How to get This[], DOTNET current instance

[dgholstein]

I'm using the .NET SqlDataReader class, MS says there's a This[]/Item[] property:

Properties

Connection	Gets the SqlConnection associated with the SqlDataReader.
Depth	Gets a value that indicates the depth of nesting for the current row.
FieldCount	Gets the number of columns in the current row.
HasRows	Gets a value that indicates whether the SqlDataReader contains one or more rows.
IsClosed	Retrieves a Boolean value that indicates whether the specified SqlDataReader instance has been closed.
Item[Int32]	Gets the value of the specified column in its native format given the column ordinal.
Item[String]	Gets the value of the specified column in its native format given the column name.
RecordsAffected	Gets the number of rows changed, inserted, or deleted by execution of the Transact-SQL statement.
VisibleFieldCount	Gets the number of fields in the SqlDataReader that are not hidden.

LabView doesn't:

I wrote a C# class method as a workaround because it was convenient and I have VS,

public static object DbGetField(SqlDataReader r, int i) {return r[i];}

but how do go direct in LV to do this?

[dgholstein]

I believe I see what's going on, it seems the properties available through LabVIEW are limited to numeric and string properties - that This[]/Item[] are .NET objects instead.  Maybe there's a recipe for casting to more generic/specific .NET objects.  EDIT: Looking at it again, I see I have no issues in adding .NET objects to a .NET class and it shows up in LabVIEW - so my assertion that because it's not a numerical or string object doesn't hold water.

[tyk007 · Accepted solution]

You are correct in that it is perfectly fine for properties to return objects.

The root cause here is that the LabVIEW only supports property syntax for "pure" properties - ie IL methods that take no parameters and return the specified data type. Recall that, for pure IL (which .NET assemblies are built on), properties are just metadata specifying pre-defined methods (eg. "get_name") backing that property. Here is the content for the Item "properties"

.property instance object Item(
		int32 i
	)
	{
		.get instance object System.Data.SqlClient.SqlDataReader::get_Item(int32)
	}
	.property instance object Item(
		string name
	)
	{
		.get instance object System.Data.SqlClient.SqlDataReader::get_Item(string)
	}

As you can see, the metadata for both properties specifies a backing IL method for each "get_Item". Since LabVIEW doesn't support properties backed by methods that take parameters, you can call the "get_Item()" method of choice using an Invoke node in LabVIEW instead.

[wiebe@CARYA]

You'd probably need to use an iterator. This is probably handled by C#\.NET automatically. Doing this in LabVIEW is sloooooow.

IIRC, I've make a small assembly that returns a 2D array .NET object of objects. Converting a 2D array .NET object in LabVIEW is pretty fast. Don't return a 2D array of .NET objects, that's slow.

If you post a small example of what you have, I could have a closer look.