I have created the below table stafftable but when I'm trying to insert it's showing an error

CREATE TYPE accounttype AS OBJECT( no varchar2(10), name varchar2(10), balance number(10), dob date, member function age return number );

CREATE TYPE BODY accounttype AS
MEMBER FUNCTION age RETURN NUMBER
AS
BEGIN
RETURN FLOOR(MONTHS_BETWEEN(sysdate,dob)/12);
END age;
END;
/

CREATE TYPE account_branchtype AS OBJECT( account REF accounttype, branch  varchar2(10) );

create type account_branchtabletype as table of account_branchtype;

create type stafftype as object(staff_id varchar2(20),name varchar2(20) ,sal number(20), other_details varchar2(20) , emp8 account_branchtabletype ,dob date , member function getage return number);

create or replace type body stafftype as member function getage return number
as
begin
return(round((sysdate-dob)/365));
end getage;
end;
/

create table stafftable of stafftype nested table emp8 store as relaccount_branch8;

insert into stafftable values(stafftype('S01','Captain','account',20000,'abc','24-apr-1993'));
insert into stafftable values(stafftype('S02','Thor','manager',30000,'pqr','14-jun-1993'));

insert into account_branchtable values('B01','manager','andheri',stafftabletype(stafftype('S01','Captain','account',20000,'abc','24-apr-1993')));
insert into account_branchtable values('B02','asst manager','sion',stafftabletype(stafftype('S02','Thor','manager',30000,'pqr','14-jun-1993')));

Showing error as inconsistent datatypes: expected schema.ACCOUNT_BRANCHTABLETYPE got CHAR when I'm trying to insert data into Stafftable.

Fiddle = https://dbfiddle.uk/zDdqEJdx.

Solution

You do not have a table account_branchtable (and you probably don't want it).

What you probably want is to create a collection of REFs:

create type account_branchtabletype as table of REF account_branchtype;

Then create your staff type:

create type stafftype as object(
  staff_id      varchar2(20),
  name          varchar2(20),
  sal           number(20),
  other_details varchar2(20),
  emp8          account_branchtabletype,
  dob           date,
  member function getage return number
);

create or replace type body stafftype as member function getage return number
as
begin
return FLOOR(MONTHS_BETWEEN(sysdate,dob)/12);
end getage;
end;
/

Then create the table:

create table stafftable of stafftype (
  staff_id PRIMARY KEY
) nested table emp8 store as relaccount_branch8;

ALTER TABLE relaccount_branch8 ADD SCOPE FOR (COLUMN_VALUE) IS account_branch;

Then you can insert the staff with the nested table values:

insert into stafftable (staff_id, name, sal, other_details, emp8, dob)
values(
  'S01',
  'Captain',
  20000,
  'abc',
  account_branchtabletype(
    (SELECT REF(b) FROM account_branch b WHERE b.account.no = '19DCS001' AND b.branch = 'Manjalpur')
  ),
  DATE '1993-04-24'
);

fiddle