Spring-Neo4j：关系检索不正确

Question

我有一个实体类，它把自己称为父类。

@NodeEntity
public class Config {

    @Id 
    @GeneratedValue 
    private Long id;

    @Relationship(type = "OVERRIDES", direction="INCOMING")
    private Config parentConfig;

    @Properties(allowCast=true, prefix="properties", delimiter=".")
    private Map<String, String> properties;
    ....
}

当我在我的 java 代码中运行内置的 findById() 方法时，“parentConfig”始终与子对象相同。我从来没有看到关系的另一端。我做错了什么？

Answer 1

这可以按预期工作，但取决于您希望如何为您的配置建模。

假设您想表达“子级覆盖父级配置”，我将其建模为

CREATE (c:Config {name: 'Parent'}) <- [:OVERRIDES] - (c2:Config {name: 'Child'})

这给了你：

然后您必须将关联建模为从子对象传出，如下所示：

import org.neo4j.ogm.annotation.GeneratedValue;
import org.neo4j.ogm.annotation.Id;
import org.neo4j.ogm.annotation.Relationship;

public class Config {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @Relationship(type = "OVERRIDES", direction = Relationship.OUTGOING)
    private Config parent;

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Config getParent() {
        return parent;
    }

    @Override public String toString() {
        return "Config{" +
            "name='" + name + '\'' +
            '}';
    }
}

把它变成一个完整的例子：

import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.neo4j.repository.Neo4jRepository;
import org.springframework.stereotype.Component;

interface ConfigRepo extends Neo4jRepository<Config, Long> {
    Optional<Config> findOneByName(String name);
}

@Component
class Example implements CommandLineRunner {

    @Autowired
    private ConfigRepo configRepo;

    @Override
    public void run(String... args) throws Exception {
        configRepo.findOneByName("Parent").ifPresent(c -> {
            System.out.println("Config " + c + " has parent " + c.getParent());
        });

        configRepo.findOneByName("Child").ifPresent(c -> {
            System.out.println("Config " + c + " has parent " + c.getParent());
        });
    }
}

@SpringBootApplication
public class SorecassocApplication {

    public static void main(String[] args) {
        SpringApplication.run(SorecassocApplication.class, args);
    }
}

会回来

2018-10-10 09:20:21.960  INFO 3832 --- [           main] o.n.o.drivers.bolt.request.BoltRequest   : Request: MATCH (n:`Config`) WHERE n.`name` = { `name_0` } WITH n RETURN n,[ [ (n)-[r_o1:`OVERRIDES`]->(c1:`Config`) | [ r_o1, c1 ] ] ], ID(n) with params {name_0=Parent}
Config Config{name='Parent'} has parent null
2018-10-10 09:20:21.984  INFO 3832 --- [           main] o.n.o.drivers.bolt.request.BoltRequest   : Request: MATCH (n:`Config`) WHERE n.`name` = { `name_0` } WITH n RETURN n,[ [ (n)-[r_o1:`OVERRIDES`]->(c1:`Config`) | [ r_o1, c1 ] ] ], ID(n) with params {name_0=Child}
Config Config{name='Child'} has parent Config{name='Parent'}

如果从孩子的角度将关系建模为 INCOMING，则必须反转节点中的关系。否则输出为：

2018-10-10 09:22:54.929  INFO 3837 --- [           main] o.n.o.drivers.bolt.request.BoltRequest   : Request: MATCH (n:`Config`) WHERE n.`name` = { `name_0` } WITH n RETURN n,[ [ (n)<-[r_o1:`OVERRIDES`]-(c1:`Config`) | [ r_o1, c1 ] ] ], ID(n) with params {name_0=Parent}
Config Config{name='Parent'} has parent Config{name='Child'}
2018-10-10 09:22:54.951  INFO 3837 --- [           main] o.n.o.drivers.bolt.request.BoltRequest   : Request: MATCH (n:`Config`) WHERE n.`name` = { `name_0` } WITH n RETURN n,[ [ (n)<-[r_o1:`OVERRIDES`]-(c1:`Config`) | [ r_o1, c1 ] ] ], ID(n) with params {name_0=Child}
Config Config{name='Child'} has parent null

以下是将示例转换为正在运行的应用程序的依赖项：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>sorecassoc</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>sorecassoc</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-neo4j</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

如果这能解决您的问题，请告诉我。