[SalesForce] any solution to simulate trigger behaviour on public group membership

If you navigate to the user detail page, there is a section for Group Memberships. If there are more than 5 records under the list, you will get a link 'Go To List' that takes you to the list of groups. We have made use of this page.

Here is the code snippet.

//create a page reference to the standard salesforce page.
//pass the id of the user in context.
PageReference page = new PageReference('/_ui/system/user/GroupMembershipPage/d?userId=005Q000000O4AK6');

//get the html content of the page
String html = page.getContent().toString();

//set of group ids
Set<Id> groupsIds = new Set<Id>();

//if you study the html code of the page, you will understand the below string we have used for the string functions.
while(html.contains('/setup/own/groupdetail.jsp?id=')) {
    html = html.subString(html.indexOf('/setup/own/groupdetail.jsp?id=') + 1);
    String groupId = html.subString(html.indexOf('=') + 1 , html.indexOf('"'));
    System.debug('***** ' + groupId);
    groupIds.add(groupId);
}

Your code will look like this:

List<GroupMember> members = [ SELECT Id, GroupId, UserOrGroupId 
                            FROM GroupMember 
                            WHERE GroupId IN (SELECT id FROM Group where Id = :groupId) ];

List<Id> ids = new List<Id>();
for(GroupMember member: members) {
   ids.add(member.UserOrGroupId);
}
List<Group> lstGroup = [SELECT Name, RelatedId, Type, Id From Group WHERE Id IN:ids];

RelatedId will be the Type of Id. For Groups of type “Role,” the ID of the associated UserRole. The RelatedId field is polymorphic.

and Type will display as User, Role, Partner User etc as shown in your picture

Description Type of the Group. One of the following values:

Regular—Standard Public Group. When you create() a Group, its type must be Regular, unless a partner portal is enabled for the organization, in which case the type can be Regular or PRMOrganization.

Role—Public Group that includes all of the User records in a particular UserRole.

RoleAndSubordinates—Public Group that includes all of the User records in a particular UserRole and all of the User records in any subordinateUserRole.

Organization—Public Group that includes all of the User records in the organization. This Group is read-only.

Case—Public group of users, members of a queue that can own a Case.

Lead—Public group of users, members of a queue that can own a Lead.

Manager—Public group that includes a user’s direct and indirect managers. This Group is read-only.

ManagerAndSubordinatesInternal—Public Group that includes a user and the user’s direct and indirect reports. This Group is read-only.

PRMOrganization—Public Group that includes all of the partners in an organization that has the partner portal feature enabled.

Queue—Public Group that includes all of the User records that are members of a queue.

Territory—Public Group that includes all of the User records in an organization that has the territory feature enabled.

TerritoryAndSubordinates—Public Group that includes all of the User records in a particular UserRole and all of the User records in any subordinateUserRole.

Collaboration—Chatter group.

Only Regular, Case, and Lead can be used when creating a group. The other values are reserved.