io.getquill.ast

The collection is treated as immutable internally but an ArrayBuffer is more efficient then Collection.list at appending which is mostly what the collection does

For Dynamic Infix Splices

Entities represent the actual tables/views being selected. Typically, something like:

`SELECT p.name FROM People p`

comes from something like:

`Map(Entity("People", Nil), Ident("p"), Property(Ident(p),
"name"))`.

When you define a querySchema, the fields you mention inside become PropertyAliass. For example something like:

`querySchema[Person]("t_person", _.name -> "s_name")`

Becomes something like:

`Entity("t_person", List(PropertyAlias(List("name"),
"s_name"))) { def renameable = Fixed }`

Note that Entity has an Opinion called renameable which will be the value Fixed when a querySchema is specified. That means that even if the NamingSchema is UpperCase, the resulting query will select t_person as opposed to T_PERSON or Person.

Ident represents a single variable name, this typically refers to a table but not always. Invisible identities are a rare case where a user returns an embedded table from a map clause:

 case class Emb(id: Int, name: String) case class Parent(id: Int,
name: String, emb: Emb) case class GrandParent(id: Int, par: Parent)

query[GrandParent] .map(g => g.par).distinct .map(p => (p.name,
p.emb)).distinct .map(tup => (tup._1, tup._2)).distinct } 

In these situations, the identity whose properties need to be expanded in the ExpandNestedQueries phase, needs to be marked invisible.

An Opinion represents a piece of data that needs to be propagated through AST transformations but is not directly related to how ASTs are transformed in most stages. For instance, Renameable controls how columns are named (i.e. whether to use a NamingStrategy or not) after most of the SQL transformations are done. Some transformations (e.g. RenameProperties will use Opinions or even modify them so that the correct kind of query comes out at the end of the normalizations. That said, Opinions should be transparent in most steps of the normalization.

Properties generally represent column selection from a table or invocation of some kind of method from some other object. Typically, something like

`SELECT p.name FROM People p`

comes from something like

`Map(Entity("People"), Ident("p"), Property(Ident(p), "name"))`

Properties also have an Opinion about how the NamingStrategy affects their name. For example something like Property.Opinionated(Ident(p), "s_name", Fixed) will become p.s_name even if the NamingStrategy is UpperCase (whereas Property(Ident(p), "s_name") would become p.S_NAME). When Property is constructed without Opinionated being used, the default opinion ByStrategy is used.