neo4j 2.0无法将事务标记为仅回滚

Question

我正在构建一个独立的java应用程序，并在嵌入式模式下使用neo4j与Cypher存储信息。我已经构建了这个函数，用于一般目的：

private ExecutionResult runCypher(String query)
{
    Transaction tx = service.beginTx();
    ExecutionResult result = null;
    boolean success = true;

    try
    {
        result = engine.execute(query);
    }
    catch(Exception e)
    {
        System.out.println(e.getMessage());
        success = false;
    }
    finally
    {
        if(success) tx.success();
        else        tx.failure();
    }

    tx.close();

    return result;
}

问题是我经常遇到这个错误：

Exception in thread "main" org.neo4j.graphdb.TransactionFailureException: Failed to    mark transaction as rollback only.
at org.neo4j.kernel.TopLevelTransaction.markAsRollbackOnly(TopLevelTransaction.java:97)
at org.neo4j.kernel.TopLevelTransaction.failure(TopLevelTransaction.java:86)

如果我修改finally子句，并且总是去tx.failure（），那么没有问题。发生了什么事？

Answer 1

我会将代码更改为：

private ExecutionResult runCypher(String query, Map params) {
    try (Transaction tx = service.beginTx()) {
        ExecutionResult result = engine.execute(query, params);
        // extract the data out of the result, you cannot iterate over it outside of a tx
        Collection resultData = ....
        tx.success();
        return resultData;
    }
}

1. 您必须在事务中迭代并从ExecutionResult中提取数据
2. 交易支持试用模式
3. 您仍然需要致电tx.success()
如果您未拨打tx.failure() ，系统会自动假设
4. tx.success()
5. 并始终使用参数。