Make JoinBuilder take to as a String Function().

angel_orm/CHANGELOG.md

@@ -3,6 +3,8 @@
 separate files.
 * **BREAKING**: Add a required `QueryExecutor` argument to `transaction`
 callbacks.
+* Make `JoinBuilder` take `to` as a `String Function()`. This will allow
+ORM queries to reference their joined subqueries.
 
 # 2.0.1
 * Apply `package:pedantic` fixes.

angel_orm/lib/src/join_builder.dart

@@ -5,7 +5,11 @@ import 'query.dart';
 class JoinBuilder {
   final JoinType type;
   final Query from;
-  final String to, key, value, op, alias;
+  final String key, value, op, alias;
+
+  /// A callback to produces the expression to join against, i.e.
+  /// a table name, or the result of compiling a query.
+  final String Function() to;
   final List<String> additionalFields;
 
   JoinBuilder(this.type, this.from, this.to, this.key, this.value,

angel_orm/lib/src/query.dart

@@ -107,13 +107,15 @@ abstract class Query<T, Where extends QueryWhere> extends QueryBase<T> {
     }
   }
 
-  String _compileJoin(tableName, Set<String> trampoline) {
+  String Function() _compileJoin(tableName, Set<String> trampoline) {
     if (tableName is String) {
-      return tableName;
+      return () => tableName;
     } else if (tableName is Query) {
+      return () {
         var c = tableName.compile(trampoline);
         if (c == null) return c;
         return '($c)';
+      };
     } else {
       throw ArgumentError.value(
           tableName, 'tableName', 'must be a String or Query');