Java spring Hibernate : Error when trying to implement a many to one relationship

I am trying to implement a many to one relationship with a user being able to have many posts. The used database is postgresql.

The error I have is the following and is caused by Hibernate: alter table post drop constraint FKl1p5mt95jngsghp4vtaw04egh :

org.hibernate.tool.schema.spi.CommandAcceptanceException: Error executing DDL "alter table post drop constraint FKl1p5mt95jngsghp4vtaw04egh" via JDBC Statement
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:67) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.applySqlString(SchemaDropperImpl.java:375) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.applySqlStrings(SchemaDropperImpl.java:359) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.applyConstraintDropping(SchemaDropperImpl.java:331) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.dropFromMetadata(SchemaDropperImpl.java:230) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.performDrop(SchemaDropperImpl.java:154) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.doDrop(SchemaDropperImpl.java:126) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.internal.SchemaDropperImpl.doDrop(SchemaDropperImpl.java:112) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:145) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:73) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:316) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:469) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1259) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) ~[spring-orm-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:391) ~[spring-orm-5.2.9.RELEASE.jar:5.2.9.RELEASE]
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[na:na]
    at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
Caused by: org.postgresql.util.PSQLException: ERROR: relation "post" does not exist
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2553) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2285) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:323) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:473) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:393) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.jdbc.PgStatement.executeWithFlags(PgStatement.java:322) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.jdbc.PgStatement.executeCachedSql(PgStatement.java:308) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.jdbc.PgStatement.executeWithFlags(PgStatement.java:284) ~[postgresql-42.2.16.jar:42.2.16]
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:279) ~[postgresql-42.2.16.jar:42.2.16]
    at com.zaxxer.hikari.pool.ProxyStatement.execute(ProxyStatement.java:95) ~[HikariCP-3.4.5.jar:na]
    at com.zaxxer.hikari.pool.HikariProxyStatement.execute(HikariProxyStatement.java) ~[HikariCP-3.4.5.jar:na]
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:54) ~[hibernate-core-5.4.21.Final.jar:5.4.21.Final]
    ... 19 common frames omitted

These are the 2 classes I use :

import lombok.Data;
import javax.persistence.*;
import java.util.Set;

@Entity
@Data
public class WebsiteUser {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String userName;
    private String password;
    private String email;
    @OneToMany(mappedBy = "user", cascade = CascadeType.REMOVE)
    private Set<Post> posts;
}

and

import lombok.Data;
import javax.persistence.*;
import java.time.Instant;

@Entity
@Data
public class Post {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String content;
    private Instant createdOn;
    private Instant updatedOn;
    @ManyToOne
    private WebsiteUser user;
}

The error occurs at the initialisation of the program before any kind of requests.

The spring.jpa.hibernate.ddl-auto is set to create so there should not be any interference from previous tables / values in my understanding.

What is causing this error ?

I am including a screen of the generated database as seen in jetbrains Idea just in case :

Answer

Your definitions don’t look to bad, and looking at the error, I would assume it’s comming from the create setting – why else Hibernate would try to drop any constraint. Can you delete your database/tables manually and try to run the program again?

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Answer