java - What is the difference between enitityManager.find and entityManager.createQuery? -

ok, using ejb 3.0 hibernate, dropped our .ear file easy-beans 1.0.1 (with hibernate) deploy directory embedded apache tomcat 6.0.18. database had persist things this:

@entity @table(name="author") public class author implements serializable {  ////////////////////////////////////////////////////////////////// // fields //////////////////////////////////////////////////////////////////  @id @generatedvalue(strategy = identity) @column(name = "a_id", unique=true, nullable = false) private integer id;  @column (name = "a_name", unique = false, nullable = false) private string name;  @column (name = "a_lastname", unique = false, nullable = false) private string lastname;  @onetomany(cascade = {all}, fetch = eager, mappedby = "author") private set<bookauthor> bookauthors = new hashset<bookauthor>();    @override   public boolean equals(object o) {       if (this == o) return true;       if (o == null || getclass() != o.getclass()) return false;        author author = (author) o;        if (id != null ? !id.equals(author.id) : author.id != null) return false;        return true;   }    @override   public int hashcode() {       return id != null ? id.hashcode() : 0;   }   }  @entity @table(name = "book" ) public class book implements serializable { ////////////////////////////////////////////////////////////////// // fields ////////////////////////////////////////////////////////////////// @id @generatedvalue (strategy = identity) @column(name = "b_id", unique = true, nullable = false) private integer bid;  @column(name = "b_year", unique = false, nullable = true) private integer year;  @column(name = "b_isbn", unique = false, nullable = false) private string isbn;  @column(name = "b_title", unique = false, nullable = false) private string title;  @onetomany(cascade = {all}, fetch = eager, mappedby = "book") private set<bookauthor> bookauthors = new hashset<bookauthor>();    @override   public boolean equals(object o) {     if (this == o) return true;     if (o == null || getclass() != o.getclass()) return false;      book book = (book) o;      if (isbn != null ? !isbn.equals(book.isbn) : book.isbn != null) return false;     if (bid != null ? !kid.equals(book.bid) : book.bid != null) return false;      return true;   }    @override   public int hashcode() {     int result = bid != null ? bid.hashcode() : 0;     result = 31 * result + (isbn != null ? isbn.hashcode() : 0);     return result;   }  }  @entity @table(name = "book_author") public class bookauthor implements serializable {    //////////////////////////////////////////////////////////////////   // fields   //////////////////////////////////////////////////////////////////   @id   @generatedvalue(strategy = identity)   @column(name = "ba_id", unique=true, nullable = false)   private integer id;    @column(name = "ba_role", unique = false, nullable = true)   private string role;    @manytoone   @joincolumn (name = "a_id", referencedcolumnname = "a_id", nullable = false)   private author author;    @manytoone   @joincolumn (name = "b_id", referencedcolumnname = "b_id", nullable = false)   private book book;    @override   public boolean equals(object o) {     if (this == o) return true;     if (o == null || getclass() != o.getclass()) return false;      bookauthor = (bookauthor) o;      if (auhtor != null ? !author.equals(that.author) : that.author != null) return false;     if (book != null ? !book.equals(that.book) : that.book!= null) return false;     if (id != null ? !id.equals(that.id) : that.id != null) return false;      return true;   }    @override   public int hashcode() {     int result = id != null ? id.hashcode() : 0;     result = 31 * result + (author != null ? author.hashcode() : 0);     result = 31 * result + (book != null ? book.hashcode() : 0);     return result;   }  } 

so when removing items had entity bean went this:

@stateless @local(deletebookauthor.class) public class deletebookauthorbean implements deletebookauthor {     @persistencecontext(unitname="library")    protected entitymanager em;     @override    public void removebyid(integer id) {       try{          query q = em.createquery("select ba bookauthor ba id = ?1");         q.setparameter(1,id);          bookauthor ba = (bookauthor) q.getsingleresult();          ba.getauthor().getbookauthors().remove(ba);         ba.getbook().getbookauthors().remove(ba);          em.remove(ba);       }catch (exception e){          e.printstacktrace();       }    } } 

unfortunatelly, when servlet calls bean returns "deleted entity passed persist" exception; changing lines:

query q = em.createquery("select ba bookauthor ba id = ?1"); q.setparameter(1,id);         bookauthor ba = (bookauthor) q.getsingleresult();  

to

bookauthor ba = em.find(bookauthor.class, id) 

makes problem go away. question ask why? in similar situation used em.createquery retrieve , delete muliple entities , worked without hitch. why won't work now?

update: calling query q=... , removing bookauthors removes bookauthors books not authors. in second case removed both sets. both ba have same hash , return true when compared using baquery.equals(bafind) .

any clarifications why 2 functions return same object calling remove behave differently depending on whether query/find called?

perhaps it's related lack of equals()/hashcode() in bookauthor. if so, looks in case of query have several different instances of bookauthor same state, not removed corresponding sets in author , book.