Add support for mapping columns to nested object properties

[jasonmcgraw]

Current functionality does not allow the user to select and map columns to nested object properties of the return type when using the Query function.

This change will allow the user to alias a column as NestedObject.PropertyName, which will instantiate the NestedObject (if no default value) and assign the value of the column to the specified PropertyName of the NestedObject.

Example:
Given the table structure and DTO

//Table
class Foo
{
	public int Id { get; set; }
	public int FooReferenceId { get; set; }
}
//Table
class FooReference
{
	public int Id { get; set; }
	public string Name { get; set; }
}

//DTO
class FooModel 
{
	public int Id { get; set; }
	public int FooReferenceId { get; set; }
	public FooReference FooReferenceProperty { get; set; }
}

Current implementation would force us to populate the nested object FooReferenceProperty and its properties by combining multiple queries and in memory assignment like so:

string fooQuery =
	 " select" +
	 " fooTable.Id as 'Id'," +
	 " fooTable.FooReferenceId as 'FooReferenceId'" +
	 " from Foo as foo" +
	 " join FooReference fooReference on foo.FooReferenceId = fooReference.Id" +
	 " where foo.Id = 1";
var fooResult = db.Query<FooModel> (fooQuery);

var fooReferenceQuery = 
	 " select" +
	 " fooReference.Id as 'Id'," +
	 " fooReference.Name as 'Name'" +
	 " from Foo as foo" +
	 " join FooReference fooReference on foo.FooReferenceId = fooReference.Id" +
	 " where foo.Id = 1";
var fooReferenceResult = db.Query<FooReference> (fooQuery);

foreach (var item in fooResult)
{
	item.FooReferenceProperty = fooReferenceResult.FirstOrDefault (x => x.Id == item.FooReferenceId);
}

Doing this can become very cumbersome, especially when several nested objects are involved.

This modified implementation of ExecuteDeferredQuery will allow us to populate the nested object FooReferenceProperty and its properties with just a single Query call:

string fooQuery =
	 " select" +
	 " fooTable.Id as 'Id'," +
	 " fooTable.FooReferenceId as 'FooReferenceId'," +
	 " fooReference.Id as 'FooReferenceProperty.Id'," +
	 " fooReference.Name as 'FooReferenceProperty.Name'" +
	 " from Foo as foo" +
	 " join FooReference fooReference on foo.FooReferenceId = fooReference.Id" +
	 " where foo.Id = 1";
var fooResult = db.Query<FooModel> (fooQuery);

Note: Mapping will only be valid to the nested objects of the root object. This change does not support mapping to nested objects of nested objects.

[cherron-aptera]

This looks really slick! Nice work on this!