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How to fetch record from db by ID?

I got this code, but I think this is bad approach, what if there are like 100k results, it will return 100k new People? Are there any other methods that I could use for e.g ResultSetExtractor but Im not quite sure how to implement that. Also, should I use try catch block?
public Optional<Person> getPerson(int id) {
String sql = "SELECT id, name FROM people WHERE id = ?";
List<Person> people = jdbcTemplate.query(sql, (result, index) -> {
return new Person(
result.getInt("id"),
result.getString("name")
);
}, id);
return people.stream().findFirst();
}

in a correct design the id field should be unique for every person so this code should only find 1 person as a result.
If the id field is not unique then it is not a good design but the code you wrote would be correct. You dont need try - catch because you a are using a list to store the results so even if theres more than 1 result it wont produce an exception. But that also doesnt make sense because in the end the method is only returning 1 person (people.stream.findFirst()).

If you change the query from
"SELECT id, name FROM people WHERE id = ?"
to
"SELECT id, name FROM people WHERE id = ? LIMIT 1"
it will only return the first person with a matching id.
However, id should ideally be unique for each person and the original query will return atmost one result in that case.

Storing the keysets from a JPQL query result in a java list

I was successfully able to execute a jpql query and print the result which is stored in a queryResults variable. What I want to achieve next is storing just the IDs (primary key column) in a list without the date (value), but I am not too sure if this is possible; perhaps using something like a java map. Is it possible? If yes, how can this be easily achieved?
private static final TestDao Test_DAO = new TestDao();
#Test
public void testById() {
List<TestEntity> queryResults = TEST_DAO.findById(""); //The record from the sql query is stored in queryResults and findById("") is the method that executes the query in a TestDao class and it is called here
for (TestEntity qResult: queryResults) { // looping through the query result to print the rows
System.out.println(qResult.getId());
System.out.println(qResult.getDate());
}
System.out.println("This is the sql result " + queryResults );
}
Output:
This is the result [TestEntity(id=101, date=2020-01-19 15:12:32.447), TestEntity(id=102, date=2020-09-01 11:04:10.0)]// I want to get the IDs 101 and 102 and store in a list without the Dates
I tried using a map this way:
Map<Integer, Timestamp> map= (Map<Integer, Timestamp>) queryResults.get(0); but I got an exception:
java.lang.ClassCastException: TestEntity cannot be cast to java.util.Map

There are some points before the implementation.
Why are you defining DAO as static? I think this is a bad implementation unless I am missing a particular reason you declared it static. You should define this as a member variable and not a static member
The naming of the method - findById() translated in English is - find Something by this Id, but you are fetching a list of Records, so naming is not correct.
Point 2 becomes invalid if ID property is not a Primary Key in your table, then it makes sense, but still naming is bad. Id is something we use to define Primary Key in the Database and should be and will be unique. But your comments suggest that ID is unique and the Primary Key. So read about how Databases work
And even if not unique, if you pass an Id to find some records, why will get different ids in the Records !!!
About implementation:
Changing in your existing code:
private TestDao Test_DAO = new TestDao();
#Test
public void testById() {
List<TestEntity> queryResults = TEST_DAO.findById("");
List<Long> listOfIds = new ArrayList<>(); // Assuming Id is Long type, same logic for any type
for (TestEntity qResult: queryResults) {
System.out.println(qResult.getId());
listOfIds.add(qResult.getId()); // Just add it to the list
System.out.println(qResult.getDate());
}
}
In case you want to be efficient with the query:
You can use JPQL and hibernate
You can then write a query like:
String query = "select te.id from TestEntity te";
// Create the TypedQuery using EntityManager and then get ResultSet back
List<Long> ids = query.getResultList();
In case of using Spring-Data-Jpa, you can define the repository and define the method and pass the query with #Query annotation. Spring Data JPA

JPA Query.getResultList() - use in a generic way

I'm creating a complex query with multiple tables and need to list the result. Usually, I'm using the EntityManager and map the result to the JPA-Representation:
UserEntity user = em.find(UserEntity.class, "5");
Then I can access all values as the user UserEntity class defines it. But how can I access the field-values returned from a native, multiple-table query? What I get is a List of Objects. That's fine so far, but what "is" that Object? Array? Map? Collection? ...
//simpleExample
Query query = em.createNativeQuery("SELECT u.name,s.something FROM user u, someTable s WHERE s.user_id = u.id");
List list = query.getResultList();
//do sth. with the list, for example access "something" for every result row.
I guess the answer is quite simple, but most examples out there just show the usage when directly casting to a targetClass.
PS: In the example I could use the class-mappings of course. But in my case someTable is not managed by JPA, and therefore I don't have the entity nor do I have a class-representation of it, and since I'm joining like 20 tables, I don't want to create all the classes just to access the values.

General rule is the following:
If select contains single expression and it's an entity, then result is that entity
If select contains single expression and it's a primitive, then result is that primitive
If select contains multiple expressions, then result is Object[] containing the corresponding primitives/entities
So, in your case list is a List<Object[]>.

Since JPA 2.0 a TypedQuery can be used:
TypedQuery<SimpleEntity> q =
em.createQuery("select t from SimpleEntity t", SimpleEntity.class);
List<SimpleEntity> listOfSimpleEntities = q.getResultList();
for (SimpleEntity entity : listOfSimpleEntities) {
// do something useful with entity;
}

If you need a more convenient way to access the results, it's possible to transform the result of an arbitrarily complex SQL query to a Java class with minimal hassle:
Query query = em.createNativeQuery("select 42 as age, 'Bob' as name from dual",
MyTest.class);
MyTest myTest = (MyTest) query.getResultList().get(0);
assertEquals("Bob", myTest.name);
The class needs to be declared an #Entity, which means you must ensure it has an unique #Id.
#Entity
class MyTest {
#Id String name;
int age;
}

The above query returns the list of Object[]. So if you want to get the u.name and s.something from the list then you need to iterate and cast that values for the corresponding classes.

I had the same problem and a simple solution that I found was:
List<Object[]> results = query.getResultList();
for (Object[] result: results) {
SomeClass something = (SomeClass)result[1];
something.doSomething;
}
I know this is defenitly not the most elegant solution nor is it best practice but it works, at least for me.

Here is the sample on what worked for me. I think that put method is needed in entity class to map sql columns to java class attributes.
//simpleExample
Query query = em.createNativeQuery(
"SELECT u.name,s.something FROM user u, someTable s WHERE s.user_id = u.id",
NameSomething.class);
List list = (List<NameSomething.class>) query.getResultList();
Entity class:
#Entity
public class NameSomething {
#Id
private String name;
private String something;
// getters/setters
/**
* Generic put method to map JPA native Query to this object.
*
* #param column
* #param value
*/
public void put(Object column, Object value) {
if (((String) column).equals("name")) {
setName(String) value);
} else if (((String) column).equals("something")) {
setSomething((String) value);
}
}
}

What if you create a bean with all required properties and cast the result using Java 8+ streams?
Like this:
public class Something {
private String name;
private String something;
// getters and setters
}
And then:
import javax.persistence.Query;
...
Query query = em.createNativeQuery("SELECT u.name,s.something FROM user u, someTable s WHERE s.user_id = u.id", Something.class);
List<?> list = query.getResultList();
return list
.stream()
.map(item -> item instanceof Something ? (Something) item : null)
.collect(Collectors.toList());
That way, you don't need to return List<Object[]> nor hide the warning with #SuppressWarnings("unchecked")
Ps.:
1 - I know that this post is very old. But... I'm here in 2021, so others will be coming here too =)
2 - This is wrong or bad practice? Let me know :D

You can also update your hibernate to a version greater than 5.4.30.final

How to avoid hibernate default order by id?

I make this query:
String query = FROM Account acc WHERE acc.id = ? OR acc.id = ? or acc.id = ?...
I have array of ids:
long[] accountIds= {327913,327652,327910,330511,330643};
Then I make
getHibernateTemplate().find(query, accountIds);
I see that the list of accounts I get back from this query is:
327652,327910,327913,330511,330643, obviously , ordered by id.
Any chance I get it back in the order I wrote the ids?
Will appreciate all the help

You may want to use Criteria and its addOrder.
Something like this:
DetachedCriteria cr = DetachedCriteria.forClass(entityClass);
//Add expressions or restrictions to your citeria
//And add your ordering
cr.addOrder(Order.asc("yourID"));
List<T> ls = getHibernateTemplate().findByCriteria(cr);
return ls;

You can't do it on query level.
You can sort after loading from db, something like this
long[] accountIds= {327913,327652,327910,330511,330643};
List<Account> afterHql = getHibernateTemplate().find(query, accountIds);
List<Account> sortedList = new ArrayList<Acount>();
for (long id : accountIds)
{
for (Account account : afterHql)
{
if (account.getId() == id)
{
sortedList.add(account);
}
}
}

It is not possible to fetch results by providing any entity in OR Query or Restrictions.in(). As by deafult when you fire this kind of query it will search for the results id wise. So it will give you results id wise only. You can change the order by using Criteria either in asc or desc. And if you want to have results as per you enter id, then second answer is the only option.

You can only order by column values returned by the query, in a sequence defined by the data type . Wouldn't it be better to pre-order the IDs you supply, and order the query result by ID, so they come out in the same order?

HQL Object set from set

I got a Set<UserDTO> collection in a not Hibernate object, and I got a User domain entity in Hibernate.
UserDTO contains less information about user (only id and name)
How can I select full Hibernate User Set/List from the DTO object?
Like this?
Set<UserDTO> setDTO = .....
String hql = "FROM User WHERE id IN (:userDTO )";
Query query = entityManager.createQuery(hql);
query.setParameter("userDTO", setDTO);
return query.getResultList();
Thanks

Almost. But you'd have to extract the IDs in a separate collection first:
Set<Long> ids = new HashSet<Long>(setDTO.size());
for (UserDTO dto : setDTO) {
ids.add(dto.getId());
}
Then proceed with the query, and pass the ids set as param.

Don't forget that you need to use Query#setParameterList() instead of Query#setParameter.