java - 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 和 Cypher 来存储信息。我已经构建了这个函数，用于一般用途:

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;
}

问题是我经常收到这个错误:

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，并始终执行 tx.failure()，则没有问题。怎么回事？

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. 事务支持 try-with 模式
3. 你仍然需要调用tx.success()
4. tx.failure() 如果您还没有调用 tx.success()
将被自动假设
5. 并始终使用参数。