If (query directive) - Revision history

Olli: /* Description */

2009-08-25T10:26:46Z

‎Description

Olli: /* Examples */

2009-08-21T07:57:40Z

‎Examples

Olli at 07:55, 21 August 2009

2009-08-21T07:55:22Z

Olli at 09:01, 20 August 2009

2009-08-20T09:01:06Z

Olli at 07:44, 20 August 2009

2009-08-20T07:44:24Z

Olli at 07:37, 20 August 2009

2009-08-20T07:37:35Z

New page

== Description ==

Returns results of one of two directives depending on the input. The conditional directive is given the input of this directive. If it returns a non empty result then the then directive is used. Otherwise the else directive is used if provided or an empty result is returned.

== Constructor ==

If(Directive cond,Directive then,Directive else) - Depending on cond, returns the results of either then or else directive.

If(Directive cond,Directive then) - Depending on cond, returns the results of then directive or an empty result.

@@ Line 3: / Line 3: @@
 Returns results of one of two directives depending on the input. The conditional directive is given the input of this directive. If it returns a non empty result then the then directive is used. Otherwise the else directive is used if provided or an empty result is returned.
-You can use a pseudo directive ''If.COND'' to return the results of the conditional directive. This is useful in a typical case where you want return results of some other directive if it is not empty and something else if it is empty. using ''If.COND'' avoids having to write and execute the same subquery in both the conditional and then part. See examples on how to use this in practice.
+You can use a pseudo directive ''If.COND'' to return the results of the conditional directive. This is useful in a typical case where you want to return results of some other directive if it is not empty and something else if it is empty. using ''If.COND'' avoids having to write and execute the same sub-query in both the conditional and then part. See examples on how to use this in practice.
 == Constructor ==

← Older revision		Revision as of 07:57, 21 August 2009
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	)		)

−	This returns the superclass of input or null if it doesn't have one. Note the condition is reused with pseudo ''If.COND'' directive. This returns whatever the conditional returned. You could achieve the same results by simply duplicating the conditional query instead of using ''If.COND'' but using ''If.COND'' is both more readable and executes faster since the condition part only needs to be executed once.	+	This returns the superclass of input or null if it doesn't have one. Note how the condition is reused with pseudo ''If.COND'' directive. This returns whatever the conditional returned. You could achieve the same results by simply duplicating the conditional query instead of using ''If.COND'' but using ''If.COND'' is both more readable and executes faster since the condition part only needs to be executed once. This is a typical case where you first check if some query returns something, if it does you return that and otherwise return something else.

@@ Line 2: / Line 2: @@
 Returns results of one of two directives depending on the input. The conditional directive is given the input of this directive. If it returns a non empty result then the then directive is used. Otherwise the else directive is used if provided or an empty result is returned.
 == Constructor ==
@@ Line 12: / Line 14: @@
 == Examples ==
   importPackage(org.wandora.query2);
   new If(
-    new Exists(new Instances()),
+    new Instances(),
     new Literals("has instances"),
     new Literals("no instances")
+  )
-This example returns a string "has instances" if the input topic has instances or "no instances" if it doesn't.
+Next example returns the base name of input or first of its subject identifier if it doesn't have a base name.

← Older revision		Revision as of 09:01, 20 August 2009
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	[[Category:Query directives]]		[[Category:Query directives]]
		+
		+	== Examples ==
		+
		+	importPackage(org.wandora.query2);
		+	new If(
		+	new Exists(new Instances()),
		+	new Literals("has instances"),
		+	new Literals("no instances")
		+	)
		+
		+	This example returns a string "has instances" if the input topic has instances or "no instances" if it doesn't.

← Older revision		Revision as of 07:44, 20 August 2009
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	If(Directive cond,Directive then) - Depending on cond, returns the results of then directive or an empty result.		If(Directive cond,Directive then) - Depending on cond, returns the results of then directive or an empty result.
		+
		+	[[Category:Query directives]]