Use AsNoTracking after you have completed all your query parameters but before you move the data into memory. In this example, you&#39;ll want:

    context.MyEntity
        .Include(i=&gt; i.Nav1)
        .Include(i=&gt; i.Nav2)
        .Where(x=&gt; x.Prop1==1)
        .AsNoTracking()
        .FirstOrDefault();

Any child objects of the parent entity will not be tracked.

I would like to use fixtures as arguments of `pytest.mark.parametrize` or something that would have the same results.

For example:

    import pytest
    import my_package
    
    @pytest.fixture
    def dir1_fixture():
        return &#39;/dir1&#39;
    
    @pytest.fixture
    def dir2_fixture():
        return &#39;/dir2&#39;

    @pytest.parametrize(&#39;dirname, expected&#39;, [(dir1_fixture, &#39;expected1&#39;), (dir2_fixture, &#39;expected2&#39;)]
    def test_directory_command(dirname, expected):
        result = my_package.directory_command(dirname)
        assert result == expected

The problem with fixture params is that every param of the fixture will get run every time it&#39;s used, but I don&#39;t want that. I want to be able to choose which fixtures will get used depending on the test.

pytest using fixtures as arguments in parametrize

I&#39;m looping over a large file that I know the length of, but am processing lazily since it&#39;s too large to fit in memory. I&#39;d like to be able to use tqdm to keep track of my progress through the file, but since it can&#39;t get the total number of examples out of the generator I&#39;m using, the only thing it shows is the estimated iterations/second. Is there any way to tell tqdm how many elements it&#39;s going to be looping over total so I can get some of the other statistics?

tqdm show progress for a generator I know the length of

I have a&#160;Linq query that fetches an entity and&#160;some of its navigation properties.

    context.MyEntity
        .AsNoTracking()
        .Include(i=&gt; i.Nav1)
        .Include(i=&gt; i.Nav2)
        .Where(x=&gt; x.Prop1==1)
        .FirstOrDefault();

my question is:

Is the above query enough to not track `MyEntity` nor the navigation properties `NAv1`&amp; `Nav2` or must I add `AsNoTracking` for each navigation&#160;property? 

like this: &#160;

    context.MyEntity
        .AsNoTracking()
        .Include(i=&gt; i.Nav1)
        .AsNoTracking()
        .Include(i=&gt; i.Nav2)
        .AsNoTracking()
        .Where(x=&gt; x.Prop1==1)
        .FirstOrDefault();



AsNoTracking() and Include

I have a Linq query that fetches an entity and some of its navigation properties.
<pre><code class="hljs language-ini">context.MyEntity
 .AsNoTracking()
 .Include(i=> i.Nav1)
 .Include(i=> i.Nav2)
 .Where(x=> x.Prop1==1)
 .FirstOrDefault();
</code></pre>
my question is:
Is the above query enough to not track <code>MyEntity</code> nor the navigation properties <code>NAv1</code>&#x26; <code>Nav2</code> or must I add <code>AsNoTracking</code> for each navigation property?
like this:  
<pre><code class="hljs language-ini">context.MyEntity
 .AsNoTracking()
 .Include(i=> i.Nav1)
 .AsNoTracking()
 .Include(i=> i.Nav2)
 .AsNoTracking()
 .Where(x=> x.Prop1==1)
 .FirstOrDefault();
</code></pre>

I&#39;m always confused on which one of these to pick. As I see it I use `Dictionary` over `List` if I want two data types as a `Key` and `Value` so I can easily find a value by its `key` but I am always confused if I should use a `ConcurrentDictionary` or `Dictionary`?

Before you go off at me for not putting much research in to this I have tried, but it seems google hasn&#39;t really got anything on `Dictionary` vs `ConcurrentDictionary` but has something on each one individually. 

I have asked a friend this before but all they said is: &quot;use `ConcurrentDictionary` if you use your dictionary a lot in code&quot; and I didn&#39;t really want to pester them in to explaining it in larger detail. Could anyone expand on this? 

When should I use ConcurrentDictionary and Dictionary?

It&#39;s my own custom nuget package that I&#39;ve not published yet and testing locally.

The nuget package consists of a dll file and nuspec file is as follows.


    &lt;?xml version=&quot;1.0&quot;?&gt;
    &lt;package &gt;
      &lt;metadata&gt;
        &lt;id&gt;MyLib&lt;/id&gt;
        &lt;version&gt;1.0.0&lt;/version&gt;
        &lt;authors&gt;Author&lt;/authors&gt;
        &lt;owners&gt;Owner&lt;/owners&gt;
        &lt;licenseUrl&gt;license url&lt;/licenseUrl&gt;
        &lt;projectUrl&gt;project url&lt;/projectUrl&gt;
        &lt;requireLicenseAcceptance&gt;false&lt;/requireLicenseAcceptance&gt;
        &lt;description&gt;some description&lt;/copyright&gt;
        &lt;tags&gt;Tag1 Tage2&lt;/tags&gt;
      &lt;/metadata&gt;
      &lt;files&gt;
        &lt;file src=&quot;bin\Debug\netstandard1.4\*.dll&quot; target=&quot;lib&quot; /&gt;
        &lt;file src=&quot;bin\Debug\netstandard1.4\*.pdb&quot; target=&quot;lib&quot; /&gt;
      &lt;/files&gt;
    &lt;/package&gt;

I&#39;ve copied the nupkg file to a location and added it to the 

    Visual studio Tools -&gt; Options -&gt; Packages -&gt; sources directory 

**Error**:

   

     
    Package MyLib 1.0.0 is not compatible with netcoreapp1.0 (.NETCoreApp,Version=v1.0). Package MyLib 1.0.0 supports: net (.NETFramework,Version=v0.0)
    Package restore failed. Rolling back package changes for &#39;WebApplication1&#39;.

Not sure how can I resolve the issue or find more information.

**More Info**

The dll file was created using template (.Net Framework 4.5.2)

    Templates -&gt; Visual C# -&gt; .NET Core -&gt; Class Library (.NET Standard)

The web application was crated using template. (Empty Web Application)

    Templates -&gt; Visual C# -&gt; .NET Core -&gt; ASP.NET Core Web Application (.NET Core)


**Edit**

I found more details under `Output` window

    One or more packages are incompatible with .NETCoreApp,Version=v1.0.

What kind of class library should I create which is compatible with .NETCoreApp?


**Edit2**

I saw this [URL][1]. it suggests to create the nupkg using `dotnet.exe pack --no-build` whereas earlier I downloaded the `nuget.exe` from nuget.org to create the package.

I tried above command but then visual studio says

    &quot;... Target pack doesn&#39;t exists in the project ... &quot;


Followed instructions on this site as well but failed [URL][2]


  [1]: https://docs.microsoft.com/en-us/dotnet/articles/csharp/getting-started/consuming-library-with-visual-studio-2017
  [2]: https://docs.microsoft.com/en-us/dotnet/articles/core/deploying/creating-nuget-packages

Nuget - Package restore failed. Rolling back package changes for &#39;WebApplication1&#39;. 0

I recently installed VS 2017 RC and then automatically my dotnet version pointed to `1.0.0-preview4-004233`. Due to that whenever I create a new project using command `dotnet new -t Console` I cannot see `project.json` though I see `.csproj` file. 

When I check dotnet versions available on my machine at - `C:\Program Files\dotnet\sdk` I see multiple versions available. 

Is there any way to switch dotnet core back to an earlier version - `1.0.0-preview2-003133` from `1.0.0-preview4-004233` without uninstalling.

Switch between dotnet core SDK versions

I&#39;m trying to understand the proper way to do authentication in ASP.NET Core. I&#39;ve looked at several Resource (Most of which are out dated).  
   

 - [Simple-Implementation-Of-Microsoft-Identity](https://weblogs.asp.net/imranbaloch/a-simple-implementation-of-microsoft-aspnet-identity)
  
 -  [Introduction to Authentication with ASP.Core](https://andrewlock.net/introduction-to-authentication-with-asp-net-core/)

 -  [MSDNs Introduction to Identity](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/identity)

Some people provide altenative solutions stating to use a cloud based solution such as Azure AD, or to Use IdentityServer4 and host my own Token Server.

In Older version Of .Net one of the simpler forms of authentication would be to create an Custom Iprinciple and store additional authentication user data inside.

    public interface ICustomPrincipal : System.Security.Principal.IPrincipal
    {
        string FirstName { get; set; }
 
        string LastName { get; set; }
    }
    
    public class CustomPrincipal : ICustomPrincipal
    {
        public IIdentity Identity { get; private set; }
 
        public CustomPrincipal(string username)
	    {
		    this.Identity = new GenericIdentity(username);
	    }
 
	    public bool IsInRole(string role)
	    {
		    return Identity != null &amp;&amp; Identity.IsAuthenticated &amp;&amp; 
		       !string.IsNullOrWhiteSpace(role) &amp;&amp; Roles.IsUserInRole(Identity.Name, role);
	    }

	    public string FirstName { get; set; }

	    public string LastName { get; set; }

	    public string FullName { get { return FirstName + &quot; &quot; + LastName; } }
    }

    public class CustomPrincipalSerializedModel
    {
        public int Id { get; set; }
 
        public string FirstName { get; set; }
 
        public string LastName { get; set; }
    }

Then you would Serialize your data into a cookie and return it back to the client.

    public void CreateAuthenticationTicket(string username) {     
 
        var authUser = Repository.Find(u =&gt; u.Username == username);  
        CustomPrincipalSerializedModel serializeModel = new CustomPrincipalSerializedModel();
      
        serializeModel.FirstName = authUser.FirstName;
        serializeModel.LastName = authUser.LastName;
        JavaScriptSerializer serializer = new JavaScriptSerializer();
        string userData = serializer.Serialize(serializeModel);
      
        FormsAuthenticationTicket authTicket = new FormsAuthenticationTicket(
        1,username,DateTime.Now,DateTime.Now.AddHours(8),false,userData);
        string encTicket = FormsAuthentication.Encrypt(authTicket);
        HttpCookie faCookie = new HttpCookie(FormsAuthentication.FormsCookieName, encTicket);
        Response.Cookies.Add(faCookie);
    }


My questions are:

  1.  How can I authenticate similar to the way done in previous version&#39;s of .Net does the old way still work or is there a newer version.

  2.  What are the pros and cons of using your own token server verses creating your own custom principle?
    
  3.  When using a cloud based solution or a separate Token server how would you Integrate that with your current application, would I would still need a users table in my application how would you associate the two?
    
  4.  Being that there are so many different solutions how can I create an enterprise application, to allow Login through Gmail/Facebook while still being able to expand to other SSO&#39;s
  5.  What are some simple implementations of these technologies?

.NET Core Identity Server 4 Authentication VS Identity Authentication

I&#39;m having some strange behavior when I try to modify my headers with a `EndRequest` event handler in a nested `HttpModule` on MVC 5.2.2 and .NET 4.6.2. If I don&#39;t modify `EndRequest` in my top level `HttpModule`, it appears that the event handler in the nested `HttpModule` never fires, even though I know `Init` was called on the nested `HttpModule`.

My question is, what is occurring in my code below to prevent the &quot;TestNested&quot; header from appearing in response headers, unless I include the commented out code that adds an `EndRequest` event handler that does nothing?

----

Dynamically register my top level `HttpModule`

    [assembly: PreApplicationStartMethod(typeof(PreApplicationStartClass), &quot;Start&quot;)]
    namespace MyNamespace
    {
        public class PreApplicationStartClass
        {
            public static void Start()
            {
                DynamicModuleUtility.RegisterModule(typeof(TopHttpModule));
            }
        }
    }

Call `Init` on all my other `HttpModules` from a single top level module

    namespace MyNamespace
    {
        public class TopHttpModule: IHttpModule
        {
            private readonly Lazy&lt;IEnumerable&lt;IHttpModule&gt;&gt; _modules = 
                new Lazy&lt;IEnumerable&lt;IHttpModule&gt;&gt;(RetrieveModules);
    
            private static IEnumerable&lt;IHttpModule&gt; RetrieveModules()
            {
                return DependencyResolver.Current.GetServices&lt;IHttpModule&gt;();
            }
    
            public void Init(HttpApplication context)
            {
                var modules = _modules.Value;
                foreach (var module in modules
                    .Where(module =&gt; module.GetType() != typeof(TopHttpModule)))
                {
                    module.Init(context);
                }
    
                context.BeginRequest += (sender, e) =&gt;
                {
                    var app = sender as HttpApplication;
                    if (app != null)
                    {
                        //This shows that NestedHttpModule was found
                        app.Context.Response.Headers.Add(
                            &quot;TestModules&quot;,
                            string.Join(&quot;,&quot;, modules.Select(_ =&gt; _.GetType().ToString())));
                    }
                };

                //Add this and the NestedHttpModule EndRequest handler works
                //context.EndRequest += (sender, e) =&gt;
                //{
                //    //Do Nothing
                //};
            }
    
            public void Dispose()
            {
                var modules = _modules.Value;
                foreach (var disposable in modules
                    .Where(disposable =&gt; disposable.GetType() != typeof(TopHttpModule)))
                {
                    disposable.Dispose();
                }
            }
        }
    }

Modify some header information in an `EndRequest` event handler

    namespace MyNamespace
    {
        public class NestedHttpModule: IHttpModule
        {
            public void Init(HttpApplication context)
            {
                //This gets called whether or not the TopHttpModule modifies context.EndRequest 
                MvcHandler.DisableMvcResponseHeader = true;
    
                context.EndRequest += Application_EndRequest;
            }
    
            public void Application_EndRequest(object sender, EventArgs e)
            {
                var app = sender as HttpApplication;
                if (app != null &amp;&amp; app.Context != null)
                {
                    //This doesn&#39;t appear to be called unless TopHttpModule modifies context.EndRequest
                    app.Context.Response.Headers.Add(&quot;TestNested&quot;, &quot;Found&quot;);
                }
            }
    
            public void Dispose()
            {
                //Do Nothing
            }
        }
    }

Why does my nested HttpModule EndRequest event handler not fire?

I have a console .net core app that uses entity framework core.
The app uses logging framework to write to file and console:

 

     serviceProvider = new ServiceCollection()
            .AddLogging()
            .AddDbContext&lt;DataStoreContext&gt;(options =&gt;
                options.UseSqlServer(Configuration.GetConnectionString(&quot;DefaultConnection&quot;)))
            .BuildServiceProvider();

        //configure console logging
        serviceProvider.GetService&lt;ILoggerFactory&gt;()
            .AddConsole(LogLevel.Debug)
            .AddSerilog();

        Log.Logger = new LoggerConfiguration()
            .MinimumLevel.Information()
            .WriteTo.RollingFile(Path.Combine(Directory.GetCurrentDirectory(), &quot;logs/vcibot-{Date}.txt&quot;))
            .WriteTo.RollingFile(Path.Combine(Directory.GetCurrentDirectory(), &quot;logs/vcibot-errors-{Date}.txt&quot;), LogEventLevel.Error)
            .CreateLogger();

        logger = serviceProvider.GetService&lt;ILoggerFactory&gt;()
            .CreateLogger&lt;Program&gt;();

Min Level for file output is set to Information. But with this setup output also contains SQL queries, here is the example:

&gt; 2017-02-06 10:31:38.282 -08:00 [Information] Executed DbCommand (0ms)
&gt; [Parameters=[], CommandType=&#39;Text&#39;, CommandTimeout=&#39;30&#39;] SELECT
&gt; [f].[BuildIdentifier], [f].[Branch], [f].[BuildDate],
&gt; [f].[StaticAssetSizeInKb] FROM [FileSizesHistoryEntries] AS [f]

Is there a way to disable the SQL queries logging  (log them only in Debug log level)


Suppress SQL Queries logging in Entity Framework core

I have this sample code:

    using Microsoft.EntityFrameworkCore;
    using Microsoft.EntityFrameworkCore.Metadata.Builders;
    using Models;

    namespace MySampleNamespace
    {
        public class MyDbContext : DbContext
        {
            public MyDbContext(DbContextOptions&lt;MyDbContext&gt; options)
                : base(options)
            {
            }

            public DbSet&lt;User&gt; Users { get; set; }

            protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                new UserMap(modelBuilder.Entity&lt;User&gt;());
            }

            public class UserMap
            {
                public UserMap(EntityTypeBuilder&lt;User&gt; entityBuilder)
                {
                    entityBuilder.ToTable(&quot;User&quot;);
                    entityBuilder.Property(s =&gt; s.Username).HasMaxLength(15).IsRequired();
                }
            }
        }
    }

I was testing out some example from MS website, but I can&#39;t find ToTable method. In the example, I checked what are the Usings and the only Using the example had is Microsoft.EntityFrameworkCore aside from the class project for the model he was using. Was this changed? How do I do this now?

EntityTypeBuilder does not contain a definition for ToTable in EF Core

I want to set the precision of all the decimal properties to (18,6). In EF6 this was quite easy:

    modelBuilder.Properties&lt;decimal&gt;().Configure(x =&gt; x.HasPrecision(18, 6));

but I can&#39;t seem to find anything similar to this in EF Core. Removing the cascade delete convention wasn&#39;t as simple as in EF6 so I found the following workaround:

EF6:
  
    modelBuilder.Conventions.Remove&lt;ManyToManyCascadeDeleteConvention&gt;();
    modelBuilder.Conventions.Remove&lt;OneToManyCascadeDeleteConvention&gt;();

EF Core:
    
    foreach (var relationship in modelBuilder.Model.GetEntityTypes().SelectMany(e =&gt; e.GetForeignKeys()))
        relationship.DeleteBehavior = DeleteBehavior.Restrict;

and after I read [this](https://stackoverflow.com/questions/30388695/entity-framework-7-set-decimal-precision-for-model-builder), I tried a similar approach:

    foreach (var entityType in modelBuilder.Model.GetEntityTypes()
        .SelectMany(x =&gt; x.GetProperties())
        .Where(x =&gt; x.ClrType == typeof(decimal)))
            {
                // what to do here?
            }

I would like if I am on the right track and how to continue, or if not, should I start putting data annotations on all the `decimal` properties.



Entity Framework Core - setting the decimal precision and scale to all decimal properties

After update to the new package Microsoft.EntityFrameworkCore.SqlServer 1.1.2  I got error when try to create DBContext:

&gt; System.IO.FileLoadException occurred   HResult=0x80131040  
&gt; Message=Could not load file or assembly
&gt; &#39;Microsoft.Extensions.DependencyInjection.Abstractions,
&gt; Version=1.1.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60&#39; or
&gt; one of its dependencies. The located assembly&#39;s manifest definition
&gt; does not match the assembly reference. (Exception from HRESULT:
&gt; 0x80131040)   Source=Microsoft.EntityFrameworkCore   StackTrace:    at
&gt; Microsoft.EntityFrameworkCore.DbContext..ctor(DbContextOptions
&gt; options)    at
&gt; Services.Infrastructure.Data.SqlServerDbContext..ctor(DatabaseOptions
&gt; databaseOptions) in
&gt; C:\src\backend\Packages\Services.Infrastructure\Data\SqlServerDbContext.cs:line
&gt; 16    at
&gt; Translations.Api.Data.TranslationsDbContext..ctor(DatabaseOptions
&gt; databaseOptions) in
&gt; C:\src\backend\Modules\Translations\Translations.Api\Data\TranslationsDbContext.cs:line
&gt; 16

My base DbContext

    public class SqlServerDbContext : DbContext
    {
    	private readonly DatabaseOptions _databaseOptions;
    
    	protected SqlServerDbContext(DatabaseOptions databaseOptions)
    	{
    		if (string.IsNullOrEmpty(databaseOptions.ConnectionString))
    			throw new Exception(&quot;Database connection string is missed.&quot;);
    
    		_databaseOptions = databaseOptions;
    	}
    
    	protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    	{
    		optionsBuilder.UseSqlServer(_databaseOptions.ConnectionString);
    	}
    }

Database options that I use

    public class DatabaseOptions
    {
    	public string ConnectionString { get; set; }
    }

Place where I create instance of context

     var dbOptions = new DatabaseOptions { ConnectionString = _connectionString };
     DbContext = (TContext) Activator.CreateInstance(typeof(TContext), dbOptions);
    // where TContext is derived class from SqlServerDbContext

All my packages are updated.  Visual Studio 2017 15.2 (26430.6). Before upgrade to 1.1.2 everything works fine. Please help to solve the problem.   

Could not load file or assembly Microsoft.Extensions.DependencyInjection.Abstractions, Version=1.1.0.0

I have a developer that is getting &quot;Build failed.&quot; when running add-migration in a .NET Core EF project, with no explanation of why the build failed. How do you troubleshoot this error?

This is what he gets in the Package Manager Console:[![enter image description here][1]][1]

**Additional information**:

We have a few other developers using the same solution code (myself included) that have not issues with add-migration.

This is what I see in Package Manager Console:[![enter image description here][2]][2]

We&#39;ve verified that the project builds, and the entire solution builds. We&#39;ve done &quot;dotnet restore&quot; and rebuild all multiple times, in addition to restarting VS2015. We&#39;ve verified that the correct default solution is selected both in Solution Explorer, and in the Package Manager Console drop-down. We&#39;ve verified that he has the correct SDK installed on his machine. I&#39;m at a loss as to what to check next...any time I&#39;ve had a failure during add-migration I&#39;ve gotten enough information to point me in the direction of what to check, but just &quot;Build failed.&quot; is a fairly useless error output.

  [1]: https://i.stack.imgur.com/xbKFA.png
  [2]: https://i.stack.imgur.com/xZiQ8.png

EF Core add-migration Build Failed

&quot;Contains&quot; in Entity Framework core should equivalent to the SQL %like% operator. Therefore &quot;Contains&quot; should be case insensitive however it is case sensitive! (at least in postgres????)

The following only outputs a result when the correct casing for keyword is used.

    context.Counties.Where(x =&gt; x.Name.Contains(keyword)).ToList();

What am I doing wrong?


Entity Framework core - Contains is case sensitive or case insensitive?

Given:

    class Program
    {
        private static readonly List&lt;(int a, int b, int c)&gt; Map = new List&lt;(int a, int b, int c)&gt;()
        {
            (1, 1, 2),
            (1, 2, 3),
            (2, 2, 4)
        };

        static void Main(string[] args)
        {
            var result = Map.FirstOrDefault(w =&gt; w.a == 4 &amp;&amp; w.b == 4);

            if (result == null)
                Console.WriteLine(&quot;Not found&quot;);
            else
                Console.WriteLine(&quot;Found&quot;);
        }
    }

In the above example, a compiler error is encountered at line `if (result == null)`.  

&gt; CS0019	Operator &#39;==&#39; cannot be applied to operands of type &#39;(int a, int b, int c)&#39; and &#39;\&lt;null\&gt;&#39;

How would I go about checking that the tuple is found prior to proceeding in my &quot;found&quot; logic?

Prior to using the new c# 7 tuples, I would have this:

    class Program
    {
        private static readonly List&lt;Tuple&lt;int, int, int&gt;&gt; Map = new List&lt;Tuple&lt;int, int, int&gt;&gt;()
        {
            new Tuple&lt;int, int, int&gt; (1, 1, 2),
            new Tuple&lt;int, int, int&gt; (1, 2, 3),
            new Tuple&lt;int, int, int&gt; (2, 2, 4)
        };

        static void Main(string[] args)
        {
            var result = Map.FirstOrDefault(w =&gt; w.Item1 == 4 &amp;&amp; w.Item2 == 4);

            if (result == null)
                Console.WriteLine(&quot;Not found&quot;);
            else
                Console.WriteLine(&quot;Found&quot;);
        }
    }

Which worked fine.  I like the more easily interpreted intention of the new syntax, but am unsure on how to null check it prior to acting on what was found (or not).

How to null check c# 7 tuple in LINQ query?

The line `price = co?.price ?? 0,` in the following code gives me the above error, but if I remove `?` from `co.?` it works fine. 

I was trying to follow [this MSDN example][1] where they are using `?` on line `select new { person.FirstName, PetName = subpet?.Name ?? String.Empty };` So, it seems I need to understand when to use `?` with `??` and when not to.

**Error**:

&gt;an expression tree lambda may not contain a null propagating operator

    public class CustomerOrdersModelView
    {
        public string CustomerID { get; set; }
        public int FY { get; set; }
        public float? price { get; set; }
        ....
        ....
    }
    public async Task&lt;IActionResult&gt; ProductAnnualReport(string rpt)
    {
        var qry = from c in _context.Customers
                  join ord in _context.Orders
                    on c.CustomerID equals ord.CustomerID into co
                  from m in co.DefaultIfEmpty()
                  select new CustomerOrdersModelView
                  {
                      CustomerID = c.CustomerID,
                      FY = c.FY,
                      price = co?.price ?? 0,
                      ....
                      ....
                  };
        ....
        ....
     }


  [1]: https://docs.microsoft.com/en-us/dotnet/csharp/linq/perform-left-outer-joins


An expression tree lambda may not contain a null propagating operator

I hope someone can prove me wrong here :)

If I do this:

    List&lt;string&gt; a = new List&lt;string&gt; { &quot;b&quot;, &quot;c&quot;, &quot;a&quot;, &quot;aa&quot; };
    var b = a.OrderBy(o =&gt; o).ToList();

I would expect the result of &#39;b&#39; to be:

    a
    aa
    b
    c

Instead, the result I get is:

    a
    b
    c
    aa

How can I get OrderBy to do a &quot;correct&quot; alphabetical sort?
Am I just plain wrong? :)

LINQ OrderBy is not sorting correctly

When profiling one of our applications, we discovered a mysterious slowdown in some code where we were calling `Enumerable.Single(source, predicate)` for a large collection that had more than one item that matched the predicate near the start of the collection.

Investigation revealed that [the implementation of `Enumerable.Single()`](https://referencesource.microsoft.com/#System.Core/System/Linq/Enumerable.cs) is as follows:

    public static TSource Single&lt;TSource&gt;(this IEnumerable&lt;TSource&gt; source, Func&lt;TSource, bool&gt; predicate) 
    {
    		TSource result = default(TSource);
    		long count = 0;
            // Note how this always iterates through ALL the elements:
    		foreach (TSource element in source) { 
    			if (predicate(element)) {
    				result = element;
    				checked { count++; }
    			}
    		}
    		switch (count) {
    			case 0: throw Error.NoMatch();
    			case 1: return result;
    		}
    		throw Error.MoreThanOneMatch();
    	}
    	

That implementation will iterate through every element of the sequence, even if more than one element has already matched the predicate.

The following implementation would appear to yield the same results:

	public static TSource Single&lt;TSource&gt;(this IEnumerable&lt;TSource&gt; source, Func&lt;TSource, bool&gt; predicate)
    {
		TSource result = default(TSource);
		long count = 0;
		foreach (TSource element in source) {
			if (predicate(element)) {
				if (count == 1) // Exit loop immediately if more than one match found.
					throw Error.MoreThanOneMatch();
					
				result = element;
				count++; // &quot;checked&quot; is no longer needed.
			}
		}

        if (count == 0)
            throw Error.NoMatch();

		return result;
	}

Does anyone know why the actual implementation doesn&#39;t use this obvious optimization? Is there something I&#39;m missing? (I can&#39;t imagine that such an obvious optimization would be overlooked, and therefore there must be some concrete reason for it.)

(Note: I realize that this question may attract answers that are opinions; I&#39;m hoping for answers that provide concrete reasons for iterating all elements. If the answer is actually &quot;because the designers didn&#39;t think such an optimization was necessary&quot;, then this question is unanswerable and I guess I should just delete it...)

---

For comparison, look at the implementation of `Single()` which does not take a predicate:

    public static TSource Single&lt;TSource&gt;(this IEnumerable&lt;TSource&gt; source) 
    {
		IList&lt;TSource&gt; list = source as IList&lt;TSource&gt;;
		if (list != null) {
			switch (list.Count) {
				case 0: throw Error.NoElements();
				case 1: return list[0];
			}
		}
		else {
			using (IEnumerator&lt;TSource&gt; e = source.GetEnumerator()) {
				if (!e.MoveNext()) throw Error.NoElements();
				TSource result = e.Current;
				if (!e.MoveNext()) return result;
			}
		}
		throw Error.MoreThanOneElement();
	}

In this case, they&#39;ve gone to the effort of adding an optimisation for `IList`.


Content Type	Original Author	Original Content on Stackoverflow
Question	Juan Pablo Gomez	View Question on Stackoverflow
Solution 1 - C#	Daniel	View Answer on Stackoverflow

AsNoTracking() and Include

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Solution 1 - C#

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