Develop Reference

How to map a OneToOne with ZeroOrOneToOne back reference in JPA?

I have a legacy app which has an entity relationship that looks like this. I changed the names of the fields to less realistic values and reduced to only the relevant fields.
CREATE TABLE `billing_target` (
`billingTargetID` int(11) NOT NULL,
`targetType` char(5) NOT NULL,
`targetID` int(11) NOT NULL
PRIMARY KEY (`billingTargetID`)
);
CREATE TABLE `Client` (
`clientID` int(11) NOT NULL,
`name` varchar(200),
`color` varchar(200),
`shape` varchar(200)
PRIMARY KEY (`clientID`),
CONSTRAINT `fk_client_billingTarget`
FOREIGN KEY (`clientID`)
REFERENCES `billing_target` (`targetID`)
);
My most current attempt which causes an issue when saving as it gives a null entity key exception.
#Data
#Entity
public class BillingTarget implements Serializable {
#Id
#Column(name = "billingTargetID")
private Integer id;
#Column(name = "targetID", nullable = false)
private Integer targetID;
#Column(name = "targetType", nullable = false)
private String type;
}
#Data
#Entity
public class Client implements Serializable {
#Id
#Column(name = "clientID")
private Integer id;
#OneToOne
#JoinColumn(name = "clientID")
#MapsId("targetID")
private BillingTarget billingTarget;
private String name;
private String color;
private String shape;
}
Here's the PlantUML code if interested
#startuml
hide circle
entity BillingTarget {
* billingTargetID <<generated>>
--
* targetType
* targetID <<unique>>
}
entity Client {
* clientID <<fk>>
--
* name
color
shape
}
BillingTarget ||--o| Client : "targetID:clientID"
#enduml
I was already thinking of using a MappedSuperclass but right now it is only one type (though it could be more). Second the billing target may be zero and not null as there's a NOT NULL constraint already present.

Hibernate trying to alter table before creating it

Simple issue here: I'm running Spring Boot 2.2.5 on a mySQL database with MySQL5Dialect. Everything was peachy until I've added #ManyToOne annotation to Slide entity referencing the User entity - now Hibernate can't create tables because it creates the users table and then tries to alter slides table which it hasn't created yet. What did I do wrong?
User:
#Entity
#Getter
#Setter
#NoArgsConstructor
#AllArgsConstructor
#ToString
#Table(name = "users")
public class User {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private boolean enabled;
private String token;
private String username;
private String password;
private String role;
private String name;
private String surname;
private String email;
private boolean emailVisible;
private String phone;
private boolean phoneVisible;
private int cohortNumber;
private String company;
private String position;
private String linkedIn;
private String function;
private String bio;
private String membership;
private Date membershipSince;
private Date membershipUntil;
}
Slide:
#Entity
#Getter
#Setter
#NoArgsConstructor
#AllArgsConstructor
#ToString(exclude = "editor")
#Table(name = "slides")
public class Slide {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
private boolean visible;
private int order;
private Date edited;
#ManyToOne
#JoinColumn(name = "editor_id")
private User editor;
private String title;
private String text;
private String picture;
}
Hibernate config specifics:
spring.jpa.hibernate.ddl-auto = update
spring.datasource.initialization-mode=always
spring.jpa.hibernate.naming-strategy = org.hibernate.cfg.ImprovedNamingStrategy
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5Dialect
And the error:
Hibernate: create table users (id integer not null auto_increment, bio varchar(255), cohort_number integer not null, company varchar(255), email varchar(255), email_visible bit not null, enabled bit not null, function varchar(255), linked_in varchar(255), membership varchar(255), membership_since datetime, membership_until datetime, name varchar(255), password varchar(255), phone varchar(255), phone_visible bit not null, position varchar(255), role varchar(255), surname varchar(255), token varchar(255), username varchar(255), primary key (id)) engine=MyISAM
Hibernate: alter table slides add constraint FKobqxptfxg36ls278o63ouq369 foreign key (editor_id) references users (id)
2020-08-11 14:27:48.201 WARN 8224 --- [ restartedMain] o.h.t.s.i.ExceptionHandlerLoggedImpl : GenerationTarget encountered exception accepting command : Error executing DDL "alter table slides add constraint FKobqxptfxg36ls278o63ouq369 foreign key (editor_id) references users (id)" via JDBC Statement
...
Caused by: java.sql.SQLSyntaxErrorException: Table '32293814_alumnicemba.slides' doesn't exist

Found the problem:
private int order;
"order" is not allowed as a field name here and Hibernate was encountering an error when trying to create the slides table but not logging that error. I've renamed the field to "sorting" and it works now.

Why this Hibernate Relation isn't working?

I try to Connect Pizzas and Ingredients in a n:m relation while all Pizzas have Ingredients as an Attribute List of Ingredients. But in the Relationstable when I create a new Pizza and try to commit there is an Error with the PizzaID in the Relationtable.
The relational Table:
CREATE TABLE `Pizza_Ingredience_Relation` (
`PizzaID` int(11) NOT NULL,
`IngredientID` int(11) NOT NULL,
`Amount` int(11) NOT NULL,
`Volume_Unit` varchar(1) NOT NULL,
PRIMARY KEY (`PizzaID`,`IngredientID`),
KEY `FKc58en2gx5a8n1swmu9tda345` (`IngredientID`),
CONSTRAINT `FK_IngredienceId` FOREIGN KEY (`IngredientID`) REFERENCES `Zutatenliste` (`ID`),
CONSTRAINT `FKc58en2gx5a8n1swmu9tda345` FOREIGN KEY (`IngredientID`) REFERENCES `Zutatenliste` (`ID`),
CONSTRAINT `FKhghfxg8raskdydyu8o8msxtfn` FOREIGN KEY (`PizzaID`) REFERENCES `Pizza` (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
The Ingredient Table:
CREATE TABLE `Zutatenliste` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`Name` varchar(20) NOT NULL,
PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
The Pizza Table:
CREATE TABLE `Pizza` (
`ID` int(11) NOT NULL AUTO_INCREMENT,
`Name` varchar(20) NOT NULL,
`PreisKlein` double NOT NULL,
`PreisMittel` double NOT NULL,
`PreisGroß` double NOT NULL,
`PreisFamilie` double NOT NULL,
PRIMARY KEY (`ID`),
UNIQUE KEY `ID` (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=12 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
I have two hibernate Entitites, one is a Pizza Entitiy and one the Ingredient Entitiy:
package Model.PizzenDB.SQLConnectionClasses.MySQL;
import Model.PizzenDB.Pizza;
import org.hibernate.annotations.CollectionId;
import org.hibernate.annotations.Where;
import javax.persistence.*;
import java.util.LinkedList;
import java.util.Set;
#Entity
#Table(name = "Pizza")
public class MySQLPizzaHibernateEntity {
#Id
#Column(name = "ID")
private int id;
#Column(name = "Name")
private String name;
#Column(name = "PreisKlein")
private double smallPrice;
#Column(name = "PreisMittel")
private double middlePrice;
#Column(name = "PreisGroß")
private double bigPrice;
#Column(name = "PreisFamilie")
private double familyPrice;
#ManyToMany(cascade = { CascadeType.ALL })
#JoinTable(
name = "Pizza_Ingredience_Relation",
joinColumns = { #JoinColumn(name = "PizzaID", referencedColumnName = "ID") },
inverseJoinColumns = { #JoinColumn(name = "IngredientID") }
)
private Set<MySQLIngredientWithAmountHibernateEntity> ingredience;
public MySQLPizzaHibernateEntity(String name, double smallPrice, double middlePrice, double bigPrice, double familyPrice) {
this.name = name;
this.smallPrice = smallPrice;
this.middlePrice = middlePrice;
this.bigPrice = bigPrice;
this.familyPrice = familyPrice;
}
public MySQLPizzaHibernateEntity() {
}
}
#Entity
#Table(name = "Zutatenliste")
#SecondaryTable(name = "Pizza_Ingredience_Relation", pkJoinColumns = #PrimaryKeyJoinColumn(name = "IngredientID", referencedColumnName = "ID"))
public class MySQLIngredientWithAmountHibernateEntity {
#Id
#Column(name = "ID")
private int id;
#Column(name = "Name")
private String name;
#Column(table = "Pizza_Ingredience_Relation", name="Amount")
private int amount;
#Column(table = "Pizza_Ingredience_Relation", name = "Volume_Unit")
private char unit;
public MySQLIngredientWithAmountHibernateEntity(String name) {
this.name = name;
}
public MySQLIngredientWithAmountHibernateEntity() {
this("");
}
}
I get the following error message:
20:41:45 [main] [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] ERROR - Field 'PizzaID' doesn't have a default value
20:41:45 [main] [org.hibernate.internal.ExceptionMapperStandardImpl] ERROR - HHH000346: Error during managed flush [org.hibernate.exception.GenericJDBCException: could not execute statement]
I'm not sure what is wrong in detail I guess it has todo with the PizzaID Foreign Key and that it isn't set properly.

For many to many relationship, you are using middle table with extra columns and you need Embeddable key for that which would comprise of Pizza and Ingredient object (names shortened). Something like:
#Embeddable
public class PizzaIngredientPk {
private MySQLPizzaHibernateEntity pizza;
private MySQLIngredientWithAmountHibernateEntity ingredient;
#ManyToOne
public MySQLPizzaHibernateEntity getPizza() {
return pizza;
}
public void setPizza(MySQLPizzaHibernateEntity pizza) {
this.pizza = pizza;
}
#ManyToOne
public MySQLIngredientWithAmountHibernateEntity getIngredient() {
return ingredient;
}
public void setIngredientID(MySQLIngredientWithAmountHibernateEntity ingredient) {
this.ingredient = ingredient;
}
}
Then this would act as Embedded Key in MySQLIngredientWithAmountHibernateEntity as
#EmbeddedId
PizzaIngredientPk pk = new PizzaIngredientPk();
But this won't work with Secondarytable which is used for one-to-one relationship. #SecondaryTable requires mapping to be with a primary key but in this case Embedded ID would become PK. In fact, you have flaw in your design. You are trying to make one side of your many to many relationship as one-to-one.
As per JPA docs There must be only one EmbeddedId annotation and no Id annotation when the EmbeddedId annotation is used.

Try to specify to Hibernate automatically produce primary keys. Put this annotation above your Id fields and re-create your database.
#GeneratedValue(strategy = GenerationType.IDENTITY)
See: https://thoughts-on-java.org/hibernate-tips-use-auto-incremented-column-primary-key/

JPA Join tables Query

I am working on a school project, and I am having trouble with joining tables so I can display output in JSP file using JSTL. I will provide all necessary code. I know that I need to connect entities somehow, but I don't know how.
SQL:
CREATE TABLE IF NOT EXISTS `totelegram`.`contacts` (
`id` INT NOT NULL AUTO_INCREMENT,
`first_name` VARCHAR(45) CHARACTER SET 'utf8' COLLATE 'utf8_unicode_ci' NOT NULL,
`last_name` VARCHAR(45) CHARACTER SET 'utf8' COLLATE 'utf8_unicode_ci' NOT NULL,
`phone_number` VARCHAR(45) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE INDEX `id_UNIQUE` (`id` ASC),
UNIQUE INDEX `phone_number_UNIQUE` (`phone_number` ASC))
ENGINE = InnoDB;
CREATE TABLE IF NOT EXISTS `totelegram`.`messages` (
`id_message` INT NOT NULL AUTO_INCREMENT,
`message` VARCHAR(2000) CHARACTER SET 'utf8' COLLATE 'utf8_unicode_ci' NOT
NULL,
`time` VARCHAR(45) NOT NULL,
`contacts_id` INT NOT NULL,
PRIMARY KEY (`id_message`),
UNIQUE INDEX `id_message_UNIQUE` (`id_message` ASC),
INDEX `fk_messages_contacts_idx` (`contacts_id` ASC),
CONSTRAINT `fk_messages_contacts`
FOREIGN KEY (`contacts_id`)
REFERENCES `totelegram`.`contacts` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB;
Contacts.java
#Entity(name = "contacts")
public class Contacts implements Serializable{
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private int id;
#javax.persistence.Column(name = "first_name")
private String firstName;
#javax.persistence.Column(name = "last_name")
private String lastName;
#javax.persistence.Column(name = "phone_number")
private String phoneNumber;
...getters/setters, constructor, toString...
Messages.java
#Entity(name = "messages")
public class Messages implements Serializable{
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#javax.persistence.Column(name = "id_message")
private int id;
private String message;
private String time;
#javax.persistence.Column(name = "contacts_id")
private int contactsId;
...getters/setters, constructor, toString...
MessagesRepository.java
public interface MessagesRepository extends JpaRepository<Messages, Integer> {
//custom query which will output this
//SELECT b.message, b.time, b.contacts_id, a.first_name, a.last_name FROM messages AS b INNER JOIN contacts as A ON (b.contacts_id=a.id) ORDER BY time ASC;
public List<Messages> findAll();
}
I hope I was clear. Thanks to everybody in advance.

As far as i understand, one contact can have N messages and you cannot have a Message without the Contact, right?
Since you have relations between classes, you have to use specific annotations in jpa, for example:
in the Message Class, you should use the #ManyToOne annotation, since you have Many Messages for One Contact. The JoinColumn will input the contacts_id in the Messages Table.
#ManyToOne
#JoinColumn(name = "contacts_id")
private Contacts contact;
in the Contacts Class, you should use #OneToMany annotation, since One Contact has Many Messages. The mappedBy makes a reference in contact at the Message Class.
#OneToMany(mappedBy = "contact")
private List<Messages> messages = new ArrayList<>();
So far you made a Bidirectional reference between Contacts and Messages. Now in your service class, i would recommend you find the Messages through the Contacts, since you cannot have a message without the contact. Its a Repository principle.
Contacts con = repository.findOne(1);
con.getMessages();
btw, sorry for the bad english.

Hibernate Exception while defining mapping

I am working on a project and using Hibernate for database interaction.
I have two tables, one is RESOURCE_PROFILE and second is PROJECT_MASTER. Below are the DDL statements.
CREATE TABLE USER_PROFILE (
FIRST_NAME VARCHAR(15) NOT NULL,
MIDDLE_NAME VARCHAR(15),
LAST_NAME VARCHAR(15) NOT NULL,
EMAIL_ID VARCHAR(40) NOT NULL,
USER_ID VARCHAR(40) NOT NULL,
PASSWORD VARCHAR(1000) NOT NULL,
ROLE VARCHAR(20),
SUPERVISOR_ID VARCHAR(20),
SUBMITTED_BY VARCHAR(20),
SUBMITTED_DATE DATE,
PRIMARY KEY (USER_ID)
);
CREATE TABLE PROJECT_MASTER (
PROJECT_ID INT NOT NULL AUTO_INCREMENT,
PROJECT_NAME VARCHAR(50) NOT NULL,
PROJECT_NUMBER VARCHAR(50) NOT NULL,
START_DATE DATE,
END_DATE DATE,
PROJECT_MANAGER_ID VARCHAR(40) NOT NULL,
PROJECT_SUPERVISOR_ID VARCHAR(40) NOT NULL,
SUBMITTED_BY VARCHAR(40),
SUBMITTED_DATE DATE,
UPDATED_BY VARCHAR(40),
PRIMARY KEY (PROJECT_ID),
FOREIGN KEY (PROJECT_MANAGER_ID) REFERENCES USER_PROFILE(USER_ID),
FOREIGN KEY (PROJECT_SUPERVISOR_ID) REFERENCES USER_PROFILE(USER_ID),
FOREIGN KEY (SUBMITTED_BY) REFERENCES USER_PROFILE(USER_ID),
FOREIGN KEY (UPDATED_BY) REFERENCES USER_PROFILE(USER_ID)
);
As you can see in the PROJECT_MASTER table I am using the USER_ID(RESOURCE_PROFILE) as a foreign key for multiple columns in PROJECT_MASTER table. Below is the entity class I created for these two tables. I am sure that I am doing something wrong in the mapping, can you please help me and point me to the right direction?
Since I have the same foreign key getting used for multiple columns, how can I achieve this mapping?
#Entity
#Table(name = "PROJECT_MASTER")
public class ProjectMasterBean {
#Id
#GeneratedValue
#Column(name="PROJECT_ID")
private int projectID;
#Column(name="PROJECT_NAME")
private String projectName;
#Column(name="PROJECT_NUMBER")
private String projectNumber;
#Column(name="START_DATE")
private Date startDate;
#Column(name="END_DATE")
private Date endDate;
#ManyToOne
#JoinColumn(name="USER_ID",insertable=false, updatable=false,
nullable=false)
private UserProfileBean projectManagerID;
#ManyToOne
#JoinColumn(name="USER_ID",insertable=false, updatable=false,
nullable=false)
private UserProfileBean projectSupervisorID;
#ManyToOne
#JoinColumn(name="USER_ID",insertable=false, updatable=false,
nullable=false)
private UserProfileBean submittedBy;
}
#Column(name="SUBMITTED_DATE")
private Date submittedDate;
#ManyToOne
#JoinColumn(name="USER_ID",insertable=false, updatable=false,
nullable=false)
private UserProfileBean updatedBy;
public class UserProfileBean {
#Id
#Column(name="USER_ID")
private String userID;
#Column(name="FIRST_NAME")
private String firstName;
#Column(name="MIDDLE_NAME")
private String middleName;
#Column(name="LAST_NAME")
private String lastName;
#Column(name="EMAIL_ID")
private String emailID;
#Column(name="PASSWORD")
private String password;
#Column(name="ROLE")
private String userRole;
#Column(name="SUPERVISOR_ID")
private String supervisorID;
#Column(name="SUBMITTED_BY")
private String submittedBy;
#Column(name="SUBMITTED_DATE")
private String submittedDate;
}
This is the exception I am getting:
Hibernate: insert into PROJECT_MASTER (PROJECT_NAME, PROJECT_NUMBER, START_DATE, END_DATE, SUBMITTED_BY, SUBMITTED_DATE, UPDATED_BY) values (?, ?, ?, ?, ?, ?, ?)
Sep 12, 2013 8:46:20 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet action threw exception
java.sql.SQLException: Field 'PROJECT_MANAGER_ID' doesn't have a default value
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3609)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3541)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
Insert Query doesn't even have those two columns. This is how the query should be.
Hibernate: insert into PROJECT_MASTER (PROJECT_NAME, PROJECT_NUMBER, START_DATE, END_DATE, PROJECT_MANAGET_ID , PROJECT_SUPERVISOR_ID , SUBMITTED_BY, SUBMITTED_DATE, UPDATED_BY) values (?, ?, ?, ?, ?, ?, ?,?,?)

You've created your table with
CREATE TABLE PROJECT_MASTER ( PROJECT_ID INT NOT NULL AUTO_INCREMENT,
PROJECT_NAME VARCHAR(50) NOT NULL, PROJECT_NUMBER VARCHAR(50) NOT
NULL, START_DATE DATE, END_DATE DATE, PROJECT_MANAGER_ID VARCHAR(40)
NOT NULL, PROJECT_SUPERVISOR_ID VARCHAR(40) NOT NULL, SUBMITTED_BY
VARCHAR(40), SUBMITTED_DATE DATE, UPDATED_BY VARCHAR(40), PRIMARY KEY
(PROJECT_ID), FOREIGN KEY (PROJECT_MANAGER_ID) REFERENCES
USER_PROFILE(USER_ID), FOREIGN KEY (PROJECT_SUPERVISOR_ID) REFERENCES
USER_PROFILE(USER_ID), FOREIGN KEY (SUBMITTED_BY) REFERENCES
USER_PROFILE(USER_ID), FOREIGN KEY (UPDATED_BY) REFERENCES
USER_PROFILE(USER_ID) );
And you've made your class uses this Table. Because you don't have a default value for a NOT NULL field, Hibernate complains. Either delete that column from the table or add a relationship in your entity mapping.
Change to
#ManyToOne
#JoinColumn(name="PROJECT_MANAGER_ID ",insertable=false, updatable=false,
nullable=false)
private UserProfileBean projectManagerID;