DbContext transaction sharing

Sample implementation of sharing transaction between two instances of the same DBContext for EntityFramework and EntityFrameworkCore.

EntityFramework

Using older EntityFramework you can achieve transaction sharing by creating new transaction using initial DbContext, reusing DbConnection to initialize new DbContext and subsequently calling UseTransaction method to instruct Database to use desired transaction.

using (var parentContext = new DatabaseContext("...connection string...")) {
    // Create transaction calling BeginTransaction method
    using (var transaction = parentContext.Database.BeginTransaction(IsolationLevel.ReadCommitted)) {
        var parent = new Entity() { Name = Guid.NewGuid().ToString() };

        parentContext.Set<Entity>().Add(parent);

        await parentContext.SaveChangesAsync();

        int entityId = parent.Id;

        // Create child DbContext using existing database connection without disposing it by passing false as contextOwnsConnection parameter
        using (var childContext = new DatabaseContext(parentContext.Database.Connection, contextOwnsConnection: false)) {
            // Instruct DbContext to use existing transaction
            childContext.Database.UseTransaction(transaction.UnderlyingTransaction);

            var reloaded = await childContext.Set<Entity>().SingleOrDefaultAsync(e => e.Id == entityId);

            reloaded.Name = $"Name {reloaded.Id}";

            await childContext.SaveChangesAsync();
        }

        transaction.Commit();
        //transaction.Rollback();
    }
}

Related info

Connection management - EF6

EntityFrameworkCore

var parentOptions = new DbContextOptionsBuilder()
            .UseSqlServer("...connection string...")
            .Options;

using (var parentContext = new DatabaseContext(parentOptions))
{
    using (var transaction = parentContext.Database.BeginTransaction(IsolationLevel.ReadCommitted)) {
        var initial = new Entity() { Name = Guid.NewGuid().ToString() };

        await parentContext.Set<Entity>().AddAsync(initial);

        await parentContext.SaveChangesAsync();

        int entityId = initial.Id;

        var childOptions = new DbContextOptionsBuilder()
            .UseSqlServer(parentContext.Database.GetDbConnection())
            .Options;

        using (var childContext = new DatabaseContext(childOptions)) {
            await childContext.Database.UseTransactionAsync(transaction.GetDbTransaction());

            var reloaded = await childContext.Set<Entity>().SingleOrDefaultAsync(x => x.Id == entityId);

            reloaded.Name = $"Name {reloaded.Id}";

            await childContext.SaveChangesAsync();
        }

        await transaction.CommitAsync();
        //await transaction.RollbackAsync();
    }
}