I want to use this SQL query:
String hql = "select e from " + Terminals.class.getName() + " e WHERE e.merchantId IN :merchant_ids";
TypedQuery<Terminals> query = entityManager.createQuery(hql, Terminals.class).setParameter("merchant_ids", merchant_ids);
List<Terminals> merchants = query.getResultList();
But I get error: the right syntax to use near ') So IN clause list into IN (....) can't be empty. Is there some solution to this problem?
It is allowable and even very fine not executing the query:
if (merchant_ids.isEmpty()) {
return new ArrayList<>();
} else {
String hql = "select e from " + Terminals.class.getName()
+ " e WHERE e.merchantId IN :merchant_ids";
return entityManager.createQuery(hql, Terminals.class)
.setParameter("merchant_ids", merchant_ids)
.getResultList();
}
I do not know what would happen if one would pass null instead of an empty list;
SQL ... IN NULL could do. On the other hand it might do a full table scan in order to return 0 results.
If x IN() would not result in 0 records (when there is an OR ...) then:
if (merchant_ids.isEmpty()) {
merchant_ids.add(-1);
String hql = "select e from " + Terminals.class.getName() + ...
Very often, I used to stuck this kind of case. I couldn't find out a proper solution. Since you are using Spring JPA But I have some workaround to suggest to you.
Implement EntityManger and create your SQL queries in runtime. So you can populate your where cause and everything.
Like this: entityManager.createNativeQuery(sql.toString())
Implement if-else block. Check if the list is empty or not, if false call actual query (with IN block) or else write another query without IN block.
Again I am telling, this may not be a proper solution. But I see this is proper workaround.
I am not familiar with hibernate but since it is an SQL error, the following should work :
TypedQuery<Terminals> query = entityManager
.createQuery(hql, Terminals.class)
.setParameter("merchant_ids",merchant_ids.size()==0?null:merchant_ids);
But as #Richard Barker mentioned , best solution is to not even execute the query when the list is empty.
You will even save on the unnecessary database call , when you already know that the query is not going to return anything.
I followed #Rambler's suggestion and created a method to return a null:
public static <T> Collection<T> nullIfEmpty(Collection<T> collection) {
return (collection == null || collection.isEmpty()) ? null : collection;
}
This was easier to add in place, but I agree that it is better to not make the call to the database.
Related
is there any proper way to handle null for example there is no existing record in the Users table, so it wont throw null pointer:
If the record does not exist in the database, do not use getSingleResult(). Looking at the javadoc, you need to be sure the record exists to use getSingleResult()
getSingleResult
java.lang.Object getSingleResult()
Execute a SELECT query that returns a single untyped result.
Returns:
the result
Throws:
NoResultException - if there is no result
NonUniqueResultException - if more than one result
Instead, use getResultList()
public long generateNextId() {
Query query = getEntityManager().createQuery("SELECT MAX(id)+1 from Users");
List<Object> objs = query.getResultList();
return objs.isEmpty() ? 1 : Long.parseLong(objs.get(0));
}
Also, further, I'd use a TypedQuery<Long> if I were you
public long generateNextId() {
TypedQuery<Long> query = getEntityManager().createQuery("SELECT MAX(id)+1 from Users", Long.class);
List<Long> objs = query.getResultList();
return objs.isEmpty() ? 1 : objs.get(0);
}
If, like documented in this question, the query can return null then you can just use a null check or use an Optional#ofNullable wrapper
I am making the following query which works and updates the info into the database as expected. But is there a way I can get an output from Single < UpdateResult >?
public Single<UpdateResult> update(UpdateEventRequest request) {
return client.rxUpdateWithParams(
"UPDATE mydb.sample SET sta_cd=?, some_ts=current_timestamp WHERE id=? RETURNING sta_cd",
new JsonArray(Arrays.asList(sta_cd, id)));
}
From the following e variable, I was hoping to get the value "10012". But it doesn't seem possible. Tried with map, flatmap and just see options available in e. The only result data in e is 'keys' which is an empty list and 'updated' which is an integer value of 1. My DB is postgres and was expecting results from from Single < UpdateResult > since am using 'RETURNING' in the query.
I have done the same for an insert operation which works but that is via the method rxQueryWithParams() and that returns a Single < ResultSet > instead. Thus wondering if this is even possible. Been having a look at docs and maybe this is not possible as an update query is returning a Single < UpdateResult > . Looking for advice if this is possible, to return data from an update query or a way around this. Please advice. Thanks.
Single<UpdateResult> result = someClass.update("10012", "78632");
result.subscribe(
e -> {
System.out.println("success: " + e); // I land here as expected
},
error -> {
System.out.println("error: " + error);
}
);
Because you are using RETURNING in these commands, treat these INSERT and UPDATE commands as queries.
Run them through rxQueryWithParams() so you can retrieve the results.
When you run rxUpdateWithParams(), the UpdateResult contains only the number of rows affected.
private ILogin results;
public ILogin authenticate(Login login) {
System.out.println(login);
System.out.println(login.getEmail());
String query = "SELECT email, id FROM Login WHERE email='"
+ login.getEmail() + "' AND password='" + login.getPassword() + "'";
results = getHibernateTemplate().find(query);
System.out.println(results);
return results;
}
How do i change results = getHibernateTemplate().find(query); I get the error in this line. But i want that in ILogin type not of List type. How do i do an Type Conversion here.
The problem isn't the type conversion per se - it's that you've executed a query which may return multiple results, but you only want a single result.
You probably want to check that the resulting list has exactly one value (0 means login not found; more than 1 probably means there's a problem in your data somewhere) and then return that first value (return (ILogin) list.get(0);).
As a slightly separate matter, you shouldn't be including the data directly in your query like that, IMO. Use query parameters, which is pretty easy in Hibernate:
String query = "SELECT email, id FROM Login WHERE email=? AND password=?";
Object[] parameters = { login.getEmail(), login.getPassword() };
List results = getHibernateTemplate().find(query, parameters);
if (results.size() != 1) {
// Probably throw an exception
}
// I'm assuming your mapping has been set up appropriately such that
// the returned value will *be* an `ILogin`.
return (ILogin) results.get(0);
Finally, you almost certainly don't want results to be an instance variable - it should probably be a local variable, as per my example above.
The dummy way is to use getHibernateTemplate().find(query).get(0); but this will result in exception in case when no such login found.
As Jon said, check your query for emptiness.
I assume spring :).
List resultsList = getHibernateTemplate().find(query);
if ( resultsList.size() == 1 ) {
results = (ILogin)resultsList.get(0);
} else {
// error no entity or mutiple entities
}
return results.
This should work.
I like the idea of Named Queries in JPA for static queries I'm going to do, but I often want to get the count result for the query as well as a result list from some subset of the query. I'd rather not write two nearly identical NamedQueries. Ideally, what I'd like to have is something like:
#NamedQuery(name = "getAccounts", query = "SELECT a FROM Account")
.
.
Query q = em.createNamedQuery("getAccounts");
List r = q.setFirstResult(s).setMaxResults(m).getResultList();
int count = q.getCount();
So let's say m is 10, s is 0 and there are 400 rows in Account. I would expect r to have a list of 10 items in it, but I'd want to know there are 400 rows total. I could write a second #NamedQuery:
#NamedQuery(name = "getAccountCount", query = "SELECT COUNT(a) FROM Account")
but it seems a DRY violation to do that if I'm always just going to want the count. In this simple case it is easy to keep the two in sync, but if the query changes, it seems less than ideal that I have to update both #NamedQueries to keep the values in line.
A common use case here would be fetching some subset of the items, but needing some way of indicating total count ("Displaying 1-10 of 400").
So the solution I ended up using was to create two #NamedQuerys, one for the result set and one for the count, but capturing the base query in a static string to maintain DRY and ensure that both queries remain consistent. So for the above, I'd have something like:
#NamedQuery(name = "getAccounts", query = "SELECT a" + accountQuery)
#NamedQuery(name = "getAccounts.count", query = "SELECT COUNT(a)" + accountQuery)
.
static final String accountQuery = " FROM Account";
.
Query q = em.createNamedQuery("getAccounts");
List r = q.setFirstResult(s).setMaxResults(m).getResultList();
int count = ((Long)em.createNamedQuery("getAccounts.count").getSingleResult()).intValue();
Obviously, with this example, the query body is trivial and this is overkill. But with much more complex queries, you end up with a single definition of the query body and can ensure you have the two queries in sync. You also get the advantage that the queries are precompiled and at least with Eclipselink, you get validation at startup time instead of when you call the query.
By doing consistent naming between the two queries, it is possible to wrap the body of the code to run both sets just by basing the base name of the query.
Using setFirstResult/setMaxResults do not return a subset of a result set, the query hasn't even been run when you call these methods, they affect the generated SELECT query that will be executed when calling getResultList. If you want to get the total records count, you'll have to SELECT COUNT your entities in a separate query (typically before to paginate).
For a complete example, check out Pagination of Data Sets in a Sample Application using JSF, Catalog Facade Stateless Session, and Java Persistence APIs.
oh well you can use introspection to get named queries annotations like:
String getNamedQueryCode(Class<? extends Object> clazz, String namedQueryKey) {
NamedQueries namedQueriesAnnotation = clazz.getAnnotation(NamedQueries.class);
NamedQuery[] namedQueryAnnotations = namedQueriesAnnotation.value();
String code = null;
for (NamedQuery namedQuery : namedQueryAnnotations) {
if (namedQuery.name().equals(namedQueryKey)) {
code = namedQuery.query();
break;
}
}
if (code == null) {
if (clazz.getSuperclass().getAnnotation(MappedSuperclass.class) != null) {
code = getNamedQueryCode(clazz.getSuperclass(), namedQueryKey);
}
}
//if not found
return code;
}
I'm trying to implement paging using row-based limiting (for example: setFirstResult(5) and setMaxResults(10)) on a Hibernate Criteria query that has joins to other tables.
Understandably, data is getting cut off randomly; and the reason for that is explained here.
As a solution, the page suggests using a "second sql select" instead of a join.
How can I convert my existing criteria query (which has joins using createAlias()) to use a nested select instead?
You can achieve the desired result by requesting a list of distinct ids instead of a list of distinct hydrated objects.
Simply add this to your criteria:
criteria.setProjection(Projections.distinct(Projections.property("id")));
Now you'll get the correct number of results according to your row-based limiting. The reason this works is because the projection will perform the distinctness check as part of the sql query, instead of what a ResultTransformer does which is to filter the results for distinctness after the sql query has been performed.
Worth noting is that instead of getting a list of objects, you will now get a list of ids, which you can use to hydrate objects from hibernate later.
I am using this one with my code.
Simply add this to your criteria:
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
that code will be like the select distinct * from table of the native sql.
A slight improvement building on FishBoy's suggestion.
It is possible to do this kind of query in one hit, rather than in two separate stages. i.e. the single query below will page distinct results correctly, and also return entities instead of just IDs.
Simply use a DetachedCriteria with an id projection as a subquery, and then add paging values on the main Criteria object.
It will look something like this:
DetachedCriteria idsOnlyCriteria = DetachedCriteria.forClass(MyClass.class);
//add other joins and query params here
idsOnlyCriteria.setProjection(Projections.distinct(Projections.id()));
Criteria criteria = getSession().createCriteria(myClass);
criteria.add(Subqueries.propertyIn("id", idsOnlyCriteria));
criteria.setFirstResult(0).setMaxResults(50);
return criteria.list();
A small improvement to #FishBoy's suggestion is to use the id projection, so you don't have to hard-code the identifier property name.
criteria.setProjection(Projections.distinct(Projections.id()));
The solution:
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
works very well.
session = (Session) getEntityManager().getDelegate();
Criteria criteria = session.createCriteria(ComputedProdDaily.class);
ProjectionList projList = Projections.projectionList();
projList.add(Projections.property("user.id"), "userid");
projList.add(Projections.property("loanState"), "state");
criteria.setProjection(Projections.distinct(projList));
criteria.add(Restrictions.isNotNull("this.loanState"));
criteria.setResultTransformer(Transformers.aliasToBean(UserStateTransformer.class));
This helped me :D
if you want to use ORDER BY, just add:
criteria.setProjection(
Projections.distinct(
Projections.projectionList()
.add(Projections.id())
.add(Projections.property("the property that you want to ordered by"))
)
);
I will now explain a different solution, where you can use the normal query and pagination method without having the problem of possibly duplicates or suppressed items.
This Solution has the advance that it is:
faster than the PK id solution mentioned in this article
preserves the Ordering and don’t use the 'in clause' on a possibly large Dataset of PK’s
The complete Article can be found on my blog
Hibernate gives the possibility to define the association fetching method not only at design time but also at runtime by a query execution. So we use this aproach in conjunction with a simple relfection stuff and can also automate the process of changing the query property fetching algorithm only for collection properties.
First we create a method which resolves all collection properties from the Entity Class:
public static List<String> resolveCollectionProperties(Class<?> type) {
List<String> ret = new ArrayList<String>();
try {
BeanInfo beanInfo = Introspector.getBeanInfo(type);
for (PropertyDescriptor pd : beanInfo.getPropertyDescriptors()) {
if (Collection.class.isAssignableFrom(pd.getPropertyType()))
ret.add(pd.getName());
}
} catch (IntrospectionException e) {
e.printStackTrace();
}
return ret;
}
After doing that you can use this little helper method do advise your criteria object to change the FetchMode to SELECT on that query.
Criteria criteria = …
// … add your expression here …
// set fetchmode for every Collection Property to SELECT
for (String property : ReflectUtil.resolveCollectionProperties(YourEntity.class)) {
criteria.setFetchMode(property, org.hibernate.FetchMode.SELECT);
}
criteria.setFirstResult(firstResult);
criteria.setMaxResults(maxResults);
criteria.list();
Doing that is different from define the FetchMode of your entities at design time. So you can use the normal join association fetching on paging algorithms in you UI, because this is most of the time not the critical part and it is more important to have your results as quick as possible.
Below is the way we can do Multiple projection to perform Distinct
package org.hibernate.criterion;
import org.hibernate.Criteria;
import org.hibernate.Hibernate;
import org.hibernate.HibernateException;
import org.hibernate.type.Type;
/**
* A count for style : count (distinct (a || b || c))
*/
public class MultipleCountProjection extends AggregateProjection {
private boolean distinct;
protected MultipleCountProjection(String prop) {
super("count", prop);
}
public String toString() {
if(distinct) {
return "distinct " + super.toString();
} else {
return super.toString();
}
}
public Type[] getTypes(Criteria criteria, CriteriaQuery criteriaQuery)
throws HibernateException {
return new Type[] { Hibernate.INTEGER };
}
public String toSqlString(Criteria criteria, int position, CriteriaQuery criteriaQuery)
throws HibernateException {
StringBuffer buf = new StringBuffer();
buf.append("count(");
if (distinct) buf.append("distinct ");
String[] properties = propertyName.split(";");
for (int i = 0; i < properties.length; i++) {
buf.append( criteriaQuery.getColumn(criteria, properties[i]) );
if(i != properties.length - 1)
buf.append(" || ");
}
buf.append(") as y");
buf.append(position);
buf.append('_');
return buf.toString();
}
public MultipleCountProjection setDistinct() {
distinct = true;
return this;
}
}
ExtraProjections.java
package org.hibernate.criterion;
public final class ExtraProjections
{
public static MultipleCountProjection countMultipleDistinct(String propertyNames) {
return new MultipleCountProjection(propertyNames).setDistinct();
}
}
Sample Usage:
String propertyNames = "titleName;titleDescr;titleVersion"
criteria countCriteria = ....
countCriteria.setProjection(ExtraProjections.countMultipleDistinct(propertyNames);
Referenced from https://forum.hibernate.org/viewtopic.php?t=964506
NullPointerException in some cases!
Without criteria.setProjection(Projections.distinct(Projections.property("id")))
all query goes well!
This solution is bad!
Another way is use SQLQuery. In my case following code works fine:
List result = getSession().createSQLQuery(
"SELECT distinct u.id as usrId, b.currentBillingAccountType as oldUser_type,"
+ " r.accountTypeWhenRegister as newUser_type, count(r.accountTypeWhenRegister) as numOfRegUsers"
+ " FROM recommendations r, users u, billing_accounts b WHERE "
+ " r.user_fk = u.id and"
+ " b.user_fk = u.id and"
+ " r.activated = true and"
+ " r.audit_CD > :monthAgo and"
+ " r.bonusExceeded is null and"
+ " group by u.id, r.accountTypeWhenRegister")
.addScalar("usrId", Hibernate.LONG)
.addScalar("oldUser_type", Hibernate.INTEGER)
.addScalar("newUser_type", Hibernate.INTEGER)
.addScalar("numOfRegUsers", Hibernate.BIG_INTEGER)
.setParameter("monthAgo", monthAgo)
.setMaxResults(20)
.list();
Distinction is done in data base! In opposite to:
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
where distinction is done in memory, after load entities!