如何从 TopLink 查询中获取前 n 行？
出于优化目的，我想在子查询中获取前 N 个结果（我获取前 N 个 ID 值），并在主查询中获取子查询中 ID 值的完整行并对它们进行排序。我现在所拥有的是
// This just adds params to the subquery
Expression managedEmp = generateExpression(p_upravljackaFilter);
ReportQuery subQuery = new ReportQuery(CustomDocument.class,
managedEmp);
subQuery.addAttribute("m_id");
Expression exp = new ExpressionBuilder().get("m_id").in(subQuery);
ReadAllQuery testQuery = new ReadAllQuery(CustomDocument.class,
exp);
testQuery.addAscendingOrdering("m_creationDate");
List documentList = (List)getTopLinkTemplate().executeQuery(testQuery, true);
到目前为止我正在尝试使用用户定义的函数，如下所示：
ExpressionOperator fetchFirst = new ExpressionOperator();
fetchFirst.setSelector(1);
Vector s = new Vector();
s.addElement("FETCH FIRST 5 ROWS ONLY");
fetchFirst.printsAs(s);
fetchFirst.bePostfix();
fetchFirst.setNodeClass(FunctionExpression.class);
ExpressionOperator.initializeOperators();
ExpressionOperator.addOperator(fetchFirst);
expression = expression.and(builder.get("m_datumKreiranja").getFunction(fetchFirst);
这实际上是我停止的地方，所以这不起作用，但它可以向您显示我正在前进的方向。这样的事情有可能吗？我正在使用 Java 1.4 和 toplink 10g。
For optimization purpose, I want to fetch first N results in a subquery (I'm getting first N ID values) and in the main query fetch full rows for the ID values in the subquery and order them. What I have now is
// This just adds params to the subquery
Expression managedEmp = generateExpression(p_upravljackaFilter);
ReportQuery subQuery = new ReportQuery(CustomDocument.class,
managedEmp);
subQuery.addAttribute("m_id");
Expression exp = new ExpressionBuilder().get("m_id").in(subQuery);
ReadAllQuery testQuery = new ReadAllQuery(CustomDocument.class,
exp);
testQuery.addAscendingOrdering("m_creationDate");
List documentList = (List)getTopLinkTemplate().executeQuery(testQuery, true);
What I'm trying so far is using a user defined function, like this:
ExpressionOperator fetchFirst = new ExpressionOperator();
fetchFirst.setSelector(1);
Vector s = new Vector();
s.addElement("FETCH FIRST 5 ROWS ONLY");
fetchFirst.printsAs(s);
fetchFirst.bePostfix();
fetchFirst.setNodeClass(FunctionExpression.class);
ExpressionOperator.initializeOperators();
ExpressionOperator.addOperator(fetchFirst);
expression = expression.and(builder.get("m_datumKreiranja").getFunction(fetchFirst);
This is literally where I stopped so this won't work but it can show you which way I'm heading. Is something like this even possible? I'm using Java 1.4 and toplink 10g.
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非常简单，只需插入第二行：
我的错误在于我尝试了这样的操作：
ManagedEmp.postfixSQL("FETCH FIRST 5 ROWS ONLY");
因为我没有读postfixSQL 是做什么的。
Really simple, just insert into second line:
My mistake was in the fact that I tried it like this:
managedEmp.postfixSQL("FETCH FIRST 5 ROWS ONLY");
because I didn't read what postfixSQL does.