JpaRepository.deleteAll() not working without calling JpaRepository.count()

I have 3 tables with 1:N relations, something like:

create table tbl1(    id bigserial primary key    name varchar unique not null    ...);create table tbl2(    id bigserial primary key,    tbl1_id bigint not null,    constraint tbl2_1_fk foreign key(tbl1_id) references tbl1.id    ...);create table tbl3(    id bigserial primary key,    tbl2_id bigint not null,    constraint tbl3_2_fk foreign key(tbl2_id) references tbl2.id    ...)

And entities for them:

@Entity@Table(name="tbl1")public class Ent1 implements Serializable {...    @OneToMany(mappedBy = "ent1", fetch = FetchType.LAZY,         cascade = CascadeType.ALL, orphanRemoval = true)    private List<Ent2> ent2 = new ArrayList<>();...}@Entity@Table(name="tbl2")public class Ent2 implements Serializable {...    @OneToMany(mappedBy = "ent2", fetch = FetchType.LAZY,         cascade = CascadeType.ALL, orphanRemoval = true)    private List<Ent3> ent3 = new ArrayList<>();    @ManyToOne(fetch = FetchType.LAZY,         cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})    @JoinColumn(name = "tbl1_id", nullable = false)    private Ent1 ent1;...}@Entity@Table(name="tbl3")public class Ent3 implements Serializable {...    @ManyToOne(fetch = FetchType.LAZY,     cascade = {CascadeType.PERSIST, CascadeType.MERGE, CascadeType.REFRESH})    @JoinColumn(name = "tbl2_id", nullable = false)    private Ent2 ent2;...}

The problem is, that I have the code that does some "import" by retrieving data from some external source and inserting it in these tables. Before importing I delete data from all three tables, then insert new, like this:

ent3Repository.deleteAll(); // Added that because of a problement2Repository.deleteAll(); // Added that because of a problement1Repository.deleteAll();...// ent1Repository.count();...Ent1 ent1=new Ent1();// Set ent1 fields hereent1Repository.save();

But, if tbl1 contains data, like a row with the name='name1', when I try to persist an entity with the same name, I'm getting an exception that unique constraint violated for the field "name". Like, data weren't deleted. But, if I call ent1Repository.count() right after deletion (which I did for checking), it returns 0 and (the most weird thing for me) insertion is working without exceptions then.

Please help - I probably don't understand something simple. Why it is working this way? How and why calling count() helps?

Thank you!