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DAO method retrieves one record

How can I write a DAO method that will only return the first record from the database as a result. For example, let's say I am looking at the Users table and I only want to get the first record, I would declare a method like:

public User getFirstUser(){
    //method logic
}

EDIT:

The user has a primary key id , if it matters at all.

I apologize if this question is too simple / stupid / no matter what I'm starting with Java so I'm trying new things. thanks

My attempt:

   public User getFirstUser(){
            try { 
                final String getQuery = "SELECT * FROM Users WHERE Id = (SELECT MIN(Id) FROM Users)"; 
                final Query query = getSession().createQuery(getQuery); 
                final int rowCount = query.executeUpdate(); // check that the rowCount is 1 
                log.debug("get successful"); 
//             return what??
            } catch (RuntimeException re) { 
                log.error("get not successful", re); 
                throw re; 
            } 
    }
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5 answers


You can



  • Using:

    Query query = session.createQuery("from User");
query.setMaxResults(1);
User result = (User) query.uniqueResult();

  • use User user = session.get(User.class, id);

    if you know the id.

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Get all users ordered by id and limit the results to 1 (but don't use LIMIT

, use setMaxResults()

to stay portable):



Query q = session.createQuery("from User u order by u.id");
q.setMaxResults(1);
User u = (User) q.uniqueResult();
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SELECT * FROM Users WHERE Id = (SELECT MIN(Id) FROM Users)

:)

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Can't remember exactly, but I think there is a getSingleResult method in JPA as well as Hibernate, so ...

But this method can throw an exception when multiple results are returned ... don't remember ...

Actually there is also getResultList returning a list of entities and you can do list.get (0) no?

Or create a query using LIMIT 1?

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In MS SQL Server we do this,

First User, Minimum ID,

SELECT TOP 1 * FROM Users ORDER BY Id

Last user, maximum id,

SELECT TOP 1 * FROM Users ORDER BY Id DESC

thanks.

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