Working with expression trees

Expression trees represent code as a structure that you can examine or execute. Expression trees are immutable so you cannot change one, but you can create a copy with the changes you want.

If you compare expression trees to functions, then although functions have flexibility in the parameter values passed to them, the structure of the function, what it does with those values, and how are all fixed. Expression trees provide a structure that can dynamically change, so what and how a function is implemented can be dynamically changed at runtime.

Expression trees are also used to represent an expression in an abstract way, so instead of being expressed using C# code, the expression is expressed as a data structure in memory. This then allows that data structure to be expressed in other ways, using other languages.

When you write a LINQ expression for the EF Core database provider, it is represented by an expression tree that is then translated...