连接字符串问题：System.Data.SqlClient.SqlException (0x80131904) - 无法连接到 SQL Server Management Studio

Question

I am trying to connect Visual Studio 2017 to SQL Server 2016 Express using the following code in my app.config:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
<!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
<section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
  </startup>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
<providers>
  <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
</providers>
  </entityFramework>

  <connectionStrings>
<add name="BlogDbContext" connectionString="Data Source=DESKTOP-I3K90LQ\SQL2016;Initial Catalog=CodeFirstDemo;Integrated Security=SSPI;" providerName="System.Data.SqlClient"/>
  </connectionStrings>
 </configuration>

I created a sample repository to test in my program.cs file

using System;
using System.Collections.Generic;
using System.Data.Entity;
sing System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
public class Post
{
    public int Id { get; set; }
    public DateTime DatePublished { get; set; }
    public DateTime DateEdited { get; set; }
    public string Title { get; set; }
    public string Body { get; set; }
}

public class BolgDbContext : DbContext
{
    public DbSet<Post> Posts { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
    }
}
}

I installed Entity Framework into my Console Application using the following command in the Package Manager Console

PM>install-package EntityFramework -version 6.1.3

Then I enable Migration and create the first migration:

PM>enable-migrations
PM>add-migrations CreatePost
PM>update-database

after submitting update-database command I get following error message:

System.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

ClientConnectionId:00000000-0000-0000-0000-000000000000
Error Number:-1,State:0,Class:20
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

So my Visual Studio is not able to connect to my SQL Server Management Studio to create a database.

If this work right, my Code First console project should be able to use a Sql instance instead of LocalDb instance to create and update a database from Visual Studio. ### I have searched google for solutions for hours last night. Some suggest that could firewall issues, that I should create a port 1433 and enable TCP/IP in the Sql Server Configuration Manager to allow VS connecting to SQL. I have all those solutions, but none of them worked for my test project.

If anyone out there have an answer, please help.

Many thanks!

Further technical details

Target Framework: .NET Framework 4.5 Operating system: IDE: (eg Visual Studio 2017 15.4)

Answer 1

Pretty sure by default EF looks for DefaultConnection connection name on your web.config. Someone can correct me if I'm wrong.

You need to override the connection name via :base() on your DbContext class.

public class BolgDbContext : DbContext
{
    public BolgDbContext() : base("name=BlogDbContext") { }
    public DbSet<Post> Posts { get; set; }
}

FYI, typo BolgDbContext is intentional, copied pasted from your code...

Answer 2

I found solution as Following:

<connectionStrings>
<add name="BlogDbContext" connectionString="Data Source=DESKTOP-I3K90LQ\SQL2016;Initial Catalog=CodeFirstDemo;Integrated Security=SSPI;" providerName="System.Data.SqlClient"/>
</connectionStrings>
<entityFramework>
<defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework">
<parameters>
<parameter value="Data Source=localhost; Integrated Security=True; MultipleActiveResultSets=True"/>
</parameters>
</defaultConnectionFactory>

<providers>
<provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
</providers>
</entityFramework>

Answer 3

So glad I found this and your solution! I'm just posting here to describe how I got the same problem and a bit more detail on how to fix it.

The same in VS2019, with EntityFramework and Update-Database. The same error message, ie A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server). A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server).

I was following a very good tutorial. It had connectionString="Data Source=.;Initial Catalog=FriendOrganizer;Integrated Security=True". This had been working for half of the tutorial, and Update-Database had created and seeded the DB, so I knew the DB was accessible.

After applying some changes in the tutorial it stopped working. I deleted the DB and Migrations, recreated the Migrations How to delete and recreate from scratch an existing EF Code First database , but it sill didn't work, with Update-Database producing this error, after a timeout.

Using the flag '-Verbose' assisted somewhat in tracking it down, but I needed this answer! I went to the Sql Server Object Explorer , right-clicked on the first '(localdb)\\MSSQLLocalDB...', and got the Connection string property. I copied this and replaced it in the connectionStrings in the App.config for the data access project. Then Update-Database worked! (When I ran the app it timed out on the connection, as I needed to do the same in the Startup Project App.config , but that may not apply in all cases, depending on whether you have two App.configs ).

For my db, FriendOrganizerDb the connection string is...

    <connectionStrings>
    <add name="FriendOrganizerDb"
         connectionString="Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=FriendOrganizer;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False;ApplicationIntent=ReadWrite;MultiSubnetFailover=False" 
         providerName="System.Data.SqlClient"/>
</connectionStrings>

FriendOrganizer is the DB for the tutorial I was following - and highly recommend! ( Building an Enterprise App with WPF, MVVM, and Entity Framework Code First )