DataObjects.Net v4.0: status update

Briefly, we're still fighting with schema evolution and LINQ support, but the end is near.

LINQ support

Currently we have the following set of issues that must be implemented to consider LINQ provider implementation project is finished:

Priority	Category	Implementation level	Task
1	Type mapping	LINQ to RSE translator	Enum
1	Type mapping	LINQ to RSE translator	Nullable vs NULL ternary logic in SQL
1	Type mapping	RSE to SQL translator	Implicit numeric casts
1	Type cast	LINQ to RSE translator	"is" operator
1	LINQ methods	Both	Concat LINQ method
1	LINQ methods	Both	Union LINQ method
1	LINQ methods	Both	Except LINQ method
1	LINQ methods	Both	Intersect LINQ method
1	LINQ methods	LINQ to RSE translator	GroupBy with aggreagates
1	LINQ methods	LINQ to RSE translator	GroupJoin
1	LINQ methods	LINQ to RSE translator	First, Single, Last, *OrDefault as subquery result (including .Select(x => new {x, x.Customers.First}) )
1	Issue	LINQ to RSE translator	EntitySet.Count property & EntitySet.Contains method
1	Issue	LINQ to RSE translator	EntitySet as IQueryable
1	Issue	LINQ to RSE translator	Correct column order for OrderBy
2	Type mapping	LINQ to RSE translator	Byte array
2	Type cast	LINQ to RSE translator	OfType LINQ method
2	Type cast	LINQ to RSE translator	Cast LINQ method
2	Type cast	LINQ to RSE translator	"as", (T) cast operators for type downcasting
2	Type cast	LINQ to RSE translator	"as" cast operator for type upcasting
2	Type cast	LINQ to RSE translator	(T) cast operator for type upcasting must lead to an error on query translation
2	Optimization	RSE optimizer	SQL APPLY rewriting
2	Optimization	RSE optimizer	Redundant join remover
2	Optimization	LINQ to RSE translator	Join first selected subquery returning * in .Select projections (including .Select(x => new {x, x.Customers}) )
2	Optimization	RSE optimizer	Index access optimization: pi.Filter(...) -> si1.Range(...).Union(si2.Range(...)) .Union(...).Join(pi, ...) .Select(...).Filter(...)
2	Issue	LINQ to RSE translator	Take, Skip after OrderBy
3	LINQ methods	LINQ to RSE translator	Contains, Any, All for parameters of collection (IEnumerable) type

Most part of tasks of priority 1 are in development now, as well as Index access optimization (priority is 2). We're planning to finish with priority 1 queue during the next week. Priority 2 & 3 queue will require 1.5-2 more weeks, but must of these features aren't really necessary now. We're working on all of them mainly to get all our LINQ tests passing.

Btw, most likely it's a very important question: how do we test our LINQ implementation? You may find that now there are ~ 470 different tests for LINQ. Some of them are written by us, but a significant part of them was imported from the following projects:
- IQToolkit (The LINQ IQueryable Toolkit)
- ADO.NET Team's 101 LINQ Samples.

That's why we're pretty sure we'll cover all aspects of LINQ in the end.


Schema evolution

The progress here is not as good as with LINQ - from the point of end users nothing works here yet. But we already implemented the following parts of the framework:
- Generic modelling framework (Xtensive.Modelling) - a set of abstract base classes allowing to describe any models similar to SQL metadata.
- Update actions support for models. Basically, we can track & pass only the changes made to some model, rather then model itself to a remote server.
- Differential comparison support for models. Allows to create hierarchical difference structure taking into account comparison hits (such as node rename), as well as convert it to a set of update actions. This part isn't fully finished yet (some bugs still exist).
- Xtensive.Storage.Indexing.Model - an implementation of indexign storage model based on Xtensive.Modelling
- Converter of SQL DOM model to Indexing model (partially done: some bugs exist)
- Converter of Xtensive.Storage.Model model (Storage model) to Indexing model (in development).

What's left:
- Translation of differences to SQL update actions (for SQL storages)
- Translation of differences to index structure update actions (for indexing storages)
- Integration of all this stuff into Domain.Build pipeline.

Hopefully first version of our schema evolution layer will be available by the end of the next week.