通连接字符串EF的DbContext代码首先

Question

我有一个从派生的DbContext类似下面的上下文：

public class StudentContext : DbContext 
{ 
public StudentContext(string connectionString) : base(connectionString) 
{ 
} 
protected override void OnModelCreating(DBModelBuilder modelBuilder) 
{ 
    base.OnModelCreating(modelBuilder); 
    System.Data.Entity.Database.SetInitializer(new MigrateDatabaseToLatestVersion<StudentContext, StudentMigrations.Configuration>()); 
} 

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

我试图通过传递连接字符串：

studentContext = new StudentContext(settings.ConnectionString) 

的设置通过读取配置文件在运行时加载。 我试过this，我也尝试过使用this.Database.Connection.ConnectionString在StudentContext构造函数中设置连接字符串。无论哪种情况，我都会得到一个异常，要求我提供一个默认构造函数或提供一个实现的IDbContextFactory。唯一可行的事情是这样的：

public class StudentContext : DbContext 
{ 
    public static string ConnectionString; 
public StudentContext(string connectionString) : base(ConnectionString = connectionString) 
{ 
} 

//And also provide a default implementation of the DbContext constructor: 
public StudentContext() : base(ConnectionString) 
{ 
} 

protected override void OnModelCreating(DBModelBuilder modelBuilder) 
{ 
    base.OnModelCreating(modelBuilder); 
    System.Data.Entity.Database.SetInitializer(new MigrateDatabaseToLatestVersion<StudentContext, StudentMigrations.Configuration>()); 
} 

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

我试图减少使用静态的代码，因此，如果我能得到工作的第一个选项，那简直太好了。

Answer 1

原来，连接字符串缓存在MigrateDatabaseToLatestVersion的只读字符串中from this answer。我只是不得不更新类：

public class StudentContext : DbContext 
{ 
    public StudentContext(string connectionString) : base(connectionString) 
    { 
    } 

    protected override void OnModelCreating(DBModelBuilder modelBuilder) 
    { 
     base.OnModelCreating(modelBuilder); 
     System.Data.Entity.Database.SetInitializer(new MigrateDatabaseToLatestVersion<StudentContext, StudentMigrations.Configuration>(true)); //Passing true here to reuse the client context triggering the migration 
    } 

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

Answer 2

我们必须指定实体连接字符串。 in DbContext

SqlConnectionStringBuilder sqlString = new SqlConnectionStringBuilder() 
     { 
    DataSource = "SOURAV-PC", // Server name 
    InitialCatalog = "efDB", //Database 
      UserID = "sourav",   //Username 
      Password = "mypassword", //Password 
     }; 
     //Build an Entity Framework connection string 

     EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder() 
     { 
      Provider = "System.Data.SqlClient", 
      Metadata = "res://*/testModel.csdl|res://*/testModel.ssdl|res://*/testModel.msl", 
      ProviderConnectionString = sqlString.ToString() 
     }; 
     return entityString.ConnectionString; 
    }