Re: Determing SQL Server Type from C# - C# Discussion Boards

29-Oct-02 9:28

Does anyone know how I can find out the SQL Server type of a db column from within C#. I know that when I obtain data in a DataTable, each of the DataColumn objects contain information about the column including the column name and the data type, however, the type that it provides is a System.* C# type. Is there any way to determine the SQL Server type name (e.g. int, smallint, etc.) programmatically?

TIA

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

leppie29-Oct-02 10:23

29-Oct-02 10:23

Hi
I presume you have a DataSet to transfer the data? Well, just look in there Smile | :)

"There are no stupid question's, just stupid people."

perlmunger29-Oct-02 10:54

29-Oct-02 10:54

I've been looking in there through the debugger as well as in the DataTable and DataColumn and I don't see anything that would tell me the type or the length of the individual columns. Do you know of something more specific?

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

leppie29-Oct-02 11:05

29-Oct-02 11:05

Your dataset contains the mapping from SQL types to .NET types, if you dont have a dataset (which I doubt), just get one of the data adapters auto generate u one. Then double click that file (the .xsd file) and it will show the equivalent SQL types. For the length of each type (of each parameter), that too get auto generated if you are using stored procedures.

Hope this helps Smile | :)

"There are no stupid question's, just stupid people."

perlmunger29-Oct-02 11:11

29-Oct-02 11:11

You say that "Your dataset contains the mapping from SQL types to .NET types...". I do have a DataSet, I just don't know where this mapping is that you are referring to. What member of the DataSet contains this information? You understand that I want to obtain this info programmatically, right?

Thanks again.

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

leppie29-Oct-02 11:39

29-Oct-02 11:39

perlmunger wrote:
You understand that I want to obtain this info programmatically, right?

No, but i do now Smile | :)

<dataset instance="">.<tablename>.Columns["Usersorwhatever"].....oh damn I have no idea, where that takes place... Confused | :confused:

You can find out the .NET types, so I assume the cast from SQL to .NET is auto, inserting values u need the SqlType and width though, so I'm not sure how this is done. I will look tomorrow, I need some desperate sleep Sleepy | :zzz:

"There are no stupid question's, just stupid people."

Stephane Rodriguez.29-Oct-02 18:36

Stephane Rodriguez.

29-Oct-02 18:36

I would avoid to use the dataset because at this point they have already done some type mapping (either CTS, or XSD).

Here is the code for retrieving the internal SQL Server data type for any database table columns :

DataTable oTable = new DataTable();
SqlDataAdapter oAdapter = new SqlDataAdapter("SELECT * FROM INFORMATION_SCHEMA.COLUMNS", m_oConnection);

This stores the result of the system query in oTable. Then you just need to lookup the rows of this table. Interesting columns are of course "COLUMN_NAME" and "DATA_TYPE".

If you have SQLServer installed, I guess this kind of things should be known by you a million times already, because you can see these things in the SQL Enterprise manager GUI.

How low can you go ?
(MS rant)

perlmunger30-Oct-02 9:07

Pass By Reference Problem

30-Oct-02 9:07

I finally found a similar answer on google this morning. I am new to SQL Server, so I had no idea. Thanks for your help.

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

perlmunger29-Oct-02 6:34

29-Oct-02 6:34

I'm not sure what is going on here, but I hope there's someone who knows why this happens. Basically, I have a base class and an inherited class, something like this:

public abstract class Base {}
public class Inherited : Base {}

I also have a class that populates inherited objects called ObjectBuilder. It is a singleton and it has a method called PopulateObject. Here is the code to do what I want:

Inherited i = new Inherited();

ObjectBuilder ob = ObjectBuilder.GetInstance();

ob.PopulateObject( ref i );

// Do something with i

The problem is that the signature for PopulateObject takes a ref to Base. If I understand the is-a relationship properly, doing so should work and in fact, when I remove the 'ref' keyword from the declaration as well as implementation, it builds fine. It just won't work properly because it is at that point passing a copy (isn't it?). What is going on here? Why will it build without error when I pass a copy, but fails when I pass by reference?

Any help would be greatly appreciated.

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

Daniel Turini29-Oct-02 6:40

Daniel Turini

29-Oct-02 6:40

Which error message is your compiler giving?

lazy isn't my middle name.. its my first.. people just keep calling me Mel cause that's what they put on my drivers license. - Mel Feik

perlmunger29-Oct-02 6:51

29-Oct-02 6:51

See below...

The best overloaded method match for 'DataNamespace.ObjectBuilder.PopulateObject( ref DataNamespace.Base)' has some invalid arguments
'Argument '1': cannot convert from 'ref DataNamespace.Inherited' to 'ref DataNamespace.Base'

Thanks.

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

leppie29-Oct-02 7:42

29-Oct-02 7:42

You are infact passing by reference by default unless your base class is infact of a value-type! Smile | :)

"There are no stupid question's, just stupid people."

perlmunger29-Oct-02 9:18

29-Oct-02 9:18

I went ahead and tried to run my app without the ref parameter and it worked--which led me to the same conclusion. I looked back at my Programming C# book (Oreilly) and sure enough, the example where he is using this is with value types. Oy!! People who think that C# and Java are the same are smoking crack. I like C# better because you can pass a value type by reference if you want to(in java you have to use the Integer, Double, etc. classes to do so). Thanks for your help.

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall

LongRange.Shooter29-Oct-02 8:42

LongRange.Shooter

29-Oct-02 8:42

There was an obscure white paper I ran across once on the MSDN site which discussed the use of ByVal vs. Ref in application of VB.NET vs. C#.NET.

It basically stated that C#, by default, passes parameters as ref. So if you specify MyMethod(ref someParameter) what you are doing is passing a pointer to the pointer for the parameter. This could explain the illegal reference compile error if you are using the parameter as a parameter pointing to a data area within the caller, rather than a pointer pointing back to a pointer which points to the data area within the caller. Dead | X|

gives me a headache just describing it. Big Grin | :-D

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Once I thought I was wrong
but I was happy to discover that was a mistake.

Condor

perlmunger29-Oct-02 9:20

29-Oct-02 9:20

I know what you mean about a headache. It's not so bad once you get used to it, I suppose, but I'm used to C++ and trying to make the transition to C#. Probably a few more headaches along the way. I guess the rule of thumb with C# is if you think it's complicated, you're probably just making it so. Thanks for your help. I appreciate it.

-Matt

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The 3 great virtues of a programmer:
Laziness, Impatience, and Hubris.
--Larry Wall