I wanted to update my database schema by adding new tables. But hibernate doesn't do anything. My database is still the same every time even I changed the property to create. But it won't change anything. And it's the first time happened.
I have added annotation and all what is needed and nothing happened.
First of all make sure that your persistence file has your Entity classes added within the class
<Class>path.EntityName </Class>
Secondly, the persistence file should also have the update property set:
<property name="hibernate.hbm2ddl.auto" value="update"/>
However, the above property does not work in the following cases:
hibernate.hbm2ddl.auto" value="update" will add a db column that doesn't already exist but will not delete a db column that is removed/no longer in your entity.
hibernate.hbm2ddl.auto" value="update" will not modify a db column
that has already been created.
hibernate.hbm2ddl.auto" value="update" won't modify existing table column definitions.
You'll need to backup the table data, drop it and restart your application to get that table's schema back in sync with your entity. Then reload your data. Or you can do it manually through SQL queries on the database tables.
Add hibernate configuration:
<prop key="hibernate.hbm2ddl.auto">create</prop>
Related
I have a problem with creating tables in data base in Hibernate. In cfg of hibernate I have:
<property name="hbm2ddl.auto">update</property>
Thats ok, but I want to remove all data from only ONE single table.
When I will change cfg to:
<property name="hbm2ddl.auto">create</property>
All of tables will be recreated and that's in not what i want.
do you mean a single table in a database? because from my understanding; when configuring hiberate, we provide just a single database connection to it using the hibernate.connection.url property, a username and password etc. you can actually drop a single table in your database using session.createSQLQuery("DROP TABLE table_name").executeUpdate();... so i am still trying to get your point
When I try to delete an entry from a db, using
session.delete(object)
then I can the following:
1) If the row is present in DB then two SQL queries are getting executed: A select and then a delete
2) If the row is not present in the DB then only the select query is getting executed
But again this is not the case for update. Irrespective of the presence of DB row, only the update query is getting executed.
Please let me know why this kind of behaviour for delete operation. Isn't it a performance issue since two queries are getting hit rather than one?
Edit:
I am using hibernate 3.2.5
Sample code:
SessionFactory sessionFactory = new Configuration().configure("student.cfg.xml").buildSessionFactory();
Session session = sessionFactory.openSession();
Student student = new Student();
student.setFirstName("AAA");
student.setLastName("BBB");
student.setCity("CCC");
student.setState("DDD");
student.setCountry("EEE");
student.setId("FFF");
session.delete(student);
session.flush();
session.close();
cfg.xml
<property name="hibernate.connection.username">system</property>
<property name="hibernate.connection.password">XXX</property>
<property name="hibernate.connection.driver_class">oracle.jdbc.OracleDriver</property>
<property name="hibernate.connection.url">jdbc:oracle:thin:#localhost:1521/orcl</property>
<property name="hibernate.jdbc.batch_size">30</property>
<property name="hibernate.dialect">org.hibernate.dialect.OracleDialect</property>
<property name="hibernate.cache.use_query_cache">false</property>
<property name="hibernate.cache.use_second_level_cache">false</property>
<property name="hibernate.connection.release_mode">after_transaction</property>
<property name="hibernate.connection.autocommit">true</property>
<property name="hibernate.connection.pool_size">0</property>
<property name="hibernate.current_session_context_class">thread</property>
<property name="hibernate.show_sql">true</property>
<property name="hibernate.hbm2ddl.auto">update</property>
hbm.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.infy.model.Student" table="STUDENT">
<id name="id" column="ID">
<generator class="assigned"></generator>
</id>
<property name="firstName" type="string" column="FIRSTNAME"></property>
<property name="lastName" type="string" column="LASTNAME"></property>
<property name="city" type="string" column="CITY"></property>
<property name="state" type="string" column="STATE"></property>
<property name="country" type="string" column="COUNTRY"></property>
</class>
The reason is that for deleting an object, Hibernate requires that the object is in persistent state. Thus, Hibernate first fetches the object (SELECT) and then removes it (DELETE).
Why Hibernate needs to fetch the object first? The reason is that Hibernate interceptors might be enabled (http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/events.html), and the object must be passed through these interceptors to complete its lifecycle. If rows are delete directly in the database, the interceptor won't run.
On the other hand, it's possible to delete entities in one single SQL DELETE statement using bulk operations:
Query q = session.createQuery("delete Entity where id = X");
q.executeUpdate();
To understand this peculiar behavior of hibernate, it is important to understand a few hibernate concepts -
Hibernate Object States
Transient - An object is in transient status if it has been
instantiated and is still not associated with a Hibernate session.
Persistent - A persistent instance has a representation in the
database and an identifier value. It might just have been saved or
loaded, however, it is by definition in the scope of a Session.
Detached - A detached instance is an object that has been persistent,
but its Session has been closed.
http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/objectstate.html#objectstate-overview
Transaction Write-Behind
The next thing to understand is 'Transaction Write behind'. When objects attached to a hibernate session are modified they are not immediately propagated to the database. Hibernate does this for at least two different reasons.
To perform batch inserts and updates.
To propagate only the last change. If an object is updated more than once, it still fires only one update statement.
http://learningviacode.blogspot.com/2012/02/write-behind-technique-in-hibernate.html
First Level Cache
Hibernate has something called 'First Level Cache'. Whenever you pass an object to save(), update() or saveOrUpdate(), and whenever you retrieve an object using load(), get(), list(), iterate() or scroll(), that object is added to the internal cache of the Session. This is where it tracks changes to various objects.
Hibernate Intercepters and Object Lifecycle Listeners -
The Interceptor interface and listener callbacks from the session to the application, allow the application to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted or loaded.
http://docs.jboss.org/hibernate/orm/4.0/hem/en-US/html/listeners.html#d0e3069
This section Updated
Cascading
Hibernate allows applications to define cascade relationships between associations. For example, 'cascade-delete' from parent to child association will result in deletion of all children when a parent is deleted.
So, why are these important.
To be able to do transaction write-behind, to be able to track multiple changes to objects (object graphs) and to be able to execute lifecycle callbacks hibernate needs to know whether the object is transient/detached and it needs to have the object in it's first level cache before it makes any changes to the underlying object and associated relationships.
That's why hibernate (sometimes) issues a 'SELECT' statement to load the object (if it's not already loaded) in to it's first level cache before it makes changes to it.
Why does hibernate issue the 'SELECT' statement only sometimes?
Hibernate issues a 'SELECT' statement to determine what state the object is in. If the select statement returns an object, the object is in detached state and if it does not return an object, the object is in transient state.
Coming to your scenario -
Delete - The 'Delete' issued a SELECT statement because hibernate needs to know if the object exists in the database or not. If the object exists in the database, hibernate considers it as detached and then re-attches it to the session and processes delete lifecycle.
Update - Since you are explicitly calling 'Update' instead of 'SaveOrUpdate', hibernate blindly assumes that the object is in detached state, re-attaches the given object to the session first level cache and processes the update lifecycle. If it turns out that the object does not exist in the database contrary to hibernate's assumption, an exception is thrown when session flushes.
SaveOrUpdate - If you call 'SaveOrUpdate', hibernate has to determine the state of the object, so it uses a SELECT statement to determine if the object is in Transient/Detached state. If the object is in transient state, it processes the 'insert' lifecycle and if the object is in detached state, it processes the 'Update' lifecycle.
I'm not sure but:
If you call the delete method with a non transient object, this means first fetched the object from the DB. So it is normal to see a select statement. Perhaps in the end you see 2 select + 1 delete?
If you call the delete method with a transient object, then it is possible that you have a cascade="delete" or something similar which requires to retrieve first the object so that "nested actions" can be performed if it is required.
Edit:
Calling delete() with a transient instance means doing something like that:
MyEntity entity = new MyEntity();
entity.setId(1234);
session.delete(entity);
This will delete the row with id 1234, even if the object is a simple pojo not retrieved by Hibernate, not present in its session cache, not managed at all by Hibernate.
If you have an entity association Hibernate probably have to fetch the full entity so that it knows if the delete should be cascaded to associated entities.
instead of using
session.delete(object)
use
getHibernateTemplate().delete(object)
In both place for select query and also for delete use getHibernateTemplate()
In select query you have to use DetachedCriteria or Criteria
Example for select query
List<foo> fooList = new ArrayList<foo>();
DetachedCriteria queryCriteria = DetachedCriteria.forClass(foo.class);
queryCriteria.add(Restrictions.eq("Column_name",restriction));
fooList = getHibernateTemplate().findByCriteria(queryCriteria);
In hibernate avoid use of session,here I am not sure but problem occurs just because of session use
I have a hibernate mapping:
<properties name="lrt_bps_bpr_acs_uk" unique="true">
<many-to-one name="activitySummary" column="bps_acs_id" class="xyz.ActivitySummary"
unique-key="lrt_bps_bpr_acs_uk"/>
<many-to-one name="bestPractice" column="bps_bpr_id" class="xyz.BestPractice"
unique-key="lrt_bps_bpr_acs_uk"/>
</properties>
I expected that hibernate would create unique constraint on database for this mapping. Nothing like that happened however.
What am I doing wrong?
Seems like you do nothing wrong. We do it the same way in our project and it works fine.
I thought to have the same problem once because I couldn't find the constaints in our oracle DB because I thought the specified unique-key attribute value (in your case 'lrt_bps_bpr_acs_uk') is used as constraint_name in the DB. But that isn't the case (at least with oracle DB).
What's the actual DDL that Hibernate is generating? What would be the DDL if you remove the unique-key parameters? What's the Hibernate version?
From the documentation, it seems you are doing it correctly:
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/mapping.html#mapping-declaration-properties
Dont specify name="lrt_bps_bpr_acs_uk" unique="true" in the properties element. It automatically takes it and applies the constraint with unique-key
I am having a querying issue in Hibernate. I have a table, 'test', with existing data. I have a requirement where I can not modify the schema of the test table, so I created another table, 'testExtension', whose primary key is a foreign key to the primary key of Test. Data in testExtension is a subset of the data in test. i.e. There will be less rows in 'testExtension' than in 'test'.
I have defined this relationship in a configuration file as follows:
<class name="Test" table="test">
<id name="testId" column="test_id">
<generator class="sequence">
<param name="sequence">test_id_seq</param>
</generator>
</id>
<property name="name"/>
<joined-subclass name="TestExtension" table="testExtension">
<key column="test_id"/>
<property name="summary" />
<property name="homepage"/>
</joined-subclass>
With this setup, I am able to create a TestExtension object in my Java program, populate it with data, 'save' it via Hibernate, and commit the transaction. And it correctly saves data in both Test and TestExtension.
My problem is occurring when I am trying to query data from these tables. Right now if I query for a particular test_id using the TestExtension.class to QBE, it will only return a row if that id exists in both Test and TestExtension. If I use the Test.class to QBE, it will return the row but I will not have access to any of the data stored in TestExtension.
My question is: how can I query these tables so that the results are based off a 'left outer join' of both Test and TestExtension? Any solution is appreciated, whether it's query by example, HQL, or something else (though preferably not raw SQL).
Thanks!
HQL is probably the easiest way to do this. Docs are here:
http://docs.jboss.org/hibernate/stable/core/reference/en/html/queryhql-joins.html
Sounds like what you might want to do is remap your relationships so that Test and TestExtension use a one-to-one relationship instead of inheritance. Then you can query for Test and TestExtension using a left outer join across the one-to-one.
If you use HQL to write a query for the Test class, it should do what you want. I assume QBE is effectively adding the class of your example entity as one of the query parameters.
So sth like:
from Test t where t.property = :value
should return either Test or TestExtension entities. Note that (at least with the versions of Hibernate I've used). In this case, Hibernate should immediately give you back the actual entities rather than a proxy too--- be aware that TestExtension entities can sometimes be returned as plain Test lazy-loading proxies.
I really want to know more about the update, export and the values that could be given to hibernate.hbm2ddl.auto
I need to know when to use the update and when not? And what is the alternative?
These are changes that could happen over DB:
new tables
new columns in old tables
columns deleted
data type of a column changed
a type of a column changed its attributes
tables dropped
values of a column changed
In each case what is the best solution?
From the community documentation:
hibernate.hbm2ddl.auto Automatically validates or exports schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly.
e.g. validate | update | create | create-drop
So the list of possible options are,
validate: validate the schema, makes no changes to the database.
create-only: database creation will be generated.
drop: database dropping will be generated.
update: update the schema.
create: creates the schema, destroying previous data.
create-drop: drop the schema when the SessionFactory is closed explicitly, typically when the application is stopped.
none: does nothing with the schema, makes no changes to the database
These options seem intended to be developers tools and not to facilitate any production level databases, you may want to have a look at the following question; Hibernate: hbm2ddl.auto=update in production?
There's also the value of none to disable it entirely.
The configuration property is called hibernate.hbm2ddl.auto
In our development environment we set hibernate.hbm2ddl.auto=create-drop to drop and create a clean database each time we deploy, so that our database is in a known state.
In theory, you can set hibernate.hbm2ddl.auto=update to update your database with changes to your model, but I would not trust that on a production database. An earlier version of the documentation said that this was experimental, at least; I do not know the current status.
Therefore, for our production database, do not set hibernate.hbm2ddl.auto - the default is to make no database changes. Instead, we manually create an SQL DDL update script that applies changes from one version to the next.
First, the possible values for the hbm2ddl configuration property are the following ones:
none - No action is performed. The schema will not be generated.
create-only - The database schema will be generated.
drop - The database schema will be dropped.
create - The database schema will be dropped and created afterward.
create-drop - The database schema will be dropped and created afterward. Upon closing the SessionFactory, the database schema will be dropped.
validate - The database schema will be validated using the entity mappings.
update - The database schema will be updated by comparing the existing database schema with the entity mappings.
The hibernate.hbm2ddl.auto="update" is convenient but less flexible if you plan on adding functions or executing some custom scripts.
So, The most flexible approach is to use Flyway.
However, even if you use Flyway, you can still generate the initial migration script using hbm2ddl.
I would use liquibase for updating your db. hibernate's schema update feature is really only o.k. for a developer while they are developing new features. In a production situation, the db upgrade needs to be handled more carefully.
Although it is quite an old post but as i did some research on the topic so thought of sharing it.
hibernate.hbm2ddl.auto
As per the documentation it can have four valid values:
create | update | validate | create-drop
Following is the explanation of the behaviour shown by these value:
create :- create the schema, the data previously present (if there) in the schema is lost
update:- update the schema with the given values.
validate:- validate the schema. It makes no change in the DB.
create-drop:- create the schema with destroying the data previously present(if there). It also drop the database schema when the SessionFactory is closed.
Following are the important points worth noting:
In case of update, if schema is not present in the DB then the schema is created.
In case of validate, if schema does not exists in DB, it is not created. Instead, it will throw an error:- Table not found:<table name>
In case of create-drop, schema is not dropped on closing the session. It drops only on closing the SessionFactory.
In case if i give any value to this property(say abc, instead of above four values discussed above) or it is just left blank. It shows following behaviour:
-If schema is not present in the DB:- It creates the schema
-If schema is present in the DB:- update the schema.
hibernate.hbm2ddl.auto automatically validates and exports DDL to the schema when the sessionFactory is created.
By default, it does not perform any creation or modification automatically on DB. If the user sets one of the below values then it is doing DDL schema changes automatically.
create - doing creating a schema
<entry key="hibernate.hbm2ddl.auto" value="create">
update - updating existing schema
<entry key="hibernate.hbm2ddl.auto" value="update">
validate - validate existing schema
<entry key="hibernate.hbm2ddl.auto" value="validate">
create-drop - create and drop the schema automatically when a session is starts and ends
<entry key="hibernate.hbm2ddl.auto" value="create-drop">
If you don't want to use Strings in your app and are looking for predefined constants have a look at org.hibernate.cfg.AvailableSettings class included in the Hibernate JAR, where you'll find a constant for all possible settings. In your case for example:
/**
* Auto export/update schema using hbm2ddl tool. Valid values are <tt>update</tt>,
* <tt>create</tt>, <tt>create-drop</tt> and <tt>validate</tt>.
*/
String HBM2DDL_AUTO = "hibernate.hbm2ddl.auto";
validate: validates the schema, no change happens to the database.
update: updates the schema with current execute query.
create: creates new schema every time, and destroys previous data.
create-drop: drops the schema when the application is stopped or SessionFactory is closed explicitly.
I Think you should have to concentrate on the
SchemaExport Class
this Class Makes Your Configuration Dynamic
So it allows you to choose whatever suites you best...
Checkout [SchemaExport]
validate: It validates the schema and makes no changes to the DB.
Assume you have added a new column in the mapping file and perform the insert operation, it will throw an Exception "missing the XYZ column" because the existing schema is different than the object you are going to insert. If you alter the table by adding that new column manually then perform the Insert operation then it will definitely insert all columns along with the new column to the Table.
Means it doesn't make any changes/alters the existing schema/table.
update: it alters the existing table in the database when you perform operation.
You can add or remove columns with this option of hbm2ddl.
But if you are going to add a new column that is 'NOT NULL' then it will ignore adding that particular column to the DB. Because the Table must be empty if you want to add a 'NOT NULL' column to the existing table.
Since 5.0, you can now find those values in a dedicated Enum: org.hibernate.boot.SchemaAutoTooling (enhanced with value NONE since 5.2).
Or even better, since 5.1, you can also use the org.hibernate.tool.schema.Action Enum which combines JPA 2 and "legacy" Hibernate DDL actions.
But, you cannot yet configure a DataSource programmatically with this. It would be nicer to use this combined with org.hibernate.cfg.AvailableSettings#HBM2DDL_AUTO but the current code expect a String value (excerpt taken from SessionFactoryBuilderImpl):
this.schemaAutoTooling = SchemaAutoTooling.interpret( (String) configurationSettings.get( AvailableSettings.HBM2DDL_AUTO ) );
… and internal enum values of both org.hibernate.boot.SchemaAutoToolingand org.hibernate.tool.schema.Action aren't exposed publicly.
Hereunder, a sample programmatic DataSource configuration (used in ones of my Spring Boot applications) which use a gambit thanks to .name().toLowerCase() but it only works with values without dash (not create-drop for instance):
#Bean(name = ENTITY_MANAGER_NAME)
public LocalContainerEntityManagerFactoryBean internalEntityManagerFactory(
EntityManagerFactoryBuilder builder,
#Qualifier(DATA_SOURCE_NAME) DataSource internalDataSource) {
Map<String, Object> properties = new HashMap<>();
properties.put(AvailableSettings.HBM2DDL_AUTO, SchemaAutoTooling.CREATE.name().toLowerCase());
properties.put(AvailableSettings.DIALECT, H2Dialect.class.getName());
return builder
.dataSource(internalDataSource)
.packages(JpaModelsScanEntry.class, Jsr310JpaConverters.class)
.persistenceUnit(PERSISTENCE_UNIT_NAME)
.properties(properties)
.build();
}
To whomever searching for default value...
It is written in the source code at version 2.0.5 of spring-boot and 1.1.0 at JpaProperties:
/**
* DDL mode. This is actually a shortcut for the "hibernate.hbm2ddl.auto"
* property. Defaults to "create-drop" when using an embedded database and no
* schema manager was detected. Otherwise, defaults to "none".
*/
private String ddlAuto;
With all above said...
Notice this property is called dll.auto and should only control dll operations(create/drop schema/table), I found surprisingly that it has to do with dml, too: only update will allow insert data, which is dml operation.
Got caught by this when trying to populate data into a in-memory database; only update works.