I've written some complex LINQ query which I'm trying to run against NHibernate, unfortunately this causes an exception when trying to evaluate the query (call .ToList()).
Here is the code, which is supposed to retrieve Issue objects with some extra data:
var list = from i in sess.Query<Issue>()
let readFlag = (from f in i.ReadFlags
where (f.User != null && f.User.Username == request.UserName)
||
(f.Device.Name == request.MachineName)
select f).FirstOrDefault()
let isUnread = readFlag == null
let unreadCommentsCount = isUnread ? 0 : (from c in i.Comments
where c.DateCreated > readFlag.LastSeenCommentDate
select c).Count()
let statusChanged = isUnread && i.Status != readFlag.LastSeenStatus
where isUnread || unreadCommentsCount > 0 || statusChanged
select new
{
Issue = i,
ReadFlag = readFlag,
IsUnread = isUnread,
UnreadCommentsCount = unreadCommentsCount
};
i.e. - for each Issue object look for related IssueReadFlag which matches current username or machine name. if the Flag exists, it also contains the "last seen comment date", so the code calculates the number of new comments for this Issue.
Unfortunately NHibernate is not able to handle this query (Exception details).
I'm looking for the most optimal solution for this problem.
Obtaining all the Issue objects and applying the query criteria on the client-side is unacceptable for me.
trying to find out what causes the issue: It started working as I've commented out evaluation of unreadCommentsCount and statusChanged both in "select" and "where" statements. Following this lead, It seems that referencing readFlag in any of these subqueries causes the issue (after removing reference to readFlag in "let unreadCommentsCount .." and "let statusChanged.." conditions, the query doesn't throw exceptions).
Now I need a tip on how to make it functional (working as expected) again ...
Further investigating the issue I've found out that NHibernate can't handle the uncertain state of readFlag existence.
I've ended up splitting the query into two parts, first of them takes all the Issues where readFlag does not exists, the second one queries the IssueReadFlag directly, calculating the Unread Comments Count and Changed Status.
This seems to be the only solution as for now.
Related
I am trying to simplify a C# method that includes the following query:
var matchingDeviceKeys =
from dev in data.Elements("Key1")
where dev.Element("Key2").Element("Key3").Element("VendorID").Value == device.Vendor &&
dev.Element("Key2").Element("Key3").Element("ProductType").Value == device.ProductType &&
dev.Element("Key2").Element("Key3").Element("ProductCode").Value == device.ProductCode
from rev in dev.Element("Key2").Element("Key3").Element("Key4").Elements("MajorRev")
where rev.Attribute("Number").Value == device.MajorRevision &&
rev.Attribute("DefaultMinorRev").Value == device.MinorRevision.ToString(CultureInfo.InvariantCulture)
select dev.Element("Key6").Element("Key7").Element("Key8");
The "rev" target for the second from clause is never used in the select line, making me wonder if that entire second from clause is doing anything. If it is doing something, what is it doing?
My apologies for obfuscating the element names. I have to be careful in sharing proprietary code.
everyone! I'm trying to do a rather simple LINQ query to find available rooms in a hotel. (That is, find a available room from a pool of rooms, and check that there are no pending cleaning etc in the room).
But when I try to execute the third query, I get the exception you see in the title. I don't actually get the exception when I execute it, but when I try to use the "unfinishedTasksInPool" variable.
I tried turning the "unfinishedTasksInPool" into a list, too see if that would help, but whenever I try to use "unfinishedTasksInPool", I get the exception.
EDIT : Whenever I exclude "availableRoomsFromPool.Contains(tasks.roomId" in the where clause in the third query, everything seems to work normally. But that doesn't exactly solve the problem tho.
var pendingReservation = database.Reservations.Where(res => res.reservationID == resId).First();
var reservationsInSameGroup = from otherReservations in database.GetTable<Reservation>()
where (otherReservations.beds == pendingReservation.beds
&& otherReservations.rank == pendingReservation.rank
&& otherReservations.roomID != null)
select otherReservations.roomID;
var availableRoomsFromPool = from rooms in database.GetTable<Room>()
where (!reservationsInSameGroup.Contains(rooms.roomId)
&& rooms.beds == pendingReservation.beds
&& rooms.roomRank == pendingReservation.rank)
select rooms.roomId;
var unfinishedTasksInPool = from tasks in database.GetTable<HotelTask>()
where (availableRoomsFromPool.Contains(tasks.roomId)
&& tasks.taskStatus < 2)
select tasks.roomId;
It's a LINQ-to-SQL restriction. You can use local sequences in queries (as long as you use them in Contains), but you can't use a local sequence that itself is the result of a query using another local sequence.
So it's alright to do...
var availableRoomsFromPool = (from ....).ToArray();
...because the query contains one local sequence (reservationsInSameGroup).
But...
var unfinishedTasksInPool = (from ...).ToArray();
...throws the exception.
The solution is to use the result of var availableRoomsFromPool = (from ....).ToArray(); in the third query, because that reduces availableRoomsFromPool to one local sequence.
This seems to be about the most generic error I've come across - multiple SO posts about it are all referring to different issues - well here's a new one :)
I get the error above when the following IQueryable is enumerated:
N.B. items is an IQueryable<tblItem> and keywords is a string
items = items.Where(p => p.heading.ToLower().Contains(keywords) ||
p.description.ToLower().Contains(keywords));
This is confusing because, as the error suggests, it should work fine when you use a Contains - does anyone know how to fix this?
If keyword is a collection that supports enumeration, then it should be other way around:
items = items.Where(p => keywords.Contains(p.heading.ToLower()) ||
keywords.Contains(p.description.ToLower()));
If items is IQueryable then the error may be there and nothing to do with your where statement.
Can you try forcing enumeration before adding your where statement?
For example, suppose you are attempting to join an in memory list with a datatable you will get that error when the query is evaluated or enumerated
List<tblCategory> categories = tblCategory.ToList();
IQueryable<tblItem> items = (from r in tblItem
join c in categories on r.CategoryID equals c.Id select r);
// items = items.Where(p => p.heading.ToLower().Contains(keywords) ||
// p.description.ToLower().Contains(keywords));
var firstMatch = items.FirstOrDefault();
// The error will be generated here even if the where is remmed out
SOLVED
Thanks sgmoore for your input - it helped arrive at this solution:
Assgning the IQueryable list to an IEnumerable list, running a ToList on it and THEN using my filters on the list worked great.
IEnumerable<tblItems> temp = items.ToList();
temp = temp.Where(p => p.heading.ToLower().Contains(keywords) ||
p.description.ToLower().Contains(keywords));
items = temp.AsQueryable();
I suspect I'm missing something rather basic, yet I can't figure this one out.
I'm running a simple linq query -
var result = from UserLine u in context.Users
where u.PartitionKey == provider.Value && u.RowKey == id.Value
select u;
UserLine user = null;
try
{
user = result.FirstOrDefault();
}
For some reason this produces a TargetInvocationException with an inner exception of NullReferenceException.
This happens when the linq query produces no results, but I was under the impression that FirstOrDefault would return Default<T> rather than throw an exception?
I don't know if it matters, but the UserLine class inherits from Microsoft.WindowsAzure.StorageClient.TableServiceEntity
there are two possible reasons:
provider.Value
id.Value
Are you sure that theese nullables have value. You might want to check HasValue before
var result = from UserLine u in context.Users
where (provider.HasValue && u.PartitionKey == provider.Value)
&& (id.HasValue && u.RowKey == id.Value)
select u;
UserLine user = null;
try
{
user = result.FirstOrDefault();
}
I thought it produced a different error, but based on the situation in which the problem is occurring you might want to look to check if context.IgnoreResourceNotFoundException is set to false? If it is try setting it to true.
This property is a flag to indicate whether you want the storage library to throw and error when you use both PartitionKey and RowKey in a query and no result is found (it makes sense when you think about what the underlying REST API is doing, but it's a little confusing when you're using LINQ)
I figured it out - the problem occured when either id or provider had '/' in the value, which the id did. when I removed it the code ran fine
Understanding the Table Service Data Model has a section on 'Characters Disallowed in Key Fields' -
The following characters are not allowed in values for the
PartitionKey and RowKey properties:
The forward slash (/) character
The backslash () character
The number sign (#) character
The question mark (?) character
Here's some fun try putting the where query the other way around like this to see if it works (I heard a while ago it does!):
where (id.HasValue && u.RowKey == id.Value) && (provider.HasValue && u.PartitionKey == provider.Value)
Other than this you can now set IgnoreResourceNotFoundException = true in the TableServiceContext to receive null when an entity is not found instead of the error.
It's a crazy Azure storage thing.
I ran into an interesting error with the following LiNQ query using LiNQPad and when using Subsonic 3.0.x w/ActiveRecord within my project and wanted to share the error and resolution for anyone else who runs into it.
The linq statement below is meant to group entries in the tblSystemsValues collection into their appropriate system and then extract the system with the highest ID.
from ksf in KeySafetyFunction where ksf.Unit == 2 && ksf.Condition_ID == 1
join sys in tblSystems on ksf.ID equals sys.KeySafetyFunction
join xval in (from t in tblSystemsValues
group t by t.tblSystems_ID into groupedT
select new
{
sysId = groupedT.Key,
MaxID = groupedT.Max(g=>g.ID),
MaxText = groupedT.First(gt2 => gt2.ID ==
groupedT.Max(g=>g.ID)).TextValue,
MaxChecked = groupedT.First(gt2 => gt2.ID ==
groupedT.Max(g=>g.ID)).Checked
}) on sys.ID equals xval.sysId
select new {KSFDesc=ksf.Description, sys.Description, xval.MaxText, xval.MaxChecked}
On its own, the subquery for grouping into groupedT works perfectly and the query to match up KeySafetyFunctions with their System in tblSystems also works perfectly on its own.
However, when trying to run the completed query in linqpad or within my project I kept running into a SQLiteException SQLite Error Near "("
First I tried splitting the queries up within my project because I knew that I could just run a foreach loop over the results if necessary. However, I continued to receive the same exception!
I eventually separated the query into three separate parts before I realized that it was the lazy execution of the queries that was killing me. It then became clear that adding the .ToList() specifier after the myProtectedSystem query below was the key to avoiding the lazy execution after combining and optimizing the query and being able to get my results despite the problems I encountered with the SQLite driver.
// determine the max Text/Checked values for each system in tblSystemsValue
var myProtectedValue = from t in tblSystemsValue.All()
group t by t.tblSystems_ID into groupedT
select new {
sysId = groupedT.Key,
MaxID = groupedT.Max(g => g.ID),
MaxText = groupedT.First(gt2 => gt2.ID ==groupedT.Max(g => g.ID)).TextValue,
MaxChecked = groupedT.First(gt2 => gt2.ID ==groupedT.Max(g => g.ID)).Checked};
// get the system description information and filter by Unit/Condition ID
var myProtectedSystem = (from ksf in KeySafetyFunction.All()
where ksf.Unit == 2 && ksf.Condition_ID == 1
join sys in tblSystem.All() on ksf.ID equals sys.KeySafetyFunction
select new {KSFDesc = ksf.Description, sys.Description, sys.ID}).ToList();
// finally join everything together AFTER forcing execution with .ToList()
var joined = from protectedSys in myProtectedSystem
join protectedVal in myProtectedValue on protectedSys.ID equals protectedVal.sysId
select new {protectedSys.KSFDesc, protectedSys.Description, protectedVal.MaxChecked, protectedVal.MaxText};
// print the gratifying debug results
foreach(var protectedItem in joined)
{
System.Diagnostics.Debug.WriteLine(protectedItem.Description + ", " + protectedItem.KSFDesc + ", " + protectedItem.MaxText + ", " + protectedItem.MaxChecked);
}
Avoid lazy evaluation by forcing an early execution with .ToList() on one of the components of the final query. The results will go into memory so try to make sure you are choosing a small set of data and don't force an unbounded query or gigantic query into a list.