Solved

DataColumn.MaxLength property always returns -1 ?

Posted on 2009-04-08
11
1,003 Views
Last Modified: 2012-05-06
The client application receives the DataSet via a web service call.

Here is the code inside the web service that populates the dataset which is sent back to the client.
Dim DA As SqlDataAdapter

                Dim DS As New DataSet

                Cmd.CommandText = strSelect

                DA = New SqlDataAdapter(Cmd)

                DA.Fill(DS, "RunSQL")

                DA.Dispose()

                Con.Close()

                Return DS

Open in new window

0
Comment
Question by:tfsln
11 Comments
 
LVL 6

Expert Comment

by:HarryNS
ID: 24104005
Are you sure that dataset is getting filled up in your web service?

If so, then in your client application you can see the count of columns, DS.Tables[0].Columns.Count
0
 
LVL 9

Expert Comment

by:Sreedhar Vengala
ID: 24104007
What is your strSelect value ?
0
 
LVL 7

Expert Comment

by:Chandan_Gowda
ID: 24104088
check the dataset and make sure, the dataset is properly filled.
0
 
LVL 15

Expert Comment

by:oobayly
ID: 24115263
What's the datatype of the column? According the MSDN, "The MaxLength property is ignored for non-text columns."
http://msdn.microsoft.com/en-us/library/system.data.datacolumn.maxlength(VS.80).aspx
0
 

Author Comment

by:tfsln
ID: 24128751
HarryNS: I dont want a column count, i want the max lengths for the columns in the dataset (as specified in the database table design)

The select query is, lets say, "Select * from tablename"

I am not trying to get the MaxLength of any other columns other than varchar (the db is sql server 2005).
0
How to run any project with ease

Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
- Combine task lists, docs, spreadsheets, and chat in one
- View and edit from mobile/offline
- Cut down on emails

 
LVL 15

Accepted Solution

by:
oobayly earned 500 total points
ID: 24128999
Add the following line after you create the DataAdapter, it will tell the DataAdapter to fetch the table schema as well as the data

More information at:
http://msdn.microsoft.com/en-us/library/system.data.missingschemaaction.aspx
DA.MissingSchemAction = MissingSchemaAction.AddWithKey

Open in new window

0
 

Author Comment

by:tfsln
ID: 24133165
This doesnt seem to work when i use a complex query... Its sensitive information so i cant paste it, but are you aware of any limitations in using this property?

I often batch queries together to return multiple datatable's inside the dataset - is this a problem? Or using joins/unions?
0
 
LVL 15

Expert Comment

by:oobayly
ID: 24133312
To be quite honest, this isn't something I've ever used, so I can't say how multiple joins or returning multiple datasets will effect using the property.

However, just doing some simple testing, selecting multiple simple tables doesn't cause any issues and neither does a query that has a single inner join.
My only thought is that you may be returning composite fields, so the schema can't be returned.
0
 

Author Comment

by:tfsln
ID: 24133334
I do include composite fields... but i would have expected those fields to return the same value for MaxLength as any other field which doesnt have a max length (i.e. datetime)

If they do error, then thats a problem... Ill have to abandon this path
0
 
LVL 15

Expert Comment

by:oobayly
ID: 24133405
Interesting, I ran the following code and in all 5 tables returned the columns had the expected MaxLength properties set.
For the composite fields, the MaxLength property set was the Length of the longest string returned, whilst for the standard fields, MaxLength = 64 for a VARCHAR(64) field etc.
      SqlDataAdapter adapter= new SqlDataAdapter("SELECT * FROM tblVehicles;SELECT * FROM tblBodyTypes;"+

        "SELECT * FROM tblVehicles INNER JOIN tblBodyTypes ON tblVehicles.fldBodyID = tblBodyTypes.fldBodyID;" +

        "SELECT 'Foo' + ' ' + 'bar' AS [Foo];" +

        "SELECT fldModelDescription + 'Foo' AS [Foo] FROM tblVehicles", conn);

      adapter.MissingSchemaAction = MissingSchemaAction.AddWithKey;

      DataSet ds = new DataSet();

      adapter.Fill(ds);

Open in new window

0
 

Author Comment

by:tfsln
ID: 24133414
Interesting... Im going to need to run more tests. It logged in to our application but then failed on one of the most complex queries we have.

Its difficult, because when i test my web service it only allows me to enter text on one line - but i need to paste it a huge query over many lines just so that i can get the error message. At the moment we use the ASPAccelerator to compress web service output and a side effect is that all errors are returned as "Xml was not well formed"
0

Featured Post

Threat Intelligence Starter Resources

Integrating threat intelligence can be challenging, and not all companies are ready. These resources can help you build awareness and prepare for defense.

Join & Write a Comment

Wouldn’t it be nice if you could test whether an element is contained in an array by using a Contains method just like the one available on List objects? Wouldn’t it be good if you could write code like this? (CODE) In .NET 3.5, this is possible…
Real-time is more about the business, not the technology. In day-to-day life, to make real-time decisions like buying or investing, business needs the latest information(e.g. Gold Rate/Stock Rate). Unlike traditional days, you need not wait for a fe…
Excel styles will make formatting consistent and let you apply and change formatting faster. In this tutorial, you'll learn how to use Excel's built-in styles, how to modify styles, and how to create your own. You'll also learn how to use your custo…
Illustrator's Shape Builder tool will let you combine shapes visually and interactively. This video shows the Mac version, but the tool works the same way in Windows. To follow along with this video, you can draw your own shapes or download the file…

762 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

23 Experts available now in Live!

Get 1:1 Help Now