Neo4j Java 驱动程序 - 无法访问此结果的记录

Question

我正在使用 neo4j java 驱动程序并尝试执行 Cyphers.I 得到一个 exception.I 我在网上搜索了很长时间。但是没有用。请帮助或尝试提供一些想法如何实现这一目标。

1.This是我添加的驱动：

        <dependency>
            <groupId>org.neo4j.driver</groupId>
            <artifactId>neo4j-java-driver-spring-boot-starter</artifactId>
            <version>4.1.1.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.neo4j/neo4j-ogm-core -->
        <dependency>
            <groupId>org.neo4j</groupId>
            <artifactId>neo4j-ogm-core</artifactId>
            <version>3.2.20</version>
        </dependency>

2.The函数：

     public Result readCyphers(String cypher) {

        Result result = null;

        Driver driver = null;
        Session session = null;

        try {
            //driver
            driver = GraphDatabase.driver(uri, AuthTokens.basic(username, password));
            //session
            session = driver.session();

            //run
            result = session.run(cypher);

        } catch (Exception e) {
            throw e;
        } finally {
            session.close();
            driver.close();
        }

        return result;
    }

3.call函数

  @Test
    void readCyphersTest() {

        String cypher = "MATCH(N:WechatDepartment) \n" +
                "WHERE N.departmentId = 117 \n" +
                "RETURN ID(N) as id, N.departmentId as departmentId, N.name as name, N.order as order, N.enable as enable";
        Result result = readCyphers(cypher);

        //There is an exception here
        System.out.println("result.list().size():" + result.list().size());
    }

4.exception：

org.neo4j.driver.exceptions.ResultConsumedException: Cannot access records on this result any more as the result has already been consumed or the query runner where the result is created has already been closed.

提前致谢

Answer 1

（如果只打算使用驱动，则不需要Neo4j OGM）

会话关闭后，您将无法访问驱动程序的 Result 实例。您应该在会话打开时遍历记录并 return 您想要的结果，例如：

    public <T> List<T> readCyphers(String cypher, Function<Record, T> mapper) {
        try (Driver driver = GraphDatabase.driver(uri, AuthTokens.basic(username, password));
             Session session = driver.session()) {

            Result result = session.run(cypher);
            return result.list(mapper);
        }
    }

但是请注意，您不应该在每次要运行查询时都创建一个 Driver 实例，因此应该在之前创建驱动程序，例如：

class CypherExecutor implements AutoCloseable {

    private final Driver driver;

    public CypherExecutor(String uri, String username, String password) {
        this.driver = GraphDatabase.driver(uri, AuthTokens.basic(username, password))
    }

    public <T> List<T> readCyphers(String cypher, Function<Record, T> mapper) {
        try (Session session = driver.session()) {
            Result result = session.run(cypher);
            return result.list(mapper);
        }
    }

    @Override
    public void close() throws Exception {
        driver.close();
    }
}

CypherExecutor 最好仅在应用程序停止时关闭（通过 try-with-resources 块）。

此外，transaction functions 更健壮（面对集群机器故障、领导者重新选举等），应该改用，所以 readCyphers 应该是（假设只读查询):

    public <T> List<T> readCyphers(String cypher, Function<Record, T> mapper) {
        try (Session session = driver.session()) {
            return session.readTransaction(tx -> tx.run(cypher).list(mapper));
        }
    }

最后一点，这种抽象并没有给 table 带来太多好处，因此您可以直接在代码库中使用驱动程序 API 而不是使用这种间接方式。

完整代码，包含导入：

import org.neo4j.driver.AuthTokens;
import org.neo4j.driver.Driver;
import org.neo4j.driver.GraphDatabase;
import org.neo4j.driver.Record;
import org.neo4j.driver.Session;

import java.util.List;
import java.util.function.Function;

class CypherExecutor implements AutoCloseable {

    private final Driver driver;

    public CypherExecutor(String username, String password, String uri) {
        this.driver = GraphDatabase.driver(uri, AuthTokens.basic(username, password))
    }

    public <T> List<T> readCyphers(String cypher, Function<Record, T> mapper) {
        try (Session session = driver.session()) {
            return session.readTransaction(tx -> tx.run(cypher).list(mapper));
        }
    }

    @Override
    public void close() throws Exception {
        driver.close();
    }
}

Neo4j Java 驱动程序 - 无法访问此结果的记录

Neo4j Java Driver - Cannot access records on this result

java

neo4j

driver