How to compare a text value in a list of sobjects?

Question

The following gives me a list of texts which are customer numbers (CUST_NUM__c)

 List<SYSTEMS__c> lst_PartnersAcc = [SELECT CUST_NUM__c
                                             FROM SYSTEMS__c WHERE Account__c IN (Select  AccountId from AccountShare where ( UserOrGroupId IN : map_group OR  UserOrGroupId =:userId )AND RowCause IN ('Territory', 'TerritoryManual', 'TerritoryRule'))
                                             ];

I have 4 text fields in another custom object orders__c==> customer_1__c,customer_2__c,customer_3__c, customer_4__c. I'm trying to find out if **lst_PartnersAcc ** contains 1 or more of the 4 text field. My Final Aim is to find a list of orders if any matches from the string in the list.

Following is what I tried...

Attempt 1:

Set<String> tempList = new Set<String>();
tempList.addAll(lst_PartnersAcc);

Error: Compile Error: Incompatible argument type List for All method on Set

Attempt 2:

List<orders__c> orders = [select id,name from orders__c WHERE customer_1__c IN( SELECT CUST_NUM__c
                                             FROM SYSTEMS__c WHERE Account__c IN             
                                             (Select  AccountId from AccountShare where ( UserOrGroupId IN : map_group OR  UserOrGroupId =:userId )AND RowCause IN ('Territory', 'TerritoryManual', 'TerritoryRule')))
                                             ];

Error: Compile Error: Nesting of semi join sub-selects is not supported

Attempt 3

List<SYSTEMS__c> lst_PartnersAcc = [SELECT CUST_NUM__c
                                             FROM SYSTEMS__c WHERE Account__c IN  (Select  AccountId from AccountShare where ( UserOrGroupId IN : map_group OR  UserOrGroupId =:userId )AND RowCause IN ('Territory', 'TerritoryManual', 'TerritoryRule'))];

List<gew_orders__c> orders = [select id,name from gew_orders__c WHERE  GEW_SAP_Bill_to__c IN: lst_PartnersAcc OR
                                    GEW_SAP_Payer__c IN: lst_PartnersAcc OR 
                                    GEW_SAP_Ship_To IN: lst_PartnersAcc OR
                                    GEW_SAP_Sold_to__c IN: lst_PartnersAcc];

Error: Compile Error: Invalid bind expression type of SYSTEMS__c for column of type String

How should I proceed to compare 4 values to a list? Thanks in advance!

Answer 1

This should work:

List lst_PartnersAcc = [SELECT CUST_NUM__c
                                             FROM SYSTEMS__c WHERE Account__c IN (Select  AccountId from AccountShare where ( UserOrGroupId IN : map_group OR  UserOrGroupId =:userId )AND RowCause IN ('Territory', 'TerritoryManual', 'TerritoryRule'))
                                             ];
Set tempList = new Set();
for(Systems__c s : lst_PartnersAcc) {
    tempList.add(s.Cust_Num__c);
}
List orders = [select id,name from orders__c WHERE customer_1__c IN :tempList OR customer_2__c IN :tempList ETC...
                                             ];

Just needed to add the Customer Number to the set individually for each Systems__c.