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Friday, August 17, 2007

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DataReaders, LINQ to XML and Range Generation

I'm doing a bunch of database / XML stuff @ work, so I decided to use to VS08 beta 2 so I can use LINQ. For reasons I don't want to get into, I needed a way to convert arbitrary database rows, read using a SqlDataReader, into XML. LINQ to SQL was out, since the code has to work against arbitrary tables (i.e. I have no compile time schema knowledge). But ~~XLinq~~ LINQ to XML helped me out a ton. Check out this example:

const string ns = "{http://some.sample.namespace.schema}"; 

   
while (dr.Read())     
{     
    XElement rowXml = new XElement(ns + tableName,     
        from i in GetRange(0, dr.FieldCount)     
        select     
            new XElement(ns + dr.GetName(i), dr.GetValue(i)));     
}

That's pretty cool. The only strange thing in there is the GetRange method. I needed an easy way to build a range of integers from zero to the number of fields in the data reader. I wasn't sure of any standard way, so I wrote this little two line function:

IEnumerable<int> GetRange(int min, int max)     
{     
    for (int i = min; i < max; i++)     
        yield return i;     
}

It's simple enough, but I found it strange that I couldn't find a standard way to generate a range with a more elegant syntax. Ruby has standard range syntax that looks like (1..10), but I couldn't find the equivalent C#. Did I miss something, or am I really on my own to write a GetRange function?

Update - As expected, I missed something. John Lewicki pointed me to the static Enumerable.Range method that does exactly what I needed.

Posted By Harry Pierson at 4:55 PM Pacific Daylight Time

Comments [4]

Friday, August 17, 2007 4:56:34 PM (Pacific Standard Time, UTC-08:00)

AFAIK there's no standard way of doing it, but you could add an extension method to 'Int32'

public static IEnumerable<int> RangeFromZero(this int number)
{
for (int i = 0; i < number; i++)
{
yield return i;
}
}

and have something like

from i in dr.FieldCount.RangeFromZero()

or

from i in dr.FieldCount.Range(0)

with a 'Range' extension method, which is the same that you wrote but a little cooler ;).

Andres Aguiar

Friday, August 17, 2007 9:04:41 PM (Pacific Standard Time, UTC-08:00)

Even better is to add an Extension method to IDataReader to make it enumerable of IDataRecord, I mean semantically it is anyway...

public static IEnumerable<IDataRecord> Enumerate(this IDataReader reader)
{

using (reader)
{

while (reader.Read())

yield return reader;

}
}

Then you can do from r in reader.Enumerate() from i in GetRange(...) etc....

Alex James

Saturday, August 18, 2007 4:22:32 AM (Pacific Standard Time, UTC-08:00)

I believe System.Linq.Enumerable.Range() is exactly the same as your GetRange method.

John Lewicki

Tuesday, August 21, 2007 9:16:04 AM (Pacific Standard Time, UTC-08:00)

Another minor improvement:

XNamespace ns = "http://some.sample.namespace.schema";
while (dr.Read())
{
XElement rowXml = new XElement(ns + tableName,
from i in Enumerable.Range(0, dr.FieldCount)
select new XElement(ns + dr.GetName(i), dr.GetValue(i)));
}

Anonymous

Comments are closed.