Change DbContext connection at run-time

c# database entity entity-framework reflection


I have 3 DBs that I want to work with: A,B and C. each one have the same tables (for example: users, products).

I want to let the user decide (on run-time) which DB he wants to work with. So... I used EF5 and created 3 edbx files which created the following classes: ADBEntities, BDBEntities and CDBEntities.

How can I let him decide the selecteddb so I could get its users?

I mean,

var dstuff = from user in selecteddb.users
             where user.UserEmail == userEmail
             select user.UserID;

I've thought of using reflection / base class (DBEntities), but didn't get far with those ideas.

11/27/2013 10:28:00 PM

Accepted Answer

a bit late on this answer but I think there's a potential way to do this with a neat little extension method. As slypete (nice name :-)) says, you only need ONE class model, assuming all tables/properties are identical. This being the case, we can take advantage of the EF convention over configuration plus a few little framework calls.

Anyway, without further ado, the commented code and example usage:

the extension method class:

public static class ConnectionTools
    // all params are optional
    public static void ChangeDatabase(
        this DbContext source,
        string initialCatalog = "",
        string dataSource = "",
        string userId = "",
        string password = "",
        bool integratedSecuity = true,
        string configConnectionStringName = "") 
        /* this would be used if the
        *  connectionString name varied from 
        *  the base EF class name */
            // use the const name if it's not null, otherwise
            // using the convention of connection string = EF contextname
            // grab the type name and we're done
            var configNameEf = string.IsNullOrEmpty(configConnectionStringName)
                ? source.GetType().Name 
                : configConnectionStringName;

            // add a reference to System.Configuration
            var entityCnxStringBuilder = new EntityConnectionStringBuilder

            // init the sqlbuilder with the full EF connectionstring cargo
            var sqlCnxStringBuilder = new SqlConnectionStringBuilder

            // only populate parameters with values if added
            if (!string.IsNullOrEmpty(initialCatalog))
                sqlCnxStringBuilder.InitialCatalog = initialCatalog;
            if (!string.IsNullOrEmpty(dataSource))
                sqlCnxStringBuilder.DataSource = dataSource;
            if (!string.IsNullOrEmpty(userId))
                sqlCnxStringBuilder.UserID = userId;
            if (!string.IsNullOrEmpty(password))
                sqlCnxStringBuilder.Password = password;

            // set the integrated security status
            sqlCnxStringBuilder.IntegratedSecurity = integratedSecuity;

            // now flip the properties that were changed
                = sqlCnxStringBuilder.ConnectionString;
        catch (Exception ex)
            // set log item if required


// assumes a connectionString name in .config of ADBEntities
var selectedDb = new ADBEntities();
// so only reference the changed properties
// using the object parameters by name
        initialCatalog: "name-of-bdb-initialcatalog",
        userId: "jackthelad",
        password: "nosecrets",
        dataSource: @".\sqlexpress" // could be ip address etc

I currently use this for exactly the purpose that you mention above and thus far, it's served me very well. Hope it helps in your instance.

11/27/2013 10:20:13 PM

Popular Answer

Pass the appropriate connection string / connection name when creating a DbContext

using (var context = new MyDbContext("Server=localhost;Database=dbA;..."))
    return context.Users.Where(u => u.Email == "").Single();

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