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    <p>I think what's happening here is an interesting interaction between the first level cache (stored in Hibernate's Session instance) and having different <code>FetchType</code> on related objects.</p> <p>When you load <code>Customer</code>, it gets put in to the <code>Session</code> cache, along with any objects that are loaded with it. This includes a proxy object for the <code>OrderItem</code> object, because you've got <code>FetchType.LAZY</code>. Hibernate only allows one instance to be associated with any particular ID, so any further operations that would be acting on the <code>OrderItem</code> with that ID <strong><em>would always be using that proxy</em></strong>. If you asked the same <code>Session</code> to get that particular <code>OrderItem</code> in another way, as you are by loading an <code>Order</code> containing it, that <code>Order</code> would have the proxy, because of Session-level identity rules.</p> <p>That's why it 'works' when you reverse the order. Load the <code>Order</code> first, it's collection is <code>FetchType.EAGER</code>, and so it (and the first level cache) have fully realized instances of <code>OrderItem</code>. Now load a <code>Customer</code> which has it's <code>lastItem</code> set to one of the already-loaded <code>OrderItem</code> instances and presto, you have a real <code>OrderItem</code>, not a proxy.</p> <p>You can see the identity rules documented in the <a href="http://docs.jboss.org/hibernate/orm/3.6/reference/en-US/html/transactions.html#transactions-basics-identity" rel="nofollow">Hibernate manual</a>: </p> <blockquote> <p>For objects attached to a particular Session... JVM identity for database identity is guaranteed by Hibernate.</p> </blockquote> <p>All that said, even if you get an <code>OrderItem</code> proxy, it should work fine as long as the associated <code>Session</code> is still active. I wouldn't necessarily expect the proxy ID field to show up as populated in the debugger or similar, simply because the proxy handles things in a 'special' way (ie, it's not a POJO). But it should respond to method calls the same way it's base class would. So if you have an <code>OrderItem.getId()</code> method, it should certainly return the ID when called, and similarly on any other method. Because it's lazily initialized though, some of those calls may require a database query.</p> <p>It's possible that the only real problem here is simply that it's confusing to have it so that any particular <code>OrderItem</code> could be a proxy or not. Maybe you want to simply change the relationships so that they're either both lazy, or both eager?</p> <p>For what it's worth, it's a bit odd that you've got the ManyToMany relationship as <code>EAGER</code> and the ManyToOne as <code>LAZY</code>. That's exactly the reverse of the usual settings, so I would at least think about changing it (although I obviously don't know your entire use case). One way to think about it: If an <code>OrderItem</code> is so expensive to fetch completely that it's a problem when querying for <code>Customer</code>, surely it's also too expensive to load <em>all</em> of them at once? Or conversely, if it's cheap enough to load all of them, surely it's cheap enough to just grab it when you get a <code>Customer</code>?</p>
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    1. COthat probably explains the situation. Weird Exceptions - the id property is null on the proxy object and proxy itself is not initialized when accessed through collection of elements
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    2. CO@Funtik ok, i updated my answer with what i think about that, and how you should move forward. good luck.
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    3. COit seems weird at first, but when we load Order object in 95% of the cases we need OrderItems. On the other hand, Customer is used in almost all cases (so we try to optimize the DB hits).
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