Using entity framework on multiple databases

Question

I am writing a payroll system that will integrate with a pre-existing system. The original system had a master database that handled user management and some global configur

Answer 1

EF6 has better support for multiple DB access from Same context. Here is a snippet from EF5. Managing the database initializer setting prior is important. You may not want to trigger ANY migrations. i.e, use this before

Database.SetInitializer(new ContextInitializerNone<MyDbContext>());

but to answer the question: Yes you can

var conn = GetSqlConn4DbName(dataSource,dbName );
var ctx = new MyDbContext(conn,true);



public DbConnection GetSqlConn4DbName(string dataSource, string dbName) {
        var sqlConnStringBuilder = new SqlConnectionStringBuilder();
        sqlConnStringBuilder.DataSource = String.IsNullOrEmpty(dataSource) ? DefaultDataSource : dataSource;
        sqlConnStringBuilder.IntegratedSecurity = true;
        sqlConnStringBuilder.MultipleActiveResultSets = true;

        var sqlConnFact = new SqlConnectionFactory(sqlConnStringBuilder.ConnectionString);
        var sqlConn = sqlConnFact.CreateConnection(dbName);
        return sqlConn;
    }


 public class ContextInitializerNone<TContext> : IDatabaseInitializer<TContext> where TContext : DbContext
{
    public void InitializeDatabase(TContext context) {  }
}

Also see StackOverflow answer using migration, sample code, and dynamic db connection

Answer 2

It is very simple. I have:

public WMSEntities() : base("name=WMSEntities") //WMSEntities is conection string name in     web.config also the name of Entitiframework
{
}

already in autogenerated Model.Context.cs of edmx folder

To connect to multiple database in runtime, I created another constructor that takes connection string as parameter like below in same file Model.Context.cs

public WMSEntities(string connStringName)
    : base("name=" + connStringName)
{
}

Now I added other connection string in Web.Config for example

<add name="WMSEntities31" connectionString="data source=TESTDBSERVER_NAME;initial catalog=TESTDB;userid=TestUser;password=TestUserPW/>

<add name="WMSEntities" connectionString="data source=TESTDBSERVER_NAME12;initial catalog=TESTDB12;userid=TestUser12;password=TestUserPW12/>

Then, when connecting to database I call below method passing connetionString name as parameter

public static List<v_POVendor> GetPOVendorList(string connectionStringName)
{
    using (WMSEntities db = new WMSEntities(connectionStringName))
    {               
        vendorList = db.v_POVendor.ToList();                 
    }
}