Message Title

the ddl generated is correct, you are using the same table name of MiddleTable4 Entity as the @JoinTable of a @ManyToMany

@Entity
@Table(name = "main_multi_pks")
public class MainMultiPks {
....

@ManyToMany(targetEntity = DestTable4.class, cascade = { CascadeType.PERSIST }, fetch = FetchType.EAGER)
    @JoinTable(name = "middle_table4",
        joinColumns = {
                @JoinColumn(name = "main_id1", referencedColumnName = "id1"),
                @JoinColumn(name = "main_id2", referencedColumnName = "id2")
        },

        inverseJoinColumns = {
                @JoinColumn(name = "dest4_id1", referencedColumnName = "id1"),
                @JoinColumn(name = "dest4_id2", referencedColumnName = "id2"),
                @JoinColumn(name = "dest4_id3", referencedColumnName = "id3")
        }
    )
    private Set<DestTable4> destTable4s = new HashSet<>();

so these columns should be not null, the issue is the MiddleTable4 id column middle4_id}}does not correspond to any column of the join table, so when a{{MainMultiPks is saved the generated SQL insert statement for the Join table

insert into middle_table4 (main_id2, main_id1, dest4_id1, dest4_id2, dest4_id3) values (?, ?, ?, ?, ?)

contains all the columns specified by the @JoinTable but obviously not the MiddleTable4 id column and this causes the error ERROR: NULL not allowed for column "MIDDLE4_ID";