Regarding your comment https://vladmihalcea.com/how-does-hibernate-store-second-level-cache-entries/#comment-51251, I created a new test which creates a bidirectional one-to-one relationship and tests loading entities from the 2nd level cache.

After I made sure all objects are cached, retrieving the object that owns the relationship produced cache hit.

On the contrary, retrieving the object that is on the inverse side only produces cache hit for that object. After that, a query is issued and the resulting object is put in the cache.

Or, more specifically, fetching PostDetails produces a cache hit, fetching the child (Post) produces also a cache hit. But, then, populating the child (Post) with its child (PostDetails) hits the database.

So my conclusion is that hibernate always issues a query to the database when trying to load entity that is on the inverse side of the relationship.

This query is visible in the log output of the test.

When I do

mvn clean test-compile

There is the error:

[ERROR] Failed to execute goal on project high-performance-java-persistence: Could not resolve dependencies for project com.vladmihalcea.book:high-performance-java-persistence:pom:1.0-SNAPSHOT: Failed to collect dependencies at com.oracle.jdbc:ojdbc8:jar:12.2.0.1: Failed to read artifact descriptor for com.oracle.jdbc:ojdbc8:jar:12.2.0.1: Could not transfer artifact com.oracle.jdbc:ojdbc8:pom:12.2.0.1 from/to maven.oracle.com (https://maven.oracle.com): Not authorized , ReasonPhrase:Authorization Required. -> [Help 1]

When removing the Oracle dependency compilation works.

Probably the Oracle JDBC cannot be obtained from Maven central. One solution would be to put the Oracle dependency in a separate Maven profile.

This test works fine with a ManyToOne/OneToMany relationship between PostTag and Tag. However, if that is changed to a OneToOne relationship, the test no longer passes.

I have following code.

public static int execute(String query) throws SQLException {
Statement stmt = null;
try {
    stmt = con.createStatement();
    int recordcount = stmt.executeUpdate(query);
    return recordcount;
} finally {
    stmt.close(); //ERROR getting exception here 
}
 
public static Connection getConnection() throws SQLException,ClassNotFoundException {
    con = DbConnectionPool.getDbConnectionPool().getConnection();
    return con;
}

con is static class variable initialize with the method getConnection() . Exception throws from execute method handle by caller method.

In most cases, it works fine but in some cases, it will give error "java.sql.SQLException: Invalid state, the Statement object is closed" when I call stmt.close() in finally block. What is the possibility of occurring such error?

Thank you Salman

Hello,

The UnidirectionalOrderedOneToManyTest failed for "delete only 1st entry" case The reason is Hibernate generated SQL and as result the integrity constraint violation between //2 and //3 table rows See details in below log. Is it expected? Regards, Alex

drop table post if exists|
drop table post_comment if exists|
drop table post_post_comment if exists|
drop sequence hibernate_sequence if exists|
create sequence hibernate_sequence start with 1 increment by 1|
create table post (id bigint not null, title varchar(255), primary key (id))|
create table post_comment (id bigint not null, review varchar(255), primary key (id))
create table post_post_comment (Post_id bigint not null, comments_id bigint not null, entry integer not null, primary key (Post_id, entry))
alter table post_post_comment add constraint UK_gb03lqukc5jc1u847l17m311q unique (comments_id)
alter table post_post_comment add constraint FKp3qg7d2x7uh1eiulxe65rhwl2 foreign key (comments_id) references post_comment
alter table post_post_comment add constraint FKdylii52824tsuhxvxsnancr51 foreign key (Post_id) references post
insert into post_comment (review, id) values ('My first review', 2)
insert into post_comment (review, id) values ('My second review', 3)
insert into post_comment (review, id) values ('My third review', 4)
insert into post_post_comment (Post_id, entry, comments_id) values (1, 0, 2)//2 - row updated and integrity constraint violation with row 3
insert into post_post_comment (Post_id, entry, comments_id) values (1, 1, 3)//3
**insert into post_post_comment (Post_id, entry, comments_id) values (1, 2, 4)//1 - row deleted
- Remove head
- Deleted PostComment{id=2, review='My first review'}
delete from post_post_comment where Post_id=1 and entry=2 //1
update post_post_comment set comments_id=3 where Post_id=1 and entry=0//2
SQL Error: -104, SQLState: 23505
integrity constraint violation: unique constraint or index violation; UK_GB03LQUKC5JC1U847L17M311Q table: POST_POST_COMMENT

Dear Vlad,

I'm taking your High-Performance Java Persistence course. While setting up the workspace with MySQL, I encountered an error in one of the MySQL commands. Raising this Pull Request to get it corrected.

Regards, Devesh Mankar

The here link is pointed to https://github.com/ursjoss/high-performance-java-persistence/blob/tb_mysql_instructions/MYSQL.md , which leads to 404 error

The correct link might be https://github.com/vladmihalcea/high-performance-java-persistence/blob/master/MYSQL.md

Hi,

recently I found that JsonTypeDescriptor.areEqual() checks can be optimized if the objects are already of type String. What do you think of the proposed change?

Cheers, Christoph

This is probably not the best place to describe an issue, but I haven't found a better one.

The ebook is only available via leanpub.com. This site uses only PayPal to process payments, and it is impossible to pay via PayPal from Russia:

http://help.leanpub.com/reader-help/im-having-a-problem-using-a-credit-card-from-russian-federation-help

https://groups.google.com/forum/#!topic/leanpub/EMVVGa9D6C4

Would you please consider additionally selling an electronic version of the book via another online store? I know that a print version is available on Amazon, but I really do not want to buy the printed one.

In case you got this error Error: unmappable character ... for encoding US-ASCII when: mvn clean test-compile

the only solution I found was to setup the UTF-8 into the /high-performance-java-persistence-master/core/pom.xml like this:

<properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 </properties>

There's a file in your repository that references both the Oracle and MS SQL dialects: https://github.com/vladmihalcea/high-performance-java-persistence/blob/master/jooq/jooq-mssql/src/test/resources/oracle/initial_schema.sql

From the contents, I suspect it is MS SQL, as Oracle doesn't have BIGINT or DATETIME2 types... This looks more like Oracle syntax: https://github.com/vladmihalcea/high-performance-java-persistence/blob/master/jooq/jooq-oracle/src/test/resources/oracle/initial_schema.sql

Bumps postgresql from 42.3.3 to 42.3.8.

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

Bumps hsqldb from 2.4.0 to 2.7.1.

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

Bumps jackson-databind from 2.12.6.1 to 2.12.7.1.

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

Hi, Vlad. I wrote some tests for equality when we have inheritance.

Test class - InheritedEntityReferenceEqualityTest

Test method - testInheritedEntityReferenceEqualityInOnTransaction

When we try to persist entity in one transaction and after it use getReference everything works as expected.

Test method - testInheritedEntityReferenceEqualityInDifferentTransactions

In this test case we separate entity persist from getReference, and after it the instanceof or o.getClass() check for inherited entity does`t work.

Example: postProxy.hashCode() == post.hashCode(); // = true postProxy.getClass() == post.getClass(); // = false postProxy instanceof Post // = false post instanceof Post // = true postProxy.equals(post); // = true post.equals(postProxy); // = false

Possible solutions to resolve this problem: use Hibernate.getClass(o) instead of !(o instanceof Topic) or getClass() != o.getClass() in equals method.

Hi, Vlad. I wrote some tests with delete operation after tricky select.

Test class - DeletingAfterFetchWithoutSQLCascadeTest

Test method - testDeleteParentAfterEagerInnerFetchInChildWithoutSQLCascadeInOneTransaction

When we try to delete parent entity (Audience) after select with join fetch with list of Lesson and inside them also join list of Group (groups also have lessons, and they have EAGER fetch mapping). The ConstraintViolationException will occur after parent (Audience) delete. Even if we try to delete child entities (Lesson) explicitly before parent delete (Audience), anyway the same exception will occur.

Test method - testDeleteParentAfterEagerInnerFetchInChildWithoutSQLCascadeThenSaveAnotherEntityInDifferentTransactions

In this test case we have the same logic, but do all operations in different transactions.

Test class - DeletingAfterFetchWithSQLCascadeTest

Test method - testDeleteParentAfterEagerInnerFetchInChildWithSQLCascadeInOneTransaction

In this test case we have similar logic, but the database lesson table doesn't have ON DELETE CASCADE constraint. And we have another exception - TransientPropertyValueException.

Test method - testDeleteParentAfterEagerInnerFetchInChildWithSQLCascadeThenSaveAnotherEntityInDifferentTransactions

In this test case we have the same logic, but if we do all operations in different transactions. And the TransientPropertyValueException will occur not after parent (Audience) delete, but in the next operation, for example - merge different Audience that doesn't belong to the main select with join fetch.

Possible solutions to resolve this problem: set fetch = FetchType.LAZY for lessons in Group OR @OnDelete(action = OnDeleteAction.CASCADE) instead of cascade = CascadeType.ALL OR entityManager.clear(); before delete Audience OR add sql cascades and @GeneratedValue(strategy = GenerationType.SEQUENCE)

Just for examination, spring data jpa issue: https://github.com/spring-projects/spring-data-jpa/issues/2281