passed dbcontext connection string to DALayer

Question

I have 4 layer in my application UI,DomainClass,Model(DBCntext),Repository.

In repository i have an abstract class like this :

 public abstract class GenericRepository<C, T> :
    IGenericRepository<T>
        where T : class
        where C : DbContext, new()
    {

        private C _entities = new C();
        public C Context
        {

            get { return _entities; }
            set { _entities = value; }
        }

        public virtual IQueryable<T> GetAll()
        {

            IQueryable<T> query = _entities.Set<T>();
            return query;
        }

        public IQueryable<T> FindBy(System.Linq.Expressions.Expression<Func<T, bool>> predicate)
        {

            IQueryable<T> query = _entities.Set<T>().Where(predicate);
            return query;
        }

        public virtual void Add(T entity)
        {
            _entities.Set<T>().Add(entity);
        }

        public virtual void Delete(T entity)
        {
            _entities.Set<T>().Remove(entity);
        }

        public virtual void Edit(T entity)
        {
            _entities.Entry(entity).State = System.Data.Entity.EntityState.Modified;
        }

        public virtual void Save()
        {
            _entities.SaveChanges();
        }

    }

All my entities inheritance from this class like this :

namespace Repository
{
    public class StationRepository : GenericRepository<ShirazRailWay.ShirazRailwayEntities, DomainClass.Station>
    {
    }
}

I UI i called this repositories. as you can see here :

  stationrepository objnew=new stationrepository();
  obnew.getall();

In UI layer i have an connection string in app.config as you can see here :

<connectionStrings>
    <add name="ShirazRailwayEntities" connectionString="metadata=res://*/RailWay.csdl|res://*/RailWay.ssdl|res://*/RailWay.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=****;initial catalog=DB-Metro;user id=sa;password=****;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
  </connectionStrings>

But i want to give an option to my users that with this option they can set their connection string by themselves.So i created a form in UI layer that when the users trying to log in it asks them the connection string .My problem is How can pass this connection string to my dbcontext?

In my model layer(dbcontext) i have this :

public partial class ShirazRailwayEntities : DbContext
    {
        public ShirazRailwayEntities()
            : base("name=ShirazRailwayEntities")
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }

        public DbSet<Advertisement> Advertisements { get; set; }
        public DbSet<Line> Lines { get; set; }
        public DbSet<Log> Logs { get; set; }
        public DbSet<Path> Paths { get; set; }
        public DbSet<Sensor> Sensors { get; set; }
        public DbSet<Station> Stations { get; set; }
        public DbSet<Train> Trains { get; set; }
        public DbSet<User> Users { get; set; }
        public DbSet<TimeTable> TimeTables { get; set; }
        public DbSet<ConfigFont> ConfigFonts { get; set; }
        public DbSet<ArrivalTime> ArrivalTimes { get; set; }
        public DbSet<ConfigColor> ConfigColors { get; set; }
    }

Answer 1

Add another constructor that takes your connection string:

public partial class ShirazRailwayEntities : DbContext
{
    public ShirazRailwayEntities()
        : base(name: "ShirazRailwayEntities")
    {
    }

    public ShirazRailwayEntities(string connectionName)
        : base(name: connectionName)
    {
    }
}

var context = new ShirazRailwayEntities("whatever connection name you want");