Change entity framework context during runtime

Question

In a solution, I have two DALs. Each accesses a different server.

The first server/database contains a table that will provide database names.

var db = "db_1"; // can be db_1, db_2, db_3, etc.

The second server contains many databases - each containing an identical table that needs to be queried.

I need to be able to dynamically switch contexts depending upon the db value. I'd like to be able to pass the db var to a business layer that returns/uses the correct Context.

Sounds like a context factory method (pull the initial column value and return a context based on the result). — Brad Christie, Jun 10 '14 at 20:26
Brad Christie - Can you elaborate? I'm fairly new to these technologies. — user1143687, Jun 10 '14 at 20:42
This code example shows how to use dynamic connection string strings. http://stackoverflow.com/a/16133150/1347784 . we use this to run a multi tenant approach. Each with the own DB. Created at Runtime. — phil soady, Jun 11 '14 at 06:11

score 0 · Answer 1 · answered Jun 10 '14 at 22:55

You can create two models for this. One for your database containing the tables that provide the database names, and the other for the other databases.

If you are using the db first approach, your context object will be created with a default connection string. Since it is a partial class you can extend it to take a connection string like so...

public partial class MyContext
{
    public MyContext(string nameOrConnectionString) : base(nameOrConnectionString)
}

This is where at runtime you will pass the connection string of the server/database you pulled from the first context. Something like this is what it will look like...

...
using(var dbNameContext = new DatabaseNameContext())
{
    var dbName = dbNameContext.DBNames.FirstOrDefault(dbn => dbn.Name == "db1");
    var connectionString = "metadata=res://*/Database..." + dbName.Name;
    using(var dbContexts = new MyContext(connectionString))
    {
        var MyDataList = dbContexts.Data.ToList();
    }
}

Obviously you should fix the connection string to be like your own and place the dbName where it belongs in the connection string.

You should make sure you have a plan intact for keeping all of the different tables in different databases the same so that the model is accurate. Otherwise you will get RTEs.

Change entity framework context during runtime

1 Answers1