我使用的是SQL Server 2016和windows 10。

首先是允许远程连接到SQL Server。 我所做的就是键入sqlservermanager13。在开始菜单打开SQL Server配置管理器。确保TCP/IP状态为启用状态。

双击TCP/IP协议名称，检查TCP端口号。通常默认值是1433。

以下步骤通过使用Microsoft管理控制台(MMC)管理单元配置Windows防火墙的高级安全。高级安全Windows防火墙只配置当前配置文件。

To open a port in the Windows firewall for TCP access On the Start menu, click Run, type WF.msc, and then click OK. In the Windows Firewall with Advanced Security, in the left pane, right-click Inbound Rules, and then click New Rule in the action pane. In the Rule Type dialog box, select Port, and then click Next. In the Protocol and Ports dialog box, select TCP. Select Specific local ports, and then type the port number of the instance of the Database Engine, such as 1433 for the default instance. Click Next. In the Action dialog box, select Allow the connection, and then click Next. In the Profile dialog box, select any profiles that describe the computer connection environment when you want to connect to the Database Engine, and then click Next. In the Name dialog box, type a name and description for this rule, and then click Finish.

另一个需要配置的东西。

To open access to SQL Server when using dynamic ports On the Start menu, click Run, type WF.msc, and then click OK. In the Windows Firewall with Advanced Security, in the left pane, right-click Inbound Rules, and then click New Rule in the action pane. In the Rule Type dialog box, select Program, and then click Next. In the Program dialog box, select This program path. Click Browse, and navigate to the instance of SQL Server that you want to access through the firewall, and then click Open. By default, SQL Server is at C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Binn\Sqlservr.exe. Click Next. In the Action dialog box, select Allow the connection, and then click Next. In the Profile dialog box, select any profiles that describe the computer connection environment when you want to connect to the Database Engine, and then click Next. In the Name dialog box, type a name and description for this rule, and then click Finish.

看看微软的文档 配置Windows防火墙访问数据库引擎

您可以测试以下方法。

a Check the connection string of the project. b Go to services and restart SQLServer Instance. c Open 'SQLServer Configuration Manager' In the left panel select 'SQLServer Network Configuration' and expanding it Select 'Protocols for MSSQLServer' In the right panel dbl click on 'TCP/IP' In the 'Protocol' tab set the 'Enabled' to 'Yes' In the 'IP Addresses' tab scroll to down In the 'IPAll' set 'TCP Port' to 1433 d Open 'Firewall with advanced security' In the right tab select 'Inbound Rules'

在中间选项卡找到“本地端口”是1433的记录，如果你找不到它，尝试用以下级别创建它

In the Start menu, click Run, type 'WF.msc', and then click OK In the left panel click the 'Windows Firewall with Advanced Security' In the right panel right-click 'Inbound Rules', and then click 'New Rule' In the Rule Type dialog box, select 'Port', and then click Next In the Protocol and Ports dialog box, select 'TCP', and select 'Specific Local Ports', and then type the port number 1433, Click Next In the Action dialog box, select Allow the connection, and then click Next In the 'Profile' dialog box, checking the Domain, Private and Public, Then click Next In the 'Name' dialog box, type 'SQL 1433 Port' and for a description write description for own. Then click Finish

Then in the middle tab double click the found item(Instance) or created item of 'SQL 1433 Port' name by you. Select 'Scope' tab in opened dialog box(SQL Server Properties) In the Local PC Go to google.com in your Browser and search 'My IP'. then copy of your 'IP' Go to the remote server and in the 'SQL Server Properties' dialog box of 'Scope' tab, in the 'Remote IP Address' select the 'These IP Addresses' option and click 'Add' button In the opened dialog box(IP Address) select 'This IP Address or Subnet' option and paste your 'IP', click OK button.

我也有这个问题，我尝试了这篇文章中建议的所有方法，但没有任何效果。最后，我通过在SQL Server中执行这个查询解决了我的问题

EXEC sp_configure 'remote access', 0 ;  
GO  
RECONFIGURE ;  
GO  

我遇到了同样的问题，问题是我在解决方案(Weband Droid)中有几个项目，即使在包管理器控制台中选择了默认项目，它也使用了Droid项目的连接字符串:

PM> update-database -Verbose
Using StartUp project 'Droid'. <-- DROID
Using NuGet project 'Web'. <-- WEB
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
<!-- BAD TARGET DATABASE -->
Target database is: 'DefaultConnection' (DataSource: .\SQLEXPRESS, Provider: System.Data.SqlClient, Origin: Convention).
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)
   [REMOVED TEXT]
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)

在包管理器控制台设置启动项目到Web和默认项目后，我得到了它的工作。

我必须运行SQL Server浏览器服务到SQL Server配置管理器。 如果没有这个，安装就不能发现新创建的服务。

我的问题开始于我试图将服务器从IIS Express更改为本地IIS(同时使用LocalDB)。

我正在使用LocalDB(用于开发目的)，当我从本地IIS恢复到IIS Express时，Visual Studio已经将我的数据源从数据源=(LocalDB)\MSSQLLocalDB切换到数据源=.\SQLEXPRESS

错误的连接字符串

< add name = " DefaultConnection connectionString =“源代码=数据。\ SQLEXPRESS; AttachDbFilename = | DataDirectory | \ SurveyTestsDB。中密度纤维板;最初用户目录= SurveyTestsDB集成安全= True;例如= True” providerName =“系统数据。SqlClient " - >

正确的连接串

< add name = " DefaultConnection connectionString =“源代码=数据(LocalDb) \ MSSQLLocalDB; AttachDbFilename = | DataDirectory | \ SurveyTestsDB。中密度纤维板最初目录》中= SurveyTestsDB;集成安全= True”providerName =“系统数据。SqlClient " - >

希望这能帮助到一些人。