Better Support for Parent/Child Records

[jonwagner]

See if we can automatically handle deserializing the common query pattern of:

SELECT parent.*, child.*
FROM parent JOIN child

Example from Issue #375:

class Beer
{
	public int ID;
	public IList<Glass> Glasses;
}

CREATE PROC GetBeerAndPossibleGlasses AS
	SELECT * FROM Beer
	SELECT b.BeerID, g.* FROM Beer JOIN Glasses ON (...)
while most SQL are written like

   SELECT * FROM Beer LEFT JOIN Glasses ON (...)

I'm thinking that we create a new record reader:

• Keep a dictionary of parentid/parent.
• Read a record.
• Look up the parentid and see if we need to create a new instance or reuse an existing.
• Add child to the parent using the parent/child relationship.

This will probably stream acceptably.

This project will require:

• New record reader
• Record reader Test cases
• Possible adjustment to the Recordset attributes for interface building
• Update the interface builder to use the new record reader
• Interface test cases
• Update documentation / samples

[jonwagner]

This is now available in v6.2.4.

The magic to make parent/child records get parsed from the same recordset is:

            var results = Connection().QuerySql(query, parameters,
				Query.Returns(Together<Parent, Child>.Records));

Using Together instead of Some alters the parsing so that the recordset is parsed, child records are grouped, and the list of unique parent records are returned.

This is compatible with all of the structure declarations, like returning two recordsets:

            var results = Connection().QuerySql(query + ";" + query, null,
				Query.Returns(Together<Parent, Child>.Records)
					.Then(Together<Parent, Child>.Records));

Finally, you can use parent/child processing in interface definitions. Setting IsParentAndChild=true on the Recordset attribute tells Insight to use Together Rather than Some when parsing the records.

		public interface IReadParentAndChildren
		{
			[Sql(query)]
			[Recordset(0, typeof(Parent), typeof(Child), IsParentAndChild = true)]
			IList<Parent> CanReturnParentAndChild();
		}

Bonus points to whoever updates the wiki.