I added Entity Framework to references but I still get an error that it does not exist .
I think this issue is from the Pluralsight video: Building an Enterprise App with WPF, MVVM, and Entity Framework Code First.
At Section 5, in the area titled: Create a DbContext Subclass, the author (T. Huber) - installs the Entity Framework 6.1.3 (not the core version) - from NuGet. When I did this, I grabbed version 6.4.4. After doing that, using System.Data.Entity; did not work. I would get:
"CS0234: The type or namespace 'Entity' does not exist in he namespace 'System.Data' (are you missing an assembly reference?)" Later I tried EF Core, only to find the base("FriendOrganizerDb") doesn't like that string in there.
My solution was to uninstall the Nuget packages, and Install NuGet Entity Framework ver 6.1.3 as per the video. That "version" of Entity Framework works with: using System.Data.Entity;
We have very little information about your project settings, but it seems that you are using .Net Core. In order to use EntityFramework in .Net Core you need to follow these steps:
.Net Core:
You need to install Microsoft.EntityFrameworkCore package instead of EntityFramework. You can install this package via nuget using: Install-Package Microsoft.EntityFrameworkCore -Version 3.1.7 (You might replace 3.1.7 with other versions if needed)
After installing the package you need to add using Microsoft.EntityFrameworkCore; to you usings list or just replcae DbContext with Microsoft.EntityFrameworkCore.DbContext
using Microsoft.EntityFrameworkCore;
namespace FriendOrganizer.DataAccess{
public class FriendOrganizerDbContext: DbContext{
...
}
}
Or
namespace FriendOrganizer.DataAccess{
public class FriendOrganizerDbContext: Microsoft.EntityFrameworkCore.DbContext{
...
}
}
However if you want to use ENtityFramework in .Net Framework you should follow these steps instead:
.Net Framework
You need to install EntityFramework package. You can install it via nuget using: Install-Package EntityFramework -Version 6.4.4 (You might replace 6.4.4 with other versions if needed),
After installing the package you need to add System.Data.Entity to your usings list or just replace the DbContext with System.Data.Entity.DbContext
using System.Data.Entity;
namespace FriendOrganizer.DataAccess{
public class FriendOrganizerDbContext: DbContext{
...
}
}
Or
namespace FriendOrganizer.DataAccess{
public class FriendOrganizerDbContext: System.Data.Entity.DbContext{
...
}
}
I am new to EF core and I'm trying to get it to work with my ASP.NET Core project.
I get the above error in my startup.cs when trying configure the DbContext to use a connection string from config. I am following this tutorial.
The problematic code is in startup.cs:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.SpaServices.Webpack;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.EntityFrameworkCore;
using tracV2.models;
using tracV2.data;
namespace tracV2
{
public class Startup
{
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddMvc();
services.AddSingleton<IConfiguration>(Configuration);
string conn = Configuration.GetConnectionString("optimumDB");
services.AddDbContext<tracContext>(options => options.usesqlserver(conn));
}
The UseSqlServer method is recognized if I put it directly into the context:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
namespace tracV2.data
{
public class tracContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer("myrealconnectionstring");
}
All my research online points to missing references, but I can't seem to find out which one I am missing (see image).
First we install the Microsoft.EntityFrameworkCore.SqlServer NuGet Package:
PM > Install-Package Microsoft.EntityFrameworkCore.SqlServer
Then, after importing the namespace with
using Microsoft.EntityFrameworkCore;
we add the database context:
services.AddDbContext<AspDbContext>(options =>
options.UseSqlServer(config.GetConnectionString("optimumDB")));
adding
using Microsoft.EntityFrameworkCore;
manually solved the problem for me
Found that here
Edit...
for dotnet core 3.1 add
Microsoft.EntityFrameworkCore.SqlServer
Follow the steps below.
Install Entity Framework Core Design and SQL Server database provider for Entity Framework Core:
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
Import Entity Framework Core:
using Microsoft.EntityFrameworkCore;
And configure your DbContext:
var connectionString = Configuration.GetConnectionString("myDb");
services.AddDbContext<MyDbContext>(options =>
options.UseSqlServer(connectionString)
);
Install below NuGet Package will solve your issue
Microsoft.EntityFrameworkCore.SqlServer
Install-Package Microsoft.EntityFrameworkCore.SqlServer
EntityFramework UseSqlServer Solved
Install-Package Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore
Install-Package Microsoft.EntityFrameworkCore.SqlServer
I believe this can be solved by adding a project reference to Microsoft.EntityFrameworkCore.SqlServer.Design
Install-Package Microsoft.EntityFrameworkCore.SqlServer.Design
Microsoft.EntityFrameworkCore.SqlServer wasn't directly installed in my project, but the .Design package will install it anyway as a prerequisite.
The Package is missing. Open Package Manager Console and execute the code below:
Install-Package Microsoft.EntityFrameworkCore.SqlServer
your solution works great.
When I saw this video till 17 Minute: https://www.youtube.com/watch?v=fom80TujpYQ
I was facing a problem here:
services.AddDbContext<PaymentDetailContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("DevConnection")));
UseSqlServer not recognizes so I did this
Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 3.1.5
&
using Microsoft.EntityFrameworkCore;
Then my problem is solved. About me: basically I am a purely PHP programmer since beginning and today only I started .net coding, thanks for good community in .net
Install the following packages from Nuget :-
Microsoft.EntityFrameworkCore
Microsoft.EntityFrameworkCore.Sqlite.Core
I was using Visual Studio Code.
1) Try to install the package 'Microsoft.EntityFrameworkCore.SqlServer' by specifying the version number.
VS Code:
'dotnet add package Microsoft.EntityFrameworkCore.SqlServer -v 1.1.1'
Visual Studio:-
'Install-Package Microsoft.EntityFrameworkCore.SqlServer -v 1.1.1'
Refer the link 'Package 'Microsoft.EntityFrameworkCore.SqlServer' is incompatible with 'all' frameworks in the project' for doing it.
2) Then add the namespace 'using Microsoft.EntityFrameworkCore;' manually in the Startup.cs file.
Refer the below link
https://github.com/aspnet/EntityFramework/issues/7891.
3) If you get any dependency issue for 'Microsoft.EntityFrameworkCore.SqlServer.Design', like "Package 'Microsoft.EntityFrameworkCore.Design' is incompatible with 'all' frameworks in project" ,we need to run the below command,
VS Code:-
dotnet add package Microsoft.EntityFrameworkCore.Design -v 1.1
Visual Studio
Install-Package Microsoft.EntityFrameworkCore.Design -v 1.1
Project -> ManageNugetPackages -> Browse -> Search "Microsoft.EntityFrameworkCore.SqlServer" and install or update.
As mentioned by top scoring answer by Win you may need to install Microsoft.EntityFrameworkCore.SqlServer NuGet Package, but please note that this question is using asp.net core mvc. In the latest ASP.NET Core 2.1, MS have included what is called a metapackage called Microsoft.AspNetCore.App
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/metapackage-app?view=aspnetcore-2.2
You can see the reference to it if you right-click the ASP.NET Core MVC project in the solution explorer and select Edit Project File
You should see this metapackage if ASP.NET core webapps the using statement
<PackageReference Include="Microsoft.AspNetCore.App" />
Microsoft.EntityFrameworkCore.SqlServer is included in this metapackage. So in your Startup.cs you may only need to add:
using Microsoft.EntityFrameworkCore;
In Visual Studio, check the NuGet Package Manager => Manage Packages for Solution, check all this packages, whether got installed in your solution or not, as below:
EntityFrameworkCore
Microsoft.EntityFrameworkCore
Microsoft.EntityFrameworkCore.InMemory
Microsoft.EntityFrameworkCore.Relational
Microsoft.EntityFrameworkCore.Sqlite.Core
Microsoft.EntityFrameworkCore.SqlServer
Microsoft.EntityFrameworkCore.Tools
I solved the same issues after check all the above packages have been installed.
Install package, EntityFrameworkCore.SqlServer:
PM> Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 3.1.3
Nuget:
https://www.nuget.org/packages/Microsoft.EntityFrameworkCore.SqlServer/
I also had the same problem. I added the following. It works for me
Microsoft.EntityFrameworkCore.SqlServer
In my case :-
I have hit the below command and it is resolved.
Command
Install-Package Microsoft.EntityFrameworkCore.SqlServer -v 1.1.1
I add SqlServer and Sqlite to my project, the same problem arises.
For me, I installed Microsoft.EntityFrameworkCore earlier, it's version is 5.0.6. Now Microsoft.EntityFrameworkCore.SqlServer version is 5.0.7. There is no UserSqlServer method after installation.
1. Try to upgrade the tool version to be consistent
Try to modify the version in csproj:
<PackageReference Include="Microsoft.EntityFrameworkCore" Version="5.0.7">
Or open NuGet to update the package.
2. Restart your Visual Studio
If it won't help you, the most important thing is to restart VS
And then, everything is OK.
reference
https://github.com/dotnet/efcore/issues/7891
For me this issue happened with Visual Studio Code and I was able to fix with 2 steps:
Manually adding using Microsoft.EntityFrameworkCore;
Running dotnet build in terminal.
first add Install-Package Microsoft.EntityFrameworkCore.SqlServer
next add in your .cs file using Microsoft.EntityFrameworkCore;
finally add this in your core Startup.cs
public void ConfigureServices(IServiceCollection services)
{
services.AddEntityFrameworkSqlServer().AddDbContext<ApplicationContext>(options => options.UseSqlServer(Configuration.GetConnectionString("MovieContext")));
}
For anyone still having this problem:
Use NuGet to install:
Microsoft.EntityFrameworkCore.Proxies
This problem is related to the use of Castle Proxy with EFCore.
Wow so many answers yet none mentioned this Microsoft.EntityFrameworkCore.InMemory package!
Add the reference to this package:
<PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="2.2.2" /> and you should be good to go.
If you are facing this issue in case of Sqlite then
.
I think this is the problem with version of Sqlite,I had the same problem when I was using this versions of SqLite
Version 2.2.4:
After checking version here I changed the version then it worked.
No error after using this
Version 2.1.2:
Easy way to fix this issue
Error message:
Solution:
to install "microsoft.entityframeworkcore.sqlserver" with NuGet
Fixed :
PS: make sure you have using EF on the content "using Microsoft.EntityFrameworkCore;"
I read and did everything instructed in every answer and I just found out my problem was a missing constructor on my DbContext
public Context(DbContextOptions<Context> options) : base(options) { }
I hope this helps anyone facing the same problem I was.
I got around this by simply:
Add SqlServerDbContextOptionsExtensions to the class in question
Resolve SqlServerDbContextOptionsExtensions
This fixes the issue, must be missing some reference by default.
I had this trouble when I moved to Microsoft.EntityFrameworkCore.SqlServer v3.0.0 and Microsoft.EntityFrameworkCore.Tools v3.0.0
When I changed back to v2.2.6 on both libraries, the error went away. This is more of a workaround than a solution but it'll get you up and running till the issue is fixed.
Currently working with Entity Framework Core 3.1.3. None of the above solutions fixed my issue.
However, installing the package Microsoft.EntityFrameworkCore.Proxies on my project fixed the issue. Now I can access the UseLazyLoadingProxies() method call when setting my DBContext options.
Hope this helps someone. See the following article:
Lazy Loading in EF Core
For asp.net core version 2.1 make sure to add the following package to fix the problem. (At least this fix the issue using SQLite)
dotnet add package Microsoft.EntityFrameworkCore.Sqlite
dotnet add package Microsoft.EntityFrameworkCore.Design
Here is the reference of the documentation using SQLite with entity framework core.
https://learn.microsoft.com/en-us/ef/core/get-started/netcore/new-db-sqlite
I had this issue, it seems that I hadn't added the required NuGet packages, although I thought I had done so, make sure to check them, one by one.
Install-Package:
**Microsoft.EntityFrameworkCore.SqlServer**
then add the top of your class:
**Microsoft.EntityFrameworkCore;**
that's worked for me
I'm working on one of those new "Class Library (NuGet Package)" projects in Visual Studio. Everything was going fine until the other day it started raising an error about a:'assembly 'EntityFramework.Core, Version=7.0.0.0 reference??
How can I install the 7.0 version of EntityFramework into my Nuget packages??
"This issue" says that you need to add a reference to:
assembly 'EntityFramework.Core, Version=7.0.0.0
You can solve it by running the following command in the Package Manager Console:
Install-Package EntityFramework.Core -Pre
The issue is the EF version is different and following 2 assemblies are not supported.
using System.Data.Objects;
using System.Data.Objects.DataClasses;
Comment the above 2 lines and the following line in the code behind of your .edmx
using System.Data.Entity.Core.Objects;
I want to use an API to get info from the interwebz. The API returns data in Json format.
I'm running Microsoft Visual Studio C# 2010 Express addition.
It appears that I have the .NET Framework 4 Client Profile set as my
"Target framework" but I'm honestly not sure exactly what this
means.
This is a Windows Forms Application...
Not much code to show because I can't really get started without the appropriate using statement...
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using System.Net;
using System.Runtime.Serialization.Json;
I get this error:
The type or namespace name 'Json' does not exist in the namespace
'System.Runtime.Serialization' (are you missing an assembly
reference?)
Am I missing a DLL file or something? Based on my hours of fruitlessly searching for solutions, I understand that the .NET 4.xx should already have the tools needed to parse up a Json formatted string?
The System.Runtime.Serialization.Json Namespace is in two different DLL's depending on your .net framework.
In .NET 3.5 It is in System.ServiceModel.Web.dll
In .NET 4.0 and above It is in System.Runtime.Serialization.dll.
Make sure you have added the correct DLL as a reference in your project and add using System.Runtime.Serialization.Json; to the top of your code file.
EDIT - Consider using JSON.NET
Even though the .NET Framework supplies its own JSON Serialization and Deserialization namespaces (DataContractJsonSerializer and JavaScriptSerializer) you should investigate whether you would be better off using JSON.NET.
JSON.NET is easier to use, better performance and has far more features.
http://www.newtonsoft.com/json/help/html/JsonNetVsDotNetSerializers.htm
you need to import System.Runtime.Serialization dll from reference
You need to add a reference to your project.
In the Solution Explorer right click references then add reference. You'll see a list of DLL's and you have to check the box next to the one you need for it to be added to the project. After you've done this you can successfully add the using statement.
Hope that helps!
The general process for serializing and deserializing JSON from C# is:
Add a reference to the System.Runtime.Serialization library.
Add using directives for System.Runtime.Serialization and System.Runtime.Serialization.Json.
Please change your Target framework from .NET Framework 4 Client Profile to .NET Framework 4
I know this is an old question, but I came across this in .NET 5.0 and the solution is to add using System.Text.Json to the top of your code.
Why might "using System.Linq" cause the following error?
The type or namespace name 'Linq' does
not exist in the namespace 'System'
Reference System.Core
And then there are others that merge this namespace too - but that's the primary one on .Net 3.5 and above.
If you're project is currently .Net 2.0, say, and you're using the right version of VS (2005 and above) - you can simply right-click on the proejct properties; and change the 'Target Framework Version' to 3.5. System.Core will then become available.
If you don't see that in the options - then I guess you're using an older VS
The most probable reason is that you are using wrong version of .NET Framework.
Try to add System.Core assembly to your project
You'll get this error if you don't have "System.Core.dll" referenced (the assembly which contains the core LINQ APIs).
System.Linq is available in .Net 3.5 and above version.
Maybe you're targeting an older framework, Linq came in with 3.5 IIRC.
You are using lower version of .NET Framework than 3.5 to compile the source code or you don't have added the System.Core assembly to your project.
Manually type using System.Linq in the starting of the project, you will not be able to find this namespace in add reference dialogue box.
If you are still getting error then try to Add Reference System.Core.
If you are getting an error that it has been already referred then you can unload your project and then edit your csproject file, manually copy reference to System tag and paste and change the name to System.Core and reload the project.
In my case the only thing that worked was:
Adding a new Razor item (e.g. MVC 5 View Page)
That automatically pulls in some NuGet packages
The package that makes System.Linq available to Razor Views IntelliSense seems to be Microsoft.AspNet.WebPages.