Entity Framework Core 2.1 - Multiple Providers

问题

What is the right way to work with multiple providers? My Example:

appsettings.json

{
  "ConnectionStrings": {
    "Sqlite": "Data Source=database.db"
  }
}

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
     services.AddDbContext<DatabaseContext>(options =>
                    options.UseSqlite(Configuration.GetConnectionString("Sqlite")));
}

DatabaseContext.cs

public class DatabaseContext : DbContext
{
    public DatabaseContext(DbContextOptions<DatabaseContext> options) : base(options) { }
    public DbSet<TestModel> TestModel{ get; set; }
}

A easy way for multiple providers?

回答1:

A solution with only one Context (Example for SQLite + MySQL + MSSQL + PostgreSQL (or others)):

appsettings.json

{
  // Add Provider and ConnectionStrings for your EFC drivers
  // Providers: SQLite, MySQL, MSSQL, PostgreSQL, or other provider...
  "Provider": "SQLite",
  "ConnectionStrings": {
    "SQLite": "Data Source=mydatabase.db",
    "MySQL": "server=localhost;port=3306;database=mydatabase;user=root;password=root",
    "MSSQL": "Server=(localdb)\\mssqllocaldb;Database=mydatabase;Trusted_Connection=True;MultipleActiveResultSets=true",
    "PostgreSQL": "Host=localhost;Database=mydatabase;Username=root;Password=root"
  }
}

Single DatabaseContext.cs

public class DatabaseContext : DbContext
{
        public DatabaseContext(DbContextOptions<DatabaseContext> options) : base(options) { }

        // add Models...
}

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    // Check Provider and get ConnectionString
    if (Configuration["Provider"] == "SQLite")
    {
        services.AddDbContext<DatabaseContext>(options =>
            options.UseSqlite(Configuration.GetConnectionString("SQLite")));
    }
    else if (Configuration["Provider"] == "MySQL")
    {
        services.AddDbContext<DatabaseContext>(options =>
            options.UseMySql(Configuration.GetConnectionString("MySQL")));
    }
    else if (Configuration["Provider"] == "MSSQL")
    {
        services.AddDbContext<DatabaseContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("MSSQL")));
    }
    else if (Configuration["Provider"] == "PostgreSQL")
    {
        services.AddDbContext<DatabaseContext>(options =>
            options.UseNpgsql(Configuration.GetConnectionString("PostgreSQL")));
    }
    // Exception
    else
    { throw new ArgumentException("Not a valid database type"); }
}

Now we can do a singel migration

Add-Migration InitialCreate

Only edit every output of Add-Migration and add driver specific attributes:

    protected override void Up(MigrationBuilder migrationBuilder)
    {
        migrationBuilder.CreateTable(
        name: "Mytable",
        columns: table => new
        {
            Id = table.Column<int>(nullable: false)
            // Add for SQLite
            .Annotation("Sqlite:Autoincrement", true)
            // Add for MySQL
            .Annotation("MySql:ValueGenerationStrategy", MySqlValueGenerationStrategy.IdentityColumn)
            // Add for MSSQL
            .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn)
            // Add for PostgreSQL
            .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.SerialColumn),
            // Or other provider...
            Name = table.Column<string>(maxLength: 50, nullable: false),
            Text = table.Column<string>(maxLength: 100, nullable: true)
        },
        constraints: table =>
        {
            table.PrimaryKey("PK_Mytable", x => x.Id);
        });
    }

EDIT: or you use string ID "DatabaseGenerated" so you would not have to edit migrationBuilder and the add migration is multiple providers capable without ".Annotation"

EXAMPLE Model:

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace WebApplication.Models
{
    public class Mytable
    {
        // This generate a String ID
        // No ID modification needed for providers
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public string Id { get; set; }

        // ....
    }
}

Now ready for Update-Database

回答2:

You may want to consider a utility like AdaptiveClient. AdaptiveClient allows you to create a single DbContext with multiple provider-specific implementations of your services (MSSQL, MySQL, SQLite, etc). AdaptiveClient injects the correct implementation based on the connection string in use.

AdaptiveClient also allows you to inject transport-specific service implementations. For example many applications run both locally (same LAN as database server) and remotely (use WCF or REST). When running locally AdaptiveClient will inject an implementation of your service that talks directly to your database. This gives a ~10x performance improvement. When running remotely AdaptiveClient injects a WCF or REST implementation.