[ https://hibernate.onjira.com/browse/HHH-7072?page=com.atlassian.jira.plug... ] Martin Berglund commented on HHH-7072: -------------------------------------- I'm having the exact same problem. The combination here seems to be @ElementCollection + @Embeddable + java.util.Set + null + MySQL. If the collection type is changed to List, it works fine. I created a very simple test-case for this, creating a Parent @Entity and a Child @Embeddable: {code:java} @Embeddable public class Child { private String value1; private String value2; public Child() {} public String getValue1() { return value1; } public void setValue1(String value1) { this.value1 = value1; } public String getValue2() { return value2; } public void setValue2(String value2) { this.value2 = value2; } } {code} {code:java} @Table(name="Parent") @Entity public class Parent { private int id; private Set<Child> children; public Parent() {} @Id public int getId() { return id; } public void setId(int id) { this.id = id; } @ElementCollection @CollectionTable(name="Children", joinColumns=@JoinColumn(name="parentId", referencedColumnName="id")) public Set<Child> getChildren() { return children; } public void setChildren(Set<Child> children) { this.children = children; } } {code} If I create one Parent object, attach one Child object and call merge (I'm using the JPA interface), I get this SQL generated by Hibernate: {noformat} Hibernate: select parent0_.id as id0_0_ from Parent parent0_ where parent0_.id=? Hibernate: insert into Parent (id) values (?) Hibernate: insert into Children (parentId, value1, value2) values (?, ?, ?) Hibernate: delete from Children where parentId=? and value1=? and value2=? Hibernate: insert into Children (parentId, value1, value2) values (?, ?, ?) {noformat} Not sure why it's inserting the same row twice, but anyhow, as the reporter is writing, MySQL doesn't support "WHERE column = null". The correct syntax would be "WHERE column IS NULL" or limit the delete query to only the foreign key ({{parentId}} above) (or "WHERE column <=> null"). Indeed, if I change the {{Set}} to {{List}}, I get this instead: {noformat} Hibernate: select parent0_.id as id0_0_ from Parent parent0_ where parent0_.id=? Hibernate: insert into Parent (id) values (?) Hibernate: insert into Children (parentId, value1, value2) values (?, ?, ?) {noformat} Then, if I modify the child object in Java and merge it again: {noformat} Hibernate: select parent0_.id as id0_0_ from Parent parent0_ where parent0_.id=? Hibernate: select children0_.parentId as parentId0_0_, children0_.value1 as value2_0_, children0_.value2 as value3_0_ from Children children0_ where children0_.parentId=? Hibernate: delete from Children where parentId=? Hibernate: insert into Children (parentId, value1, value2) values (?, ?, ?) {noformat} Trying to modify and merge with the {{Set}} will cause the rows to multiply, since it's trying to delete each row one by one, and each delete fails, then insert all the rows again. -- This message is automatically generated by JIRA. For more information on JIRA, see: http://www.atlassian.com/software/jira