataset, this fails. Here is some test code for that:
Yes, because as I said above you are NOT returning an object as you think.
So, is this only a problem with datasets?

No, the problem is with your understanding of whats going on. Webservices
CANNOT return objects.
--
Chad Z. Hower (a.k.a. Kudzu) - http://www.hower.org/Kudzu/
"Programming is an art form that fights back"

Blog: http://blogs.atozed.com/kudzu

[Myron Marston]

I understand the difference between value types and reference types.
Maybe I haven't been using the term "object" in a clear manner, but all
value types are objects (after all, System.ValueType derives from
System.Object, and Int32, DateTime, etc derive from System.ValueType).
Of course the webservice does not return the entire object but only a
serialized xml version of it that is deserialized into the
corresponding type on the client.

Still, my question remains: why does it work for the value type to be
correctly recognized by the client in the first example (where it was
only returning a single value) but not in the second example (where it
returned the value inside of a dataset)?

[Chad Z. Hower aka Kudzu]

"Myron Marston" <gu***********@hotmail.com> wrote in
news:11*********************@o13g2000cwo.googlegro ups.com:

For a WebService I am developing, I return a DataSet that contains a
table listing Field Names and Field Values. The FieldValue column is
given the type object becuase it can potentially contain any of the
primative value types (date, int, decimal, string, bool, etc).
However, when my client consumes the webservice, it is always a string,
even if the value wasn't a string when it was put into the dataset.
How do I return different types of objects in the same column of a
dataset, and get a client to recognize it?

Web services cannot return objects. Objects are not "portable". So whats
happening is its serializing it, and for the object that you are searlizing
thats whats happening.

You can convert each one to a string (ToString or so) and then reparse on the
other side.
--
Chad Z. Hower (a.k.a. Kudzu) - http://www.hower.org/Kudzu/
"Programming is an art form that fights back"

Blog: http://blogs.atozed.com/kudzu

[Myron Marston]

It appears that Web services can return objects. I wrote a test
webservice that returns an object based on the parameter, and my client
recognized it correctly. Here is the code that works:

<WebMethod()> _
Public Function GetObject(ByVal ObjectType As String) As Object
Select Case ObjectType
Case "Date"
Return Date.Today
Case "Int"
Return 23
Case "Decimal"
Return 23.34534D
Case "Bool"
Return False
Case Else
Return New Object
End Select
End Function

However, when I try to stuff an object in a column in a datatable and
return the dataset, this fails. Here is some test code for that:

<WebMethod()> _
Public Function GetDataSet(ByVal ObjectType As String) As DataSet
Dim ds As New DataSet
Dim dt As DataTable = ds.Tables.Add("Test")
dt.Columns.Add("Object", GetType(Object))
Dim dr As DataRow = dt.NewRow
dr("Object") = GetObject(ObjectType)
dt.Rows.Add(dr)
Return ds
End Function

So, is this only a problem with datasets?

[Chad Z. Hower aka Kudzu]

"Myron Marston" <gu***********@hotmail.com> wrote in
news:11**********************@g14g2000cwa.googlegr oups.com:

It appears that Web services can return objects. I wrote a test
No, it cant. Webservcies can return VALUE types, or objects that can
convert themselves to strings. That is very different.
<WebMethod()> _
Public Function GetObject(ByVal ObjectType As String) As Object
Select Case ObjectType
Case "Date"
Return Date.Today
Case "Int"
Return 23
Case "Decimal"
Return 23.34534D
Case "Bool"
Return False
Case Else
Return New Object
End Select
End Function
Thats not returning an object.
However, when I try to stuff an object in a column in a datatable and
return the dataset, this fails. Here is some test code for that:
Yes, because as I said above you are NOT returning an object as you think.
So, is this only a problem with datasets?

No, the problem is with your understanding of whats going on. Webservices
CANNOT return objects.
--
Chad Z. Hower (a.k.a. Kudzu) - http://www.hower.org/Kudzu/
"Programming is an art form that fights back"

Blog: http://blogs.atozed.com/kudzu

[Myron Marston]

I understand the difference between value types and reference types.
Maybe I haven't been using the term "object" in a clear manner, but all
value types are objects (after all, System.ValueType derives from
System.Object, and Int32, DateTime, etc derive from System.ValueType).
Of course the webservice does not return the entire object but only a
serialized xml version of it that is deserialized into the
corresponding type on the client.

Still, my question remains: why does it work for the value type to be
correctly recognized by the client in the first example (where it was
only returning a single value) but not in the second example (where it
returned the value inside of a dataset)?