NH-2401 - Method for specifying IType of LINQ parameter

[rjperes]

Implementation and simple unit test
https://nhibernate.jira.com/browse/NH-2401
@oskarb @hazzik: Debugging the code, it is clear that the parameter type is being correctly set, but I'm not sure how to do it in a unit test, have you got any suggestions?

[oskarb]

Construct several test cases with basically the same query, but using different "mapped as", in such a way that the outcome of the different queries are different. For instance, if a datetime is treated as a date the time of day will be lost, which could perhaps give different results with a comparison operator. Or a string property with different length.

[rjperes]

Thanks, will try. BTW, these errors don't occur on my machine...:-/

[rjperes]

I have added some unit tests and support for type conversions, as currently supported (ToString(), Convert.ToInt32(), Convert.ToDecimal() and Convert.ToDouble()).
This means that it is possible to do this:

from Orders o where Convert.ToInt32(o.OrderDate.MappedAs(NHibernateUtil.Int32)) ...
from Orders o where o.OrderDate.MappedAs(NHibernateUtil.String).ToString() ...

as well as the previous kind:
from Orders o where o.OrderDate.MappedAs(NHibernateUtil.String) ...

[rjperes]

Any feedback on this? Can this make it to 4.1?

[hazzik]

Set to 4.1.0, but I don't like the implementation. Will look closer at the weekends.

[rjperes]

Why don't you like it?

[hazzik]

This random thought: can we have different MappedAs for all IType which can make sense, instead of generic one?

[rjperes]

Like this:

public static decimal MappedAs(this decimal parameter, NHibernate.Type.IType type)

?
Sure... it may make sense... want me to update the pull request?
BTW, not related, but why don't we also support, at least, Convert.ToDateTime() in a LINQ query?

[hazzik]

Hooray, you've learnt how to use line comments... sorry, just trying to joke.

Like this:
public static decimal MappedAs(this decimal parameter, NHibernate.Type.IType type)

Probably

public static decimal MappedAs(this decimal parameter, NHibernate.Type.DecimalType type)

But I see now, that this is a bad idea.

but why don't we also support, at least, Convert.ToDateTime() in a LINQ query?

Just because (c) my 4yo. Just because we forgot to support it.

[rjperes]

Not a specific type, we need to allow passing arbitrary types! BTW, why is that a bad idea?

[hazzik]

I dont know why I did not like it when I'd written, it was just my feeling.

[rjperes]

1. OK for "as" instead of "is"
2. I'm not checking the method because, if the code gets there, then it's the right one
3. By traces of debugging you mean having unnecessary variables? Yes, perhaps
4. You would like to add all the logic to MappedAsGenerator? I think yes, but then we have to check if the arguments are conversions and apply the same logic as I placed in ConvertToXXXGenerator

[oskarb]

The generic version will show up in intellisense everywhere. The impact will be mitigated if you gather nhibernate linq queries in e.g. repository or query classes so you don't include the namespace everywhere. But I guess there's not many alternatives.

[hazzik]

@rjperes but why in your version .MappedAs applied to a property of a mapped class instead of an parameter?

[rjperes]

Hmm, now that you mention it... Not sure! Will check it out.

[hazzik]

@rjperes any updates?

[rjperes]

Nopes, maybe in the weekend.

[rjperes]

Updated pull request to make it clear that the MappedAs extension can be applied to the parameter or the property.

[hazzik]

@rjperes I'm going to remove MappedAsGenerator and other stuff. Leave only changes to ExpressionParameterVisitor, LinqExtensionMethods, and tests.

See here: master...hazzik:NH-2401

[hazzik]

It seems that MappedAs from this pull request does not work on parameters at all, because it is being stripped by NhPartialEvaluatingExpressionTreeVisitor before ExpressionParameterVisitor have a chance to process it.