public partial class Product : Entity
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public Nullable<byte> ProductTypeId { get; set; }
    }

 public partial class ProductType : Entity
    {
        public byte Id { get; set; }
        public string Name { get; set; }
    }

            List<Assembly> allAssemblies = new List<Assembly>();
            string path = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);

            foreach (string dll in Directory.GetFiles(path, "*.Common.dll"))
                allAssemblies.Add(Assembly.LoadFile(dll));

            var type = typeof(Entity);
      
            List<Type> types = allAssemblies
             .SelectMany(s => s.GetTypes())
             .Where(p => type.IsAssignableFrom(p)).ToList();

            List<string> entities = new List<string>();
            foreach (var item in types)
            {
                entities.Add(item.Name);
            }

            types.Add(typeof(Entity));

public class ContextGenerator
    {
        public void Generate(List<string> entities, params Type[] types)
        {
            StringBuilder code = new StringBuilder();

            code.AppendLine(@"
           using System.Data.Entity;
           using System.Data.Entity.Core.EntityClient;
           using SampleProject1.Common.Models;
           using SampleProject1.Common.Models.Mapping;
           using SampleProject2.Common.Models;
           using SampleProject2.Common.Models.Mapping;

           namespace DbContextGenerator
           {
                public partial class TestContext : DbContext
                {
                    static TestContext()
                    {
                        Database.SetInitializer<TestContext>(null);
                    }

                    public TestContext()
                        : base(""Data Source=.;Initial Catalog=Test;Integrated Security=True;MultipleActiveResultSets=True"")
                    {
                        }
                ");

            var pluralizeHelper = new PluralizeHelper();

            foreach (var entity in entities)
            {
                code.AppendLine($@"public DbSet<{entity}> {pluralizeHelper.Pluralize(entity)} {{ get; set; }}");
            }

            code.AppendLine(@"protected override void OnModelCreating(DbModelBuilder modelBuilder)");
            code.AppendLine(@"{");

            foreach (var entity in entities)
            {
                code.AppendLine($@"modelBuilder.Configurations.Add(new {entity}Map());");
            }
            code.AppendLine(@"}");
            code.AppendLine(@"}");
            code.AppendLine(@"}");
           
            CSharpCodeProvider provider = new CSharpCodeProvider();
            CompilerParameters parameters = new CompilerParameters();

            parameters.ReferencedAssemblies.Add("System.Drawing.dll");
            parameters.ReferencedAssemblies.Add("System.Data.dll");
            parameters.ReferencedAssemblies.Add("System.Data.Entity.dll");
            parameters.ReferencedAssemblies.Add("System.ComponentModel.dll");

            foreach (var type in types)
            {
                parameters.ReferencedAssemblies.Add(type.Assembly.Location);
            }

            parameters.ReferencedAssemblies.Add(typeof(DbSet).Assembly.Location);
            parameters.ReferencedAssemblies.Add(typeof(DbContext).Assembly.Location);
            parameters.ReferencedAssemblies.Add(typeof(IQueryable).Assembly.Location);
            parameters.ReferencedAssemblies.Add(typeof(IQueryable<>).Assembly.Location);
            parameters.ReferencedAssemblies.Add(typeof(System.ComponentModel.IListSource).Assembly.Location);

            parameters.GenerateExecutable = false;
            parameters.GenerateInMemory = false;
            parameters.OutputAssembly = "ProjectContext.dll";

            CompilerResults results = provider.CompileAssemblyFromSource(parameters, code.ToString());

            if (results.Errors.HasErrors)
            {
                StringBuilder sb = new StringBuilder();

                foreach (CompilerError error in results.Errors)
                {
                    sb.AppendLine(String.Format("Error ({0}): {1}", error.ErrorNumber, error.ErrorText));
                }

                throw new InvalidOperationException(sb.ToString());
            }
        }

    }

 static DbContext _dbContext=null;
        public static DbContext GetDbContextInstance()
        {
            if (_dbContext == null)
            {
                string path = Path.GetDirectoryName(Assembly.GetEntryAssembly().Location);
                var dllversionAssm = Assembly.LoadFile(path + "\\ProjectContext.dll");
                Type type = dllversionAssm.GetType("DbContextGenerator.TestContext");
                _dbContext = (DbContext)Activator.CreateInstance(type);
            }
            return _dbContext;
        }

public static System.Data.Entity.DbSet<T> Get<T>() where T : class
        {
            var set = GetDbContextInstance().Set<T>();
            return set;
        }

            var products = Get<Product>().ToList();

            var productTypes = Get<ProductType>().ToList();


            var query = from p in Get<Product>()
                        join pt in Get<ProductType>() on p.ProductTypeId equals pt.Id
                        select new
                        {
                            Id = p.Id,
                            Name = p.Name,
                            ProductType = pt.Name

                        };

            var JoinResult = query.ToList();

dotnet tool install --global dotnet-ef --version 3.0.0-*

dotnet tool update --global dotnet-ef --version 3.0.0-*