Fixes #3195 (#3201)

* Adds error reproduction

* Fix transform in order to accept nested array results in $in/$nin

The error originated by the nesting of 2 array in $in [["..."]], using _.flatMap with those will guarantee at the lower level
that the query is properly resolved

* nits

* _.flatMap the $in/$nin values

spec/ParseQuery.spec.js

@@ -2467,6 +2467,35 @@ describe('Parse.Query testing', () => {
     });
   });
 
+  it("should match a key in an array (#3195)", function(done) {
+    var AuthorObject = Parse.Object.extend("Author");
+    var GroupObject = Parse.Object.extend("Group");
+    var PostObject = Parse.Object.extend("Post");
+
+    return new AuthorObject().save().then((user) => {
+      const post = new PostObject({
+        author: user
+      });
+
+      const group = new GroupObject({
+        members: [user],
+      });
+
+      return Parse.Promise.when(post.save(), group.save());
+    }).then((p) => {
+      return new Parse.Query(PostObject)
+        .matchesKeyInQuery("author", "members", new Parse.Query(GroupObject))
+        .find()
+        .then((r) => {
+          expect(r.length).toEqual(1);
+          if (r.length > 0) {
+            expect(r[0].id).toEqual(p.id);
+          }
+          done();
+        }, done.fail);
+    });
+  });
+
   it('should find objects with array of pointers', (done) => {
     var objects = [];
     while(objects.length != 5) {

src/Adapters/Storage/Mongo/MongoTransform.js

@@ -223,8 +223,9 @@ function transformQueryKeyValue(className, key, value, schema) {
   }
 
   // Handle query constraints
-  if (transformConstraint(value, expectedTypeIsArray) !== CannotTransform) {
-    return {key, value: transformConstraint(value, expectedTypeIsArray)};
+  const transformedConstraint = transformConstraint(value, expectedTypeIsArray);
+  if (transformedConstraint !== CannotTransform) {
+    return {key, value: transformedConstraint};
   }
 
   if (expectedTypeIsArray && !(value instanceof Array)) {
@@ -508,7 +509,14 @@ function transformConstraint(constraint, inArray) {
   if (typeof constraint !== 'object' || !constraint) {
     return CannotTransform;
   }
-
+  const transformFunction = inArray ? transformInteriorAtom : transformTopLevelAtom;
+  const transformer = (atom) => {
+    const result = transformFunction(atom);
+    if (result === CannotTransform) {
+      throw new Parse.Error(Parse.Error.INVALID_JSON, `bad atom: ${JSON.stringify(atom)}`);
+    }
+    return result;
+  }
   // keys is the constraints in reverse alphabetical order.
   // This is a hack so that:
   //   $regex is handled before $options
@@ -524,10 +532,7 @@ function transformConstraint(constraint, inArray) {
     case '$exists':
     case '$ne':
     case '$eq':
-      answer[key] = inArray ? transformInteriorAtom(constraint[key]) : transformTopLevelAtom(constraint[key]);
-      if (answer[key] === CannotTransform) {
-        throw new Parse.Error(Parse.Error.INVALID_JSON, `bad atom: ${constraint[key]}`);
-      }
+      answer[key] = transformer(constraint[key]);
       break;
 
     case '$in':
@@ -536,12 +541,14 @@ function transformConstraint(constraint, inArray) {
       if (!(arr instanceof Array)) {
         throw new Parse.Error(Parse.Error.INVALID_JSON, 'bad ' + key + ' value');
       }
-      answer[key] = arr.map(value => {
-        const result = inArray ? transformInteriorAtom(value) : transformTopLevelAtom(value);
-        if (result === CannotTransform) {
-          throw new Parse.Error(Parse.Error.INVALID_JSON, `bad atom: ${value}`);
-        }
-        return result;
+      answer[key] = _.flatMap(arr, value => {
+        return ((atom) => {
+          if (Array.isArray(atom)) {
+            return value.map(transformer);
+          } else {
+            return transformer(atom);
+          }
+        })(value);
       });
       break;
     }

src/Adapters/Storage/Postgres/PostgresStorageAdapter.js

@@ -1,5 +1,6 @@
 import { createClient } from './PostgresClient';
 import Parse            from 'parse/node';
+import _                from 'lodash';
 
 const PostgresRelationDoesNotExistError = '42P01';
 const PostgresDuplicateRelationError = '42P07';
@@ -296,10 +297,10 @@ const buildWhereClause = ({ schema, query, index }) => {
         }
       }
       if (fieldValue.$in) {
-        createConstraint(fieldValue.$in, false);
+        createConstraint(_.flatMap(fieldValue.$in, elt => elt), false);
       }
       if (fieldValue.$nin) {
-        createConstraint(fieldValue.$nin, true);
+        createConstraint(_.flatMap(fieldValue.$nin, elt => elt), true);
       }
     }