I have a Java8 application using SpringBoot, which is pulling in Hibernate core 5.3.10 (connected to PostgreSQL 11). A simplified explanation: the application is maintaining a history of changes to a series of bespoke UserData records, containing two LocalDateTime columns for startDate and endDate, and a userId column (plus other columns).
The semantics of the application are that a history of changes to the UserData are maintained by the start_date and end_date contain no duplicates (respectively), and that any row where the endDate is null is the currently active record for a user. (Accordingly, a user may have no currently active record.)
It is a simple matter to retrieve all of the active rows, and this is working well.
However, I have a requirement to retrieve the latest row for all users irrespective of whether the row is active or not.
One way to achieve this outcome using SQL is with a query something like the following:
select ud1.* from user_data ud1
where ud1.start_date = (select max(ud2.start_date) from user_data ud2
where ud2.user_id = ud1.user_id);
I have been attempting to write a CriteriaQuery to replicate the SQL, but I have run into a data type problem with the CriteriaBuilder.max method. The max method is complaining that it will only accept a type Number column. The code looks like this:
final CriteriaBuilder builder = entityManager.getCriteriaBuilder();
final CriteriaQuery<UserDate> criteriaQuery = builder.createQuery(UserData.class);
final Root<UserData> ud1 = criteriaQuery.from(UserData.class);
final Subquery<LocalDateTime> maxUserDataStartDate = criteriaQuery.subquery(LocalDateTime.class);
final Root<UserData> ud2 = maxUserDataStartDate.from(UserData.class);
maxUserDataStartDate.select(builder.max(ud2.get("startDate"));
// ...
The problem is with the last line, where it complains that ud2.get("startDate") is not an extension of type Number - which is true, of course.
Does anybody know how to fix this situation? Especially, does anybody have an example they can share that does what I'm after?
You can do order by start_date desc and get top 1
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<UserData> criteriaQuery = builder.createQuery(UserData.class);
Root<UserData> ud = criteriaQuery.from(UserData.class);
criteriaQuery.orderBy(builder.desc(ud.get("startDate")));
entityManager.createQuery(criteriaQuery).getFirstResult();
Related
I'm trying to group entities by date intervals using JPA's Criteria API. I use this way of querying for entities as this is a part of the service that serves API requests which may ask for any field of any entity, including sorting, filtering, grouping and aggregations. Everything works fine except for grouping by date fields. My underlying DBMS i PostgreSQL.
To give a minimal example, here's my entity class:
#Entity
#Table(name = "receipts")
public class DbReceipt {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private Date sellDate;
// Many other fields
}
This example discusses grouping my "month" interval (therefore grouping by year+month), but in the end I'm looking for a solution that would let me group by any interval, such as "year", "day" or "minutes".
What I'm trying to achieve is the following query, but using Criteria API:
SELECT TO_CHAR(sell_date, 'YYYY-MM') AS alias1 FROM receipts GROUP BY alias1;
My attempt to do so is this:
#Service
public class ReceiptServiceImpl extends ReceiptService {
#Autowired
private EntityManager em;
#Override
public void test() {
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Object[]> query = cb.createQuery(Object[].class);
Root<?> root = query.from(DbReceipt.class);
Expression<?> expr = cb.function("to_char", String.class, root.get("sellDate"), cb.literal("YYYY-MM"));
query.groupBy(expr);
query.multiselect(expr);
TypedQuery<Object[]> typedQuery = em.createQuery(query);
List<Object[]> resultList = typedQuery.getResultList();
}
}
The reason I use to_char function and not MONTH and similar is that I need entities like 2019-05 and 2020-05 to not be grouped together. I also narrow this example down to only year and month to keep things short, but the goal is to group by any date interval.
The code above creates the following query (SQL logging enabled) which results in an error:
Hibernate: select to_char(dbreceipt0_.sell_date, ?) as col_0_0_ from receipts dbreceipt0_ group by to_char(dbreceipt0_.sell_date, ?)
24-05-2020 12:16:30.071 [http-nio-1234-exec-5] WARN o.h.e.jdbc.spi.SqlExceptionHelper.logExceptions - SQL Error: 0, SQLState: 42803
24-05-2020 12:16:30.071 [http-nio-1234-exec-5] ERROR o.h.e.jdbc.spi.SqlExceptionHelper.logExceptions - ERROR: column "dbreceipt0_.sell_date" must appear in the GROUP BY clause or be used in an aggregate function
Position: 16
which to me is caused by the fact that the whole expression is put into the 'group by' part of the query, rather than just an alias. Now, I've tried to assign an alias to the expression (which returns Selection<T> and groupBy accepts expressions, therefore I can only really use that in the multiselect), but that didn't affect how the query is performed - nothing changed.
How do I achieve grouping by year and month as described above using Criteria API? Maybe there's a different way other than using to_char? Maybe there's a way to give an alias to the groupBy method that would cause it to group by an alias instead of the whole expression?
I think it's a bug in PostgreSQL (the error comes from there, not from Hibernate). I have tried a slightly modified version of your code with EclipseLink + Derby and works perfectly.
Note that I had to use numbers instead of strings because Derby DB doesn't have an equivalent of TO_CHAR function.
Expression<Integer> year = cb.function("YEAR", Integer.class, root.get("sellDate"));
Expression<Integer> month = cb.function("MONTH", Integer.class, root.get("sellDate"));
Expression<Integer> expr = cb.sum(month, cb.prod(12, year));
query.groupBy(expr);
query.multiselect(expr);
This returns the following SQL:
SELECT (MONTH(MY_DATE) + (12 * YEAR(MY_DATE)))
FROM MY_DATE_TABLE
GROUP BY (MONTH(MY_DATE) + (12 * YEAR(MY_DATE)))
Note that there are no portable solutions for manipulating dates in JPA criteria queries. If the number of groups to be queried simultaneously is not too high I'd go with a more practical approach where you find the dates in Java and pass them as literals to the query builder.
Another workaround is to query with a groupBy(root.get("sellDate")) and then aggregate the results in Java according to the desired time period.
Post Scriptum: I don't think it's relevant, however I modified the query's return type from Object[] to Object.
I'm using hibernate and jpa in a spring boot application.
I have a hibernate entity with 2 columns, type (string) and date (LocalDate).
I want to select all the columns and the difference of days between my date column and now.
I succeeded in PostgreSQL: select date, date - current date from table;
I'm using an interface which extends JpaRepository. Until now i was successfully to insert new queries through #Query annotations.
I can't figure it out how to select my columns and a column containing the difference of days in jpql.
Kind regards,
Indeed you can use query creator. You have to create a new entity which has the same columns as the original table and in addition the calculated difference between the date column and now. You have to be careful which date type is your column.
In my experience only Date from java.util can be used for differences with CURRENT_DATE (i may be wrong).
public List<NewEntity> getTest() {
String queryStr = "select new com.entity.NewEntity(n.type, n.date - CURRENT_DATE as
time) from Table as n"
TypedQuery<PunteInspectieTimpRamas> query = entityManager.createQuery(queryStr,
NewEntity.class);
return query.getResults()
}
Not sure you can do this with jpql.
But you can use your query as a native query, directly in you repository:
#Query(value = "SELECT ... ", nativeQuery = true)
ClassToReturn methodName();
see https://www.baeldung.com/spring-data-jpa-query
I'm using Entity Framework to map database to a class in my application.
The class is automatically generated as partial class by EF and I also added some other properties in my own file to the same partial class.
I use these queries to get a list of entities from the table (they are equivalent as far as I can tell):
db.DailyEntry.ToList
db.DailyEntry.SqlQuery("SELECT * FROM DailyEntry").ToList
db.Database.SqlQuery(Of DailyEntry)("SELECT DailyEntry.DailyEntryId, DailyEntry.Driver, DailyEntry.Billing, DailyEntry.EntryDate FROM DailyEntry").ToList
I then added a field to this class:
Public Property IsHoliday As Boolean = False
I iterated through the list and calculated whether the date falls on a bank holiday. I have a database table of holidays:
For Each entry As DailyEntry in _myList_
entry.IsHoliday = db.Database.SqlQuery(Of Boolean)("SELECT IsHoliday FROM Holiday WHERE HolidayDate = {0}", entry.EntryDate).FirstOrDefault
Next
This all works fine but as the amount of records increased, so did the number of database calls and I need to speed the application up by merging these into a single call.
I modified the query to include the holiday info:
SELECT DailyEntry.*, Holiday.IsHoliday AS IsHoliday FROM DailyEntry LEFT OUTER JOIN Holiday ON DailyEntry.EntryDate = Holiday.HolidayDate;
or
SELECT DailyEntry.DailyEntryId, DailyEntry.Driver, DailyEntry.Billing, DailyEntry.EntryDate, Holiday.IsHoliday AS IsHoliday FROM DailyEntry LEFT OUTER JOIN Holiday ON DailyEntry.EntryDate = Holiday.HolidayDate;
and a few similar tries. They work well when I test them as queries on the database and return expected data, but when I try to use them in my app:
db.Database.SqlQuery(Of DailyEntry)("SELECT DailyEntry.*, Holiday.IsHoliday AS IsHoliday FROM DailyEntry LEFT OUTER JOIN Holiday ON DailyEntry.EntryDate = Holiday.HolidayDate").ToList
the IsHoliday property is always left at default value (False).
Is there a way to get these calculated columns that are not part of the original database table to map to my properties?
Thanks in advance,
Zdenek
I have two entities, assume they are called Container and Record. They have a master-child relationship: a 'container' can hold many records.
The Records table in the database has the following columns:
Id
Date
Container_Id
RecordType_Id
The Record entity does not have any navigation properties that back reference the Container.
I am writing a LINQ query for my repository that will retrieve ONLY the records for a container that have the most recent date for each RecordType_Id. All older records should be ignored.
So if a container has say 5 records, one for each RecordType_Id, with the date 24/May/2011. But also has another 5 records for each RecordType_Id but with the date 20/May/2011. Then only the first 5 with the 24/May date will be retrieved and added to the collection in the container.
I came up with an SQL query that does what I need (but maybe there is some more efficient way?):
select t.*
from Records t
inner join (
select Container_Id, RecordType_Id, max(Date) AS MaxDate
from Records
group by Container_Id, RecordType_Id ) g
on t.Date = g.MaxDate
and t.Container_Id = g.Container_Id
and t.RecordType_Id = g.RecordType_Id
order by t.Container_Id
, t.RecordType_Id
, t.Date
However I am struggling to translate this into a proper LINQ query. EF is already generating a fairly large query all by itself just to load the entities, which makes me unsure of how much of this SQL query is actually relevant to the LINQ query.
Off the top of my head:
var q = from c in Container
from r in c.Records
group r by r.RecordType.RecordType_Id into g
select new
{
Container = c,
RecordType_Id = g.Key,
Records = from gr in g
let maxDate = g.Max(d => d.Date)
where gr.Date == maxDate
select gr
};
Try using LinqPad, it helps you test linq queries easily. Even against an existing EF model (which is in your project). Visit http://www.linqpad.net/
I'm stuck trying to map this sql:
select dt.Id, dateadd(dd,datediff(dd,0,dt.CreatedAt),0) as Ct, DId, Amount
from dt, ad
where dt.ADId = ad.ADId and ad.Id = '13B29A01-8BF0-4EC9-80CA-089BA341E93D'
order by dateadd(dd,datediff(dd,0,dt.CreatedAt),0) desc, DId asc
Into an Entity Framework-compatible lambda query expression. I'd appreciate any help.
I think something like the code below should work.
Guid dtId = new Guid("13B29A01-8BF0-4EC9-80CA-089BA341E93D");
DateTime compareDt = new DateTime(...);
var q = from dt in dts
where dt.id == dtId
orderby dt.Ad.CreatedAt, Did
select new
{
dt.Ad,
(dt.CreatedAt - compareDt).Days,
DId,
Amount
};
dtId has to be outside of the query, because the entity framework mapper doesn't understand constructors that take parameters, similar for the DateTime. I couldn't completely figure out the datediff/dateadd part, looks like you're determining the total amount of days since a given datetime, which is what I assumed.
It could be that the datetime subtraction followed by TimeSpan.Days doesn't work in the query. If that's the case, pull it outside like so:
var q = from dt in dts
where dt.id == dtId
orderby dt.Ad.CreatedAt, Did
select new
{
dt.Ad,
dt.CreatedAt,
DId,
Amount
};
This creates an IEnumerable of objects that have a DateTime CreatedAt property. If you call .ToList() now, the query is executed, and you can calculate stuff that Entity Framework doesn't support. Again, if the first attempt worked, that's the best solution if the number of days since X is what you need.
from item in q.ToList()
select new
{
dt.Ad
(dt.CreatedAt - compareDt).Days,
DId,
Amount
};