Generated code - QuerySpec, Specifying correlation predicates / relationships

When creating a correlated sub-query, it's easier to specify the predicates through a specific method, based on a generated relation. This helps avoiding memorizing which FK fields tie which entities together. Correlation predicates can be specified directly using the .Where() extension method of a query object as with any other predicate for the query or by using the method .CorrelatedOver(predicate). To specify a specific correlation relation for a subquery, use the method .CorrelatedOver(relation).

The CorrelatedOver(relation) method has some overloads to specify aliases for start and/or end entity. The relation specified in the overloads which accept an EntityRelation is used to produce the predicate to correlate the two queries, based on the fk/pk fields in the relationship.

The correlation predicate (either specified directly or constructed from the relation specified) will be appended to the Where clause specified with And as a normal predicate

CorrelatedOver(relation) is only available on an EntityQuery instance.

Example

The following example will fetch a list of order collections based on a query on the related customer entity: per customer matching the outer query a query on the orders is executed which is correlated to the outer query.

var qf = new QueryFactory();
var q = qf.Customer
	   .Where(CustomerFields.CustomerId.NotIn(new List<string>() { "FISSA", "PARIS" }))
	   .Select(() => qf.Order
			.CorrelatedOver(OrderEntity.Relations.CustomerEntityUsingCustomerId)
			.ToResultset()
		 );

// generated SQL:
SELECT [Northwind].[dbo].[Orders].[CustomerID] AS [CustomerId],
	[Northwind].[dbo].[Orders].[EmployeeID] AS [EmployeeId],
	[Northwind].[dbo].[Orders].[Freight],
	[Northwind].[dbo].[Orders].[OrderDate],
	[Northwind].[dbo].[Orders].[OrderID] AS [OrderId],
	[Northwind].[dbo].[Orders].[RequiredDate],
	[Northwind].[dbo].[Orders].[ShipAddress],
	[Northwind].[dbo].[Orders].[ShipCity],
	[Northwind].[dbo].[Orders].[ShipCountry],
	[Northwind].[dbo].[Orders].[ShipName],
	[Northwind].[dbo].[Orders].[ShippedDate],
	[Northwind].[dbo].[Orders].[ShipPostalCode],
	[Northwind].[dbo].[Orders].[ShipRegion],
	[Northwind].[dbo].[Orders].[ShipVia]
FROM [Northwind].[dbo].[Orders]
WHERE ((((EXISTS
	(SELECT [Northwind].[dbo].[Customers].[CustomerID] AS [CustomerId]
	FROM [Northwind].[dbo].[Customers]
	WHERE (((([Northwind].[dbo].[Customers].[CustomerID] NOT IN ('FISSA' /* @p1 */, 'PARIS' /* @p2 */))))
		AND [Northwind].[dbo].[Orders].[CustomerID] = [Northwind].[dbo].[Customers].[CustomerID]))))))