XPath on an XmlDataDocument

[jmagaram]

I have a DataSet I want to work with as Xml using XmlDataDocument. I can't
figure out how to query the resultant Xml using XPath. From the following XML
below, what XPath query will return the list of orders for each Male customer?

Because some tables in my DataSet have >1 foreign key columns, it is not
possible to set up a nested DataRelation for all relationships - a DataTable
can only be the child of at most one nested DataRelation. As a result, the
XmlDataDocument is tricky to navigate because I have to perform "joins" and I
don't know that XPath can do them. If there is no way to do this with XPath,
what would the XSL look like to transform the Xml below so Order appears as a
child element of Customer, in which case the XPath becomes straightforward.
In general, I want to be able to traverse my DataSet using XPath and be able
to follow every DataRelation, regardless of whether it is nested.

<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<customer>
<customerName>Justin</customerName>
<gender>Male</gender>
</customer>
<customer>
<customerName>Bob</customerName>
<gender>Male</gender>
</customer>
<customer>
<customerName>Mary</customerName>
<gender>Female</gender>
</customer>
<customer>
<customerName>Erin</customerName>
<gender>Female</gender>
</customer>
<order>
<customerName>Justin</customerName>
<orderNumber>32</orderNumber>
</order>
<order>
<customerName>Justin</customerName>
<orderNumber>74</orderNumber>
</order>
<order>
<customerName>Mary</customerName>
<orderNumber>132</orderNumber>
</order>
<order>
<customerName>Bob</customerName>
<orderNumber>98</orderNumber>
</order>
<order>
<customerName>Erin</customerName>
<orderNumber>204</orderNumber>
</order>
</root>

[Martin Honnen]

jmagaram wrote:

I have a DataSet I want to work with as Xml using XmlDataDocument. I can't
figure out how to query the resultant Xml using XPath. From the following XML
below, what XPath query will return the list of orders for each Male customer?

This XPath expression
/root/order[customerName = /root/customer[gender = 'Male']/customerName]
selects the order elements where the customerName is equal to a customer
with gender being 'Male'.

XPath can't reorder/restructure the existing document, if you need that
then you need to use an XSLT stylesheet.

Because some tables in my DataSet have >1 foreign key columns, it is not
possible to set up a nested DataRelation for all relationships - a DataTable
can only be the child of at most one nested DataRelation. As a result, the
XmlDataDocument is tricky to navigate because I have to perform "joins" and I
don't know that XPath can do them. If there is no way to do this with XPath,
what would the XSL look like to transform the Xml below so Order appears as a
child element of Customer, in which case the XPath becomes straightforward.
In general, I want to be able to traverse my DataSet using XPath and be able
to follow every DataRelation, regardless of whether it is nested.

<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<customer>
<customerName>Justin</customerName>
<gender>Male</gender>
</customer>
<customer>
<customerName>Bob</customerName>
<gender>Male</gender>
</customer>
<customer>
<customerName>Mary</customerName>
<gender>Female</gender>
</customer>
<customer>
<customerName>Erin</customerName>
<gender>Female</gender>
</customer>
<order>
<customerName>Justin</customerName>
<orderNumber>32</orderNumber>
</order>
<order>
<customerName>Justin</customerName>
<orderNumber>74</orderNumber>
</order>
<order>
<customerName>Mary</customerName>
<orderNumber>132</orderNumber>
</order>
<order>
<customerName>Bob</customerName>
<orderNumber>98</orderNumber>
</order>
<order>
<customerName>Erin</customerName>
<orderNumber>204</orderNumber>
</order>
</root>

--

Martin Honnen --- MVP XML
http://JavaScript.FAQTs.com/

[jmagaram]

It works. But how? The 'order[customerName = /root/customer[gender...' part
is confusing. If the text was 'order[customerName = Justin' I'd understand
it. But how can you have a nodeset on the right side of the '='. The '='
seems to be functioning like a set comparison - is the item on the left of
the '=' in the set on the right side. Could you explain how this works?

"Martin Honnen" wrote:

>

jmagaram wrote:

I have a DataSet I want to work with as Xml using XmlDataDocument. I can't
figure out how to query the resultant Xml using XPath. From the following XML
below, what XPath query will return the list of orders for each Male customer?

This XPath expression
/root/order[customerName = /root/customer[gender = 'Male']/customerName]
selects the order elements where the customerName is equal to a customer
with gender being 'Male'.

XPath can't reorder/restructure the existing document, if you need that
then you need to use an XSLT stylesheet.

Because some tables in my DataSet have >1 foreign key columns, it is not
possible to set up a nested DataRelation for all relationships - a DataTable
can only be the child of at most one nested DataRelation. As a result, the
XmlDataDocument is tricky to navigate because I have to perform "joins" and I
don't know that XPath can do them. If there is no way to do this with XPath,
what would the XSL look like to transform the Xml below so Order appears as a
child element of Customer, in which case the XPath becomes straightforward.
In general, I want to be able to traverse my DataSet using XPath and be able
to follow every DataRelation, regardless of whether it is nested.

<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<customer>
<customerName>Justin</customerName>
<gender>Male</gender>
</customer>
<customer>
<customerName>Bob</customerName>
<gender>Male</gender>
</customer>
<customer>
<customerName>Mary</customerName>
<gender>Female</gender>
</customer>
<customer>
<customerName>Erin</customerName>
<gender>Female</gender>
</customer>
<order>
<customerName>Justin</customerName>
<orderNumber>32</orderNumber>
</order>
<order>
<customerName>Justin</customerName>
<orderNumber>74</orderNumber>
</order>
<order>
<customerName>Mary</customerName>
<orderNumber>132</orderNumber>
</order>
<order>
<customerName>Bob</customerName>
<orderNumber>98</orderNumber>
</order>
<order>
<customerName>Erin</customerName>
<orderNumber>204</orderNumber>
</order>
</root>

--

Martin Honnen --- MVP XML
http://JavaScript.FAQTs.com/

[Martin Honnen]

jmagaram wrote:

It works. But how? The 'order[customerName = /root/customer[gender...' part
is confusing. If the text was 'order[customerName = Justin' I'd understand
it. But how can you have a nodeset on the right side of the '='. The '='
seems to be functioning like a set comparison - is the item on the left of
the '=' in the set on the right side. Could you explain how this works?

In

> /root/order[customerName = /root/customer[gender = 'Male']/customerName]

/root/order selects all order elements which are children of the root
element. What follows in square brackets is a predicate that filters out
nodes based on the condition. The condition compares customerName child
element(s) of the order to customerName child elements of customer
elements which have a gender child element with string value 'Male'.

For such a comparison of two node sets the rule

"If both objects to be compared are node-sets, then the comparison
will be true if and only if there is a node in the first node-set and a
node in the second node-set such that the result of performing the
comparison on the string-values of the two nodes is true."

from the XPath specification <http://www.w3.org/TR/xpath#booleans>
holds. So the string value of one of the customerName child elements of
order needs to be equal to the string value of one of the customer name
child elements of the customer elements for which the gender is as
specified.

--

Martin Honnen --- MVP XML
http://JavaScript.FAQTs.com/