{previous:ids:current_id}

Description

Returns the id that comes immediately before current_id in a dash-separated list of ids. Use it to build a backward (Previous) link on a detail page: feed a list of item ids and the id of the item being shown, and previous gives you the id of the preceding item. The list is usually a query result from ids, but any dash-separated list works (the values need not be ids). Returns an empty string when current_id is the first entry, is not found in the list, or when either argument is empty - so a Previous link naturally disappears on the first item. The list is split on the dash and empty segments from a doubled or trailing dash are dropped, which can break the lookup; keep the separators clean. The mirror command next returns the id after current_id.

Parameters

ids required

Dash-separated list of ids (or any values) to step through, in order. Usually the output of {ids:...} - a query result - but any dash-separated string works. Empty segments from a doubled or trailing dash are dropped and can shift positions, so keep the separators clean.

current_id required

The id whose predecessor you want, taken from the ids list. It must be the same id type (long or short) as the entries in ids. If current_id is the first entry, is not found in the list, or is empty, previous returns an empty string.

Examples

test{previous:12-34-56:34}

Expected12

Actual12

The basic shape. Given a dash-separated list and the current value 34, previous returns the value that comes before it, 12.

test{previous:alpha-beta-gamma-delta:gamma}

Expectedbeta

Actualbeta

The entries do not have to be ids - previous steps through any dash-separated list. The value before gamma is beta.

test{previous:12-34-56:12}

When current_id is the first entry in the list, previous returns an empty string. This is how a Previous link hides itself on the first item.

test{previous:12-34-56:99}

If current_id is not found in the list, previous returns an empty string (it does not guess or return the last item).

test{previous:{ids:9e1d2b9f88e3d6c3bf0eb967378610d6}:4f3362a62847fe1f8c59ba28a92d42c0}

Expected5726c2c6b035d7aab450d1794e9e90d7

Actual5726c2c6b035d7aab450d1794e9e90d7

The everyday pattern: feed a queried set straight into previous. {ids:...} returns the ids of a slice in display order, and previous gives the id that precedes the current one - here the id of the item shown before 4f3362a62847fe1f8c59ba28a92d42c0.

test{previous:12--56:56}

A doubled dash leaves an empty segment, which previous drops while keeping the original positions. That leaves a gap right before 56, so previous finds nothing and returns empty. Keep the separators clean - usually the list comes straight from {ids:...}.

test{iftext:{previous:12-34-56:34}:Previous is {previous:12-34-56:34}:no previous}

ExpectedPrevious is 12

ActualPrevious is 12

The detail-page idiom, made concrete. iftext prints its middle branch only when the condition is non-empty, so a Previous link shows only when a preceding item exists. On the first item previous returns empty and the link disappears.

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