如何使用C＃覆盖在运行时在Web.config文件中设置的数据库？

Question

I have a Context class that will accept a connection name in the constructor. Then it allows me to connect to a specific server.

I would like to know how to change the default database for that connection at run time.

Here is what I have done

In the Web.config file I added the following connection strings

  <connectionStrings>
    <add name="BaseConnection" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=ScripterDynamo;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\ScripterDynamo.mdf" providerName="System.Data.SqlClient" />
    <add name="conn1" connectionString="Server=Serv1;Database=db1;UserId=myUser; Password=myPassword;" providerName="System.Data.SqlClient" />
    <add name="conn2" connectionString="Server=Serv2;Database=db2;UserId=myUser; Password=myPassword;" providerName="System.Data.SqlClient" />
    <add name="conn3" connectionString="Server=Serv3;Database=db3;UserId=myUser; Password=myPassword;" providerName="System.Data.SqlClient" />
    <add name="conn4" connectionString="Server=Serv4;Database=db4;UserId=myUser; Password=myPassword;" providerName="System.Data.SqlClient" />
  </connectionStrings>

Then I create a simple context class like so

using ScripterEngine.Models;
using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.Core.EntityClient;
using System.Data.SqlClient;
using System.Linq;
using System.Web;

namespace ScripterEngine.DataAccessLayer
{
    public class BaseContext : DbContext
    {
        public DbSet<Campaign> Campaign { get; set; }
        public DbSet<TableMeta> Campaign { get; set; }

        public BaseContext(string connectionName = "BaseConnection")
            : base(connectionName)
        {

        }
    }
}

Using this context class I can connect to conn4 like this

BaseConnection conn4 = BaseConnection("conn4");

The only problem here is that the connection "conn4" will connect to the database called db4 which is set by default in the connection string. This is expect and fine in most cases. But in my case, I want to be able to change what database to connect to at run time.

My question, how can I change the database on the fly? Is there a way to add a method in the context class which will override the default database only?

UPDATED

Here is what I have changed my context class hoping that the setDatabase method will allow me to change the database at run time

using ScripterEngine.Models;
using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.Core.EntityClient;
using System.Data.SqlClient;
using System.Linq;
using System.Web;

namespace ScripterEngine.DataAccessLayer
{
    public class BaseContext : DbContext
    {
        protected string connectionName;
        public DbSet<Campaign> Campaign { get; set; }
        public DbSet<TableMeta> TableMeta { get; set; }

        public BaseContext(string connName = "BaseConnection")
            : base(connName)
        {
            connectionName = connName;
        }

        public BaseContext setDatabase(string databaseName)
        {
            var connection = System.Configuration.ConfigurationManager.ConnectionStrings[connectionName].ConnectionString;

            //change the database before creating the new connection
            return new BaseContext(connection);
        }


    }
}

I would use it like so

        BaseContext db1 = new BaseContext("conn4";
        var connToNewDB = db1.setDatabase("SomeNewDatabase");

Answer 1

You can do something like this, this ExampleData is just an example to understand, you can acossiate the values here you need, you connection string stay something like that:

<connectionStrings>
        <add name="ConnectionString.Properties.Settings.CustomConnectionString"
            connectionString="Persist Security Info=True" providerName="System.Data.SqlClient" />
    </connectionStrings>

This is just example to initialize data using System;

namespace ConnectionStringCustom
{
    public static class ExampleData
    {
        public static String connUserName = "user";
        public static String connPassword = "pass";
        public static String connServerName = "servername";
        public static String connDatabaseName = "databasename";
    }
}



namespace ConnectionStringCustom.Properties
   {

   internal sealed partial class Settings
      {


      void Settings_SettingsLoaded( object sender, System.Configuration.SettingsLoadedEventArgs e )
         {
             this["CustomConnectionString"] = "Data Source=" + ExampleData.connServerName + ";"
                                          + "Initial Catalog=" + ExampleData.connDatabaseName + ";"
                                          + "Persist Security Info=false;"
                                          + "User ID=" + ExampleData.strConnUserName + ";"
                                          + "Password=" + ExampleData.connPassword + ";";
         }

      }

   }

With this you can change all proprieties.

EDIT: See your changes I think probably you need something like

https://stackoverflow.com/a/7692708/5842138

But I think is not an good practice, why you dont simply create many ConnectionStrings ?

Hope this help

Answer 2

Try to set DbConnection.ConnectionString property.

dataContextInstance.Database.Connection.ConnectionString = "new connection string";

But I am not sure that you don't need to reinitialize some of your properties/code after changing connection string.

Answer 3

I created a 2 contexts.

1. BaseContext: This context does not change and I use it to design my app using Code first approach.

2. DynamicContext: This context will change at run time.

To get the DynamicContext to work, I created a dynamic connection in my connection file.

I basiclly added this to my block

<add name="DynamicConnection" connectionString="Server=DefaultServer;Initial Catalog=I3_IC;User ID=defaultUser; Password=defaultPassword;" providerName="System.Data.SqlClient" />

Then I created a new context class like this

using System; using System.Collections.Generic; using System.Data.Common; using System.Data.Entity; using System.Data.Entity.Core.EntityClient; using System.Data.SqlClient; using System.Linq; using System.Web;

namespace MyApp.DataAccessLayer
{
    public class DynamicContext : DbContext
    {
        protected string connectionName = "DynamicConnection";

        protected string myServerName;

        protected string myUserId;

        protected string myPassword;

        /**
         * Created the connection to the server using the giving connection string name.
         * This constructor will allow you to connect to any connection string found in the Web.config file
         * 
         * @param connName
         */
        public DynamicContext(string serverName = null, string userID = null, string password = null)
            : base("DynamicConnection")
        {
            myServerName = serverName;

            myUserId = userID;

            myPassword = password;
        }

        /**
         * This constructor will allow you to construct a context by giving a string and it can only be call from the class itself
         * 
         */
        private DynamicContext(string connectionString)
            : base(connectionString)
        {
        } 


        /**
         * Changes the default database
         * 
         * @param databaseName
         */
        public DynamicContext setDatabase(string databaseName)
        {
            //Get the existing string for dynamic connection
            var connectionString = System.Configuration.ConfigurationManager.ConnectionStrings[connectionName].ConnectionString;

            //convert the existsing string into an object
            SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder(connectionString);

            //change the database before creating the new connection
            builder.InitialCatalog = databaseName;

            if (myServerName != null){
                builder.DataSource = myServerName;
            }

            if (myUserId != null){
                builder.UserID = myUserId;
            }

            if (myPassword != null){
                builder.Password = myPassword;
            }

            return new DynamicContext(builder.ConnectionString);
        }

    }
}

Then I use this like so

//Create a dynamic context, note that you can also change the username and the password of the default user by using the second and third parameters.
var dbDynamic = new DynamicContext(serverName);

//Finally, you can set the correct table
var conn1 = dbDynamic.setDatabase('table1');

//If you want to connect to a different table
var conn2 = dbDynamic.setDatabase('table2');