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29 lines
1.4 KiB
Plaintext
29 lines
1.4 KiB
Plaintext
created: 20190802113703788
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modified: 20190802132727925
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tags: Filters
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title: Conditional Operators
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type: text/vnd.tiddlywiki
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<<.from-version "5.1.20">>The conditional filter operators allow ''if-then-else'' logic to be expressed within filters.
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The foundation is the convention that an empty list can be used to represent the boolean value ''false'' and a list with at one (or more) entries to represent ''true''.
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The conditional operators are:
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* [[then Operator]] replaces any input values with a constant string. For example:
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** <<.inline-operator-example "[[HelloThere]is[missing]then[FOO]]">>
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** <<.inline-operator-example "[[Missing Tiddler]is[missing]then[FOO]]">>
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* [[else Operator]] if the title list is empty then returns a constant string, otherwise returns the original title list
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** <<.inline-operator-example "[[HelloThere]is[tiddler]else[BAR]]">>
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** <<.inline-operator-example "[[Missing Tiddler]is[tiddler]else[BAR]]">>
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These operators can be combined. For example:
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<<.inline-operator-example "[[New Tiddler]is[missing]then[I am missing]else[No I am not missing]]">>
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The [[else Operator]] can be used to apply a defaults for missing values. In this example, we take advantage of the fact that the [[get Operator]] returns an empty list if the field or tiddler does not exist:
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<<.inline-operator-example "[[HelloThere]get[custom-field]else[default-value]]">>
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<<list-links "[tag[Conditional Operators]]">>
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