How can I make this lesser than or equal work in my .Where() clause? I am getting an error.
var filteredProducts = Products.Where(p => p.State.Contains("Bruikbaar"))
.Where(p => p.Privilege <= ui.GetPrivilegeNumber())
.ToList();
Error:
LINQ to Entities does not recognize the method 'Int32 GetPrivilegeNumber()' method, and this method cannot be translated into a store expression.
I hope this question is never asked before. Googled couldn't find it either or I am using the wrong words to express my problem.
ui.GetPrivilegeNumber() is not a recognized method.
Use this:
var uiPrivilege = ui.GetPrivilegeNumber();
var filteredProducts = Products.Where(p => p.State.Contains("Bruikbaar"))
.Where(p => p.Privilege <= uiPrivilege)
.ToList();
And as other users mentionted, you can optimize your Where.
EF does not execute method calls which you use in predicates. It stores them as expression (i.e. syntax tree) and then analyzes this tree to build SQL query by translating C# code to SQL code. It cannot translate GetPrivilegeNumber() method call into SQL, because there is no appropriate SQL code for that. So all you need is move this method call out of expression and pass only result of method call instead:
var privilegeNumber = ui.GetPrivilegeNumber();
var filteredProducts = Products.Where(p => p.State.Contains("Bruikbaar"))
.Where(p => p.Privilege <= privilegeNumber)
.ToList();
Now privilegeNumber is just an integer variable which is translated into SQL parameter
SELECT * FROM Products p
WHERE p.State LIKE '%Bruikbaar%' AND p.Privilege <= #privilegeNumber
You need to move ui.GetPrivilegeNumber() outside of the query. You can also merge those Where queries into a single one:
var privilegeNumber = ui.GetPrivilegeNumber();
var filteredProducts = Products.Where(p =>
p.State.Contains("Bruikbaar")
&& p => p.Privilege <= privilegeNumber)
.ToList();
You can use other evaluation method inside LinQ. To simplified the code, you can use it in little old way of writing LinQ.
var uiPrivilege = ui.GetPrivilegeNumber();
var filteredProducts =(from p in Products
where p.State.Contains("Bruikbaar") && p.Privilege <= uiPrivilege
select p).ToList();
The above query generate same output but easy to understood.
Related
I have a rather complex condition for my WHERE query in the database. If I were to use straight SQL I probably would put that part of the SQL query into a named variable to signify its semantic purpose.
If I were to use straight Linq I would use a function-call that matches the Where() predicate where the function name would tell me the purpose of the filter.
Unfortunately one can't seem to use sub-functions in Linq to SQL because then the query cannot be resolvd to SQL.
Is there a way to achieve this?
Here is the original Linq-to-SQL query:
query = query.Where(
f => f.Table1.Any(
t1 =>
(t1.Table2.Any(t2 => t2.Header == Decoder.Identifier
&& DbFunctions.Like(t2.Content, pattern)))
||
(!t1.Table2.Any(t2 => t2.Header == Decoder.Identifier)
&& DbFunctions.Like(t1.Text, pattern))
));
What I would like is something like this:
query = query.Where(
f => f.Table1.Any(
t1 =>
HasCondition1(t1, pattern)
||
HasCondition2(t1, pattern)
));
How to get Session["UserId"] value in Linq Query
var result = (from c in db.UserMaster
where c.UserID == Session["vUSerID"].ToString()
select C ).ToList();
but when i execute it gives me error as follows
LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression.
Please guide me how to works with ToString()
You need to materialize the value before you send it off to be translated to SQL:
var userId = Session["vUSerID"].ToString();
var result = (from c in db.UserMaster
where c.UserID == userId
select C ).ToList();
Alternatively, you could try bringing entity into memory first, and then apply the condition to get the filtered result, although not recommended because of the potential performance issue.
var result = db.UserMaster.Select(x => x).ToList().Where(x => x.UserId == Session["vUSerID"].ToString()).ToList();
I have a StudentReceipts table which stores ReceiptNo as string(001,002,003,..,099,..).
I want go get the last receiptno details inorder to increment the receiptno for next transaction.
This is what I have tried
var _lastGeneratedRecDetails = _db.StudentReceipts
.AsEnumerable()
.Where(r => r.Status == true
&& EntityFunctions.TruncateTime(r.DueDate.Value) >= _startDate.Date
&& EntityFunctions.TruncateTime(r.DueDate.Value) <= _endDate.Date)
.OrderByDescending(x => Int32.Parse(x.ReceiptNo))
.FirstOrDefault();
But there i am getting the following exception
this function can only be invoked from linq to entities
Any help will be highly appreciated.
By calling .AsEnumerable() you are going from Linq-To-Entities to Linq-To-Object. By calling it, you are also filtering all the results in memory, so you are pulling the whole StudentReceipts table from the database everytime you do that query as it gets executed past the .AsEnumerable() method. The general rule is to try to do as much as you can on the database side:
var _lastGeneratedRecDetails =
_db.StudentReceipts.Where(r => r.Status == true
&& EntityFunctions.TruncateTime(r.DueDate.Value) >= _startDate.Date
&& EntityFunctions.TruncateTime(r.DueDate.Value) <= _endDate.Date)
.AsEnumerable()
.OrderByDescending(x => Int32.Parse(x.ReceiptNo))
.FirstOrDefault();
If you do it like this, you will filter everything in the database and fetch the filtered results. I don't know what type x.ReceiptNo is though, but calling Int.Parse isn't allowed in Linq-To-Entities. You can filter first and then call AsEnumerable to be able to do the parsing and ordering in memory.
In my case, I was re-using a Func / Filter expression that included DbFunctions.TruncateTime in a follow-up processing statement AFTER I had already processed the query in SQL. Removing it cleared the instance of the exception for me.
use and
.AsQueryable()
var _lastGeneratedRecDetails = _db.StudentReceipts
.AsEnumerable().AsQueryable()
I am relatively new to Entity Framework 6.0 and I have come across a situation where I want to execute a query in my C# app that would be similar to this SQL Query:
select * from periods where id in (select distinct periodid from ratedetails where rateid = 3)
Is it actually possible to execute a query like this in EF or would I need to break it into smaller steps?
Assuming that you have in your Context class:
DbSet<Period> Periods...
DbSet<RateDetail> RateDetails...
You could use some Linq like this:
var distincts = dbContext.RateDetails
.Where(i => i.rateId == 3)
.Select(i => i.PeriodId)
.Distinct();
var result = dbContext.Periods
.Where(i => i.Id)
.Any(j => distincts.Contains(j.Id));
Edit: Depending on your entities, you will probably need a custom Comparer for Distinct(). You can find a tutorial here, and also here
or use some more Linq magic to split the results.
Yes, this can be done but you should really provide a better example for your query. You are already providing a bad starting point there. Lets use this one:
SELECT value1, value2, commonValue
FROM table1
WHERE EXISTS (
SELECT 1
FROM table2
WHERE table1.commonValue = table2.commonValue
// include some more filters here on table2
)
First, its almost always better to use EXISTS instead of IN.
Now to turn this into a Lambda would be something like this, again you provided no objects or object graph so I will just make something up.
DbContext myContext = this.getContext();
var myResults = myContext.DbSet<Type1>().Where(x => myContext.DbSet<Type2>().Any(y => y.commonValue == x.commonValue)).Select(x => x);
EDIT - updated after you provided the new sql statement
Using your example objects this would produce the best result. Again, this is more efficient than a Contains which translates to an IN clause.
Sql you really want:
SELECT *
FROM periods
WHERE EXISTS (SELECT 1 FROM ratedetails WHERE rateid = 3 AND periods.id = ratedetails.periodid)
The Lamda statement you are after
DbContext myContext = this.getContext();
var myResults = myContext.DbSet<Periods>()
.Where(x => myContext.DbSet<RateDetails>().Any(y => y.periodid == x.id && y.rateid == 3))
.Select(x => x);
Here is a good starting point for learning about lamda's and how to use them.
Lambda Expressions (C# Programming Guide).
this is your second where clause in your query
var priodidList=ratedetails.where(x=>x.rateid ==3).DistinctBy(x=>x.rateid);
now for first part of query
var selected = periods.Where(p => p.id
.Any(a => priodidList.Contains(a.periodid ))
.ToList();
Hi I am using a linq query which is throwing the error LINQ to Entities does not recognize the method 'System.String ToString(Int32)' method, and this method cannot be translated into a store expression.
List<string> resultMap = (from item in mapResult
select Convert.ToString(item.ResultDE)).ToList();
Error is throwing in this below statement
List<Result_DE> resultList = (from result in db.Result_DE
where result.IsActive == "1"
&& resultMap.Contains(Convert.ToString(Convert.ToInt32(result.ID)))
select result).ToList();
please tell me the proper way of writing this query.
You cannot use these conversion functions in a LINQ to Entities statement, they cannot be translated to SQL, you need to do the conversions in memory. But I don't think you need to do that at all.
If you were just using the resultMap to get your resultList, filtered by Results of which the Id is present in mapResult, do the following:
var resultList = db.Result_DE
.Where(r => r.IsActive == "1" && mapResult.Any(mr => mr.ResultDE == r.ID));
.ToList();
If mapResult is an in-memory collection, instead of an IQueryable that is attached to the db context, you need to do the following:
var resultIds = mapResult.Select(mr => mr.ResultDE).ToList();
var resultList = db.Result_DE
.Where(r => r.IsActive == "1" && resultIds.Contains(r.ID));
.ToList();
Before you call any method (e.g. ToString()), you need to convert LINQ to Object using AsEnumerable().
if your item.ResultDE and result.ID is variable type of Int32,
why don directly create a List<Int32> ?
List<Int32> resultMap = (from item in mapResult
select item.ResultDE).ToList<Int32>();
List<Result_DE> resultList = (from result in db.Result_DE
where result.IsActive == "1"
&& resultMap.Contains(result.ID)
select result).ToList<Result_DE>();
Use SqlFunctions.StringConvert instead of Convert.ToString.
A similar question was asked and answered here