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Trigger.oldMap
Learn Trigger.oldMap in Apex with a construct-specific explanation, a unique example, a practical boundary, and a mastery check.
Trigger.oldMap is an atomic Apex topic inside Triggers. The example below uses the actual construct named by the lesson rather than a generic placeholder.
Focus on what Trigger.oldMap changes: the input, binding, control path, object state, collection, runtime effect, or language contract. Then alter one value and verify that the behavior changes for a reason specific to this feature.
Topic-specific example
trigger OppTrigger on Opportunity (after update) { Opportunity oldOpp=Trigger.oldMap.get(Trigger.new[0].Id); }
Check the input collection shape, whether the operation mutates or returns a new value, and what happens for an empty collection.