Dynamic MySQL database connection for Entity Framework 6
It's now 2019 of course things have changed a bit but Franciso's example really helped me on this. This is the simplest solution I could find and the only one that actually worked. I did change it a bit from what he has shown. Follow this to completion you should end up with a working solution.
I had to change a few things. I am going to be very explicit in what has to be done and I am going to use my actual file names etc so that you don't have to guess about substitutions. Many examples are also short on how to make it work at the end. This example has everything you need to know.
This was built on visual studio 2015 Entityframework 6 using MySql server 8.0.16.0.
Unfortunately the MySql connectors and libraries are a complete mess. The 8.0.xx.0 connector / net and MySql.Data.Entity.EF6 and MySql.Data are completely useless.
I have installed Connector Net 6.10.7.0, MySql.Data.Entity.EF6 6.10.7.0, and MySql.Data 6.10.7.0. That works for me and I will vigorously oppose changing this.
This is for MySql but I really don't know why it could not work for any db.
Scenario
I have a multi tenant situation where I have a common db and multiple tentant databases, one per customer The customer id is kept in the common db for login purposes and authorizaton and the customer id directs which database to use. The client db's are all called myclientdb_x where x is the client number. myclientdb_1, myclientdb_2, myclientdb_35 and so on.
I need to dynamically switch to whatever clientdb_x the code is currently serving. There is a initial database client called myclient_0 which is the template for all of the other myclient_x databases.
Step1
I created a specific connection string in my Web.config for this it looks like this. It allows connections to the clientdb_0
<add name="DefaultClientConnection" providerName="MySql.Data.MySqlClient"
connectionString="server=localhost;user id=xxx;
password=xxxx; persistsecurityinfo=True;database=clientdb_0" />
Step2
I created a new entity called ClientDbUserUpdater using the wizard. The data entity is called
ClientDbUserUpdater.edmx
I told it to use "DefaultClientConnection" as the DB connection I told it to save this new connection string in the Web.config
This created new entity connection string in the Web.config file and it will look like
<add name="myclient_0Entities" connectionString="metadata=
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.csdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.ssdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.msl;
provider=MySql.Data.MySqlClient;provider connection string="
server=localhost;user id=xxxx;password=yyyyy;
persistsecurityinfo=True;database=myclient_0"" providerName="System.Data.EntityClient" />
You might have to dig a bit because the wizard is not good about putting in \n in appropriate places.
Notice that this connection string is fundamentally the same as the initial connection string except for its name and the fact that it has
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.csdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.ssdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.msl;
The res: strings are needed by the data entity and its why you can't just send a standard connection string into the data entity.
If you try to send in the initial connection string
<add name="DefaultClientConnection" providerName="MySql.Data.MySqlClient"
connectionString="server=localhost;user id=xxx;
password=xxxx; persistsecurityinfo=True;database=clientdb_0" />
you will get an exception from
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
Step3
This new connection string is the one you need to alter. I have not tested it but I am pretty sure if change the data entity model with the wizard you will need to make this change again. Take string:
<add name="myclient_0Entities" connectionString="metadata=
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.csdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.ssdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.msl;
provider=MySql.Data.MySqlClient;provider connection string="
server=localhost;user id=xxxx;password=yyyyy;
persistsecurityinfo=True;database=myclient_0"" providerName="System.Data.EntityClient" />
and change it to:
<add name="myclient_0Entities" connectionString="metadata=
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.csdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.ssdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.msl;
provider=MySql.Data.MySqlClient;provider connection string="
server=localhost;user id=xxxx;password=yyyyy;
persistsecurityinfo=True;database={0}"" providerName="System.Data.EntityClient" />
Notice that the only part changed is database=myclient_0 to database={0}
Step 4
The data entity created some code behind ClientDbUserUpdater.edmx. The file is called ClientDbUserUpdater.Context.cs.
The code is ...
namespace what.ever.your.namespace.is
{
using System;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
public partial class client_0Entities : DbContext
{
public client_0Entities()
: base("name=client_0Entities")
{
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
public virtual DbSet<user> users { get; set; }
}
}
Notice that this a partial class. This means you can extend this class and add a new constructor.
Add the following class.
using System;
using System.Configuration ;
using System.Data.Entity ;
namespace what.ever.your.namespace.is
{
public partial class client_0Entities : DbContext
{
public client_0Entities(string dbName) : base(GetConnectionString(dbName))
{
}
public static string GetConnectionString(string dbName)
{
var connString = ConfigurationManager.ConnectionStrings["client_0Entities"].ConnectionString.ToString();
// obviously the next 2 lines could be done as one but creating and
// filling a string is better for debugging. You can see what happened
// by looking a conn
// return String.Format(connString, dbName);
string conn = String.Format(connString, dbName);
return conn ;
}
}
}
The class adds a new constructor which allows you to get the base connection string for the data entity model which from above looks like:
<add name="myclient_0Entities" connectionString="metadata=
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.csdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.ssdl|
res://*/Areas.Authorizations.Models.ClientDbUserUpdater.msl;
provider=MySql.Data.MySqlClient;provider connection string="
server=localhost;user id=xxxx;password=yyyyy;
persistsecurityinfo=True;database={0}"" providerName="System.Data.EntityClient" />
and modfiy it at run time to change the schema.
The String.Format() call in the new partial class swaps out the database schema name in this connection string at run time.
At this point all configuration is done.
Step 5
Now you can make it go. For better understanding of this example it is nice to know what the model looks like for this entity. It is very simple because I was just testing and trying to make it go.
Drilling down through ClientDbUserUpdater.edmx and into into ClientDbUserUpdater.tt you will find your model in modelname.cs . My model is called "user" so my file name is called user.cs
namespace what.ever.your.namespace.is
{
using System;
using System.Collections.Generic;
public partial class user
{
public int UserId { get; set; }
public string Email { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public Nullable<bool> Active { get; set; }
}
}
Now you can generally access your model like this.
client_0Entities _client_0Entities = new client_0Entities("schemaName");
and this code can be anywhere in your solution that can see class client_0Entities.
which in practice is a line similar to any of the 3 below which are connection to databases client_19, client_47 and client_68 respectively.
client_0Entities _client_0Entities = new client_0Entities("client_19");
client_0Entities _client_0Entities = new client_0Entities("client_47");
client_0Entities _client_0Entities = new client_0Entities("client_68");
the following is an actual code example that works on my system. Obviously I am going to not hard code in "client_19" but its better for demo purposes.
here is actual code with real names that works and adds a new row to the user table on database client_19
string _newSchema = "client_19"
using(client_0Entities _client_0Entities = new client_0Entities(_newSchema))
{
user _user = new user();
_user.UserId = 201;
_user.Email = "[email protected]"
_user.FirstName ' "Someone";
_user.LastName = "New";
_user.Active = true;
client_0Entities.users.Add ( _user ) ;
client_0Entities.SaveChangesAsync ( ) ;
}
Hopefully this helps some people. I spent about 20 hrs looking at different solutions which simply did not work or provide enough information to complete them. As I said, finding Franciso's example allowed me to get it working.
Regards,
Entity Framework 6 offers some handy subtle changes which aid in both getting MySQL working and also creating dynamic database connections.
Getting MySQL working with Entity Framework 6
First, at the date of my answering this question, the only .Net connector drivers compatible with EF6 is the MySQL .Net Connectior 6.8.1 (Beta development version) which can be found at the official MySQL website here.
After installing, reference the following files from your Visual Studio solution:
- Mysql.Data.dll
- Mysql.Data.Entity.EF6.dll
You will also need to copy these files somewhere where they will be accessible to the project during build time, such as the bin directory.
Next, you need to add some items to your Web.config (or App.config if on desktop based) file.
A connection string:
<connectionStrings>
<add name="mysqlCon"
connectionString="Server=localhost;Database=dbName;Uid=username;Pwd=password"
providerName="MySql.Data.MySqlClient" />
</connectionStrings>
Also add the provider, inside the <entityFramework /> and <providers /> nodes, optionally (this is an absolute must in the second part of my answer, when dealing with dynamically defined databases) you may change the <defaultConnectionFactory /> node:
<entityFramework>
<defaultConnectionFactory type="MySql.Data.Entity.MySqlConnectionFactory, MySql.Data.Entity.EF6" />
<providers>
<provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.Entity.EF6" />
</providers>
</entityFramework>
If you change the defaultConnectionFactory from the default sql server connection, don't forget to remove the <parameter> nodes which are nested in the defaultConnectionFactory node. The MysqlConnectionFactory does not take any parameters for its constructor and will fail if the parameters are still there.
At this stage, it's quite easy to connect to MySQL with Entity, you can just refer to the connectionString above by name. Note that if connecting by name, this will work even if the defaultConnectionFactory node still points at SQL Server (which it does by default).
public class ApplicationDbContext: DbContext
{
public ApplicationDbContext() : base("mysqlCon")
{
}
}
The it is just a matter of connecting normally:
ApplicationDbContext db = ApplicationDbContext();
Connecting to a dynamically selected database name
At this point it's easy to connect to a database which we can pass as a parameter, but there's a few things we need to do.
Important Note
If you have not already, you MUST change the defaultConnectionFactory in Web.config if you wish to connect to MySQL dynamically. Since we will be passing a connection string directly to the context constructor, it will not know which provider to use and will turn to its default connection factory unless specified in web.config. See above on how to do that.
You could pass a connection string manually to the context like this:
public ApplicationDbContext() : base("Server:localhost;...")
{
}
But to make it a little bit easier, we can make a small change to the connection string we made above when setting up mySQL. Just add a placeholder as shown below:
<add name="mysqlCon" connectionString="Server=localhost;Database={0};Uid=username;Pwd=password" providerName="MySql.Data.MySqlClient" />
Now we can build a helper method and change the ApplicationDbContext class as shown below:
public class ApplicationDbContext: DbContext
{
public ApplicationDbContext(string dbName) : base(GetConnectionString(dbName))
{
}
public static string GetConnectionString(string dbName)
{
// Server=localhost;Database={0};Uid=username;Pwd=password
var connString =
ConfigurationManager.ConnectionStrings["mysqlCon"].ConnectionString.ToString();
return String.Format(connString, dbName);
}
}
If you are using database migrations, the following step is important
If you are using migrations, you will find that the ApplicationDbContext will be passed to your Seed method by the framework and it will fail because it will not be passing in the parameter we put in for the database name.
Add the following class to the bottom of your context class (or anywhere really) to solve that problem.
public class MigrationsContextFactory : IDbContextFactory<ApplicationDbContext>
{
public ApplicationDbContext Create()
{
return new ApplicationDbContext("developmentdb");
}
}
Your code-first migrations and seed methods will now target the developmentdb schema in your MySQL database.
Hope this helps someone :)