I have a LINQ query which outputs ToList it works fine other than the fact each time it's run it updates the original record instead of creating a new one.
On every run through this code the data.EventID changes so I'd like every record to appear in the list.
The code:
foreach(var data in vehicleqry)
{
bool inUK = boundryChecker.IsLongLatInUK((double)data.declatfloat, (double)data.declongfloat);
if (inUK == true)
{
var qryevent = (from e in db.events
where e.eventID == data.EventID
select new
{
e.eventID,
e.sysdatetime,
e.vehicleID
}).ToList();
}
{
I also have a list with the eventIDs in if I can use this to query the list?
I think what you actually want is to only run a single query instead of looping around. You can do this by making use of the Contains method:
var vehicleqry = ...;
// Get all of the individual event IDs for entries that are "inUK"
var vehicleEventIds = vehicleqry
.Where(ve => boundryChecker
.IsLongLatInUK((double)ve.declatfloat, (double)ve.declongfloat)
.Select(ve => ve.EventID);
// Get all the matching events
var qryevent = (from e in db.events
where vehicleEventIds.Contains(e.eventID)
select new
{
e.eventID,
e.sysdatetime,
e.vehicleID
}).ToList();
Related
I try to join two different databases tables in c# but it gives me an error how can I handle that ?
this is my query:
var list = (from h in db.database1.AsEnumerable()
join j in NV_DB.database2.AsEnumerable()
on h.Creation_Date equals j.Creation_Date
where j.Ship_Status == 3 && h.CustomerNo == CustomerNo
select new
{
shipName = h.ShipName,
creationDate = j.Creation_Date,
endingDate = j.Ending_Date
}
).ToList();
if I do like this it gives me System.OverflowException error. But when I run this in sql, it gives me just 30 records*
You need to remove °AsEnumerable`. While it does not run the sql, when you use it in the where it actually brings the entire tables in memory and then performs the job where part of your query
Your answer is basically the first comment in the accepted answer here: Am I misunderstanding LINQ to SQL .AsEnumerable()?
While AsEnumerable doesn't evaluate the query at the time that it's called , it definitely has an effect. Anything further called on the query will be evaluated using LINQ to objects, so you can't compose additional elements onto the query (another Where or an OrderBy or anything of that nature) that will become part of the SQL statement.
In depth explanation here: https://www.codeproject.com/Articles/732425/IEnumerable-Vs-IQueryable
While querying data from database, IEnumerable executes select query on server side, load data in-memory on client side and then filter data. Hence does more work and becomes slow.
While querying data from database, IQueryable executes select query on server side with all filters. Hence does less work and becomes fas
To debug this, start dividing your statements into smaller steps:
var list1 = db.database1.AsEnumerable().ToList();
var list2 = NV_DB.database2.AsEnumerable().ToList();
var joinResult = list1.Join(list2, // join list1 and list2
list1Row => list1Row.CreationDate, // from every row in list1 take the CreationDate
list2Row => list2Row.CreationDate, // from every row in list2 take the CreationDate
(list1Row, list2Row) => new // when they match, make one new object
{
// You only need the following properties:
ShipName = list1Item.ShipName,
CreationDate = list2Item.CreationDate,
EndingDate = list2Item.EndingDate,
ShipStatus = list2Item.ShipStatus,
CustomerNo = list1Item.CustomerNo,
})
.ToList();
var whereResult = joinResult
.Where(joinedRow => joinedRow.ShipStatus == 3
&& joinedRow.CustomerNo == customerNo)
.ToList();
var selectResult = whereResult.Select(whereResultRow => new
{
ShipName = whereResultRow.ShipName,
CreationDate = whereResultRow.CreationDate,
EndingDate = whereResultRow.Ending_Date,
})
.ToList();
This is executed completely as enumerable (in your local process, not by the database management system). My guess would be that this runs smoothly.
Now combine thw first few statements:
var joinResult = db.database1.AsEnumerable()
.Join(NV_DB.database2.AsEnumerable(), // join list1 and list2
list1Row => list1Row.CreationDate, // from every row in list1 take the CreationDate
list2Row => list2Row.CreationDate, // from every row in list2 take the CreationDate
(list1Row, list2Row) => new // when they match, make one new object
{
// You only need the following properties:
ShipName = list1Item.ShipName,
CreationDate = list2Item.CreationDate,
EndingDate = list2Item.EndingDate,
ShipStatus = list2Item.ShipStatus,
CustomerNo = list1Item.CustomerNo,
})
.ToList();
When this works, add the Where:
var whereResult = db.database1.AsEnumerable()
.Join(NV_DB.database2.AsEnumerable(), ...)
.Where(joinedRow => joinedRow.ShipStatus == 3
&& joinedRow.CustomerNo == customerNo)
.ToList();
Etc.
Using your debugger, you'll find the problem within a few minutes (depending on your compilation time). My guess is that it is within your join.
I am trying to link up the RestaurantId in the RestaurantReservationEventsTbl with the RestaurantID in the RestaurantTbl to display reservations that are only made for the currently logged in restaurant.
I am receiving the following error in my code operator == cannot be applied to operands of type int and iqueryable int
Here is what I am doing in my home controller
var RestaurantIDRestaurantTbl = from r in db.Restaurants select r.RestaurantID;
//var listOfRestaurantsReservations = db.RestaurantReservationEvents.ToList();
var listOfRestaurantsReservations = db.RestaurantReservationEvents.Where(x => x.RestaurantID == RestaurantIDRestaurantTbl).ToList();
//return View(restaurants.Where(x => x.RestaurantEmailAddress == UserEmail).ToList());
//create partial view called _RestaurantReservation
return PartialView("_RestaurantReservations", listOfRestaurantsReservations);
You have to change your code to materialize the restaurantIds like this:
var RestaurantIDRestaurantTbl = (from r in db.Restaurants
select r.RestaurantID).ToList();
Then you may change the code as below for the comparison to work:
var listOfRestaurantsReservations = db.RestaurantReservationEvents.Where(x => RestaurantIDRestaurantTbl.Contains(x.RestaurantID)).ToList();
Anyway this is not the best solution. I will write another example for you, just try this example if it is working or not and let me know for the result.
I would considering changing the code as below to be much more efficient:
var listOfRestaurantsReservations = (from r in db.Restaurants
join e in db.RestaurantReservationEvents
on r.RestaurantID equals e.RestaurantID
//where r.RestaurantID == something //if where condition needed
select e).ToList();
If your tables are not connected with foreignkeys please consider to read this documentation here to make a better structure of the tables since they are related to each-other.
If your tables are related as in documentation article you might have something like that:
var RestaurantIDRestaurantTbl = db.Restaurants.SingleOrDefault(x => x.RestaurantID == something);
if(RestaurantIDRestaurantTbl != null)
{
var listOfRestaurantsReservations = RestaurantIDRestaurantTbl.RestaurantReservationEvents.ToList();
}
{
// This will give you a list of IDs
var RestaurantIDRestaurantTbl = db.Restaurants
.Select(p => p.RestaurantID)
.ToList();
// Using .Any() is a better choice instead of .Contains()
// .Contains is used to check if a list contains an item while .Any will look for an item in a list with a specific ID
var listOfRestaurantsReservations = db.RestaurantReservationEvents
.Where(p => RestaurantIDRestaurantTbl.Any(r => r.pRestaurantID == p))
.ToList();
}
Have searched ant tested many examples in this forum but can't get a fully working method.
I am using linq to bulk insert a list of entity classes (RemoteReadings).
Due to unique constraints I need to filter out any items already inserted.
Uniqiuness is composed of 2 columns meterid and datetime in RemoteReadings table.
// approx 5000 records (I need to do this in batches of 2000 due to a
// constraint in L2S,but can do this after get this working)
List<RemoteReading> lst = createListFromCSV();
// Option 1:
// This does not work as am comparing memory list to db list. I need to use contains() method.
// Actually am trying to accomplish this infollowing examples.
List<RemoteReading> myLst = (from ri in db.RemoteReadings
from l in lst
where l.meterid = ri.meterid
&& l.date = r.date
select ri).ToList();
////
// Option2:
// Get the list from DB that are in memory lst
List<RemoteReading> myLst = (from ri in db.RemoteReadings
where
// where in this list by comparing meaterid and datemeaured
(from l in lst
select
/// help here !
///
select ri).ToList<RemoteInterconnectorReading>();
// Option3:
// Get the list from lst that are not in database
// I am bit confused here !
// Tried also to remove from list any duplicates:
List<RemoteReading> result = List<RemoteReading>)myLst.Except(lst).ToList<RemoteReading>();
// Ultimately
db.RemoteReading.InsertAllOnSubmit(result);
db.submitChanges();
Any help please?
Due to limitations in EF, we can't join DB query with in-memory list. Also, Contains can only be used with primitive list. So we need to make some efforts to find the duplicates on two columns.
var newItems = createListFromCSV();
var meterIds = newItems.Select(n=> n.meterid).Distinct().ToList();
var dates = newItems.Select(n=> n.date).Distinct().ToList();
var probableMatches = (from ri in db.RemoteReadings
where (meterIds.Contains(ri.meterids)
|| dates.Contains(ri.date)
select new {ri.merterid, ri.date}).ToList();
var duplicates = (from existingRi in probaleMatches
join newRi in newItems
on new {existingRi.meterid, existingRi.date}
equals {newRi.meterid, newRi.date}
select newRi).ToList();
var insertList = newItems.Except(duplicates).ToList();
db.RemoteReadings.Insert(insertList); // or whatever
With the great help of aSharma and some other tweaks, I finally got a working and tested method. As my lists contain over 5000 items I had to execute in batches to override the 2112 SQL RPC call limitation. Added some comments and credits :)
/// List<RemoteReadings> contains a list of database Entity Classes RemoteReadings
public List<RemoteReadings> removeDublicatesFirst(List<RemoteReadings> lst)
{
try
{
DataClasses1DataContext db = new DataClasses1DataContext();
var meterIds = lst.Select(n => n.meterId).Distinct().ToList();
var dates = lst.Select(n => n.mydate).Distinct().ToList();
var myfLst = new List<RemoteReadings>();
// To avoid the following SqlException, Linq query should be exceuted in batches as follows.
//{System.Data.SqlClient.SqlException
// The incoming tabular data stream (TDS) remote procedure call (RPC) protocol stream is incorrect.
// Too many parameters were provided in this RPC request. The maximum is 2100.
foreach (var batch in dates.Batch(2000))
{
// Gets a list of possible matches from DB.
var probableMatches = (from ri in db.RemoteReadingss
where (meterIds.Contains(ri.meterId)
&& batch.Contains(ri.mydate))
select new { ri.meterId, ri.mydate }).ToList();
// Join the probableMatches with the lst in memory on unique
// constraints meterid.date to find any duplicates
var duplicates = (from existingRi in probableMatches
join newRi in lst
on new
{
existingRi.meterId,
existingRi.mydate
}
equals new { newRi.meterId, newRi.mydate }
select newRi).ToList();
//Add duplicates in a new List due to batch executions.
foreach (var s in duplicates)
{
myfLst.Add(s);
}
}
// Remove the duplicates from lst found in myfLst;
var insertList = lst.Except(myfLst).ToList();
return insertList;
}
catch
(Exception ex)
{
return null;
}
}
// Found this extension Class to divide IEnumerable in batches.
// http://stackoverflow.com/a/13731854/288865
public static class MyExtensions
{
public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> items,
int maxItems)
{
return items.Select((item, inx) => new { item, inx })
.GroupBy(x => x.inx / maxItems)
.Select(g => g.Select(x => x.item));
}
}
I have the below code to return a list of strings.
public List<string> Top5CodesForToday()
{
var date = DateTime.Now;
var resultList = new List<string>();
using (var db = new PillowContext())
{
var qry = (from d in db.DownTimes
where DbFunctions.TruncateTime(d.DateTime) == DbFunctions.TruncateTime(date)
group d by new {d.Code}
into g
let total = g.Sum(x => x.Amount)
orderby total descending
let top5 = g.Take(5).ToList()
select new {g.Key.Code, Total = total});
foreach (var item in qry)
{
int x = item.Code;
var results = from r in db.DownTimeCodes
where r.Code == x
select r.Description;
resultList.Add(results.ToString());
}
}
return resultList;
}
When I look at the contents of returnList I am seeing the correct number of items however each item is made up of the actual query syntax, not the data itself. I have seen this before and usually solve it by doing .ToList() however I am unsure how I could change my code to solve this
The problem here is that when you are calling ToString the query is not executed yet, so essentially you are calling ToString on a IQueryable object, receiving the query instead of results. You need to call something to execute the query.
You can call ToList() still:
var results = (from r in db.DownTimeCodes
where r.Code == x
select r.Description).ToList();
resultList.AddRange(results);
Or, if you expect just one result, call FirstOrDefault()/SingleOrDefault():
var results = (from r in db.DownTimeCodes
where r.Code == x
select r.Description).FirstOrDefault();
resultList.Add(results);
You are calling ToString() on List<>. As default for most complex types, it just writes out type name not the data.
This line
resultList.Add(results.ToString());
should be changed to
resultList.AddRange(results);
I have a linq query that works when it I had a list of a single value now that I change to having a List that has several properties I need to change the where clause
So this works:
List<string> etchList = new List<string>();
etchList.Add("24");
var etchVect = (from vio in AddPlas
where etchList.Any(v => vio.Key.Formatted.Equals(v))
let firstOrDefault = vio.Shapes.FirstOrDefault()
where firstOrDefault != null
select new
{
EtchVectors = firstOrDefault.Formatted
}).ToList();
However I have a new hard coded list (which will represent incoming data:
List<ExcelViolations> excelViolations = new List<ExcelViolations>();
excelViolations.Add(new ExcelViolations
{
VioID = 24,
RuleType = "SPACING",
VioType = "Line-Line",
XCoordinate = 6132,
YCoordinate = 10031.46
});
So the NEW Linq query looks like this, but is obviously will not work as
AddPlas is a List and so using this other list of excelviolations, I wish to have it do where on each one of the properties in the excelviolations list
var etchVect = (from vio in AddPlas
where excelViolations.Any(vioId => vio.Key.Formatted.Equals(vioId))
let firstOrDefault = vio.Shapes.FirstOrDefault()
select new
{
EtchVectors = firstOrDefault.Formatted
}).ToList();
Now, since this is a list within a list, I would like to do something like add in each of the properties
so for example:
where excelViolations.VioID.Any(vioId => vio.Key.Formatted.Equals(vioId))
However that is not possible, but you see that I'm trying to access the property of VioID that is in the excelViolations and match it to the Key which is in vio list
Just change this line
where excelViolations.Any(vioId => vio.Key.Formatted.Equals(vioId))
to
where excelViolations.Any(excelVio => vio.Key.Formatted.Equals(excelVio.VioID))
then i thought it will works