# Switch to another DBMS for Entity Framework Core

**[The application startup template](Startup-Templates/Application.md)** comes with SQL Server provider pre-configured for the Entity Framework Core. Entity Framework Core supports [many other DBMSs](https://docs.microsoft.com/en-us/ef/core/providers/) and you can use any of them with your ABP based applications.

ABP framework provides integration packages for some common DBMSs to make the configuration a bit easier (see the [entity framework core document](Entity-Framework-Core.md) for a list of available integration packages). However, you can configure your DBMS provider without these integration packages.

While using the integration package is always recommended (it also makes standard for the depended version across different modules), you can do it manually if there is no integration package for your DBMS provider.

This document explains how to switch to MySQL without using [the MySQL integration package](Entity-Framework-Core-MySQL.md).

## Replace the SQL Server Dependency

* Remove the [Volo.Abp.EntityFrameworkCore.SqlServer](https://www.nuget.org/packages/Volo.Abp.EntityFrameworkCore.SqlServer) NuGet package dependency from the `.EntityFrameworkCore` project.
* Add the [Pomelo.EntityFrameworkCore.MySql](https://www.nuget.org/packages/Pomelo.EntityFrameworkCore.MySql/) NuGet package dependency to your `.EntityFrameworkCore` project.

## Remove the Module Dependency 

Remove the `AbpEntityFrameworkCoreSqlServerModule` from the dependency list of your ***YourProjectName*EntityFrameworkCoreModule** class.

## Change the UseSqlServer() Calls

Find the following code part inside the *YourProjectName*EntityFrameworkCoreModule class:

````csharp
Configure<AbpDbContextOptions>(options =>
{
    options.UseSqlServer();
});
````

Replace it with the following code part:

````csharp
Configure<AbpDbContextOptions>(options =>
{
    options.Configure(ctx =>
    {
        if (ctx.ExistingConnection != null)
        {
            ctx.DbContextOptions.UseMySql(ctx.ExistingConnection);
        }
        else
        {
            ctx.DbContextOptions.UseMySql(ctx.ConnectionString);
        }
    });
});
````

* `UseMySql` calls in this code is defined by the Pomelo.EntityFrameworkCore.MySql package and you can use its additional options if you need.
* This code first checks if there is an existing (active) connection to the same database in the current request and reuses it if possible. This allows to share a single transaction among different DbContext types. ABP handles the rest of the things.
* It uses `ctx.ConnectionString` and passes to the `UseMySql` if there is no active connection (which will cause to create a new database connection). Using the `ctx.ConnectionString` is important here. Don't pass a static connection string (or a connection string from a configuration). Because ABP [dynamically determines the correct connection string](Connection-Strings.md) in a multi-database or [multi-tenant](Multi-Tenancy.md) environment.

## Change the Connection Strings

MySQL connection strings are different than SQL Server connection strings. So, check all `appsettings.json` files in your solution and replace the connection strings inside them. See the [connectionstrings.com]( https://www.connectionstrings.com/mysql/ ) for details of MySQL connection string options.

You typically will change the `appsettings.json` inside the `.DbMigrator` and `.Web` projects, but it depends on your solution structure.

## Change the Migrations DbContext

MySQL DBMS has some slight differences than the SQL Server. Some module database mapping configuration (especially the field lengths) causes problems with MySQL. For example, some of the the [IdentityServer module](Modules/IdentityServer.md) tables has such problems and it provides an option to configure the fields based on your DBMS.

The startup template contains a *YourProjectName*MigrationsDbContext which is responsible to maintain and migrate the database schema. This DbContext basically calls extension methods of the depended modules to configure their database tables.

Open the *YourProjectName*MigrationsDbContext and change the `builder.ConfigureIdentityServer();` line as shown below:

````csharp
builder.ConfigureIdentityServer(options =>
{
    options.DatabaseProvider = EfCoreDatabaseProvider.MySql;
});
````

Then `ConfigureIdentityServer()` method will set the field lengths to not exceed the MySQL limits. Refer to related module documentation if you have any problem while creating or executing the database migrations.

## Re-Generate the Migrations

The startup template uses [Entity Framework Core's Code First Migrations](https://docs.microsoft.com/en-us/ef/core/managing-schemas/migrations/). EF Core Migrations depend on the selected DBMS provider. So, changing the DBMS provider will cause the migration fails.

* Delete the Migrations folder under the `.EntityFrameworkCore.DbMigrations` project and re-build the solution.
* Run `Add-Migration "Initial"` on the Package Manager Console (select the `.DbMigrator`  (or `.Web`) project as the startup project in the Solution Explorer and select the `.EntityFrameworkCore.DbMigrations` project as the default project in the Package Manager Console).

This will create a database migration with all database objects (tables) configured.

Run the `.DbMigrator` project to create the database and seed the initial data.

## Run the Application

It is ready. Just run the application and enjoy coding.