I have this query
_ctx.TestPackageReportDetails.GroupBy(i => new {i.Status, i.TestPackageId})
.Where(m => m.Count(i => i.Status == "Accept") == 5)
The result :
And this query :
var q2 = _ctx.TestPackages.ToList();
Now i create a join between two result :
_ctx.TestPackageReportDetails.GroupBy(i => new { i.Status, i.TestPackageId })
.Where(m => m.Count(i => i.Status == "Accept") == 5)
.Join(_ctx.TestPackages, i => i.Key.TestPackageId, m => m.Id, (i, m) => new { pack = m, det = i })
.Sum(i => i.pack.Size);
I create a joint based on testpackageid and i need the sum of size value with this condition Where(m => m.Count(i => i.Status == "Accept") == 5),but it doesn't work ,and the query calculates all package size not the package size with this condition Where(m => m.Count(i => i.Status == "Accept") == 5)
You need to filter out the records with the status that you don't need. Also you need to start to make use of the Elegant Query-Syntax which is more readable. Like this:
var sum = (from i in _ctx.TestPackageReportDetails
where i.Status == "Accept"
group i by new { i.Status, i.TestPackageId } into grouping
where grouping.Count() == 5
join m in _ctx.TestPackages
on grouping.Key.TestPackageId equals m.Id
select m.Size).Sum();
You´ve got a problem with either your connectionstring, your database or your code. The reason for this error when you remove Sum() is because after removing this the execute of this LINQ Statement is deferred when you first call a function that executes it. This could be a foreach or a toList() or something similar. In one of your calling methods EntityFramework internally opens another DataReader so if you want to solve this problem you should check up if your connectionstring has the MultipleActiveResultSets Option enabled.
Server=myServerAddress;Database=myDataBase;Trusted_Connection=True;MultipleActiveResultSets=true;
If you enable this, you should be able to open multiple DataReaders at once.
Related
I have the following code where I get error when loading Peers:
Value cannot be null. Parameter name: source
I am using FirstOrDefault and DefaultIfEmpty methods, and inside the select statement I am also checking if the object is empty m => m == null ?. But, I cannot avoid the error. Any ideas?
ReviewRoundDTO_student results = _context.ReviewRounds
.Include(rr => rr.ReviewTasks).ThenInclude(rt => rt.ReviewTaskStatuses)
.Include(rr => rr.Submissions).ThenInclude(s => s.PeerGroup.PeerGroupMemberships).ThenInclude(m => m.User)
.Include(rr => rr.Rubric)
.Where(rr => rr.Id == reviewRoundId)
.Select(rr => new ReviewRoundDTO_student
{
Id = rr.Id,
SubmissionId = rr.Submissions.FirstOrDefault(s => s.StudentId == currentUser.Id).Id,
Peers = rr.Submissions.FirstOrDefault(s => s.StudentId == currentUser.Id)
.PeerGroup.PeerGroupMemberships.DefaultIfEmpty()
.Select(m => m == null ? new ApplicationUserDto { } : new ApplicationUserDto
{
//FullName = m.User.FullName,
//Id = new Guid(m.UserId)
}),
}).FirstOrDefault();
Try avoiding FirstOrDefault().Something construct - expression trees do not support ?. operator which you'd normally use in similar LINQ to Objects query, and EF Core currently has issues translating it correctly - if you look at the exception stack trace, most likely the exception is coming deeply from EF Core infrastructure with no user code involved.
I would recommend rewriting the LINQ query w/o such constructs, for instance something like this:
var results = _context.ReviewRounds
.Where(rr => rr.Id == reviewRoundId)
.Select(rr => new ReviewRoundDTO_student
{
Id = rr.Id,
SubmissionId = rr.Submissions
.Where(s => s.StudentId == currentUser.Id)
.Select(s => s.Id)
.FirstOrDefault(),
Peers = rr.Submissions
.Where(s => s.StudentId == currentUser.Id)
.Take(1)
.SelectMany(s => s.PeerGroup.PeerGroupMemberships)
.Select(m => new ApplicationUserDto
{
FullName = m.User.FullName,
Id = m.UserId
})
.ToList(),
})
.FirstOrDefault();
Note that Include / ThenInclude are not needed in projection queries, because they are ignored.
I inherited the LINQ query below and I feel that the query can be refactored for efficiency. The query currently takes about 6-8 seconds of processing time to return one record to the user on the front-end of the application. LINQ is not my strong suite, so any help would be greatly appreciated.
The query should ultimately produce a distinct list of CA_TASK_VW objects that are tied to a list of distinct CA_OBJECT_ID's obtained from the CA_OBJECT, CA_PEOPLE, and CA_CONTRACTOR tables.
var data = (from a in _db.CA_TASK_VW
where a.TASK_TYPE == "INSPECTION" && a.TASK_AVAILABLE_FLAG == "Y" && a.TARGET_END_DATE == null
select a).AsQueryable();
data = data.Join(_db.CA_OBJECT.Where(o => o.ENTERED_BY == _userId),
o => o.CA_OBJECT_ID, p => p.CA_OBJECT_ID,
(t, p) => t)
.Union(data.Join(_db.CA_PEOPLE.Where(p => p.EMAIL == _email),
t => t.CA_OBJECT_ID, p => p.CA_OBJECT_ID,
(t, p) => t))
.Union(data.Join(_db.CA_CONTRACTOR.Where(c => c.CONTRACTOR.EMAIL == _email),
t => t.CA_OBJECT_ID, c => c.CA_OBJECT_ID,
(t, c) => t));
The code seems to be using Join/Union to execute basically a where predicate on the list of CA_TASK_VW, filtering it step by step to the final result, so what happens if you just specify the where condition directly?
var data = from a in _db.CA_TASK_VW
where a.TASK_TYPE == "INSPECTION" && a.TASK_AVAILABLE_FLAG == "Y" && a.TARGET_END_DATE == null
select a;
data = data.Where(t => _db.CA_OBJECT.Where(o => o.ENTERED_BY == _userId).Select(o => o.CA_OBJECT_ID).Contains(t.CA_OBJECT_ID) ||
_db.CA_PEOPLE.Where(p => p.EMAIL == _email).Select(p => p.CA_OBJECT_ID).Contains(t.CA_OBJECT_ID) ||
_db.CA_CONTRACTOR.Where(c => c.CONTRACTOR.EMAIL == _email).Select(c => c.CA_OBJECT_ID).Contains(t.CA_OBJECT_ID));
You could try using UNION ALL if you don`t really care about duplicates in your query results as it works much faster than UNION
As shown in the below code, the API will hit the database two times to perform two Linq Query. Can't I perform the action which I shown below by hitting the database only once?
var IsMailIdAlreadyExist = _Context.UserProfile.Any(e => e.Email == myModelUserProfile.Email);
var IsUserNameAlreadyExist = _Context.UserProfile.Any(x => x.Username == myModelUserProfile.Username);
In order to make one request to database you could first filter for only relevant values and then check again for specific values in the query result:
var selection = _Context.UserProfile
.Where(e => e.Email == myModelUserProfile.Email || e.Username == myModelUserProfile.Username)
.ToList();
var IsMailIdAlreadyExist = selection.Any(x => x.Email == myModelUserProfile.Email);
var IsUserNameAlreadyExist = selection.Any(x => x.Username == myModelUserProfile.Username);
The .ToList() call here will execute the query on database once and return relevant values
Start with
var matches = _Context
.UserProfile
.Where(e => e.Email == myModelUserProfile.Email)
.Select(e => false)
.Take(1)
.Concat(
_Context
.UserProfile
.Where(x => x.Username == myModelUserProfile.Username)
.Select(e => true)
.Take(1)
).ToList();
This gets enough information to distinguish between the four possibilities (no match, email match, username match, both match) with a single query that doesn't return more than two rows at most, and doesn't retrieve unused information. Hence about as small as such a query can be.
With this done:
bool isMailIdAlreadyExist = matches.Any(m => !m);
bool isUserNameAlreadyExist = matches.LastOrDefault();
It's possible with a little hack, which is grouping by a constant:
var presenceData = _Context.UserProfile.GroupBy(x => 0)
.Select(g => new
{
IsMailIdAlreadyExist = g.Any(x => x.Email == myModelUserProfile.Email),
IsUserNameAlreadyExist = g.Any(x => x.Username == myModelUserProfile.Username),
}).First();
The grouping gives you access to 1 group containing all UserProfiles that you can access as often as you want in one query.
Not that I would recommend it just like that. The code is not self-explanatory and to me it seems a premature optimization.
You can do it all in one line, using ValueTuple and LINQ's .Aggregate() method:
(IsMailIdAlreadyExist, IsUserNameAlreadyExist) = _context.UserProfile.Aggregate((Email:false, Username:false), (n, o) => (n.Email || (o.Email == myModelUserProfile.Email ? true : false), n.Username || (o.Username == myModelUserProfile.Username ? true : false)));
I had written a Query in NHibernate as below:
var queryResult = CurrentSession.QueryOver()
.Where(r => r.StatusId == 1)
.JoinQueryOver(a => a.ActorList)
.Where(s=>s.IsActor==1)
.List()
.Distinct()
.ToList();
I am trying to retrieve only Where(s=>s.IsActor==1), But It Is Getting Records
Where(s=>s.IsActor==0) also...
How can I get only IsActor==1 records?
Thanks in Advance
You need to specify a predicate in the join, so that it is applied to the join not the top where:
(will look something like ...LEFT JOIN actor on actor.Id = p.ActorId AND IsActor = 1)
Actor actorAlias = null;
var queryResult = CurrentSession.QueryOver()
.Where(r => r.StatusId == 1)
.Left.JoinQueryOver(r => r.ActorList, () => actorAlias, a => a.IsActor==1)
.List()
.Distinct()
.ToList();
I try to change that query to QueryOver<> to be able to do the Distinct operation yet inside the (generated sql) query
var result = (from x in Session.Query<Events>()
join o in Session.Query<Receivers>() on x.ID equals o.ID
where x.Owner.ID == 1 //the user is the owner of that Event (not null)
||
x.EVType.ID == 123 //(not null)
||
x.Receivers.Count(y => y.User.ID == 1) > 0 //the user is one of the Event Receivers
select x.StartDate)
.Distinct();
I tried something like that
Events x = null;
List<Receivers> t = null;
var result = Session.QueryOver<Events>(() => x)
.JoinAlias(() => x.Receivers, () => t)
.Where(() => x.Owner.ID == 1
||
x.EVType.ID == 123
||
t.Count(y => y.User.ID == 1) > 0)
.TransformUsing(Transformers.DistinctRootEntity)
.Select(a => a.StartDate)
.List();
but then I got the Value can not be null. Parameter name: source exception. Any ideas how can I fix that query ?
edit
thanks to the xanatos' answer, the final SQL query is correct (I used his 2nd approach):
SELECT distinct this_.StartDate as y0_
FROM Events this_
WHERE
(
this_.UserID = ?
or
this_.EventTypeID = ?
or
exists (SELECT this_0_.ID as y0_
FROM Receivers this_0_
WHERE this_0_.UserID = ?)
)
"In QueryOver, aliases are assigned using an empty variable. The variable can be declared anywhere (but should be empty/default at runtime). The compiler can then check the syntax against the variable is used correctly, but at runtime the variable is not evaluated (it's just used as a placeholder for the alias)." http://nhibernate.info/blog/2009/12/17/queryover-in-nh-3-0.html
Setting List<Receivers> t to empty collection as you did (as you have mentioned in comments) means that you check is event id in local empty collection - doesn't have sense at all.
You can try do your query with subquery (should work but i'm not sure, I wrote it without testing, "by hand"):
Receivers receiversSubQueryAlias = null;
var subquery = session.QueryOver<Events>()
.JoinQueryOver<Receivers>(x => x.Receivers, () => receiversSubqueryAlias, JoinType.Inner)
.Where(()=> receiversSubQueryAlias.UserId == 1)
.Select(x => x.Id)
.TransformUsing(Transformers.DistinctRootEntity);
Events eventsAlias = null;
var mainQueryResults = session.QueryOver<Events>(() => eventsAilas)
.Where(Restrictions.Disjunction()
.Add(() => eventAlias.OwnerId == 1)
.Add(() => eventAlias.EVType.Id == 123)
.Add(Subqueries.WhereProperty<Events>(() => eventAlias.Id).In(subquery))
).Select(x => x.StartDate)
.TransformUsing(Transformers.DistinctRootEntity)
.List();
As written by #fex, you can't simply do a new List<Receivers>. The problem is that you can't mix QueryOver with "LINQ" (the t.Count(...) part). The QueryOver "parser" tries to execute "locally" the t.Count(...) instead of executing it in SQL.
As written by someone else, TransformUsing(Transformers.DistinctRootEntity) is client-side. If you want to do a DISTINCT server-side you have to use Projections.Distinct .
You have to make an explicit subquery. Here there are two variants of the query. the first one is more similar to the LINQ query, the second one doesn't use the Count but uses the Exist (in LINQ you could have done the same by changing the Count(...) > 0 with a Any(...)
Note that when you use a .Select() you normally have to explicitly tell the NHibernate the type of the .List<something>()
Events x = null;
Receivers t = null;
// Similar to LINQ, with COUNT
var subquery2 = QueryOver.Of<Receivers>(() => t)
.Where(() => t.SOMETHING == x.SOMETHING) // The JOIN clause between Receivers and Events
.ToRowCountQuery();
var result2 = Session.QueryOver<Events>(() => x)
.Where(Restrictions.Disjunction()
.Add(() => x.Owner.ID == 1)
.Add(() => x.EVType.ID == 123)
.Add(Subqueries.WhereValue(0).Lt(subquery2))
)
.Select(Projections.Distinct(Projections.Property(() => x.StartDate)))
.List<DateTime>();
// With EXIST
var subquery = QueryOver.Of<Receivers>(() => t)
.Where(() => t.SOMETHING == x.SOMETHING) // The JOIN clause between Receivers and Events
.Select(t1 => t1.ID);
var result = Session.QueryOver<Events>(() => x)
.Where(Restrictions.Disjunction()
.Add(() => x.Owner.ID == 1)
.Add(() => x.EVType.ID == 123)
.Add(Subqueries.WhereExists(subquery))
)
.Select(Projections.Distinct(Projections.Property(() => x.StartDate)))
.List<DateTime>();
Note that you'll have to set "manually" the JOIN condition in the subquery.
Hopefully this answer can help others. This error was being caused by declaring
List<Receivers> t = null;
followed by the query expression
t.Count(y => y.User.ID == 1) > 0
The QueryOver documentation states "The variable can be declared anywhere (but should be empty/default at runtime)." Since in this case, the place holder is a List, you must initialize it as an empty list.
List<Receivers> t = new List<Receivers>();
Otherwise, when you try to reference the Count method, or any other method on the placeholder object, the source (t) will be null.
This however still leaves a problem as #fex and #xanatos, in which it makes no sense to reference Count() from the alias List t, as it won't convert into SQL. Instead you should be creating a subquery. See their answers for more comprehensive answer.