Determines DbContext is Database-First or not.

EntityFrameworkHelper.cs

public static class EntityFrameworkHelper
{
    private static readonly System.Reflection.ConstructorInfo s_constructor =
        typeof(System.Data.Entity.Infrastructure.UnintentionalCodeFirstException).GetConstructor(System.Type.EmptyTypes);

    private static readonly System.Collections.Concurrent.ConcurrentDictionary<System.Type, bool> s_caches =
        new System.Collections.Concurrent.ConcurrentDictionary<System.Type, bool>();

    public static bool IsDatabaseFirst<TDbContext>() where TDbContext : System.Data.Entity.DbContext
        => IsDatabaseFirst(typeof(TDbContext));

    public static bool IsDatabaseFirst(System.Type dbContextType)
    {
        if (dbContextType is null) throw new System.ArgumentNullException(nameof(dbContextType));

        if (!s_caches.TryGetValue(dbContextType, out var isDatabaseFirst))
        {
            var onModelCreating = dbContextType.GetMethod("OnModelCreating", (System.Reflection.BindingFlags)36);
            var cilBytes = onModelCreating.GetMethodBody().GetILAsByteArray();
            using (var br = new System.IO.BinaryReader(new System.IO.MemoryStream(cilBytes)))
            {
                while (br.BaseStream.Position != br.BaseStream.Length)
                {
                    if (br.ReadByte() == 0x73) // newobj
                    {
                        var metadataToken = br.ReadInt32();
                        var ctor = dbContextType.Module.ResolveMethod(metadataToken);
                        if (s_constructor == ctor &&
                            br.ReadByte() == 0x7A) // throw
                        {
                            isDatabaseFirst = true;
                            goto Leave;
                        }
                    }
                }
            }
            isDatabaseFirst = false;
        Leave:
            s_caches.TryAdd(dbContextType, isDatabaseFirst);
        }
        return isDatabaseFirst;
    }
}