How to query insert data not duplicate angular firebase?

How to query insert data not duplicate angular firebase when I have old data but I want insert new data only don't insert old data.

service

  setAddTasks(id: any, tasks: any) {      this.afs.collection('ticket').doc(id)        .collection('tasks')        .add({          subject: tasks.subject,          assignTasks: tasks.assignTasks,          deadlineDate: tasks.deadlineDate        })    }  

.ts

  saveTasks() {      if (this.depositTasks.length != 0) {        for (let i = 0; this.depositTasks.length > i; i++) {          this.ticketService.setAddTasks(            this.id,            this.depositTasks[i]          )        }      }    }  

https://stackoverflow.com/questions/66881093/how-to-query-insert-data-not-duplicate-angular-firebase March 31, 2021 at 11:06AM