General Trigger Pattern

General Trigger Pattern

trigger someTrigger on MyObject__c (before|after insert|update|delete){
    // Declare a collection to hold values we want to query against
    Set<Id> myIdsSet = new Set<Id>();

    // Iterate over a collection of objects, and gather the values we want to query
    //  against
    for(MyObject__c myObj :trigger.new){
        myIdsSet.add(myObj.someLookup__c);
    }

    // Declare a collection to hold records that we want to update
    List<OtherObject__c> otherObjsToUpdate = new List<OtherObject__c>();

    // Perform the main query you want to run, using the data gathered earlier
    //   to filter the query
    for(OtherObject__c otherRec :[SELECT <fields> FROM OtherObject__c WHERE Id IN :myIdsSet]){
        // The main parts of your trigger logic generally go in here

        // After you're done with the main logic, add the record to be updated
        otherObjsToUpdate.add(otherRec);
    }

    // Perform the final DML to update the records we worked on so the results are persisted
    update otherObjsToUpdate;
}