I have multiple dao classes, I want to replace them with Hibernate ORM. I have generated all the POJOs and mapping for each table. Now, I don't know how to move ahead. Can someone help ? Thanks in advance.
You don't have to replace the SQL queries, just setup the hibernate configuration & use the createSQLQuery method
String sql = "SELECT * FROM EMPLOYEE";
SQLQuery query = session.createSQLQuery(sql);
Related
I want to get all the values from a particular column in JPA and store all values into a list. currently, I am using the below approach but I am getting records in something else format.can someone please help me out
Query q1 = factory.createNativeQuery("select * from booking_attendee where booking_id="+id);
List<String> em1=q1.getResultList();
return em1;
query otput
em=[[Ljava.lang.Object;#68606667, [Ljava.lang.Object;#2cd7f99a, [Ljava.lang.Object;#137a5a5, [Ljava.lang.Object;#a45cc1c, [Ljava.lang.Object;#61fdc06d, [Ljava.lang.Object;#72f5eee1, [Ljava.lang.Object;#4e536797]
If you want to create a native query for this, it is more about how to solve this in SQL. You do not say SELECT * which means all columns. You would have to say SELECT your_column_name to select only a specific column.
Query q1 = factory.createNativeQuery("SELECT your_column FROM booking_attendee");
List<String> em1 = q1.getResultList();
The WHERE clause could and should be defined with the parameter binding of JPA. There are several advantages concerning performance and SQL injection.
Named parameter binding is special to the persistence provider (e.g. Hibernate). The common way for JPA is using ? to let your code be portable to other providers.
Query q1 = factory.createNativeQuery("SELECT your_column FROM booking_attendee b WHERE b.booking_id = ?");
q1.setParameter(1, id);
List<String> em1 = q1.getResultList();
Native queries offer the possibilities to use original SQL. Like this, some features which are specific for your database could be used with this. Nevertheless, if you do not have very specific SQL code, you should also have a look in JPQL, the specific query language of JPA, and the JPA Criteria API which offers advantages when you want to refactor your code, shows errors during compile time and makes the dynamic creation of queries easier.
I am working on some project where I used spring data jpa to query against DB2. Suppose used query "Select a,b from sometable where a='XX' ". So now based on sql code I want to perform some operation but how I will get sql return code as I am using spring data JPA.
Thanks in advance
I have a spring application that should connect to an existing database and just query an entity for existence based on some attributes.
I don't want to create a #Entity class for this. But I still want to use the spring managed EntityManager etc.
When using Spring, what is the best approach to just query a select for that entity? Using em.createNamedQuery(QUERY); with String QUERY = "SELECT count(*) from my_table where username =: username AND email := email)";?
Answers from #predrag-maric and #pL4Gu33 are both correct but if you use JPA in your project (for example, Hibernate) you might consider using #NamedNativeQuery annotation as well.
More about named native queries.
simple example of native query
#PersistenceContext
EntityManager em;
public String test(Integer id)
{
Query query = em.createNativeQuery("SELECT name FROM Accounts where id=?");
query.setParameter(1,id);
return query.getSingleResult();
}
You can use this method from entitymanager. http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#createNativeQuery%28java.lang.String%29
Use em.createNativeQuery(QUERY). Also, you'll have to use positional parameters (?1) instead of named parameters (:email), because only positional parameters are supported by JPA in native queries.
Is there a way to retrieve the name of all tables in the database using hibernate?
I executed the query SELECT TABLE_NAME FROM USER_TABLES in an oracle Db and it works just fine.
But when it comes to DB2, it wont.
You can use
List<Object> list = session.createQuery("from java.lang.Object").list();
This will return all persistent entities (thanks to HQL implicit polymorphism), and this is db independent. Note that it will exclude tables with no records.
If you need all tables, including the empty ones, you can use native sql query
List<Object[]> list = session.createSQLQuery("select * from sysibm.systables").list();
The drawback for the native query is that it is specific for each database, for example, on Oracle the query is "select * from user_tables".
currently I am using the following to pull rows from a table called Table:
return getHibernateTemplate().find("from Table");
How do I use hibernate to pull only the first n rows from the table (i.e. like a mySql limit would do)?
Thanks.
Update: so is this the proper way to do it?
getHibernateTemplate().setMaxResults(35);
return getHibernateTemplate().find("from Table");
Use HIbernateTemplate setMaxResults to limit the results.
I ended up using a Hibernate Criteria query to do this and it works properly. I made use of the setFirstResult() and setLastResults() methods.