2 many-to-one relationships, stack overflow error

[patk]

Hi all,
I am new to hibernate and spring and I've tried to model my code after the petclinic example and the hibernate book.
I have a class Prof that has one-to-many relationship with class Pattern. I have another class Type that also has one-to-many relationship with class Pattern. Pattern has 2 many-to-one relationships with Type and Prof. I am getting a stack overflow exception when I try to save a pattern. Inside the Prof and Type POJOs, I declared Set patterns. Before I save the Pattern, I try to add the pattern to the set in Prof and the set in Type. The exception occurs when I try to add the pattern to the second set. It doesn't matter which one I add first, I switched the order and it always occurs on the second time I try to add. Does anyone have any idea what I am doing wrong? Any help is appreciated!
Here is the table structure:
Table Prof
pro_id PK

Table Type
type_id PK

Table Pattern
pat_id PK
pro_id FK
type_id FK

Below is the mapping file, pojo's and code. I followed the petclinic example and the hibernate book to get this code.

Hibernate Mapping

<hibernate-mapping>
<class name="Prof" table="prof" >
        <id name="pro_id" column="pro_id" type="java.lang.Integer">
            <generator class="increment">
            </generator>
        </id>

        <set name="patterns" inverse="true" >
              <key column="pro_id"></key>
              <one-to-many class="Pattern"/>
        </set> 
</class>

<class name="Pattern" table="pattern" >
        <id name="pat_id" column="pat_id" type="java.lang.Integer">
            <generator class="increment"></generator>
        </id>
        <many-to-one name="prof" class="Prof" column="pro_id" />
        <many-to-one name="type" class="Type" column="type_id" />
</class>

<class name="Type" table="type" >
        <id name="type_id" column="type_id" type="java.lang.Integer">
            <generator class="increment"></generator>
        </id>
        <set name="patterns" inverse="true" >
              <key column="type_id"></key>
              <one-to-many class="Pattern"/>
        </set>
</class>
</hibernate-mapping>

snippet of test case:

...get prof from db...
...get typ from db...

pattern = new Pattern()
...set pattern properties...        
typ.addPattern(pattern);
prof.addPattern&#40;pattern&#41;; <--second time add pattern to a set, stack overflow&#40;see Prof POJO&#41;
dao.savePattern&#40;pattern&#41;;

POJO's

public class Prof extends BaseObject{
  private Integer pro_id;
  private Set patterns;
...
  public Set getPatterns() {
		if (this.patterns == null){
			this.patterns = new HashSet();			
		}
		return this.patterns;
	}
	
	public void setPatterns(Set patterns) {
		this.patterns = patterns;
	}
	public void addPattern(Pattern ptn){
		getPatterns&#40;&#41;.add&#40;ptn&#41;; <--this line causes stack overflow
		ptn.setProf&#40;this&#41;;
	&#125;
    &#125;

public class Pattern extends BaseObject &#123;
    private Integer pat_id;
    private Prof prof;
    private Type typ;
...
   public Prof getProf&#40;&#41; &#123;
		return prof;
	&#125;
	
	public void setProf&#40;Prof prof&#41; &#123;
		this.prof = prof;
	&#125;
	public Type getType&#40;&#41; &#123;
		return typ;
	&#125;
	
	public void setType&#40;Type typ&#41; &#123;
		this.typ = typ;
	&#125;	
&#125;

public class Type extends BaseObject&#123;
   private Integer type_id;
   private Set patterns;
...                
   public Set getPatterns&#40;&#41; &#123;
		
		if &#40;this.patterns == null&#41;&#123;
			this.patterns = new HashSet&#40;&#41;;			
		&#125;
		return this.patterns;
	&#125;
	
	public void setPatterns&#40;Set patterns&#41; &#123;
		this.patterns = patterns;
	&#125;
	public void addPattern&#40;Pattern ptn&#41;&#123;
		getPatterns&#40;&#41;.add&#40;ptn&#41;;
		ptn.setType&#40;this&#41;;
	&#125;
&#125;

thanks in advance.
pat

[Costin Leau]

You are going into a infinite loop(that's what StackOverFlow usually stand for). Can you post also the code for BaseObject - what usually happens in this case is having objects A and B with A trying to set automatically the relation with B and B doing the same thing with A.
In short:

1 add B to A will make
2. B add automatically a relation to A (through some logic inside the setter)
which tries to do 1.

Put some logging inside your code or use a debugger if you cannot spot the loop.

[patk]

Costin
Thanks for your reply. The BaseObject I am using is the one that came with equinox when I did the Spring Quick Start Tutorial. I will post that code below. Do you know how I should model these relationships?

public class BaseObject implements Serializable {
    public String toString() {
        return ToStringBuilder.reflectionToString(this,
                ToStringStyle.MULTI_LINE_STYLE);
    }

    public boolean equals(Object o) {
        return EqualsBuilder.reflectionEquals(this, o);
    }

    public int hashCode() {
        return HashCodeBuilder.reflectionHashCode(this);
    }
}

thanks
pat

[Costin Leau]

Sorry for the delay - I was traveling.
EqualsBuilder and HashCodeBuilders when used with reflection methods are dangerous - remove them and implement your own hashcode and equals builder.
Your code goes into an infinite loop because when you add the BaseObject to a set, the Set implementation checks for duplicates (meaning equals). However EqualsBuilder will try to compute one based on the object properties - so if A has a member B the EqualsBuilder for A will call equals for B which is actually EqualsBuilder again which calss equals for A and so on.

[patk]

I changed my java classes to implement Serializable instead of extending the BaseObject. Everything is working now. Thank you so much for your help.
pat