[apex] New Rule: OperationWithHighCostInLoop

[tprouvot]

Proposed Rule Name: OperationWithHighCostInLoop

Proposed Category: Performance

Description:
Methods Schema.getGlobalDescribe() or Schema.describeSObjects should be called once per an apex transaction and should never be called inside a loop.

Code Sample: This should include code, that should be flagged by the rule. If possible, the "correct" code
according to this new rule should also be demonstrated.

//to avoid
Set<String> fieldNameSet = new Set<String> {'Id'};
		for (String fieldNameOrDefaultValue : fieldNameOrDefaultValueList) {
			if (Schema.getGlobalDescribe().get(objectName).getDescribe().fields.getMap().containsKey(fieldNameOrDefaultValue.trim() )) {
				fieldNameSet.add(fieldNameOrDefaultValue);
			}
		}
//correct
Set<String> fieldNameSet = new Set<String> {'Id'};
		Map<String, Schema.SObjectField> fieldMap = Schema.getGlobalDescribe().get(objectName).getDescribe().fields.getMap();
		for (String fieldNameOrDefaultValue : fieldNameOrDefaultValueList) {
			if (fieldMap.containsKey(fieldNameOrDefaultValue.trim())) {
				fieldNameSet.add(fieldNameOrDefaultValue);
			}
		}

Additional Information:
See also: Why is Schema.describeSObjects(types) Slower Than Schema.getGlobalDescribe()?

Possible Properties:

• Should this rule be customizable via properties?