Question

I recently refactored a WPF app so that it no longer wraps each use of the DbContext in a using clause (see this question). Instead, my app just uses the same DbContext singleton throughout.

This works great except for one small problem. I have a routine that rebuilds the database from scratch and inserts some default data. This routine uses ADO.NET directly (not the DbContext), so the DbContext is unaware that the database is now completely different.

Is there a method to reset the DbContext without disposing it? I’d like to avoid disposing if possible because this would break several references to the original singleton throughout the app.

Answer 1

I was not able to come up with a method to reset the global DbContext. I was able to solve my problem, however, by injecting a DbContextLocator into any class that needs a DbContext instead of passing the DbContext itself.

My goal was to maintain a global DbContext, but allow it to be reset whenever needed (such as after a database rebuild or import).

My solution uses an abstract base class and a concrete class.

Base Class

using System.Data.Entity;

namespace CommonLibrary.Database
{
    public abstract class DbContextLocator
    {
        private DbContext _dbContext;

        public DbContext Current
        {
            get { return _dbContext; }
        }

        public DbContextLocator()
        {
            _dbContext = GetNew();
        }

        public virtual void Reset()
        {
            _dbContext.Dispose();
            _dbContext = GetNew();
        }

        protected abstract DbContext GetNew();
    }
}

Concrete Class

using System.Data.Entity;
using CommonLibrary.Database;
using ExperimentBase.EntityModels;

namespace MainProject.Models    
{
    public class MainDbContextLocator : DbContextLocator
    {
        public new MainDbContext Current
        {
            get { return (MainDbContext)base.Current; }
        }

        protected override DbContext GetNew()
        {
            return new MainDbContext();
        }
    }
}

Usage

Get the current DbContext:

var dbContext = dbContextLocator.Current;

Reset the DbContext:

dbContextLocator.Reset();
//Note: normally followed by code that re-initializes app data

---

Edit

Based on Shimmy’s feedback, I made DbContextLocatorBase into a generic. (I’m also now implementing IDisposable.)

Base Class

public class DbContextLocator<TContext> : IDisposable
    where TContext : DbContext, new()
{
    private TContext _dbContext;

    public TContext Current
    {
        get { return _dbContext; }
    }

    public DbContextLocator()
    {
        _dbContext = GetNew();
    }

    public virtual void Reset()
    {
        _dbContext.Dispose();
        _dbContext = GetNew();
    }

    protected virtual TContext GetNew()
    {
        return new TContext();
    }

    public void Dispose()
    {
        _dbContext.Dispose();
    }
}

Concrete Class (optional, since the base class is no longer abstract)

public class MainDbContextLocator : DbContextLocator<MainDbContext> { }