How to define a map with id and list<case> of records

Question

I need to store it in a map with List as child and Id as parent

For an example my data spit something like this just to give you an idea:

DEBUG|//PId :  500o0000008V0alBAC
DEBUG|//Child: CaseNumber: 12345A Status: Not Started

DEBUG|//PId :  500o0000008V0alBAC
DEBUG|//Child: CaseNumber: 12345B Status: Not Started

DEBUG|//PId :  500o0000008V0alBAC
DEBUG|//Child: CaseNumber: 12345C Status: Not Started

DEBUG|//PId :  500o0000008V0alBAC
DEBUG|//Child: CaseNumber: 12345D Status: Not Started 

//many more different Pid and Child ....

How can I store that in Map?, something like this?

 Map<Id, List<Case>> parentChildCase = new map<Id, List<Case>>();

Here is my code that render the above debug code:

Map<id, id> pcids = new Map<id, id>(); 
//....

for(Case c :[/*SOQL*/]) {
   if(pcids.containskey(c.ParentId) {
     system.debug('//Pid: ' + parents.get(c.pareintid));
     system.debug('Child: ' + c);
   }
}

Answer 1

If i'm understanding this correctly you have a Case, and that case can have any number of cases under it. So you need a Map<ID, List<Case>>, this is how I would solve that.

Map<Id, List<Case>> parentChildCase = new Map<Id, List<Case>>();
Map<ID, Case> cMap = new Map<ID, Case>([SELECT Id, ..., FROM Case]);

for(ID c : cMap.keySet()) 
{
    if(parentChildCase.containsKey(cMap.get(c).ID)) 
    {
        parentChildCase.get(cMap.get(c).ID).add(cMap.get(c));
    }
    else
    {
        List<Case> cases = new List<Case>();
        cases.add(cMap.get(c));
        parentChildCase.put(cMap.get(c).ID, cases);
    }
}   

Answer 2

Check to see if you map containsKey of the parent Id. If it does not contain the key then create a new list and add it to the map. If it does contain the key then get the list from the map, add the new values, then add the list back to the map..