Hibernate: New Session without dropping the tables

Question

I am new to Hibernate (implementing since yesterday) and i succesfully created a method, that transfers my Customer Objects to the Database.

After i quit my application and start it again and create a new session (in an other method) based on my hibernate.cfg.xml file with this setting:

<property name="hibernate.hbm2ddl.auto">create</property>

It leads to that point, that all relevant tables, created with Hibernate are being deleted. So maybe that is a comprehension question, but i think "transparent persistence by hibernate" means also, that my POJO's are persistent beyond the runtime of my application!?

So i read several topics on Stackoverflow and tried it with this setting:

<property name="hibernate.hbm2ddl.auto">update</property>

But this leads to SQL errors:

com.mysql.jdbc.exceptions.MySQLIntegrityConstraintViolationException: Duplicate entry '1' for key 'PRIMARY'

Of course i don't want have duplicates, so i suppose that hibernate doesn't send a SQL Statement referring to an existing object.

It sends a Statement like this:

UPDATE `customer` SET `id`=1,`birthday`='1990-10-05 00:00:00',`forename`='TestCustomer',`gender`='F',`generatedProfitsLastYear`='0',`generatedProfitsTotal`='0',`surename`='A',`gcid`='1'

But i need the same statement, with a

Where `id`=1

at the end.

So basically what i want is, that hibernate doesn't drop all the tables and creates it again when i restart my application and create a new session based on the configuration file. So after i open a new session, i can transfer the Customer Objects stored in the database to POJOs. Did i understand the concept of hibernate incorrectly or am i making a typical beginners mistake?

Below you will find my Customer Class:

@Entity
@Table(name="CUSTOMER")

public class Customer {
    private int id;
    private String forename;
    private String surname;
    private char gender;
    private Date birthday;
    private double generatedProfitsTotal;
    private double generatedProfitsLastYear;    
    private CustomerGroup assignedTo;

    public Customer(int id, String forename, String surname, char gender,
            Date birthday) {
        super();
        this.id = id;
        this.forename = forename;
        this.surname = surname;
        this.gender = gender;
        this.birthday = birthday;
    }

    @Id
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Column(name = "forename")
    public String getForename() {
        return forename;
    }

    public void setForename(String forename) {
        this.forename = forename;
    }
    @Column(name = "surename")
    public String getSurname() {
        return surname;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }
    @Column(name = "gender")
    public char getGender() {
        return gender;
    }

    public void setGender(char gender) {
        this.gender = gender;
    }
    @Column(name = "birthday")
    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    @Column(name = "generatedProfitsTotal")
    public double getGeneratedProfitsTotal() {
        return generatedProfitsTotal;
    }

    public void setGeneratedProfitsTotal(double generatedProfitsTotal) {
        this.generatedProfitsTotal = generatedProfitsTotal;
    }
    @Column(name = "generatedProfitsLastYear")
    public double getGeneratedProfitsLastYear() {
        return generatedProfitsLastYear;
    }

    public void setGeneratedProfitsLastYear(double generatedProfitsLastYear) {
        this.generatedProfitsLastYear = generatedProfitsLastYear;
    }


    @ManyToOne(fetch=FetchType.EAGER)
    @JoinColumn(name="gcid", nullable=true, insertable=true, updatable=true)
    public CustomerGroup getAssignedTo() {
        return assignedTo;
    }

    public void setAssignedTo(CustomerGroup assignedTo) {
        this.assignedTo = assignedTo;
    }
}

my hibernate config file:

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.password">root</property>
        <property name="hibernate.connection.url">jdbc:mysql://127.0.0.1/hibernatetesting</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <property name="show_sql">true</property>
        <property name="hibernate.hbm2ddl.auto">update</property>
        <mapping class="studyproject.Customer"/>
         <mapping class="studyproject.CustomerGroup"/>
         <mapping class="studyproject.BonusPackage"/>

    </session-factory>
</hibernate-configuration>

Thanks

please, have a look: http://stackoverflow.com/questions/438146/hibernate-hbm2ddl-auto-possible-values-and-what-they-do — melli-182, Jul 06 '15 at 18:48
Thanks, maybe i don't understand it, but when i am using update i am on the right track, right? Unfortunately "Update" leads to a wrong SQL Statement, wihout an WHERE id=X at the end. So that leads to that "duplicate" error. — UDE_Student, Jul 06 '15 at 18:55
i have edited my starting post with the statement that Hibernate sends and what i want that hibernate should send. — UDE_Student, Jul 06 '15 at 19:00
i found a solution, before i used session.persist(Customer), i had to use session.saveOrUpdate(Customer) — UDE_Student, Jul 06 '15 at 19:12
But i have the problem, if i reopen a new session and try to get all the Customer objects in a List, i get NULL. allCustomers=ArrayList) session.createQuery("FROM Customer").list(); ----- — UDE_Student, Jul 06 '15 at 19:20

score 1 · Accepted Answer · edited Sep 02 '22 at 11:33

1

try session.saveOrUpdate() method where you have used session.save() it will prevent your database from dropping while fetching data use it with hbm2ddl.auto update. it worked for me. hope it helps.

edited Sep 02 '22 at 11:33

Omkar Nath Singh

3,375
2
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answered Aug 28 '22 at 08:08

Naina

26
1

score 0 · Answer 2 · answered Jul 08 '15 at 03:20

0

What did you do where the 'duplicate error' occurs? Now I have the hibernate.hbm2ddl.auto configured as yours, but it's okay saving or updating entity in my local.

answered Jul 08 '15 at 03:20

Sky

7,343
8
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Hibernate: New Session without dropping the tables

2 Answers2