monogatari

Cannot DataSet be read from streaming XmlReader?

DataSet.ReadXml() is still hot - here "hot" does not mean any good, especially confronting upcoming beta1 release.

In the comment to my blog post, I was asked if we can provide XmlDocument-less DataSet.ReadXml(). I have been developing anothe implementation , but I had no certain answer about that question. However, I found one problematic design in MS.NET.

MS.NET infers a data columns in a certain order. It infers:

1. A Hidden primary key column: If the table element contains another table element


2. Element columns: that will be either a Hidden reference column, or a simple type element. They are in appeared order (i.e. unorderd by their ColumnMapping types).
   
3. Finally Attribute columns

This instance will assert my inference above.

Then, there is a problem. Because

1. Attributes can be read only when the XmlReader is on startElement


2. We cannot fill a datarow for detached column


3. We cannot change column orders (at least without removal of the existing column content for each row)

So if the column order is their "design", then Microsoft's ReadXml() implementation is bound to DOM.

Then what shuold we do? Two ideas occured to me: A) ignore such column orders (or addint column order replacement internally), or B) separate inference engine and data loading engine. My current implementation is A) but I think B) would be better since it won't be complicated. Moreover, there are many System.Data hackers so that I don't want to impact on the basic class changes
except for xml support stuff. However, I have no idea if we have enough time to develop B)... I have many things that should be fixed such as ReadXmlSchema(), TypedDataSetGenerator, XmlDataDocument, SqlTypes etc.

Posted by atsushi at April 29, 2004 09:55 AM