Databases
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    <p>This one compiles without errors. However, I did not try to run it, so you may get some exceptions (e.g. from <code>queryRoot.asInstanceOf[Root[T]]</code>, I have a little bit bad feeling about it):</p> <pre><code> def findByAttributes(attributes:AttributeValuePair[_]*):ArrayList[T] = { val cq = cb.createQuery(m.erasure) val queryRoot = cq.from(m.erasure) var criteria = cb.conjunction for (pair &lt;- attributes) { criteria = pred(pair, cb, queryRoot.asInstanceOf[Root[T]]) } cq.where(Seq(criteria):_*) val results = em.createQuery(cq).getResultList results.asInstanceOf[ArrayList[T]] } def pred[A](pair: AttributeValuePair[A], cb: CriteriaBuilder, queryRoot: Root[T]): Predicate = cb.and(cb.equal(queryRoot.get(pair._1),pair._2)) </code></pre> <p>BTW in <code>SuperDAO.findByAttributes</code> the parentheses/params of <code>cb.equal</code> seems to be a bit mixed up. It looks OK in the other method.</p> <p>About the <code>_$1</code> type: I think when you say <code>SingularAttribute[T,_]</code> it will be a so called existential type. It is a shorthand for <code>SingularAttribute[T,X] forSome { type X }</code>. So the <code>_</code> means that we don't really know what X is, but for sure there is a fixed type there. As you can have several existential types the compiler just calls them <code>_$1</code>, <code>_$2</code> and so on. They are synthetically created names instead of <code>X</code>-es.<br> Existential types are used mostly when you use Java generics with wildcard or raw types. In these cases some tricks (like introducing an extra method with it's own type param) may be needed for proper type checking.</p>
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    1. POMove the implementation of a generic method to an abstract super class
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    1. USSandor Murakozi
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    1. COImpressive. Seems to work so far! Will do some testing...
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    2. COCool. I hope it will work. One thing that came to my mind was that maybe you could use the type given by m.erasure instead of T inside of the method (or in another extracted from it). This way you might be able to avoid the ugly asInstanceOf, which is not 100% correct from the typing point of view, just Java probably does not care about it because of erasure.
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