@ManyToMany注解死循环详解及JPA相关实例

最新推荐文章于 2022-09-09 10:28:43 发布

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最新推荐文章于 2022-09-09 10:28:43 发布 · 1k 阅读

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CC 4.0 BY-SA版权

文章标签：

#java #spring #spring boot

本文详细解析了在项目中使用Hibernate和JPA遇到的ManyToMany注解导致的死循环问题，以及如何通过@JsonIgnoreProperties避免。同时，分享了处理复杂SQL查询的方法，包括JPA的@Query注解和原生SQL的使用，以及如何通过自定义类接收查询结果。此外，还展示了完整的代码示例，包括学生、教师表的创建，数据插入、查询和删除操作。

由于项目中用了Hibernate和JPA。最近被ManyToMany注解死循环及一些复杂SQL的操作搞得焦头烂额，这里给出这几天对这方面概念的思考。

相信这篇文章不会浪费朋友们的时间，也希望朋友们能中得到收获。demo中没有严格区别VO，PO，DTO，DO等概念，请朋友们不要在意这些细节。

闲话少说，直接上全部代码，文章后面有具体的分析。

代码部分

项目目录

数据库表概述

学生表：存储任务信息

教师表：存储任务详情信息

关系

任务详情 N:N 标签（外键关联）

建表语句

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

DROP TABLE IF EXISTS `students`;
DROP TABLE IF EXISTS `teachers`;
DROP TABLE IF EXISTS `teachers_students`;

CREATE TABLE `students`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `gender` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '学生表' ROW_FORMAT = Dynamic;

CREATE TABLE `teachers`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `tname` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = '教师表' ROW_FORMAT = Dynamic;

CREATE TABLE `teachers_students`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `sid` int(11) NULL DEFAULT NULL,
  `tid` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

alter table teachers_students add constraint FK_Reference_1 foreign key (sid)
      references students (id) on delete restrict on update restrict;

alter table teachers_students add constraint FK_Reference_2 foreign key (tid)
      references teachers (id) on delete restrict on update restrict;

SET FOREIGN_KEY_CHECKS = 1;

maven依赖

<?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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.5</version>
        <relativePath/>
    </parent>

    <groupId>com.yipeng.task</groupId>
    <artifactId>task-demo</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <!--统一管理jar包和版本-->
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <junit.version>4.12</junit.version>
        <log4j.version>1.2.17</log4j.version>
        <lombok.version>1.16.18</lombok.version>
        <mysql.version>8.0.18</mysql.version>
        <druid.verison>1.1.16</druid.verison>
    </properties>

    <dependencies>
        <!--spring boot 2.4.5-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.76</version>
        </dependency>


        <!-- MySql -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>${mysql.version}</version>
        </dependency>
        <!-- Druid -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>${druid.verison}</version>
        </dependency>

        <!--lombok-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${lombok.version}</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${junit.version}</version>
        </dependency>
        <!-- log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>${log4j.version}</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <fork>true</fork>
                    <addResources>true</addResources>
                </configur