Exists (XmlDoc/XmlNode function): Difference between revisions
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{{Template:XmlDoc/XmlNode:Exists subtitle}} | {{Template:XmlDoc/XmlNode:Exists subtitle}} | ||
<var>Exists</var> returns a [[Using Boolean enumerations|Boolean enumeration]] whose value is <code>True</code> if the XPath result is non-empty, and <code>False</code> otherwise. | |||
==Syntax== | ==Syntax== | ||
{{Template:XmlDoc/XmlNode:Exists syntax}} | {{Template:XmlDoc/XmlNode:Exists syntax}} | ||
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<table class="syntaxTable"> | <table class="syntaxTable"> | ||
<tr><th>%boolean</th> | <tr><th>%boolean</th> | ||
<td>A declared enumeration object of type Boolean to contain the returned value of <var>Exists</var>. </td></tr> | <td>A declared enumeration object of type <var>[[Boolean]]</var> to contain the returned value of <var>Exists</var>.</td></tr> | ||
<tr><th>nr</th> | <tr><th>nr</th> | ||
<td>An <var>XmlDoc</var> or <var>XmlNode</var>, used as the context node for the < | <td>An <var>XmlDoc</var> or <var>XmlNode</var>, used as the context node for the <var class="term">XPath</var> expression. If an <var>XmlDoc</var>, the <var>Root</var> node is the context node.</td></tr> | ||
<tr><th>xpath</th> | <tr><th>xpath</th> | ||
<td>A <var>Unicode</var> string that is an XPath expression that results in a nodelist. The expression default is a period (.), that is, the node referenced by the method object ( | <td>A <var>Unicode</var> string that is an XPath expression that results in a <var>nodelist</var>. The expression default is a period (<code>.</code>), that is, the node referenced by the method object (<var class="term">nr</var>). | ||
Prior to <var class="product">[[Sirius Mods|"Sirius Mods"]]</var> Version 7.6, this is an EBCDIC string.</td></tr> | |||
</table> | </table> | ||
==Usage notes== | ==Usage notes== | ||
<ul> | <ul> | ||
<li>If you are only checking for the existence of some nodes in the document, | <li>If you are only checking for the existence of some nodes in the document, <var>Exists</var> is the most efficient method. | ||
<var>Exists</var> is the most efficient method. | <ul><li><var>[[SelectCount (XmlDoc/XmlNode function)|SelectCount]]</var> has the relative disadvantage that it may continue to examine the <var>XmlDoc</var> tree after the first matching node is found. | ||
<var>[[SelectCount (XmlDoc/XmlNode function)|SelectCount]]</var> has the relative disadvantage that it may | <li><var>[[SelectSingleNode (XmlDoc/XmlNode function)|SelectSingleNode]]</var> has a similar disadvantage: it may visit nodes in an order other than the document order, and, since it guarantees to return the first node in <var>XmlDoc</var> order, it may continue even after the first match is found. | ||
continue to examine the <var>XmlDoc</var> tree after the first matching node is found. | </ul></ul> | ||
<var>[[SelectSingleNode (XmlDoc/XmlNode function)|SelectSingleNode]]</var> has a similar | |||
disadvantage: it may visit nodes in an order | |||
other than the document order, and, since it guarantees to | |||
return the first node in <var>XmlDoc</var> order, it may continue even after | |||
the first match is found. | |||
</ul> | |||
The following request tests two XPath results: | ===Examples=== | ||
<p class="code"> | <ol><li>The following request tests two XPath results: | ||
%d | <p class="code">begin | ||
%d = New | %d object xmlDoc | ||
%d = New | |||
print 'Root exist?' And %d:Exists('.'):ToString | |||
print 'Elem of empty doc exist?' And %d:Exists('*'):ToString | |||
end | |||
</p> | </p> | ||
The example results follow: | The example results follow: | ||
<p class="code">Root exist? True | <p class="code">Root exist? True | ||
Elem of empty doc exist? False | Elem of empty doc exist? False | ||
</p> | </p></ol> | ||
===Request-Cancellation Errors=== | ===Request-Cancellation Errors=== | ||
| Line 55: | Line 44: | ||
==See also== | ==See also== | ||
<ul> | <ul> | ||
<li>For more information about using XPath expressions, see [[XPath|"XPath"]]. | <li>For more information about using XPath expressions, see [[XPath|"XPath"]]. | ||
</ul> | </ul> | ||
{{Template:XmlDoc/XmlNode:Exists footer}} | |||
Revision as of 12:38, 27 April 2011
Is XPath result non-empty? (XmlDoc and XmlNode classes)
Exists returns a Boolean enumeration whose value is True if the XPath result is non-empty, and False otherwise.
Syntax
%boolean = nr:Exists( xpath) Throws XPathError
Syntax terms
| %boolean | A declared enumeration object of type Boolean to contain the returned value of Exists. |
|---|---|
| nr | An XmlDoc or XmlNode, used as the context node for the XPath expression. If an XmlDoc, the Root node is the context node. |
| xpath | A Unicode string that is an XPath expression that results in a nodelist. The expression default is a period (.), that is, the node referenced by the method object (nr).
Prior to "Sirius Mods" Version 7.6, this is an EBCDIC string. |
Usage notes
- If you are only checking for the existence of some nodes in the document, Exists is the most efficient method.
- SelectCount has the relative disadvantage that it may continue to examine the XmlDoc tree after the first matching node is found.
- SelectSingleNode has a similar disadvantage: it may visit nodes in an order other than the document order, and, since it guarantees to return the first node in XmlDoc order, it may continue even after the first match is found.
Examples
- The following request tests two XPath results:
begin %d object xmlDoc %d = New print 'Root exist?' And %d:Exists('.'):ToString print 'Elem of empty doc exist?' And %d:Exists('*'):ToString end
The example results follow:
Root exist? True Elem of empty doc exist? False
Request-Cancellation Errors
- xpath is invalid.
- Insufficient free space exists in CCATEMP.
See also
- For more information about using XPath expressions, see "XPath".