feat(Subselects): Add subselect helper

The subselect helper will ensure you can access your
property via getters.  The property cannot be updated or inserted.
It additionally ensures the original columns are selected (if needed)
and limits the result of the subquery to 1.

models/BaseEntity.cfc

@@ -307,8 +307,11 @@ component accessors="true" {
             .set_Loaded( true );
     }
 
-    function newEntity() {
-        return variables._entityCreator.new( this );
+    function newEntity( name ) {
+        if ( isNull( name ) ) {
+            return variables._entityCreator.new( this );
+        }
+        return variables._wirebox.getInstance( name );
     }
 
     function reset() {
@@ -746,6 +749,27 @@ component accessors="true" {
         return variables.query;
     }
 
+    public function addSubselect( name, subselect ) {
+        if ( ! variables._attributes.keyExists( retrieveAliasForColumn( name ) ) ) {
+            variables._attributes[ name ] = name;
+            variables._meta.properties.append( { "name" = name, "update" = false, "insert" = false } );
+        }
+
+        if ( retrieveQuery().getColumns().isEmpty() ||
+        ( retrieveQuery().getColumns().len() == 1 && isSimpleValue( retrieveQuery().getColumns()[ 1 ] ) && retrieveQuery().getColumns()[ 1 ] == "*" ) ) {
+            retrieveQuery().select( retrieveQuery().getFrom() & ".*" );
+        }
+
+        var subselectQuery = subselect;
+        if ( isClosure( subselectQuery ) ) {
+            subselectQuery = retrieveQuery().newQuery();
+            subselectQuery = subselect( subselectQuery );
+        }
+
+        retrieveQuery().subselect( name, subselectQuery.retrieveQuery().limit( 1 ) );
+        return retrieveQuery();
+    }
+
     /*=====================================
     =            Magic Methods            =
     =====================================*/
@@ -781,12 +805,8 @@ component accessors="true" {
 
         var columnName = variables._str.slice( missingMethodName, 4 );
 
-        if ( isColumnAlias( columnName ) ) {
-            return retrieveAttribute( retrieveColumnForAlias( columnName ) );
-        }
-
         if ( hasAttribute( columnName ) ) {
-            return retrieveAttribute( columnName );
+            return retrieveAttribute( retrieveColumnForAlias( columnName ) );
         }
 
         return;

tests/resources/app/models/User.cfc

@@ -19,6 +19,26 @@ component extends="quick.models.BaseEntity" accessors="true" {
         return query.where( "type", type );
     }
 
+    function scopeWithLatestPostId( query ) {
+        addSubselect( "latestPostId", newEntity( "Post" )
+            .select( "post_pk" )
+            .whereColumn( "users.id", "user_id" )
+            .latest() );
+
+        /*
+        // can also use closures
+        addSubselect( "latestPostId", function( q ) {
+            // you don't have to use an entity.
+            // it just helps with scopes, column names, tables, etc.
+            // there is also a query passed to you.
+            return newEntity( "Post" )
+                .select( "post_pk" )
+                .whereColumn( "users.id", "userId" )
+                .latest();
+        } );
+        */
+    }
+
     function posts() {
         return hasMany( "Post", "user_id" );
     }

tests/specs/integration/BaseEntity/SubqueriesSpec.cfc

@@ -0,0 +1,27 @@
+component extends="tests.resources.ModuleIntegrationSpec" appMapping="/app" {
+
+    function beforeAll() {
+        super.beforeAll();
+        controller.getInterceptorService().registerInterceptor( interceptorObject = this );
+    }
+
+    function run() {
+        describe( "Subqueries Spec", function() {
+            beforeEach( function() {
+                variables.queries = [];
+            } );
+
+            it( "can add a subquery to an entity", function() {
+                var elpete = getInstance( "User" ).withLatestPostId().findOrFail( 1 );
+                expect( elpete.getLatestPostId() ).notToBeNull();
+                expect( elpete.getLatestPostId() ).toBe( 523526 );
+                expect( variables.queries ).toHaveLength( 1, "Only one query should have been executed. #arrayLen( variables.queries )# were instead." );
+            } );
+        } );
+    }
+
+    function preQBExecute( event, interceptData, buffer, rc, prc ) {
+        arrayAppend( variables.queries, interceptData );
+    }
+
+}