Debugging Entity Framework SQL statements

For debugging EF queries, the easiest thing is to cast the query to ObjectQuery and use ToTraceString:

var query = myContext.MyTable
    .Where(r => r.Id == searchId)
    .Select(r => r);

Console.WriteLine(((ObjectQuery)query).ToTraceString());

This will show the underlying SQL for the query, and you can run the queries manually to debug why they are slow. Here is the MSDN link:

http://msdn.microsoft.com/en-us/library/system.data.objects.objectquery.totracestring.aspx

If you're trying to get the SQL which is run when you call SaveChanges() on your context, it's not as easy. You could take a look at EFTracingProvider:

http://blogs.msdn.com/b/jkowalski/archive/2009/06/11/tracing-and-caching-in-entity-framework-available-on-msdn-code-gallery.aspx

Or, assuming you use SQL Server, you can go directly to SQL Profiler and capture the T-SQL statements (this is my preferred approach).

In EF6, you can also do this in the constructor of your dbcontext

Example

public BookServiceContext() : base("name=BookServiceContext")
{
    // New code:
    this.Database.Log = s => System.Diagnostics.Debug.WriteLine(s);
}

This will log to the console every SQL query EF generates. See this article for more information http://blog.oneunicorn.com/2013/05/08/ef6-sql-logging-part-1-simple-logging/

EF 7:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    base.OnConfiguring(optionsBuilder);
    optionsBuilder
        .UseSqlServer("...")
        .LogTo(Console.WriteLine, LogLevel.Information);
}

Another example might be very helpful for someone.

public class MyDbContext : DbContext
{
    private readonly ILoggerFactory _loggerFactory;

    public MyDbContext(DbContextOptions<MyDbContext> options, ILoggerFactory loggerFactory) : base(options)
    {
        _loggerFactory = loggerFactory ?? throw new ArgumentNullException(nameof(loggerFactory));
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        // Enable logging
        optionsBuilder.UseLoggerFactory(_loggerFactory);

        if (System.Diagnostics.Debugger.IsAttached)
            optionsBuilder.EnableSensitiveDataLogging();

        base.OnConfiguring(optionsBuilder);
    }
}