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POManyToMany in Hibernate without composite keys
 

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  1. POManyToMany in Hibernate without composite keys
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    <p>I am dealing with legacy database. And I am writing unit test using pojos &amp; hibernate &amp; <strong>HSQLDB</strong>. And I am getting the following error:</p> <pre>17:09:03,946 ERROR SchemaExport:349 - Attempt to define a second primary key in statement</pre> <p>Let's say I have <code>Post</code> and <code>Tag</code> entities (and of course their tables <code>posts</code> and <code>tags</code>). And there is another table to define many-to-many between <code>Post</code> and <code>Tag</code> called <code>post_tags</code>.</p> <p>Because <code>post_tags</code> contains some extra information about the relation, like <code>active</code> and <code>deleted</code> columns. I created another Entity called <code>PostTag</code> to handle this.</p> <p>To describe my problem here are the pseudo classes:</p> <pre><code>@Entity @Table(name="post_tags") public class PostTag { @Id @GeneratedValue(strategy=GenerationType.AUTO) private int id; @ManyToOne private Post post; @ManyToOne private Tag tag; // setters and getters } @Entity @Table(name = "tags") public class Tag { @Id @GeneratedValue(strategy=GenerationType.AUTO) private int id; @ManyToMany(mappedBy = "tags",cascade = {CascadeType.PERSIST, CascadeType.MERGE}) private Set&lt;Post&gt; posts; // setters and getters } @Entity @Table(name = "posts") public class Post { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; @ManyToMany @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE}) @JoinTable(name = "post_tags", joinColumns = { @JoinColumn(name = "post_id") }, inverseJoinColumns = { @JoinColumn(name = "tag_id") }) private Set&lt;Tag&gt; tags; // setters and getters } </code></pre> <p>When I look at the statement that generates the error it seems Hibernate is trying to make a composite key using <code>PRIMARY KEY (post_id, tag_id)</code>, and also it tries to make <code>post_id</code> <code>identity</code>.</p> <p>Can anyone help me to fix my problem?</p> <p>UPDATE:</p> <p>Because I am dealing with a legacy database this was just an example to demonstrate the problem. But I will try to translate the actual statement according to the example (PS: It is not <code>ALTER TABLE</code> it is a <code>CREATE TABLE</code>):</p> <pre><code>create table post_tags (id integer not null, post integer, tag integer, post_id integer generated by default as identity (start with 1), tag_id integer not null, primary key (post_id, tag_id) </code></pre>
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    1. COCan you please post the ALTER TABLE line, too? The one which causes the error?
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      1. POManyToMany in Hibernate without composite keys
      1. USAaron Digulla
 

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