Entity framework code-first connect server error

Question

I am new in Entity framework. I have a simple project using code-first approach.

This is codes:

 public class Student
    {
        public Student()
        {

        }

        [Key]
        public int id { get; set; }
        public string StudentName { get; set; }
    }

   

    public class SchoolContext:DbContext
    {
        public SchoolContext() : base()
        {
            Console.WriteLine(Database.Connection.ConnectionString);

        }

        public DbSet<Student> Students { get; set; }
    }

 static void Main(string[] args)
        {
            Student aa = new Student();
            aa.id=1 ;
            aa.StudentName = "eeee";
            using (var scContext = new SchoolContext())
            {
                scContext.Students.Add(aa);
                scContext.SaveChanges();
            }

            Console.Write("success");
        }

The connection string automatic create by Entity framework:

Data Source=(localdb)\mssqllocaldb;Initial Catalog=EFExample.Model.SchoolContext;Integrated Security=True;MultipleActiveResultSets=True

I installed sqlserver 2012 express, with 2 instances:

NT Service\MSSQLSERVER

NT Service\MSSQL$SQLEXPRESS

When i ran the program, i get an error :

*An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in EntityFramework.dll

Additional information: 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*

App.config

<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=v4.5.2" />
  </startup>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="mssqllocaldb" />
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
</configuration>

Please help me what is wrong? Thank in advance.

Please could you post the <connectionStrings> section of your app.config? — Chris Pickford
(localdb) usually refers to SQL Server LocalDB, which is a file based SQL database (like SqLite). Try changing that to Data Source=localhost\mssqllocaldb. — CodingGorilla
@ Chris Pickford: i don't use connectionstring in app.config. I think EF will automatic create a connection string. — nguyenmy
For SQLExpress instances I usually use this format: <add name="ConnectionStringName" providerName="System.Data.SqlClient" connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=DatabaseName;Integrated Security=True;MultipleActiveResultSets=True"/> Please check your app.config just to be sure. — Gareth van der Berg
Though it seems to be related with connStr as others said, could you also add Inner exception, just in case it might give us a clue. Also, your casing is inconsistent. Some variables are camelCase and some are PascalCase. Better stick to either, preferably camelCase as it's considered to be standard. — uTeisT

Gareth van der Berg Gareth van der Berg · Accepted Answer · 2016-03-23T15:43:11

I'd suggest explicitly adding your own connectionstring in the app.config

`<connectionStrings>
    <add connectionString="Data Source=.\SQL_INSTANCE_NAME;Initial Catalog=DBName;Connection Timeout=60;Integrated Security=True;MultipleActiveResultSets=False" name="DbConnectionString" providerName="System.Data.SqlClient" />
</connectionStrings>`

Entity framework code-first connect server error

3 Answers