Can I inject dependency into migration (using EF-Core code-first migrations)?

Question

I tried to inject IConfiguration into the migration (in constructor), and got exception: \"No parameterless constructor defined for this object.\"

any worka

Answer 1

There's a way to do what you want to do. In my scenario, I would like to use the database name in the connection string through the DbContext. EF core 2.1.1 is used. The code is modified from here

Create a custom MigrationsAssembly service

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Internal;
using Microsoft.EntityFrameworkCore.Migrations;
using Microsoft.EntityFrameworkCore.Migrations.Internal;
using System;
using System.Reflection;

public class ContextAwareMigrationsAssembly : MigrationsAssembly
{
    private readonly DbContext context;

    public ContextAwareMigrationsAssembly(
        ICurrentDbContext currentContext,
        IDbContextOptions options,
        IMigrationsIdGenerator idGenerator,
        IDiagnosticsLogger logger) : base(currentContext, options, idGenerator, logger)
    {
        context = currentContext.Context;
    }

    /// 

    /// Modified from http://weblogs.thinktecture.com/pawel/2018/06/entity-framework-core-changing-db-migration-schema-at-runtime.html
    /// 
    /// 
    /// 
    /// 
    public override Migration CreateMigration(TypeInfo migrationClass, string activeProvider)
    {
        var hasCtorWithDbContext = migrationClass
                .GetConstructor(new[] { typeof(DbContext) }) != null;

        if (hasCtorWithDbContext)
        {
              var instance = (Migration)Activator.CreateInstance(migrationClass.AsType(), context);
              instance.ActiveProvider = activeProvider;
              return instance;
        }

        return base.CreateMigration(migrationClass, activeProvider);
    }
}

Replace the IMigrationAssembly service in your DbContext with your custom class

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.ReplaceService();
}

Then you can add a DbContext parameter in your migration.

public Migration20180801(DbContext context)
{
    DatabaseName = context.Database.GetDbConnection().Database;
}

In your case, you can replace all the DbContext references with IConfiguration and the relevant instance in the CreateMigration override.