Distinct support for null (#4559)

* distinct support for null

* better testing

spec/ParseQuery.Aggregate.spec.js

@@ -589,6 +589,30 @@ describe('Parse.Query Aggregate testing', () => {
       }).catch(done.fail);
   });
 
+  it('distinct null field', (done) => {
+    const options = Object.assign({}, masterKeyOptions, {
+      body: { distinct: 'distinctField' }
+    });
+    const user1 = new Parse.User();
+    user1.setUsername('distinct_1');
+    user1.setPassword('password');
+    user1.set('distinctField', 'one');
+
+    const user2 = new Parse.User();
+    user2.setUsername('distinct_2');
+    user2.setPassword('password');
+    user2.set('distinctField', null);
+    user1.signUp().then(() => {
+      return user2.signUp();
+    }).then(() => {
+      return rp.get(Parse.serverURL + '/aggregate/_User', options);
+    }).then((resp) => {
+      expect(resp.results.length).toEqual(1);
+      expect(resp.results).toEqual(['one']);
+      done();
+    }).catch(done.fail);
+  });
+
   it('does not return sensitive hidden properties', (done) => {
     const options = Object.assign({}, masterKeyOptions, {
       body: {

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -511,13 +511,16 @@ export class MongoStorageAdapter implements StorageAdapter {
     }
     return this._adaptiveCollection(className)
       .then(collection => collection.distinct(fieldName, transformWhere(className, query, schema)))
-      .then(objects => objects.map(object => {
+      .then(objects => {
+        objects = objects.filter((obj) => obj != null);
+        return objects.map(object => {
           if (isPointerField) {
             const field = fieldName.substring(3);
             return transformPointerString(schema, field, object);
           }
           return mongoObjectToParseObject(className, object, schema);
-      }));
+        });
+      });
   }
 
   aggregate(className: string, schema: any, pipeline: any, readPreference: ?string) {

src/Adapters/Storage/Postgres/PostgresStorageAdapter.js

@@ -1464,7 +1464,8 @@ export class PostgresStorageAdapter implements StorageAdapter {
     debug('distinct', className, query);
     let field = fieldName;
     let column = fieldName;
-    if (fieldName.indexOf('.') >= 0) {
+    const isNested = fieldName.indexOf('.') >= 0;
+    if (isNested) {
       field = transformDotFieldToComponents(fieldName).join('->');
       column = fieldName.split('.')[0];
     }
@@ -1480,7 +1481,10 @@ export class PostgresStorageAdapter implements StorageAdapter {
 
     const wherePattern = where.pattern.length > 0 ? `WHERE ${where.pattern}` : '';
     const transformer = isArrayField ? 'jsonb_array_elements' : 'ON';
-    const qs = `SELECT DISTINCT ${transformer}($1:raw) $2:raw FROM $3:name ${wherePattern}`;
+    let qs = `SELECT DISTINCT ${transformer}($1:name) $2:name FROM $3:name ${wherePattern}`;
+    if (isNested) {
+      qs = `SELECT DISTINCT ${transformer}($1:raw) $2:raw FROM $3:name ${wherePattern}`;
+    }
     debug(qs, values);
     return this._client.any(qs, values)
       .catch((error) => {
@@ -1490,7 +1494,7 @@ export class PostgresStorageAdapter implements StorageAdapter {
         throw error;
       })
       .then((results) => {
-        if (fieldName.indexOf('.') === -1) {
+        if (!isNested) {
           results = results.filter((object) => object[field] !== null);
           return results.map(object => {
             if (!isPointerField) {