Cache query plan for DML LINQ queries

[bahusoid]

Fixes #2222

Maybe I'm wrong but it seems cached constants are not possible with DML queries (as no result transformers are supported). So let's just ignore CanCachePlan check for DML queries.

Regarding changes in #1544. I think of another fix for cached constants - we should "parametrize" them. So that such queries should be cachable. I mean for query like:

from c in db.Customers
where c.CustomerId == "ALFKI"
select new { c.CustomerId, c.ContactName, Constant = 1 }

Currently transformer is generated with embedded constants inside. Which for query above should generate something like:

public object ItemTransfomer(object[] row)
{
return new{CustomerId = row[0], ContactName = row[1], Constant = 1};
}

Instead we should generate something like this:

public object ItemTransfomer(object[] row, IDictionoray<string, object> parameters)
{
return new{CustomerId = row[0], ContactName = row[1], Constant = (int)parameters["p1"]};
}

And provide NhLinqExpression.ParameterValuesByName for parameters parameter.

[hazzik]

Not sure if it is a good idea to cache a DML query.

[hazzik]

Or is it about a query plan cache?

[bahusoid]

Yes. It's exactly about query plan cache.

[fredericDelaporte]

Regarding changes in #1544. I think of another fix for cached constants - we should "parametrize" them.

This is not straightforward to do, as far as I remember when I have looked into this for #1544. Parameterized constant works as parameters in the generated SQL queries, but these projections are run in-memory, and are not translated to SQL.