Hey guys I have problem mapping my three table together using Hibernate. Not sure which part I mess up. Thanks
I have create three table:
CREATE TABLE `topic` ( `topic_id` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(100) default null, PRIMARY KEY (`topic_id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; CREATE TABLE `question` ( `question_id` int(11) unsigned NOT NULL AUTO_INCREMENT, `topic_id` int(11) unsigned NOT NULL,question `question` varchar(100) not null, PRIMARY KEY (`question_id`), KEY `topic_id` (`topic_id`), CONSTRAINT `items_ibfk_1` FOREIGN KEY (`topic_id`) REFERENCES `topic` (`topic_id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; CREATE TABLE `option` ( `option_id` int(11) unsigned NOT NULL AUTO_INCREMENT, `question_id` int(11) unsigned NOT NULL, `option` varchar(100) not null, PRIMARY KEY (`option_id`), KEY `question_id` (`question_id`), CONSTRAINT `items_ibfk_2` FOREIGN KEY (`question_id`) REFERENCES `question` (`question_id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8; The three entity: ---- Topic @Entity @Table(name="topic") public class Topic {
@Id @GeneratedValue(strategy=GenerationType.IDENTITY) @Column(name="topic_id") private int id; @Column(name="name") private String name; @OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL) @JoinColumn(name="topic_id") private List<Question> questions; // Define Constructors public Topic() { } public Topic(String name) { this.name = name; } // Define Getter/Setter public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public List<Question> getQuestions() { return questions; } public void setQuestions(List<Question> questions) { this.questions = questions; } } --- Question
@Entity @Table(name="question") public class Question { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) @Column(name="question_id") private int id; @Column(name="question") private String question; @Column(name="answer") private String answer; @Column(name="topic_id") private int topic_id; @OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.ALL) @JoinColumn(name="question_Id") private List<Option> options; // Define Constructors public Question() {} public Question(String question, String answer, int topic_id) { this.question = question; this.answer = answer; this.topic_id = topic_id; } // Define Getter/Setter public int getId() { return id; } public void setId(int id) { this.id = id; } public String getQuestion() { return question; } public void setQuestion(String question) { this.question = question; } public String getAnswer() { return answer; } public void setAnswer(String answer) { this.answer = answer; } public int getTopic_id() { return topic_id; } public void setTopic_id(int topic_id) { this.topic_id = topic_id; } public List<Option> getOptions() { return options; } public void setOptions(List<Option> options) { this.options = options; } } --- Option
@Entity @Table(name="option") public class Option { @Id @GeneratedValue(strategy=GenerationType.IDENTITY) @Column(name="option_id") private int id; @Column(name="option") private String option; @Column(name="question_id") private int question_id; // Define Constructors public Option() {} public Option(String option, int question_id) { this.option = option; this.question_id = question_id; } // Define Getter/Setter public int getId() { return id; } public void setId(int id) { this.id = id; } public String getOption() { return option; } public void setOption(String option) { this.option = option; } public int getQuestion_id() { return question_id; } public void setQuestion_id(int question_id) { this.question_id = question_id; } } -- I test in Postman: GET http://localhost:8080/api/topic/1 the message show
"message": "Could not write JSON: could not extract ResultSet; nested exception is com.fasterxml.jackson.databind.JsonMappingException: could not extract ResultSet (through reference chain: com.generator.ExamMaker.entity.Topic["questions"]->org.hibernate.collection.internal.PersistentBag[0]->com.generator.ExamMaker.entity.Question["options"])",
-- Eclipse console message show
2021-05-02 20:51:42.825 WARN 2452 --- [nio-8080-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 1064, SQLState: 42000 2021-05-02 20:51:42.825 ERROR 2452 --- [nio-8080-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'option options0_ where options0_.question_id=1' at line 1 2021-05-02 20:51:42.830 WARN 2452 --- [nio-8080-exec-2] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: could not extract ResultSet; nested exception is com.fasterxml.jackson.databind.JsonMappingException: could not extract ResultSet (through reference chain: com.generator.ExamMaker.entity.Topic["questions"]->org.hibernate.collection.internal.PersistentBag[0]->com.generator.ExamMaker.entity.Question["options"])] 2021-05-02 20:54:44.578 WARN 2452 --- [l-2 housekeeper] com.zaxxer.hikari.pool.HikariPool : HikariPool-2 - Retrograde clock change detected (housekeeper delta=29s614ms), soft-evicting connections from pool. 
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