Why we cannot perform DML operation on SET type collection variable in Salesforce?

Hello Kapil,

Yes, we can't perform DML operation on Set collection -

1) List -> Ordered(Allows indexing), Allow duplicacy and Allow DML.
List<Integer> lstArr = new List<Integer>{1, 2, 3};
system.debug(lstArr[1]); //Valid

1) Set-> Unordered(Does not allows indexing) and did't Allow duplicacy.
Set<Integer> setArr= new Set<Integer>{1, 2, 3};
system.debug(setArr[1]); //Not valid

For DML operation - In the case of sets ,we can't use DML over sObjects. in that we need to add all Data in set to list and go for DML once again.

Hope it helps

Hi,

One reason may be that Set<SObject> is a risky mechanism to use: equality is based on all the fields (so is expensive) and if fields are changed logic can easily break. Same problem using SObject as a Map key. So not a pattern to be encouraged.

But perhaps just because also supporting Set<SObject> adds a bunch of extra methods that need documenting and supporting

Hope this helps.