Using connection string in Web.config when enabling code-first migrations

Question

I have multiple connection strings in Web.config (for databases that should all have the same exact schema), and my DbContext is initialized with a connection string dynamically:

public MyDbContext(string connectionStringName) : base(connectionStringName)
{

}

I do not have a default constructor for MyDbContext as it is meaningless in my case. I decide which connection string to use based on the Id value of each entity (custom sharding).

I'm trying to run enable-migrations for my DbContext, but I'm getting the following error:

The target context 'MyDbContext' is not constructible. Add a default constructor or provide an implementation of IDbContextFactory.

I've seen a sample implementation of IDbContextFactory like so:

public class MyDbContextFactory : IDbContextFactory<MyDbContext>
{
    public MyDbContext Create()
    {
        return new MyDbContext("connectionStringName");
    }
}

How is this going to help me? Isn't the connection string still hard-coded? How could I add migrations for each database?

mr100 · Accepted Answer · 2014-05-07 10:16:13Z

3

+50

And how about providing default constuctor for that DbContext and then when you call scripts add-migration and update-database you may use -ConnectionStringName and -ConnectionProviderName attributes to point to database you want to use.

By the way - enable-migrations script does not do much - it addes Migrations folder to your project and Configuration class. You might do it yourself.

answered May 7, 2014 at 10:16

mr100

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2 Comments

Mark13426 Over a year ago

Thanks. Is there a way to automate "update-database" execution rather than manually type a connection string name for every single database and run the command in package manager console? Maybe via a powershell script?

mr100 Over a year ago

Of course that would be good solution. The easiest case would be to store whole command saved somewhere and copy it to Power Shell Commandline. Then by clicking Up Arrow you may call this command over and over. Aletrantively you might use migrate.exe tool and run it with batch script.

Anshul Nigam · Accepted Answer · 2014-05-12 05:55:57Z

0

Best Soution is to use a separate file where you will mention list of Id values against a connection e.g in

<connectionStrings>
     <add name="MyConn1"
          connectionString="#your connection string"
      />

     <add name="MyConn2"
          connectionString="#your connection string"
      />

and then in

<appSettings>
      <add key="MyConn1" value="entity1,entity2" />
      <add key="MyConn2" value="entity3,entity4" />
</appSettings>

Then dynamically load your connection string in some global variable

public MyDbContext() : base(MyConnectionManager.connectionStringName)
{

}

answered May 12, 2014 at 5:55

Anshul Nigam

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Comments

aamir sajjad · Accepted Answer · 2014-05-12 06:03:41Z

0

You can do it using IoC as well. Look at the sample code.

https://github.com/aamir-poswal/CodeSample

Especially
- Bootstrapper.cs
- CRMContext.cs
- DatabaseFactory.cs which you need to customize in your context

answered May 12, 2014 at 6:03

aamir sajjad

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