java - HQL how to use sum function for list in entity -

hi need help;

how use sum function of hql list of entity onetomany.

i try explain problem via code examples.

here invoice entity

@entity public class invoice extends extendedbaseentity {  @column(nullable = true,length = 50) private string invoiceno;  @column(nullable = true) @jsonformat(shape = jsonformat.shape.string, pattern = "yyyy-mm-dd't'hh:mm:ss.sssxxx", timezone = "eet") private date invoicedate;  @column(nullable = true,precision = 10,scale = 2) private bigdecimal amount; getters , setters..... 

and here file entity.this entity hold invoice list onetomany

@entity     public class file extends extendedbaseentity { @column(nullable = true, length = 50) private string name;  @column(nullable = true, length = 50) private string surname;  @column(nullable = true, length = 50) private string lawyercode;  @column(nullable = true, length = 50) private string sellercode;  @onetomany(cascade = cascadetype.remove, fetch = fetchtype.eager) @fetch(fetchmode.select) @joincolumn(name = "mbsfile_oid") private list<invoice> invoices = new arraylist<invoice>(); setters , getters .... 

and here hql, want sum(invoice.amount). query didn't work through, got wrong results.

select distinct             sum(invoice.amount) totalamount file  left join file.invoices invoice 

how can cope this? me,please?