Identity (query directive) - Revision history

Olli: /* Examples */

2009-08-25T10:23:33Z

‎Examples

2009-08-25T10:18:27Z

2009-08-21T07:14:08Z

‎Examples

2009-08-20T10:45:52Z

2009-08-20T07:46:51Z

2009-08-20T07:46:33Z

New page

== Description ==

Returns the input row as is.

== Constructor ==

Identity()

[[Category:Query directive]]

@@ Line 15: / Line 15: @@
   importPackage(org.wandora.query2);
   new If(
-    new Exists(new Instances()),
+    new Instances(),
     new Literals("has instances").as("#text").join(new Identity()),
     new Literals("no instances").as("#text").join(new Identity())

@@ Line 13: / Line 13: @@
 It might seem at first that there is little use for ''Identity'' directive. There are however a few cases where it is needed. You may want to join the input with results of some other directive that does not do this internally. Most common case is ''Literals'' directive. Following example returns one row with a text label indicating if the input has instances or not and the actual input. If we didn't join results of the ''Literals'' directives with ''Identity'' we would only get the text label without the input topic.
-importPackage(org.wandora.query2);
+ importPackage(org.wandora.query2);
-new If(
+ new If(
-  new Exists(new Instances()),
+   new Exists(new Instances()),
-  new Literals("has instances").as("#text").join(new Identity()),
+   new Literals("has instances").as("#text").join(new Identity()),
-  new Literals("no instances").as("#text").join(new Identity())
+   new Literals("no instances").as("#text").join(new Identity())
-−
+ )
 Identity can also be useful with ''If'' directive. You may want to modify the input if some condition is met and otherwise return the row as is. Next example returns the base names of the input topic but changes an null value to "empty" literal.

@@ Line 20: / Line 20: @@
+)
-Identity can also be useful with ''If'' directive. You may want to modify the input if some condition is met and otherwise return the row as is.
+Identity can also be useful with ''If'' directive. You may want to modify the input if some condition is met and otherwise return the row as is. Next example returns the base names of the input topic but changes an null value to "empty" literal.
-importPackage(org.wandora.query2);
+ importPackage(org.wandora.query2);
-new If(
+ new If(
-  new Identity().as("#compare").join(
+   new Compare("#DEFAULT","!=",null),
-    new Null().as("#null")
+   new Identity(),
-  ).where("#compare","!=","#null"),
+   new Literals("empty")
-  new Identity(),
+ ).from(new BaseName())
-  new Literals("empty")
+ .from(new Instances())
 ).from(new BaseName())

← Older revision		Revision as of 10:45, 20 August 2009
Line 8:		Line 8:

	[[Category:Query directives]]		[[Category:Query directives]]
		+
		+	== Examples ==
		+
		+	It might seem at first that there is little use for ''Identity'' directive. There are however a few cases where it is needed. You may want to join the input with results of some other directive that does not do this internally. Most common case is ''Literals'' directive. Following example returns one row with a text label indicating if the input has instances or not and the actual input. If we didn't join results of the ''Literals'' directives with ''Identity'' we would only get the text label without the input topic.
		+
		+	importPackage(org.wandora.query2);
		+	new If(
		+	new Exists(new Instances()),
		+	new Literals("has instances").as("#text").join(new Identity()),
		+	new Literals("no instances").as("#text").join(new Identity())
		+	)
		+
		+	Identity can also be useful with ''If'' directive. You may want to modify the input if some condition is met and otherwise return the row as is.
		+
		+	importPackage(org.wandora.query2);
		+	new If(
		+	new Identity().as("#compare").join(
		+	new Null().as("#null")
		+	).where("#compare","!=","#null"),
		+	new Identity(),
		+	new Literals("empty")
		+	).from(new BaseName())