What is the difference between JoinQueryOver and JoinAlias?

Question

I need to know what is the difference between JoinQueryOver and JoinAlias, and when to use each?

Answer 1

QueryOver Series - Part 2: Basics and Joining by Andrew Whitaker gives a very good explanation:

Summary:

• IQueryOver is a generic type with two type parameters TRoot and TSubType
• .Select operates on TRoot while other QueryOver methods operate on TSubType.
• TRoot stays the same as you’re building a query, but TSubType changes when you join using JoinQueryOver
• JoinQueryOver and JoinAlias add joins to your query. JoinAlias doesn’t change TSubType, but JoinQueryOver does.
• You can use aliases when building a query to refer to properties that don’t belong to TRoot or TSubType