I'm a Seam newbie in an already established project, so a lot of code I use is borrowed and I'm not always fully sure how things work. My problem is that I am using a query object extended from EntityQuery to back a list page with search and sort capabilities that needs to search across a many-to-many relationship and a separate many-to-one relationship which must also be used to sort. Because the many-to-many relationship has to be joined in to allow for the search capability, the query returns duplicate records for each assignment. That's not a big deal because I just added "distinct" to the ejbql and that worked fine. However, when I try to order by the other many-to-one relationship, Oracle throws an error. It appears that Oracle will not accept an order by column that is not in the select clause when using the distinct keyword http://ora-01791.ora-code.com/, and http://oraclequirks.blogspot.com/2009/04/ora-01791-not-selected-expression.html.
Here are the relationships as they are defined in the entities: [Subject m:m JobFunction] (obviously through an assignment table [Subject o:m Subject_JobFunction m:o JobFunction]), and [Subject m:o Type]. Because I need to search Subject by JobFunction, it is joined in in the ejbql which requires the distinct keyword to only return distinct Subjects to the list page. When I try to order by the Type.name (through the many-to-one relationship), the resulting query makes Oracle angry and throws the "ORA-01791: not a SELECTed expression" error. SubjectQuery code:
#Override
public String getEjbql() {
return "select subject from Subject subject left outer join subject.jobFunctions as jobFunction";
}
#Override
#SuppressWarnings("rawtypes")
public List<ValueExpression> getRestrictions() {
ValueExpression[] RESTRICTIONS = {
createValueExpression("lower(subject.name) like #{subjectQuery.prepRestriction(subjectQuery.subject.name)}"),
createValueExpression("subject.active = #{subjectQuery.active}"),
createValueExpression("subject.type.name = #{subjectQuery.typeName}"),
createValueExpression("jobFunction.name = #{subjectQuery.jobFunctionName}")
};
return Arrays.asList(RESTRICTIONS);
}
When I set the query order when a user sorts by the Type name through the front end:
"#{subjectQuery.order=='UPPER(subject.type.name) asc'}"
I get the Oracle error. If I take the distinct out of the ejbql, the sort works fine, but I get duplicate Subject records. When I add the distinct keyword the list works fine without duplicate records, but the sort throws an error. Does anyone have any suggestions about how I can restructure the ejbql to return distinct records without the distinct keyword to make the sort happy, or how to do the sort without making Oracle angry that the sort column referenced in the query is not in the select clause? I have read several places that my answer might be in the the Hibernate Criteria API, but I have no idea how to leverage it in the context of an extended EntityQuery class with what I am trying to accomplish. Please Help!
If you are adding a DISTINCT, then something is broken.
"Because the many-to-many relationship has to be joined in to allow for the search capability, the query returns duplicate records for each assignment. "
Consider the case that a person can work on many projects and a project can have many persons. There is a uniqueness of a 'person/project'. If you want a list of people that work in either project A or B (or both) then you may get
FRED/PROJ_A
BILL/PROJ_A
FRED/PROJ_B
TOM/PROJ_B
BILL/PROJ_C
If you only show the names (not the projects), you can still order by project, but you will see
FRED
BILL
FRED
TOM
BILL
If you do a DISTINCT, you can no longer order by project, because you don't know whether the FRED is the one from PROJ_A or PROJ_B or whether BILL comes before TOM (based on PROJ_A) or after TOM (based on PROJ_C).
So remove the DISTINCT and always show the column on which you are ordering (because then you'll see why the duplicates aren't actually duplicates).
I'm not sure how the generated query(ies) is(are) different, but I found an answer. I wasn't aware of the fetch command for hibernate, which fixes the need for the distinct keyword (again, not sure exactly how, maybe by subquerying?). After changing the ejbql to:
#Override
public String getEjbql() {
return "select subject from Subject subject left join fetch subject.jobFunctions jobFunction";
}
the distinct is no longer needed and therefore, Oracle does not complain about the order by column not being in the select clause. The list works as expected and the sort column works! Yay!
Predictably, I found the answer here on stackoverflow. The question was not exactly the same, but the hql syntax worked for me: HQL order by within a collection
Related
I have 2 tables in a one-to-many mapping, layoutFeature and layoutPadData.
Parent table layoutFeature has 2 columns: layoutId (Pkey) and colorHex.
Child table layoutPadData has 5 columns:
layoutId (Fkey), padId (Pkey), longitude, latitude, padName
Now I want to write a query which from database will fetch data like this projection:
public interface LayoutFeatureInfo {
String getColorHex();
List<LayoutPadDataInfo> getPadLevelDataList();
interface LayoutPadDataInfo {
double getLatitude();
double getLongitude();
String getPadName();
}
}
I wrote this query :
But this doesn't work since the query returns:
All rows of layoutPadData table but I want selective of them under padLabelDataList
As I had done join, I get multiple rows of colorHex as well but I what I want is single property of parent and list of child interface something like this will be response of api when I fetch from DB:
Can anyone help me with the query please.
My personal experience with projections and join fetching has been really bad in spring boot (vanilla JPQL).
One approach is the one explained here https://vladmihalcea.com/one-to-many-dto-projection-hibernate/
Another approach is to use a 3rd party lib like https://github.com/Blazebit/blaze-persistence
I've heard great things about it but I've never used it before.
For your second problem a simpler issue is query child entity based on parent key and return a list of the things you want (hibernate is not good to understand and "turn" the sql like result-set into a single entity).
I've got 2 classes
Reports - objectID, Title, Date & relationItem ( Relation type column linked up to Items)
Items - ObjectID, Title, Date etc
I want to query all the Items that are equal to a objectID in reports. Users create reports then add items to them. These items are found in the Items table.
I've looked at the https://parseplatform.github.io/docs/ios/guide/#relations but don't see anything for swift3.
I've tried a few things with little success. This snipplet below i did find, but not sure how to apply it to my classes.
var relation = currentUser.relationForKey("product")
relation.query()?.findObjectsInBackgroundWithBlock({
Would love somebody to direct me into the right direction! Thanks
Tried this code below too!
var query = PFQuery(className:"Items")
query.whereKey("relationItem ", equalTo: PFObject(withoutDataWithClassName:"Reports", objectId:"MZmMHtobwQ"))
Ok so i had to change the table slightly to get this to work to prevent a query within a query.
I've added a relation Type to the Items table instead of the Reports Table
Then i managed to retrieve all the Items based of that report ObjectId like this:
let query = PFQuery(className:"Items")
query.whereKey("reportRelation", equalTo: PFObject(withoutDataWithClassName:"Reports", objectId:"3lWMYwWNEj"))
This then worked. Note that reportRelation is the Relational Type Column.
Thanks
When you’re thinking about one-to-many relationships and whether to implement Pointers or Arrays, there are several factors to consider. First, how many objects are involved in this relationship? If the “many” side of the relationship could contain a very large number (greater than 100 or so) of objects, then you have to use Pointers. If the number of objects is small (fewer than 100 or so), then Arrays may be more convenient, especially if you typically need to get all of the related objects (the “many” in the “one-to-many relationship”) at the same time as the parent object.
http://parseplatform.github.io/docs/ios/guide/#relations
If you are working with one to many relation, use pointer or array. See the guide for examples and more explanation.
im trying to run an hql query which aggragets (sum) number of transactions made on a specific account, i dont need a group by since my where clause has a specific account filter (where account = :account)
i do, however, want to return the aggregated value only if it is smaller/bigger than some given value.
when im adding 'having' after the where clause without 'group by' im getting an error -
unexpected token: having
in native sql i succeeded adding 'having' without group by
any ideas on how to make it work with hql?
thanks alot
The reason why databases don't let you mix grouped columns with non-grouped and non-aggregated ones is, that for non-grouped/non-aggregated columns it would have to choose one row's value per group, but doesn't know how to pick one.
If you don't care, then you could just leave it away and if it doesn't matter because they're all the same, you could group by them, too.
It is not hql, but if you have native query, then run it like:
Query query = session.createSQLQuery("select, *** ,... blah blah")
//set If you need
query.setParameter("myparam", "val");
List result = query.list();
In my eyes this is nonsense. 'having' is done for conditions on a 'group by' result. If you don't group, then it does not make much sense.
I would say HQL can't do it. Probably the Hibernate programmers didn't think of this case because they considered it as not important.
And anyway, you don't need it.
If it is a simple query, then you can decide in your java code if you want the result or if you don't need it.
If it is in a subselect, then you can solve the problem with a where condition in the main select.
If you think it is really necessary then your invited to give a more concrete example.
I am looking for a way to have a query that returns a tuple first sorted by a column, then grouped by another (in that order). Simply .sort_by().group_by() didn't appear to work. Now I tried the following, which made the return value go wrong (I just got the orm object, not the initial tuple), but read for yourself in detail:
Base scenario:
There is a query which queries for test orm objects linked from the test3 table through foreign keys.
This query also returns a column named linked that either contains true or false. It is originally ungrouped.
my_query = session.query(test_orm_object)
... lots of stuff like joining various things ...
add_column(..condition that either puts 'true' or 'false' into the column..)
So the original return value is a tuple (the orm object, and additionally the true/false column).
Now this query should be grouped for the test orm objects (so the test.id column), but before that, sorted by the linked column so entries with true are preferred during the grouping.
Assuming the current unsorted, ungrouped query is stored in my_query, my approach to achieve this was this:
# Get a sorted subquery
tmpquery = my_query.order_by(desc('linked')).subquery()
# Read the column out of the sub query
my_query = session.query(tmpquery).add_columns(getattr(tmpquery.c,'linked').label('linked'))
my_query = my_query.group_by(getattr(tmpquery.c, 'id')) # Group objects
The resulting SQL query when running this is (it looks fine to me btw - the subquery 'anon_1' is inside itself properly sorted, then fetched and its id aswell as the 'linked' column is extracted (amongst a few other columns SQLAlchemy wants to have apparently), and the result is properly grouped):
SELECT anon_1.id AS anon_1_id, anon_1.name AS anon_1_name, anon_1.fk_test3 AS anon_1_fk_test3, anon_1.linked AS anon_1_linked, anon_1.linked AS linked
FROM (
SELECT test.id AS id, test.name AS name, test.fk_test3 AS fk_test3, CASE WHEN (anon_2.id = 87799534) THEN 'true' ELSE 'false' END AS linked
FROM test LEFT OUTER JOIN (SELECT test3.id AS id, test3.fk_testvalue AS fk_testvalue
FROM test3)
AS anon_2 ON anon_2.fk_testvalue = test.id ORDER BY linked DESC
)
AS anon_1 GROUP BY anon_1.id
I tested it in phpmyadmin, where it gave me, as expected, the id column (for the orm object id), then the additional columns SQL_Alchemy seems to want there, and the linked column. So far, so good.
Now my expected return values would be, as they were from the original unsorted, ungrouped query:
A tuple: 'test' orm object (anon_1.id column), 'true'/'false' value (linked column)
The actual return value of the new sorted/grouped query is however (the original query DOES indeed return a touple before the code above is applied):
'test' orm object only
Why is that so and how can I fix it?
Excuse me if that approach turns out to be somewhat flawed.
What I actually want is, have the original query simply sorted, then grouped without touching the return values. As you can see above, my attempt was to 'restore' the additional return value again, but that didn't work. What should I do instead, if this approach is fundamentally wrong?
Explanation for the subquery use:
The point of the whole subquery is to force SQLAlchemy to execute this query separately as a first step.
I want to order the results first, and then group the ordered results. That seems to be hard to do properly in one step (when trying manually with SQL I had issues combining order and group by in one step as I wanted).
Therefore I don't simply order, group, but I order first, then subquery it to enforce that the order step is actually completed first, and then I group it.
Judging from manual PHPMyAdmin tests with the generated SQL, this seems to work fine. The actual problem is that the original query (which is now wrapped as the subquery you were confused about) had an added column, and now by wrapping it up as a subquery, that column is gone from the overall result. And my attempt to readd it to the outer wrapping failed.
It would be much better if you provided examples. I don't know if these columns are in separate tables or what not. Just looking at your first paragraph, I would do something like this:
a = session.query(Table1, Table2.column).\
join(Table2, Table1.foreign_key == Table2.id).\
filter(...).group_by(Table2.id).order_by(Table1.property.desc()).all()
I don't know exactly what you're trying to do since I need to look at your actual model, but it should look something like this with maybe the tables/objs flipped around or more filters.
I have a simple LINQ EF query below using the method syntax. I'm using my Include statement to join four tables: Event and Doc are the two main tables, EventDoc is a many-to-many link table, and DocUsage is a lookup table.
My challenge is that I'd like to shape my results by only selecting specific columns from each of the four tables. But, the compiler is giving a compiler is giving me the following error:
'System.Data.Objects.DataClasses.EntityCollection does not contain a definition for "Doc' and no extension method 'Doc' accepting a first argument of type 'System.Data.Objects.DataClasses.EntityCollection' could be found.
I'm sure this is something easy but I'm not figuring it out. I haven't been able to find an example of someone using the multi-table include but also shaping the projection.
Thx,Mark
var qry= context.Event
.Include("EventDoc.Doc.DocUsage")
.Select(n => new
{
n.EventDate,
n.EventDoc.Doc.Filename, //<=COMPILER ERROR HERE
n.EventDoc.Doc.DocUsage.Usage
})
.ToList();
EventDoc ed;
Doc d = ed.Doc; //<=NO COMPILER ERROR SO I KNOW MY MODEL'S CORRECT
DocUsage du = d.DocUsage;
Very difficult to know what is going on without a screencap of your model, including the navigational properties on each entity.
But if your saying it's a many-to-many between Event and Doc (with EventDoc being the join table), and assuming your join table has nothing but the FK's and therefore doesn't need to be mapped, then shouldn't a single Event have many Doc's?
This query:
var query = ctx.Event.Include("EventDoc.Doc");
Would imply (based on the lack of pluralization): a single Event has a single EventDoc which has a single Doc.
But shouldn't that be: a single Event has a single EventDoc which has many Doc's.
Therefore your projection doesn't really make sense. Your trying to project to an anonymous type, with EventDate and Filename for a single Doc, but an Event has many Docs.
Maybe a projection like this would be more suitable:
var query = ctx.Event.Include("EventDoc.Docs.DocUsage")
.Select(x => new
{
EventDate = x.EventDate,
DocsForEvent = x.EventDocs.Docs
}).ToList();
And for that you work you need to fix up your model. Im surprised it even validates/compiles.
Either your model is wrong or your description of the database cardinalities in your question is. :)
Of course, i could be completely misunderstanding your database and/or model - so if i am let me know and i'll remove this answer.