我有一个相邻列表表帐户，带有列 account_id , name ，和 parent_account_id . 为了便于排序和显示，我创建了一个包含以下列的闭包表： ancestor , descendant ，和 depth . 因此，为了自动保持深度，我为account表创建了一个触发器和一个触发器函数：

create or replace function insert_account_relations_after_insert_account()
    returns trigger as
$$
declare
    _ancestor account_relations%rowtype;
begin

    insert into account_relations (ancestor, descendant, depth, created_by, updated_by)
    values (NEW.account_id, NEW.account_id, 0, NEW.created_by, NEW.updated_by);

    if (NEW.parent_account_id is not null) then
        for _ancestor in select ar.ancestor, ar.depth from account_relations ar where ar.descendant = NEW.parent_account_id
            loop
                insert into account_relations (ancestor, descendant, depth, created_by, updated_by)
                values (_ancestor.ancestor, NEW.account_id, _ancestor.depth + 1, NEW.created_by, NEW.updated_by);
            end loop;
    end if;

    return NEW;
end;
$$
    language plpgsql;

drop trigger if exists trigger_insert_account_relations_after_insert_account on accounts;
create trigger trigger_insert_account_relations_after_insert_account
    after insert
    on accounts
execute procedure insert_account_relations_after_insert_account();

但是，当我插入一个全新的帐户（无论 parent_account_id 是否设置），hibernate抛出 DataIntegrityViolationException 具体如下：

Resolved DataIntegrityViolationException with error ERROR: null value in column "ancestor" of relation "account_relations" violates not-null constraint
Detail: Failing row contains (159489f1-3a05-411b-a723-efb3c769af95, null, null, 0, 2021-04-19 02:41:15.907311+07, 2021-04-19 02:41:15.907311+07, null, null).
Where: SQL statement "insert into account_relations (ancestor, descendant, depth, created_by, updated_by)
    values (NEW.account_id, NEW.account_id, 0, NEW.created_by, NEW.updated_by)"

我想知道这里的根本原因是什么，如何明确解决？任何人都可以帮忙。
非常感谢，