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POMany-to-many relationship - hibernate
 

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  1. POMany-to-many relationship - hibernate
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    <p>I am using hibernate-jpa-2.0-api 1.0.0.Final and hibernate 3.5.5-Final.</p> <p>I have User and Role entities each having many-to-many relationships to each other(bidirectional). I have the following requirements below: </p> <p><strong>1-</strong> If the deleteRole(role) method is called and this role having users then hibernate should throw exception otherwise the role can be deleted successfully.<br> <strong>2-</strong> If the deleteUser(user) method is called user can be deleted successfully, and related records deleted from the relationship table automatically but its role should not be deleted.<br> <strong>3-</strong> Furhermore; if I create new Role and add some users into its set and finally persist the Role, its users should be persisted without an extra persist operations. </p> <p>Let's say <strong>Role</strong> is <strong>Test1</strong> and the <strong>User</strong> is <strong>Test2</strong>. The entities:</p> <p><em><strong>Test1(Role)</em></strong> </p> <pre><code>import java.util.HashSet; import java.util.Set; import javax.persistence.CascadeType; import javax.persistence.Entity; import javax.persistence.JoinColumn; import javax.persistence.JoinTable; import javax.persistence.ManyToMany; import com.ttnet.model.BaseModel; @Entity public class Test1 extends BaseModel { @ManyToMany(targetEntity = Test2.class, cascade = { CascadeType.ALL }) @JoinTable(name = "test1_test2", joinColumns = { @JoinColumn(name = "id1", nullable = false, updatable = false) }, inverseJoinColumns = { @JoinColumn(name = "id2", nullable = false, updatable = false) }) private Set&lt;Test2&gt; test2s = new HashSet&lt;Test2&gt;(0); public Set&lt;Test2&gt; getTest2s() { return test2s; } public void setTest2s(Set&lt;Test2&gt; test2s) { this.test2s = test2s; } } </code></pre> <p><em><strong>Test2(User)</em></strong> </p> <pre><code>import java.util.HashSet; import java.util.Set; import javax.persistence.Entity; import javax.persistence.ManyToMany; import com.ttnet.model.BaseModel; @Entity public class Test2 extends BaseModel { @ManyToMany(targetEntity=Test1.class, mappedBy = "test2s") private Set&lt;Test1&gt; test1s = new HashSet&lt;Test1&gt;(0); public Set&lt;Test1&gt; getTest1s() { return test1s; } public void setTest1s(Set&lt;Test1&gt; test1s) { this.test1s = test1s; } } </code></pre> <p>TestCode </p> <pre><code> Test1Bo test1Bo = (Test1Bo) context.getBean("test1Bo"); Test2Bo test2Bo = (Test2Bo) context.getBean("test2Bo"); Test1 t1 = new Test1(); Test2 t21 = new Test2(); Test2 t22 = new Test2(); Set&lt;Test2&gt; t2Set = t1.getTest2s(); t2Set.add(t21); t2Set.add(t22); test1Bo.addTest1(t1); </code></pre> <p>This code successfully adds expected entires to all 3 tables. However, at first I tried only the Cascade.PERSIST, and Cascade.MERGE and it gives unsaved object exception. Then I tried ALL, and it completed with a success. Interesting thing is that, I added all javax Cascade operations I mean individualy but no success same exception thrown(unsaved obj...). Now, the problem is that whenever I delete the t1 it deletes t21 and t22 also and this violates the req.1. </p>
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    1. COyou could `if (!t1.getTest2s().size > 0) throw new Exception();` no?
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    2. COyes ofcourse, but I want to know is there a hibernate annotatable way for this issue. Plus, one more question where should you put your suggestion, in bo or dao layer? I mean that considering the role-based-access-control design, is this restriction relevant to bussiness requirements or data modeling?
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    3. COi don't think that hibernate has something builtin because this smells a lot like buisiness rule. I would incorporate the check into the buisiness layer. It might also change to "if a role is deleted move all its users to default Role"
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