All Questions
709
questions
64
votes
11
answers
109k
views
Get List<> element position in c# using LINQ
I have a List with numbers,
and I'd like to find the position of the minimum (not value) using LINQ
Example:
var lst = new List<int>() { 3, 1, 0, 5 };
Now I am looking for a function returning ...
newUser
61
votes
9
answers
70k
views
You must add a reference to assembly mscorlib, version=4.0.0
I'm having some trouble migrating a web project from RC1 to RC2. When I switched, I'm getting a bunch of these errors throughout the project.
The type 'Func<,>' is defined in an assembly that is ...
- 2,639
34
votes
3
answers
120k
views
The LINQ expression could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation
I have C# application (.NET Core 3.1) and I have written the following LINQ expression.
public ActionResult<bool> GetItems(string title)
{
var items = _service.All.GetItems()....
- 575
25
votes
1
answer
24k
views
Entity Framework Core: many-to-many relationship with same entity
I am trying to map many-to-many relationship with the same entity. The User entity has an IList<User> data field for Contacts, which stores users' contacts/friends information:
public class ...
- 3,317
25
votes
2
answers
28k
views
How to perform a group join in .NET Core 3.0 Entity Framework?
With the changes to .NET Core 3.0 I am getting
... NavigationExpandingExpressionVisitor' failed. This may indicate
either a bug or a limitation in EF Core. See
https://go.microsoft.com/fwlink/?...
- 2,137
19
votes
2
answers
7k
views
EF Core queries all columns in SQL when mapping to object in Select
While trying to organize some data access code using EF Core I noticed that the generated queries were worse than before, they now queried columns that were not needed. The basic query is just ...
- 18.4k
18
votes
3
answers
6k
views
Nice examples of using .NET 4 dynamic keyword with Linq?
So I Just got a recommendation from Amazon for LINQ to Objects Using C# 4.0: Using and Extending LINQ to Objects and Parallel LINQ (PLINQ).
It says that the book introduces using the dynamic keyword ...
- 7,027
16
votes
2
answers
19k
views
Include / ThenInclude with where in EF Core [duplicate]
I need to use where in ThenInclude
var templatesFields = await _context.Sections
.Include(x => x.Subtitles)
.ThenInclude(r => r.Fields.Where(t=>t.TemplatesFields.TemplateID==TemplateID))
....
- 183
15
votes
2
answers
1k
views
Does "where" position in LINQ query matter when joining in-memory?
Situation: Say we are executing a LINQ query that joins two in-memory lists (so no DbSets or SQL-query generation involved) and this query also has a where clause. This where only filters on ...
- 14.8k
13
votes
5
answers
15k
views
Union with EF Core returns unable to translate set operation since both operands have different 'Include' operations
In a .NET Core 5 WebAPI project with EF Core 5, I'm trying to do a union on a LINQ query but I always get an error "unable to translate". The two entities I'm trying to concatenate are the ...
- 4,963
13
votes
2
answers
13k
views
Use LinqKit PredicateBuilder for related model (EF Core)
I want to use LinqKit's PredicateBuilder and pass the predicate into .Any method for related model.
So I want to build a predicate:
var castCondition = PredicateBuilder.New<CastInfo>(true);
...
- 3,149
10
votes
4
answers
8k
views
Linq WHERE EF.Functions.Like - Why direct properties work and reflection does not?
I try to perform a simple LIKE action on the database site, while having query building services based on generic types. I found out while debugging however, that performing EF.Functions.Like() with ...
- 391
9
votes
4
answers
14k
views
ToAsyncEnumerable().Single() vs SingleAsync()
I'm constructing and executing my queries in a way that's independent of EF-Core, so I'm relying on IQueryable<T> to obtain the required level of abstraction. I'm replacing awaited SingleAsync()...
- 4,508
9
votes
3
answers
4k
views
How to group by week in Entity Framework Core?
In Entity Framework 6 I can use SqlFunctions.DatePart() method:
var byWeek = data.GroupBy(x => SqlFunctions.DatePart("week", x.Date));
But these classes (DbFunctions and SqlFunctions are not ...
- 16.7k
8
votes
2
answers
2k
views
Why is LastOrDefault(predicate) in LINQ faster than FirstOrDefault(predicate)
Introduction
While testing performance differences with certain LinQ functions today, I noticed, that LastOrDefault(predicate) was almost always faster than FirstOrDefault(predicate), which got me a ...
- 559
8
votes
1
answer
975
views
What does IPartition do in .NET Core?
I had a look at the .NET Core source in order to find out whether calls to IEnumerable.Last() (LINQ) are optimized when the collection implements IList which I suspected to be the case after some ...
user2037593
7
votes
1
answer
228
views
Why am I seeing a difference between.Cast<int>() and .Select(a => (int)a)?
I'm trying to work out the difference between the following:
someListOfEnums.Cast<int>()
and
someListOfEnums.Select(a => (int)a)?
I have found that the former causes an exception when ...
- 4,132
7
votes
1
answer
6k
views
LINQ expression is not being translated to SQL
I'm trying to achieve a compiled SQL query from LINQ which will check if query is substring of any of three columns in database (case insensitive).
I'm using .NET Core 1.1
Query that I come up with ...
- 1,290
7
votes
1
answer
3k
views
EF Core Include On Collection Class Property [duplicate]
I keep getting errors like
: The property expression 'met => {from TrM x in met select [x].Tm}' is not valid. The expression should represent a property access: 't => t.MyProperty'.
I have a ...
- 3,780
6
votes
1
answer
27k
views
How can I implement a LEFT OUTER JOIN in LINQ using lambda syntax on Entity Framework Core 2.0?
I am trying to implement a LEFT OUTER JOIN in Linq against an Entity Framework Core 2.0 DbContext. It's important that the query is translated to SQL, rather than evaluated locally. I've reviewed ...
- 5,835
6
votes
1
answer
12k
views
Can Entity Framework (LINQ) select rows based on JSON where clause?
I have a column in a SQL database table of JSON data. Can I use Entity Framework and LINQ to query and filter based on a field/value in the SQL JSON column?
I am using SQL 2016, VS 2017, EF Core 2.0, ...
- 2,418
6
votes
3
answers
17k
views
Null reference exception being thrown in EF LINQ query if-clause
I couldn't find the exact words to explain what's happening, so if this is a duplicated question, I apologize.
I tried to do a quite simple AND condition if-clause inside a LINQ Query, in order to ...
- 411
6
votes
1
answer
789
views
Visual Studio assumes return value from FirstOrDefaultAsync() cannot be null
I have the following query.
var railcarInfo = await (from rt in DbContext.RailcarTrips
where rt.WaybillRailcar.RailcarNumber == clm.RailcarNumber &&
...
- 65.9k
6
votes
3
answers
1k
views
How to translate TimeSpan calculations to SQL via LINQ
I'm having an entity with a TimeSpan property (Start) and an int (Duration in minutes) property.
I want to perform a linq query that will fetch all the rows that apply to the following logic:
Start &...
- 69
5
votes
3
answers
15k
views
Return async task using LINQ select
I want to implement function that return list of child items from database asynchronously. So I write a function:
public async Task<IEnumerable<object>> GetFiles(int parentId)
{
...
- 12k
5
votes
1
answer
10k
views
Entity Framework Core linq query returns InvalidCastException
I am currently creating a web api in .net CORE with Entity Framework.
Whenever I try to select a single record by ID with linq, I get the following error:
An exception of type 'System....
- 2,424
5
votes
2
answers
1k
views
C#/LINQ Taking Sum of Decimals show different results
I have a list of objects that I am attempting to take sum of after multiple 3 of the fields by each other. The problem is that the final result is NOT matching when I run the calculation by the ...
- 1,050
5
votes
2
answers
362
views
Is the IEnumerable.OrderBy().First() optimisation in .Net Core 3.1 documented anywhere?
One of the .Net Core versions (I'm not sure which) introduced an optimisation such that if you write code like this:
int smallest = new[]{ 7, 2, 4, 6, 0, 1, 6, 9, 8 }.OrderBy(i => i).First();
then ...
- 107k
5
votes
1
answer
824
views
How to map complex linq to object
Looking for a some help with Ef Core and Linq.
Lets say I'm making big request to receive all support tickets with info about product, company, and so on. It's quite simple, just joining things:
...
- 679
4
votes
2
answers
18k
views
How to get all items of container in cosmos db with dotnet core
Hi I would like to get all items of a container in a database in cosmos DB. I can see that there are already a lot of methods available but I don't see any getAllItems or a lookalike.
Is there an ...
- 45
4
votes
2
answers
9k
views
DotNet Core , No database provider has been configured for this DbContext
I want to select data from my table "Header" using a simple LINQ command but I faced error.
My Action
public HeaderModel GetHeaderInformation()
{
using(var context = new ...
- 1,768
4
votes
1
answer
1k
views
Reflection .NET Core Create Lambda Expression
I'm trying to create a lambda expression (using Reflection) which looks like this
IServiceProvider provider => provider.GetService<TDbContext>()
Or, to be more specific, as GetService is an ...
- 431
4
votes
2
answers
2k
views
Entity Framework LINQ complex query - combine multiple predicates
I'm trying to create a complex Linq query that goes like this:
Get all organisations which have employees that match the given filter parameters.
Example filter:
Firstname: John
Name: Smith
My first ...
- 71
4
votes
1
answer
5k
views
EF Core Decryption of SQL Column Level Encryption
My team and I are attempting to decrypt values from a db (Azure SQL) that has column level encryption turned on; with certs stored in key vault.
Expected Result:
var someLinqQuery = _contex.Users....
4
votes
2
answers
86
views
How to order by 1 expression or 2 expressions based on a condition?
I am displaying businesses and people in a single result and would like to order them together.
Pseudocode:
if business name is not null
order by business name
else
order by first name then last ...
- 8,019
4
votes
1
answer
2k
views
Client projection contains reference to constant expression of through instance method
I am getting this error on my LINQ Code
Client projection contains reference to constant expression of through instance method
This could potentially cause memory leak. Consider making the method ...
- 347
4
votes
1
answer
214
views
Unexpected behavior of LINQ Except()
I have encountered a strange bahavior of LINQ Except method which I don't understand. I can totally rewrite my code differently so that it works, that is not my problem. I just want to understand why ...
- 3,201
4
votes
2
answers
906
views
EF Core: LINQ Select "many-to-many-to-many" to "many-to-many"
I do have a table "Reference" and a table "Article" where a article references other articles.
I do have simple references like:
A -> B
SQL:
select ab.*
from Article a
inner join Reference ab on ab....
- 475
4
votes
2
answers
7k
views
.NET Core 3.1 and Could not load file or assembly System.Data.Entity, Version=4.0.0.0
What Nuget package is System.Data.Entity in?
I am converting a .NET Framework 4.5 app to .NET Core 3.1. In .NET Framework, it is using System.Linq.Dynamic, and the app is crashing when running this ...
- 3,417
4
votes
1
answer
4k
views
Does .Net Core 2.1 Support LINQ and Lambda Expressions?
I have tried the following code on Visual Studio Code with OmniSharp extension has been installed. I installed .Net core 2.1.3.
List<MyType> listName = dataTableName.AsEnumerable().Select(m =&...
- 197
4
votes
1
answer
663
views
Accessing transparent identifier in select throws it is not referenced from scope
Accessing transparent identifier in select throwing exception.
var result = (from t1 in table1
join t2 in table2 on t1.col1 equals t2.col1 into myTable1
from a in myTable1....
- 249
4
votes
4
answers
1k
views
Comparing sql with c# list in query?
I have a problem with comparing a value in my sql database with a list of object in my code.
The object does not exist in DB
Example of an object in the list:
{
public long CompareId
public ...
- 622
4
votes
0
answers
465
views
EF Core define query using list instead of dbset in dbcontext
In EF Core using the modelBuilder a query can be defined for keyless entities like this:
modelBuilder.Entity<UrlResource>()
.ToInMemoryQuery(() => context.Blogs.Select(b => new ...
- 251
4
votes
0
answers
2k
views
Entity Framework Core `HasConversion` property configuration not used when querying data with postgresql
I am using Entity Framework with Postgre through Npgsql, part of my configuration for the Cashout type which maps to the Cashouts table involves:
public void Configure(EntityTypeBuilder<Cashout>...
- 8,533
4
votes
0
answers
561
views
InvalidCastException in MySqlConnector while Math.Round inside LINQ-to-Entities
I have a question that I can not answer myself for now. The problem arose in the real scenario, but I simplified it for the question. I just wanted to make the rounding inside Select in LINQ. Perhaps ...
- 53
4
votes
1
answer
3k
views
ToListAsync throws 'Value cannot be null.' Exception
Having IQueryable
var query = _db
.ApplicationPaidServices
.Include(it => it.Application)
.Include(it => it.Application.User)
.Where(it => Enum1.Value1 == it.Application....
- 8,190
3
votes
3
answers
9k
views
How to create a dummy database for functional tests in .NET Core?
My app is built on .NET Core with Entity Framework 6. There are some complex C# LINQ queries that I am making against the db context. While I have XUnit unit tests that mock up the db and check the ...
- 6,546
3
votes
1
answer
187
views
Does Microsoft recommend method or query syntax? [closed]
Does Microsoft Net Core 3 recommend method syntax or query syntax for Linq Entity Framework queries? This is a debate in our workplace, we are curious.
This is not Opinion based question, but fact, ...
- 109
3
votes
3
answers
105
views
select from linq statement with await
This seems like it should be very simple, I have the following code
var additionalInformation= response.AdditionalInformation.Select( async x => new AdditionalInformationItem
{
...
- 4,169
3
votes
1
answer
1k
views
.net core - combine a list of func with or to a single func
Hello i try to generate a single Func from a list combined by or.
var funcs = new List<Func<User, bool>>()
{
(u) => u.Id.Equals(entityToFind.Id),
(u) => u.UserName == ...
- 1,199