[SalesForce] Build a Map from a List

Assuming I have the following objects

Map<id,String> mapA = new Map<id,String>();
List<Object__c> listA =new List<Object__c>([Select id,name from Object__c]);

for(Object__c obj : listA)
mapA.put(obj.id,obj.name);

Instead of creating a map of by looping through the elements of the list, is there a faster more efficient way of achieving this?

I know that I can get some thing like Map<id,Object__c> mapA= new Map<id,Object__c>([Select id from Object__c]);
but I only want to store a name string not the whole Object__c. Is it possible to achieve this or looping through a list is the only option?

Best Answer

Per Map of sObjects, the special auto-mapping constructor only works on entire SObject values.

When working with SOQL queries, maps can be populated from the results returned by the SOQL query. The map key should be declared with an ID or String data type, and the map value should be declared as an sObject data type. (Emphasis mine)

You can't map anything other than the Id field of the SObject for the key, and you can't map anything other than the SObject itself for the value. Any other type of map must use a loop to populate the values. As I've pointed out in other answers, you can also map AggregateResult by using a Map<Id, AggregateResult> map when one of the fields that are grouped is an ID data type and aliased with the value Id (case sensitive).

Related Solutions

[SalesForce] Convert Map to List using SObject field values

There is no out of the box way to do what you want. You have to iterate. You can write some simple filter mechanisms or use a library like Selector to make your life easier. With that library, you can do things like:

List<Financial__c> paidOnly = Select.Field.isEqual(Financial__c.Status__c, 'Paid')
    .filter(idWithParent.values());

If your just checking simple equality, it's pretty easy to genericize sans library.

public static List<SObject> filterIsEqual
    (SObjectField field, Object value, List<SObject> records)
{
    List<SObject> output = new List<SObject>();
    for (SObject record : records)
        if (record.get(field) == value)
            output.add(record);
    return output;
}

[SalesForce] Creating a Map with String, Object combination

You need to index into your list. Before you do so, however, you have to check if the list is empty.

for (Account record : [/*query*/])
{
    if (!record.Children__r.isEmpty())
        accountMap.put(record.AccountNumber, record.Children__r[0].Status__c);
}

If you omit the empty check, than any iteration over a record without an active child would throw this error:

System.ListException: List index out of bounds: 0

Best Answer

Related Solutions

[SalesForce] Convert Map to List using SObject field values

[SalesForce] Creating a Map with String, Object combination

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