Joins

A join takes two sequences and pairs up elements that share a common key. In an e-commerce app, you almost always have data split across collections (customers in one list, their orders in another) and you need to combine them by customer ID. LINQ gives you two join operators (Join and GroupJoin), each available in method syntax and query syntax, with patterns built on top of them for left joins and multi-key joins. This lesson covers all of those, the limitations LINQ to Objects has compared to SQL, and the hash-based algorithm that makes joins fast.