spring boot hibernate query invalid user error

Question

Hi I am new to Spring Boot. I try to connect to Oracle and list related records. My code worked in a stub environment, that is without connecting to a db. When I tried to connect to the db from Spring, I got the error as given in EDIT 2:

HomeController

package blog.controllers;

import blog.models.Post;
import blog.services.PostService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

import java.util.List;
import java.util.stream.Collectors;

@Controller
public class HomeController {

    @Autowired
    private PostService postService;

    @RequestMapping("/")
    public String index(Model model){

        List<Post> latest5Posts = postService.findLatest5();
        model.addAttribute("latest5posts", latest5Posts);

        List<Post> latest3Posts = latest5Posts.stream()
                .limit(3).collect(Collectors.toList());
        model.addAttribute("latest3posts", latest3Posts);

        return "index";

    }
}

Posts Entity class

package blog.models;

import javax.persistence.*;
import java.util.Date;

@Entity
@Table(name = "POSTS")
public class Post {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 300)
    private String title;

    @Lob @Column(nullable = false)
    private String body;

    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    private User author;

    @Column(nullable = false)
    private Date creation_date = new Date();

    public Long getId() {return id;}
    public void setId(Long id) {this.id = id;}
    public String getTitle() {return title;}
    public void setTitle(String title) {this.title = title;}
    public String getBody() {return body;}
    public void setBody(String body) {this.body = body;}
    public User getAuthor() {return author;}
    public void setAuthor(User author) {this.author = author;}
    public Date getCreation_date() {return date;}
    public void setCreation_date(Date creation_date) {this.creation_date = creation_date;}

    public Post() { }

    public Post(Long id, String title, String body, User author) {

        this.id=id; this.title=title; this.body=body; this.author=author;
    }

    @Override
    public String toString() {
        return "Post{" + "id=" + id + ", title='" + title + '\'' +
                ", body='" + body + '\'' +
                ", author='" + author + '\'' +
                ", date=" + Creationdate +
                '}';
    }

}

Users Entity class

package blog.models;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;


@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 30, unique = true)
    private String username;

    @Column(length = 60)
    private String passwordHash;

    @Column(length = 100)
    private String fullName;

    @OneToMany(mappedBy = "author")
    private Set<Post> posts = new HashSet<>();


    public Long getId() {return id;}

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

    public String getUsername() {return username;}

    public void setUsername(String username) {this.username = username;}

    public String getPasswordHash() {return passwordHash;}

    public void setPasswordHash(String passwordHash) {this.passwordHash = passwordHash;}

    public String getFullName() {return fullName;}

    public void setFullName(String fullName) {this.fullName = fullName;}

    public Set<Post> getPosts() {return posts;}

    public void setPosts(Set<Post> posts) {this.posts = posts;}

    public User() { }

    public User(Long id, String username, String fullName) {
        this.id = id; this.username = username; this.fullName = fullName;
    }

    @Override
    public String toString() {
        return "User{" + "id=" + id + ", username='" + username + '\'' +
                ", passwordHash='" + passwordHash + '\'' +
                ", fullName='" + fullName + '\'' + '}';
    }
}

Repository

package blog.repositories;

import blog.models.Post;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;

import org.springframework.data.domain.Pageable;
import java.util.List;


@Repository
public interface PostRepository extends JpaRepository<Post, Long> {
    @Query("SELECT p FROM Post p LEFT JOIN FETCH p.author ORDER BY p.creation_date DESC")
    List<Post> findLatest5Posts(Pageable pageable);
}

Service

package blog.services;

import blog.models.Post;
import org.springframework.stereotype.Service;

import java.util.List;


@Service
public interface PostService {

    List<Post> findAll();
    List<Post> findLatest5();
    Post findById(Long id);
    Post create(Post post);
    Post edit(Post post);
    void deleteById(Long id);
}

Service Implementation

package blog.services;

import blog.models.Post;
import blog.repositories.PostRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Primary;
import org.springframework.data.domain.PageRequest;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
@Primary
public class PostServiceJpaImpl implements PostService {
    @Autowired
    private PostRepository postRepository;

    @Override
    public List<Post> findAll() {
        return this.postRepository.findAll();
    }
    @Override
    public List<Post> findLatest5() {
        return this.postRepository.findLatest5Posts(new PageRequest(0, 5));
    }
    @Override
    public Post findById(Long id) {
        return this.postRepository.findOne(id);
    }
    @Override
    public Post create(Post post) {
        return this.postRepository.save(post);
    }
    @Override
    public Post edit(Post post) {
        return this.postRepository.save(post);
    }
    @Override
    public void deleteById(Long id) {
        this.postRepository.delete(id);
    }
}

As for my tables in the db:

create table users (
id number,
username varchar2(30),
passwordHash varchar2(60),
fullName varchar2(100),
constraint users_pk primary key (id));

create table posts (
id number,
author_id number,
title varchar2(300),
body clob,
creation_date timestamp,
primary key (id));

p.s. I have also tried the following by changing the repository:

@Query(value = "SELECT * FROM POSTS aa LEFT JOIN USERS bb ON aa.AUTHOR_ID=bb.ID", nativeQuery = true)

This time I had the following error:

    org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfiguration.class]: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory
    at ...
Caused by: org.hibernate.tool.schema.spi.SchemaManagementException: Unable to execute schema management to JDBC target [alter table posts add constraint FK6xvn0811tkyo3nfjk2xvqx6ns foreign key (author_id) references users]
    at org.hibernate.tool.schema.internal.TargetDatabaseImpl.accept(TargetDatabaseImpl.java:59) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.schema.internal.SchemaMigratorImpl.applySqlString(SchemaMigratorImpl.java:431) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.schema.internal.SchemaMigratorImpl.applySqlStrings(SchemaMigratorImpl.java:420) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.schema.internal.SchemaMigratorImpl.applyForeignKeys(SchemaMigratorImpl.java:386) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.schema.internal.SchemaMigratorImpl.doMigrationToTargets(SchemaMigratorImpl.java:214) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.schema.internal.SchemaMigratorImpl.doMigration(SchemaMigratorImpl.java:60) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.hbm2ddl.SchemaUpdate.execute(SchemaUpdate.java:134) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.tool.hbm2ddl.SchemaUpdate.execute(SchemaUpdate.java:101) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:470) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:444) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:879) ~[hibernate-entitymanager-5.0.9.Final.jar:5.0.9.Final]
    ... 27 common frames omitted
Caused by: java.sql.SQLSyntaxErrorException: ORA-02268: referenced table does not have a primary key

    at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:439) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:395) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:802) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:436) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:186) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:521) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CStatement.doOall8(T4CStatement.java:194) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CStatement.executeForRows(T4CStatement.java:1000) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1307) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OracleStatement.executeUpdateInternal(OracleStatement.java:1814) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OracleStatement.executeUpdate(OracleStatement.java:1779) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OracleStatementWrapper.executeUpdate(OracleStatementWrapper.java:277) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at org.hibernate.tool.schema.internal.TargetDatabaseImpl.accept(TargetDatabaseImpl.java:56) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    ... 37 common frames omitted

What am I missing?

Thanks in advance!

EDIT:

POM.XML

<?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>

    <groupId>softuni</groupId>
    <artifactId>mvc-blog</artifactId>
    <version>1.0-SNAPSHOT</version>


    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.0.RELEASE</version>
    </parent>


    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
            <exclusions>
                <exclusion>
                    <artifactId>jackson-databind</artifactId>
                    <groupId>com.fasterxml.jackson.core</groupId>
                </exclusion>
            </exclusions>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>

        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>2.10.0</version>
        </dependency>


        <dependency>
            <groupId>cosine-lsh</groupId>
            <artifactId>cosinelsh</artifactId>
            <version>1.0</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc6</artifactId>
            <version>11.2.0.4</version>
        </dependency>

    </dependencies>

    <properties>
        <java.version>1.8</java.version>
        <spark.version>1.4.1</spark.version>
        <!--<scala.version>2.10.0</scala.version>-->
    </properties>


</project>

application.properties

#Turn off Thymeleaf cache
spring.thymeleaf.cache = false

spring.datasource.driver-class-name = oracle.jdbc.driver.OracleDriver
spring.datasource.url = jdbc:oracle:thin:@...
spring.datasource.username = usrnm
spring.datasource.password = psswrd
# Configure Hibernate DDL mode: create / update
spring.jpa.properties.hibernate.hbm2ddl.auto = update

#hibernate config
spring.jpa.database-platform=org.hibernate.dialect.Oracle10gDialect

spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl

spring.data.jpa.repositories.enabled=true

# Show or not log for each sql query
spring.jpa.show-sql = true

user repository

package blog.repositories;

import blog.models.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
}

user service

package blog.services;

import blog.models.User;

import java.util.List;

public interface UserService {

    List<User> findAll();
    User findById(Long id);
    User create(User user);
    User edit(User user);
    void deleteById(Long id);
}

user service implementation

package blog.services;

import blog.models.User;
import blog.repositories.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Service;
import java.util.List;

@Service
@Primary
public class UserServiceJpaImpl implements UserService {
    @Autowired
    private UserRepository userRepository;
    @Override
    public List<User> findAll() {
        return this.userRepository.findAll();
    }
    @Override
    public User findById(Long id) {
        return this.userRepository.findOne(id);
    }
    @Override
    public User create(User user) {
        return this.userRepository.save(user);
    }
    @Override
    public User edit(User user) {
        return this.userRepository.save(user);
    }
    @Override
    public void deleteById(Long id) {
        this.userRepository.delete(id);
    }
}

@SpringBootApplication

package blog;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;


@SpringBootApplication
public class BlogMvcApplication {

    public static void main(String[] args) {

        SpringApplication.run(BlogMvcApplication.class, args);

    }
}

EDIT 2:

Error lines for JPA query (when native query is not used)

java.sql.SQLSyntaxErrorException: ORA-01747: invalid user.table.column, table.column, or column specification

    at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:439) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:395) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:802) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:436) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:186) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:521) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:205) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.T4CPreparedStatement.executeForDescribe(T4CPreparedStatement.java:861) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(OracleStatement.java:1145) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1267) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3449) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:3493) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at oracle.jdbc.driver.OraclePreparedStatementWrapper.executeQuery(OraclePreparedStatementWrapper.java:1491) ~[ojdbc6-11.2.0.4.jar:11.2.0.1.0]
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:70) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.getResultSet(Loader.java:2117) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1900) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1876) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.doQuery(Loader.java:919) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:336) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.doList(Loader.java:2617) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.doList(Loader.java:2600) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2429) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.Loader.list(Loader.java:2424) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:501) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:371) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:216) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1326) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.internal.QueryImpl.list(QueryImpl.java:87) ~[hibernate-core-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:606) ~[hibernate-entitymanager-5.0.9.Final.jar:5.0.9.Final]
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:483) ~[hibernate-entitymanager-5.0.9.Final.jar:5.0.9.Final]
    at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:114) ~[spring-data-jpa-1.10.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:78) ~[spring-data-jpa-1.10.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:102) ~[spring-data-jpa-1.10.2.RELEASE.jar:na]
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:92) ~[spring-data-jpa-1.10.2.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:482) ~[spring-data-commons-1.12.2.RELEASE.jar:na]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:460) ~[spring-data-commons-1.12.2.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61) ~[spring-data-commons-1.12.2.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) ~[spring-tx-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:280) ~[spring-tx-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136) ~[spring-tx-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:133) ~[spring-data-jpa-1.10.2.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213) ~[spring-aop-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at com.sun.proxy.$Proxy87.findLatest5Posts(Unknown Source) ~[na:na]
    at blog.services.PostServiceJpaImpl.findLatest5(PostServiceJpaImpl.java:23) ~[classes/:na]
    at blog.controllers.HomeController.index(HomeController.java:26) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_31]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_31]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_31]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_31]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:87) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.4.jar:8.5.4]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.2.RELEASE.jar:4.3.2.RELEASE]

Answer 1

It seems that the problem is following:

Because of this property:

spring.jpa.properties.hibernate.hbm2ddl.auto = update

And the fact that the Posts entity has been changed to reference the User, Hibernate tries to add a foreign key constraint:

alter table posts add constraint FK6xvn0811tkyo3nfjk2xvqx6ns foreign key (author_id) references users

But gets this error:

ORA-02268: referenced table does not have a primary key

Not sure why hibernate does not add a primary key to this table as the @Id annotation is clearly there.

Try to add a primary key constraint manually to the Users.id column:

ALTER TABLE users
 ADD CONSTRAINT users_pk PRIMARY KEY (id);

Update

The problem might with the Post.data mapping as you are using it in the order by clause.

The doc says:

This annotation must be specified for persistent fields or properties of type java.util.Date and java.util.Calendar. It may only be specified for fields or properties of these types.

As you are using java.util.Date, then you need to add this:

@Temporal(TemporalType.DATE)
private Date date = new Date();