c# - SQL Network Interfaces, error: 50 - Local Database Runtime error occurred. Cannot create an automatic instance -

i trying build asp.net mvc 5 web application has mydatabase.mdf file in app_data folder. have sql server 2014 express installed localdb instance. can edit database tables using server explorer, when debug application , go page database needed following error.

a network-related or instance-specific error occurred while establishing connection sql server. server not found or not accessible. verify instance name correct , sql server configured allow remote connections. (provider: sql network interfaces, error: 50 - local database runtime error occurred. cannot create automatic instance. see windows application event log error details.

so looked in event viewer under application , see 1 warning on , on again.

the directory specified caching compressed content c:\users\user1\appdata\local\temp\iisexpress\iis temporary compressed files\clr4integratedapppool invalid. static compression being disabled.

so tried rebooting server, still no go. same error 50 before.

i have created class under models have class called post.

namespace myapplication.models {     public class post     {         public int id { get; set; }         public string title { get; set; }         public string content { get; set; }     }      public class mydatabase : dbcontext     {         public dbset<post> posts { get; set; }     } } 

i have controller setup list posts mydatabase.

namespace myapplication.controllers {     public class postscontroller : controller     {         private mydatabase db = new mydatabase();          // get: posts         public actionresult index()         {             return view(db.posts.tolist());         }     } 

in web.config file connection string looks this...

<connectionstrings>     <add name="defaultconnection"           connectionstring="data source=(localdb)\v12.0;attachdbfilename=|datadirectory|\mydatabase.mdf;integrated security=true"           providername="system.data.sqlclient" /> </connectionstrings> 

i've tried suggestion posted here didn't work. tried this.

i notice mydatabase instance gets disconnected after start running application. if refresh database using server explorer in visual studio can view tables.

how can connect database , edit within visual studio 2013 when debug application cannot connect database?

breaking changes localdb: applies sql 2014; take on article , try use (localdb)\mssqllocaldb server name connect localdb automatic instance, example:

<connectionstrings>   <add name="productscontext" connectionstring="data source=(localdb)\mssqllocaldb;    ... 

the article mentions use of 2012 ssms connect 2014 localdb. leads me believe might have multiple versions of sql installed - leads me point out this answer suggests changing default name of localdb "instance" avoid other version mismatch issues might arise going forward; mentioned not source of issue, raise awareness of potential clashes multiple sql version installed on single dev machine might lead ... , in habit of in order avoid some.

another thing worth mentioning - if you've gotten instance in unusable state due tinkering try , fix problem, might worth starting on - uninstall, reinstall - try using mssqllocaldb value instead of v12.0 , see if corrects issue.