Perform aggregate query on multiple nested fields.
Sum income field and output field respectively for each document.

The expected result:

To use MongoDB script to handle the multiple fields, you need to store values of income and output fields as arrays using project+filter+cond method under aggregate, split them into records, get the cumulative sum and then group records by _id and concatenate them. This is complicated.

Since grouping by product isn’t required, you can use esProc SPL to get this done. The sum values of each record can be calculated by performing sum operation on sequences.
Download esProc installation package HERE.

Directions to implement the esProc algorithm:

1. Write SPL script computer.dfx in esProc:

2． Debug and execute the script and view A2’s value as follows:

3. Execute the script and return the final result:

esProc provides JDBC interface, so you can easily integrate the script into a Java program:

public static void doComputer() {
  Connection con = null;
  java.sql.Statement st;
 
  try{
    Class.forName("com.esproc.jdbc.InternalDriver");
    con = DriverManager.getConnection("jdbc:esproc:local://"); 
// Call script computer.dfx
    st=con.createStatement();
ResultSet rst = st.executeQuery("call computer");
 
     System.out.println(rst);
   } catch(Exception e){
     System.out.println(e);
   } finally{
    // Close database connection
    if (con!= null) {
      try {
        con.close();
       } catch(Exception e) {
        System.out.println(e);
       }
    }
   }
}
 

Read How to Call an SPL Script in Java to learn more about integration of esProc SPL script into a Java program.