Efficiently Generate a Set from List

Question:

I have a SOQL query that returns a List<SObject> structure, and I need to convert this into a Set<Id> to pass to another method. The method’s signature cannot be changed, so I must provide the data in the required format. What is the best way to achieve this conversion? Would a simple for loop suffice, or are there other options I should consider?

Answer:

Yes, a simple for loop can accomplish this. By iterating through the List<SObject>, you can extract the IDs and add them to a Set<Id>. This approach is both straightforward and efficient for typical use cases where the List<SObject> does not contain duplicates.

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Here’s an example:

List<SObject> records = [SELECT Id FROM Account LIMIT 10];
Set<Id> recordIds = new Set<Id>();
for (SObject record : records) {
    recordIds.add(record.Id);
}

Code explanation:
The code performs a SOQL query to retrieve up to 10 Account records and stores them in a List<SObject>. It then iterates through the list, extracts the Id of each record, and adds it to a Set<Id>, ensuring a collection of unique IDs.

However, there are alternative methods that can be used depending on your requirements.

1.Using a Map to Avoid Duplicates:

If the source of the List<SObject> is not guaranteed to be unique (e.g., if the list was constructed manually or processed elsewhere), using a Map<Id, SObject> is a safer option. This avoids issues caused by duplicate IDs in the list, which can lead to runtime errors. Here’s an example:

List<SObject> records = new List<SObject>();
records.add([SELECT Id FROM Account LIMIT 1]); // Add a record
records.add(records[0]); // Add a duplicate

Map<Id, SObject> recordsMap = new Map<Id, SObject>();
recordsMap.putAll(records); // Handles duplicates internally
Set<Id> recordIds = recordsMap.keySet();

Code explanation:
The code demonstrates handling duplicates in a List<SObject> by using a Map<Id, SObject>. Adding the list to the map with putAll ensures only unique records are retained, as duplicate IDs are automatically overwritten, and the resulting Set<Id> is extracted using the map’s keySet() method.

2.Using SOQL Results Directly:

If you are working with SOQL query results directly, the Map<Id, SObject> constructor provides a compact solution. This works because SOQL guarantees unique IDs for query results:

List<SObject> records = [SELECT Id FROM Account LIMIT 10];
Set<Id> recordIds = new Map<Id, SObject>(records).keySet();

Code explanation:
The code performs a SOQL query to fetch 10 Account records and stores them in a List<SObject>. It then creates a Map<Id, SObject> using the list, automatically mapping each record’s Id as the key, and extracts the keys as a Set<Id> for further use.

3.Utility Method Example:

public static Set<Id> getRecordIds(List<SObject> records) {
    return new Map<Id, SObject>(records).keySet();
}

Code explanation:
The getRecordIds method converts a List<SObject> into a Set<Id> by leveraging the Map<Id, SObject> constructor, which automatically uses the IDs of the records as keys. This ensures any duplicate IDs are handled efficiently, and the resulting keySet() provides a unique collection of IDs.

Using the Map approach is robust but may be slower than a basic for loop due to additional overhead. For guaranteed unique SOQL results, all methods work seamlessly. If working with potentially non-unique lists, prefer the Map method for safety.

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