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  1. PO
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    <p>I cannot help noticing that there is an inconsistency in your question.</p> <p>You first state that:</p> <blockquote> <p>Leafs of these trees can have several children/parents.</p> </blockquote> <p>This in my believe makes the relationship between leafs <strong>many to many</strong>.</p> <p>As I make of your question that <code>EtlWorkflowSeq</code> represent leafs, I think <code>EtlWorkflowSeqNode</code> represents the relationship between <code>EtlWorkflowSeq</code> objects?</p> <p>However, the nodes point to <strong>one</strong> parent and <strong>many</strong> children.</p> <p>You can use something like this to create something similar:</p> <pre><code>@Entity @Table(name="WORKFLOW_SEQ") public class EtlWorkflowSeq { @Id @GeneratedValue @Column(name="WORKFLOW_SEQ_ID") public Integer id; @ManyToOne @JoinColumn(name="WORKFLOW_ID") public EtlWorkflow etlWorkflow; @ManyToMany @JoinTable(name = "WORKFLOW_SEQ_REL") private Set&lt;EtlWorkflowSeq&gt; children; @ManyToMany(mappedBy = "children") private Set&lt;EtlWorkflowSeq&gt; parents; @ManyToOne @JoinColumn(name = "JOB_ID", referencedColumnName = "id") private Job job; } </code></pre> <p>This would make <code>EtlWorkflowSeqNode</code> and <code>EtlWorkflowSeqNodeId</code> obsolete.</p> <p>I also would like to state that when using an <code>@Embeddable</code> you should only use base types in them. Using other than base types is not possible/causes problems/is not standard (correct me if I'm wrong).</p> <p>If you would like to use foreign keys in a composite primary key you can use this:</p> <pre><code>@Entity public class Foo { @Id private Long id; } @Entity public class Bar { @EmbeddedId private BarPK key; @MapsId(value = "fooId") @ManyToOne @JoinColumns({ @JoinColumn(name = "foo_id", referencedColumnName = "id") }) private Foo foo; } @Embeddable public class BarPK { @Column(name = "id") private Long id; @Column(name = "foo_id") private Long fooId; } </code></pre>
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    1. PODeclare JPA entity for a tree element
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    1. USsiebz0r
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    1. CO1. I could make a mistake while annotating my entity field. But the concept that a leaf can have several children and parents is true. You are absolutely right. Sorry, I didn't mention it. The **EtlWorkflowSeq** is a leaf and the **EtlWorkflowSeqNode** represents relationship between EtlWorkflowSeq. Thank you, I'm looking for your solution and trying to apply it.
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      1. USSergey
    2. CO@ManyToOne @Column(name = "JOB_ID") private Job job; JOB_ID is in WORKFLOW_SEQ, not in WORKFLOW_SEQ_REL... And I don't understand how does job_id helps to determine different trees stored in one table. JOB_ID is a field to distinguish several trees stored in one table... If I want to get a tree I need to know JOB_ID. I need to goto WORKFLOW_SEQ_REL and select all records wit specified JOB_ID. Then starting from REL_WORKFLOW_SEQ_ID=0 I do construct a tree from resultset. Also links between nodes to have attributes, anyway I need a way to specify them is a model.
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    3. CO@Sergey I'm not certain about the job_id part as I cannot see that code and do not fully understand the database design. If this is a new design, try to go with my solution. If this is an existing design you need to figure out how to map the job_id as this doesn't fully relate to the question. I think.
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