Builds HQL Equality nodes and used in joins

Performs the equivalent of a ToString() on an expression. Swaps out constants for parameters so that, for example: from c in Customers where c.City = "London" generate the same key as from c in Customers where c.City = "Madrid"

Locates constants in the expression tree and generates parameters for each one

All joins are created as outer joins. An optimization in WhereJoinDetector finds joins that may be inner joined and calls MakeInner()()()() on them. QueryModelVisitor's VisitAdditionalFromClause(AdditionalFromClause, QueryModel, Int32) will then emit the correct HQL join.

Represents a possible set of values for a computation. For example, an expression may be null, it may be a non-null value, or we may even have a constant value that is known precisely. This class contains operators that know how to combine these values with each other. This class is intended to be used to provide static analysis of expressions before we hit the database. As an example for future improvement, we could handle ranges of numeric values. We can also improve this by handling operators such as the comparison operators and arithmetic operators. They are currently handled by naive null checks.