public static void assignOwnerId(List<Inventory__c> invList){

    List<User> userList = new List<User>([SELECT SAP_External_Id__c, Id
                                          FROM User
                                          WHERE SAP_External_Id__c > '0' ]);

    Map<String, String> userMap = new Map<String, String>();

    for (User userLoop:userList) {
        userMap.put(userLoop.SAP_External_Id__c, userLoop.Id);
    }

    for (Inventory__c invLoop : invList) {
        invLoop.RecordTypeID = ttiProductRecId;
        if (invLoop.SAP_Account__c  != null && userMap.get(invLoop.SAP_Account__c) != null) {
            invLoop.OwnerID = userMap.get(invLoop.SAP_Account__c);
        }
    }
}

public static void assignOwnerId(List<Inventory__c> invList){


    Set<String> sapAccountNumbers = new Set<String>();
    for (Inventory__c invLoop : invList) {
        if (invLoop.SAP_Account__c  != null) {
            sapAccountNumbers.add(invLoop.SAP_Account__c);
        }
    }

    if (sapAccountNumbers.isEmpty()) {
        return;
    }

    Map<String, Id> userMap = new Map<String, Id>();
    for (User userLoop : [SELECT SAP_External_Id__c, Id
                          FROM User
                          WHERE SAP_External_Id__c
                          IN :sapAccountNumbers]) {
        userMap.put(userLoop.TTI_SAP_Cust_No__c, userLoop.Id);
    }

    for (Inventory__c invLoop : invList) {
        invLoop.RecordTypeID = ttiProductRecId;
        if (invLoop.SAP_Account__c  != null && userMap.containsKey(invLoop.SAP_Account__c)) {
            invLoop.OwnerID = userMap.get(invLoop.SAP_Account__c);
        }
    }
}