each Route contains Locations in specific order.
For example:
NY -> LA is different from LA -> NY.
I would like to write a method that gets locations array and return true or false whether route with the same locations and order exists.
I need to do it using linq to entities and entity framework (Route and Location are entities).
Here is what I wrote:
public bool IsRouteExists(IList<LocationInRoute> locationsInRoute)
{
Route route = null;
if (locationsInRoute.Count > 0)
{
var query = GetRoutesQuery().
Where(x => x.Locations.Count() == locationsInRoute.Count);
for (int i = 0; i < locationsInRoute.Count; i++)
{
long locationId = locationsInRoute[i].LocationId;
query = query.Where(x =>
x.Locations.ElementAt(i).LocationId == locationId); //THROWS EXCEPTION
}
route = query.SingleOrDefault();
}
return route!=null;
}
I get the following exception in the marked line:
Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
What is the reason for this exception?
EDIT
The exception accurs when executing route = query.SingleOrDefault(); and the exception complains about Where(x => x.Locations.ElementAt(i).LocationId == locationId);.
I believe this query is completely wrong. First of all it is not linq-to-entities query and it will never be because linq to entities is not able to work with indexes. I think comparing ordered sequences will have to be executed in memory = linq-to-objects.
Another problem is this:
for (int i = 0; i < locationsInRoute.Count; i++)
{
long locationId = locationsInRoute[i].LocationId;
query = query.Where(x => x.Locations.ElementAt(i).LocationId == locationId);
}
route = query.SingleOrDefault();
I think this is known gotcha when using Linq, query built in loop and deferred execution - I believe this always compares locationId with the last element.
In my opinion the most efficient way to do this is stored procedure with table valued parameter passing your expected sequence and using SQL cursor to compare sequences in the stored procedure.
Looks like perhaps your x.Locations.Count() might be less than your locationsInRoute.Count. are you sure it's not? I'm saying that b/c you're calling x.Locations.ElementAt(i), which will throw if i > Count().
As a sidenote, a better solution to what you're doing is to override equality or implement an IComparer on your class that you want unique and then you can use things like Any() and Contains() for your test.
If you getting an index out of range exception it must mean that number of elements in the locationsRoute collection exceeds the number of elements in IQueryable. If you attempting to test that each location in the provided list is contained in route you should be able to do something like:
var locationIds = locationsInRoute.Select(l => l.LocationId);
query = query.Where(r => r.Locations.All(l => locationIds.Contains(l.LocationId)))
I'm guessing it has to do with your use of ElementAt, which can't be translated to SQL (see the Operators with No Translation section), to operate on your IQueryable. This materializes the IQueryable's result set on the first iteration and so subsequent iterations Route items will be unable to access their related Locations sets. This should probably only happen on the second iteration, but the myriad implications of the deferred execution nature of LINQ is not entirely clear to me in ever case ;-) HTH
You could put a breakpoint at SingleOrDefault and inspect the SQL statement it is executing there, to see why there is no record returned for the SingleOrDefault to find. Though the SQL may be pretty ugly depending on how many routes you have.
Thanks to #Ladislav Mrnka's advice, here is the solution:
public class LocationSequenceEqual : IEqualityComparer<Location>
{
public bool Equals(Location x, Location y)
{
return x.Id == y.Id;
}
public int GetHashCode(Location obj)
{
return obj.Id.GetHashCode();
}
}
public bool IsRouteExists(IList<LocationInRoute> locationsInRoute)
{
Route route = null;
if (locationsInRoute.Count > 0)
{
var query = GetRoutesQuery().
Where(x => x.Locations.Count() == locationsInRoute.Count);
query = query.Where(x => x.Locations.OrderBy(l => l.Order).
Select(l => l.Location).SequenceEqual(locations, new LocationSequenceEqual()));
route = query.FirstOrDefault();
}
return route!=null;
}
If Location has Order as you indicate above, this can be done entirely in (Linq to) SQL:
public bool IsRouteExists(IList<LocationInRoute> locationsInRoute)
{
Route route = null;
if (locationsInRoute.Count == 0)
return;
var possibleRoutes = GetRoutesQuery().
Where(x => x.Locations.Count() == locationsInRoute.Count);
var db = GetDataContext(); //get a ref to the DataContext or pass it in to this function
for (var i = 0; i < locationsInRoute.Length; i++)
{
var lcoationInRoute = locationsInRoute[i];
possibleRoutes = possibleRoutes.Where(x => x.Locations.Any(l => l.Id == locationInRoute.Id && l.Order == locationInRoute.Order));
}
route = possibleRoutes.FirstOrDefault();
return route!=null;
}
Related
I wanna find the next ID (ID_Titel) by selecting ID_Artiest. I try it by using LINQ (lambda-query). What do I do wrong.
By example:
For ID_Artiest 2, I wanna have ID_Titel n+1.
First I try it without .DefaultIfEmpty(). and then I get a message: Sequence Contains No Element
Second I try it with .DefaultIfEmpty().: And then I get the message: Object reference not set to an instance of an object.
This is the source:
private void UpdateTitel(NoteringDataType itemDezeWeek)
...
...
TitelDataType titel = new TitelDataType();
if (Titelslijst.Count > 0)
titel.ID_Titel = Titelslijst.Where(t => t.ID_Artiest == itemDezeWeek.ID_Artiest).OrderBy(t => t.ID_Titel).DefaultIfEmpty().Max(t => t.ID_Titel) + 1;
else
titel.ID_Titel = 1;
Both of the errors you got are expected if the first Where doesn't find any matching values.
Please try this:
titel.ID_Titel = Titelslijst.Where(t => t.ID_Artiest == itemDezeWeek.ID_Artiest)
.Select(t => t.ID_Titel)
.OrderByDescending(t => t)
.FirstOrDefault() + 1;
Since the Select transforms the collection to an enumeration of ints (I am assuming), the .FirstOrDefault() should return 0 if the Where() didn't return any matches. In your code, .DefaultIfEmpty() would have returned an IEnumerable<T> containing null because it was called on an enumeration of whatever Titelslijst contains.
Apparently the errors you see happen when nothing in the list matches your where condition. DefaultIfEmpty in this case will give you just a single list with null, which does not help a lot.
To avoid such situations you should really assign ID to 1 if there no entries found. So the logic should be like:
TitelDataType titel = new TitelDataType();
int id = 1;
if (Titelslijst.Count > 0)
{
var titles = Titelslijst.Where(t => t.ID_Artiest == itemDezeWeek.ID_Artiest);
if (titles.Any())
id = titles.Max(t => t.ID_Titel) + 1;
}
titel.ID_Titel = id;
More short, more right:
Titelslijst.Where(t => t.ID_Artiest == itemDezeWeek.ID_Artiest).Select(t => t.ID_Artiest).Max();
I have code:
if (request.OrderBy != "PricesCount")
query = query.ApplyOrder(request);
else
{
if (request.OrderDirection == "ASC")
{
query = query.ToList().OrderBy(p => p.Prices.Count).AsQueryable(); //must be optimize!
}
else
query = query.ToList().OrderByDescending(p => p.Prices.Count).AsQueryable(); //must be optimize!
}
query = query.Page(pageNumber, pageSize);
var result = query.ToList();
query has type NHibernate.Linq.NhQueryable<Book>
I must remove the ToList() which causes loading all Books from DB.
If I try to use some code:
query = query.OrderBy(p => p.Prices.Count);
...
var result = query.ToList();//I have Antlr.Runtime.NoViableAltException
Exception of type 'Antlr.Runtime.NoViableAltException' was thrown. [.Take[Book](.Skip[Book](.OrderBy[Book,System.Int32](NHibernate.Linq.NhQueryable`1[Book], Quote((p, ) => (p.Prices.Count)), ), p1, ), p2, )]
result = query.Where(p=>p.Price > 5).ToList(); //put whatever filter you want
You don't need to do .ToList().AsQueryable().ToList() like you are in your first segment.
If you can't filter results, then you should implement some sort of paging:
result = query.Skip(x).Take(y).ToList(); //You will need to send in X and Y based on what page you are on and how many items per page you use
result = query.Where(p=>p.Price>5).OrderBy(p=>p.Prices.Count).ToList()
Like I said in comments, if you don't provide a where clause, or if you don't do .Take(y) then this will return all items in the database. You will pass in X and Y yourself if you do .Skip(x).Take(y), you need to determine what is appropriate paging for your application.
I have a piece of code that's performing badly, and need to rewite it to introduce a proper where clause before starting the .ToList however, that's where I'm getting stuck.
Currently the code looks lke this (roughly, I've taken some of the search criteria out to make it easier to display)
var Widgets = from b in _caspEntities.Widgets.Include("WidgetRegionLogs")
.Include("WidgetStatusLogs").Include("WidgetVoltageTests")
select b;
IEnumerable<Widget> results = Widgets.ToList();
if (comboBoxRegion.SelectedValue.ToString() != "0")
{
results = from b in results
where b.CurrentRegionLog != null && b.CurrentRegionLog.RegionId == int.Parse(comboBoxRegion.SelectedValue.ToString())
select b;
}
if (comboBoxStatus.SelectedValue != null)
{
results = from b in results
where b.CurrentStatusLog != null && b.CurrentStatusLog.StatusId == comboBoxStatus.SelectedValue.ToString()
select b;
}
if (txtCode.Text.Trim().Length > 0)
{
results = from b in results
where b.CodeNumber == txtCode.Text.Trim()
select b;
}
dataGridViewWidget.DataSource = results.ToList();
I can write the SQL easily enough, essentially the model is simple, I have a Widget it has a RegionLog and a StatusLog, both of which store a history. The current region and status are retrieved from this by grouping by WidgetID and selecting the most recent Date Updated (and then going off to Region and Status tables to get the actual value).
So, I need to translate this into LINQ, but to be honest I don't have a clue but am ken and willing to learn. In my head, I think I need to add some better where clauses, and then do the Widget.toList after I have applied the where clauses. I'm struggling with the CurrentRegionLog and CurrentStatusLog concepts as they are not populated until I run the IEnumerable.
If anyone can give some pointers, I'd be grateful,
Thanks
Edit - Added
public BatteryRegionLog CurrentRegionLog
{
get { return _currentRegionLog; }
}
private BatteryRegionLog _currentRegionLog
{
get
{
if (this.BatteryRegionLogs.Count > 0)
{
BatteryRegionLog log = this.BatteryRegionLogs.OrderByDescending(item => item.LastModifiedDate).First();
return log;
}
else
{
return null;
}
}
}
You can compose the query like this:
if (comboBoxRegion.SelectedValue.ToString() != "0")
{
var id = int.Parse(comboBoxRegion.SelectedValue.ToString()
Widgets = from b in Widgets
let currentRegionLog =
b.BatteryRegionLogs
.OrderByDescending(item => item.LastModifiedDate)
.FirstOrDefault()
where currentRegionLog.RegionId == id)
select b;
}
... // Same for the other criteria.
dataGridViewWidget.DataSource = Widgets.ToList();
The whole query is not executed before you do ToList(). As everything is translated to SQL you don't need the null check b.CurrentRegionLog != null. SQL will evaluate b.CurrentRegionLog.RegionId == id just fine when there is no CurrentRegionLog.
Edit
Since CurrentRegionLog is a calculated property of your Widget class it cannot be translated into SQL. I made an effort to incorporate the code of calculated property into the query in a way that only the basic navigation property is used, so EF can translate it to SQL again.
try remove this line:
IEnumerable<Widget> results = Widgets.ToList();
and just use the Widgets variable you get in at the top
The .ToList() goes to the database and materialiaze all the data into entities.
if you don't call the .ToList() the query is still "open" for a where clause
Here is some sample code I have basically written thousands of times in my life:
// find bestest thingy
Thing bestThing;
float bestGoodness = FLOAT_MIN;
foreach( Thing x in arrayOfThings )
{
float goodness = somefunction( x.property, localvariable );
if( goodness > bestGoodness )
{
bestGoodness = goodness;
bestThing = x;
}
}
return bestThing;
And it seems to me C# should already have something that does this in just a line. Something like:
return arrayOfThings.Max( delegate(x)
{ return somefunction( x.property, localvariable ); });
But that doesn't return the thing (or an index to the thing, which would be fine), that returns the goodness-of-fit value.
So maybe something like:
var sortedByGoodness = from x in arrayOfThings
orderby somefunction( x.property, localvariable ) ascending
select x;
return x.first;
But that's doing a whole sort of the entire array and could be too slow.
Does this exist?
This is what you can do using System.Linq:
var value = arrayOfThings
.OrderByDescending(x => somefunction(x.property, localvariable))
.First();
If the array can be empty, use .FirstOrDefault(); to avoid exceptions.
You really don't know how this is implemented internally, so you can't assure this will sort the whole array to get the first element. For example, if it was linq to sql, the server would receive a query including the sort and the condition. It wouldn't get the array, then sort it, then get the first element.
In fact, until you don't call First, the first part of the query isn't evaluated. I mean this isn't a two steps evaluation, but a one step evaluation.
var sortedValues =arrayOfThings
.OrderByDescending(x => somefunction(x.property, localvariable));
// values isn't still evaluated
var value = sortedvalues.First();
// the whole expression is evaluated at this point.
I don't think this is possible in standard LINQ without sorting the enuermable (which is slow in the general case), but you can use the MaxBy() method from the MoreLinq library to achieve this. I always include this library in my projects as it is so useful.
http://code.google.com/p/morelinq/source/browse/trunk/MoreLinq/MaxBy.cs
(The code actually looks very similar to what you have, but generalized.)
I would implement IComparable<Thing> and just use arrayOfThings.Max().
Example here:
http://msdn.microsoft.com/en-us/library/bb347632.aspx
I think this is the cleanest approach and IComparable may be of use in other places.
UPDATE
There is also an overloaded Max method that takes a projection function, so you can provide different logic for obtaining height, age, etc.
http://msdn.microsoft.com/en-us/library/bb534962.aspx
I followed the link Porges listed in the comment, How to use LINQ to select object with minimum or maximum property value and ran the following code in LINQPad and verified that both LINQ expressions returned the correct answers.
void Main()
{
var things = new Thing [] {
new Thing { Value = 100 },
new Thing { Value = 22 },
new Thing { Value = 10 },
new Thing { Value = 303 },
new Thing { Value = 223}
};
var query1 = (from t in things
orderby GetGoodness(t) descending
select t).First();
var query2 = things.Aggregate((curMax, x) =>
(curMax == null || (GetGoodness(x) > GetGoodness(curMax)) ? x : curMax));
}
int GetGoodness(Thing thing)
{
return thing.Value * 2;
}
public class Thing
{
public int Value {get; set;}
}
Result from LinqPad
The following LINQ statement:
public override List<Item> SearchListWithSearchPhrase(string searchPhrase)
{
List<string> searchTerms = StringHelpers.GetSearchTerms(searchPhrase);
using (var db = Datasource.GetContext())
{
return (from t in db.Tasks
where searchTerms.All(term =>
t.Title.ToUpper().Contains(term.ToUpper()) &&
t.Description.ToUpper().Contains(term.ToUpper()))
select t).Cast<Item>().ToList();
}
}
gives me this error:
System.NotSupportedException: Local
sequence cannot be used in LINQ to SQL
implementation of query operators
except the Contains() operator.
Looking around it seems my only option is to get all my items first into a generic List, then do a LINQ query on that.
Or is there a clever way to rephrase the above LINQ-to-SQL statement to avoid the error?
ANSWER:
Thanks Randy, your idea helped me to build the following solution. It is not elegant but it solves the problem and since this will be code generated, I can handle up to e.g. 20 search terms without any extra work:
public override List<Item> SearchListWithSearchPhrase(string searchPhrase)
{
List<string> searchTerms = StringHelpers.GetSearchTerms(searchPhrase);
using (var db = Datasource.GetContext())
{
switch (searchTerms.Count())
{
case 1:
return (db.Tasks
.Where(t =>
t.Title.Contains(searchTerms[0])
|| t.Description.Contains(searchTerms[0])
)
.Select(t => t)).Cast<Item>().ToList();
case 2:
return (db.Tasks
.Where(t =>
(t.Title.Contains(searchTerms[0])
|| t.Description.Contains(searchTerms[0]))
&&
(t.Title.Contains(searchTerms[1])
|| t.Description.Contains(searchTerms[1]))
)
.Select(t => t)).Cast<Item>().ToList();
case 3:
return (db.Tasks
.Where(t =>
(t.Title.Contains(searchTerms[0])
|| t.Description.Contains(searchTerms[0]))
&&
(t.Title.Contains(searchTerms[1])
|| t.Description.Contains(searchTerms[1]))
&&
(t.Title.Contains(searchTerms[2])
|| t.Description.Contains(searchTerms[2]))
)
.Select(t => t)).Cast<Item>().ToList();
default:
return null;
}
}
}
Ed, I've run into a similiar situation. The code is below. The important line of code is where I set the memberList variable. See if this fits your situation. Sorry if the formatting didn't come out to well.
Randy
// Get all the members that have an ActiveDirectorySecurityId matching one in the list.
IEnumerable<Member> members = database.Members
.Where(member => activeDirectoryIds.Contains(member.ActiveDirectorySecurityId))
.Select(member => member);
// This is necessary to avoid getting a "Queries with local collections are not supported"
//error in the next query.
memberList = members.ToList<Member>();
// Now get all the roles associated with the members retrieved in the first step.
IEnumerable<Role> roles = from i in database.MemberRoles
where memberList.Contains(i.Member)
select i.Role;
Since you cannot join local sequence with linq table, the only way to translate the above query into SQL woluld be to create WHERE clause with as many LIKE conditions as there are elements in searchTerms list (concatenated with AND operators). Apparently linq doesn't do that automatically and throws an expception instead.
But it can be done manually by iterating through the sequence:
public override List<Item> SearchListWithSearchPhrase(string searchPhrase)
{
List<string> searchTerms = StringHelpers.GetSearchTerms(searchPhrase);
using (var db = Datasource.GetContext())
{
IQueryable<Task> taskQuery = db.Tasks.AsQueryable();
foreach(var term in searchTerms)
{
taskQuery = taskQuery.Where(t=>t.Title.ToUpper().Contains(term.ToUpper()) && t.Description.ToUpper().Contains(term.ToUpper()))
}
return taskQuery.ToList();
}
}
Mind that the query is still executed by DBMS as a SQL statement. The only drawback is that searchTerms list shouldn't be to long - otherwise the produced SQL statement won'tbe efficient.