From f365e1fffeb75e8e2534f8e34cf6c3b282729d31 Mon Sep 17 00:00:00 2001
From: Arvind Satyanarayan <arvind@users.noreply.github.com>
Date: Thu, 7 Jan 2021 13:44:59 -0500
Subject: [PATCH] fix: parse field projections after encodings to prevent
 duplicates (#7164)

---
 src/compile/selection/project.ts     | 17 +++++++++--------
 test/compile/selection/parse.test.ts | 14 ++++++++++++++
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/src/compile/selection/project.ts b/src/compile/selection/project.ts
index 6506edfc35..38a29ec0c6 100644
--- a/src/compile/selection/project.ts
+++ b/src/compile/selection/project.ts
@@ -96,14 +96,6 @@ const project: SelectionCompiler = {
       }
     }
 
-    // TODO: find a possible channel mapping for these fields.
-    for (const field of fields ?? []) {
-      const p: SelectionProjection = {type: 'E', field};
-      p.signals = {...signalName(p, 'data')};
-      proj.items.push(p);
-      proj.hasField[field] = p;
-    }
-
     for (const channel of encodings ?? []) {
       const fieldDef = model.fieldDef(channel);
       if (fieldDef) {
@@ -158,6 +150,15 @@ const project: SelectionCompiler = {
       }
     }
 
+    // TODO: find a possible channel mapping for these fields.
+    for (const field of fields ?? []) {
+      if (proj.hasField[field]) continue;
+      const p: SelectionProjection = {type: 'E', field};
+      p.signals = {...signalName(p, 'data')};
+      proj.items.push(p);
+      proj.hasField[field] = p;
+    }
+
     if (init) {
       selCmpt.init = (init as any).map((v: SelectionInitMapping | SelectionInitIntervalMapping) => {
         return proj.items.map(p => (v[p.channel] !== undefined ? v[p.channel] : v[p.field]));
diff --git a/test/compile/selection/parse.test.ts b/test/compile/selection/parse.test.ts
index 6cca6606d7..5e61ee6160 100644
--- a/test/compile/selection/parse.test.ts
+++ b/test/compile/selection/parse.test.ts
@@ -282,6 +282,20 @@ describe('Selection', () => {
         }
       ]);
     });
+
+    it('does not add duplicate projections', () => {
+      const component = parseUnitSelection(model, [
+        {
+          name: 'one',
+          select: {type: 'interval', fields: ['Horsepower', 'Miles_per_Gallon'], encodings: ['x', 'y']}
+        }
+      ]);
+
+      expect(component['one'].project.items).toEqual([
+        {field: 'Horsepower', channel: 'x', type: 'R', signals: {data: 'one_Horsepower', visual: 'one_x'}},
+        {field: 'Miles_per_Gallon', channel: 'y', type: 'R', signals: {data: 'one_Miles_per_Gallon', visual: 'one_y'}}
+      ]);
+    });
   });
 
   it('materializes a selection', () => {