Fix for count being very slow on large Parse Classes' collections (Postgres) (#5330)

* Changed count to be approximate. Should help with postgres slowness

* refactored last commit to only fall back to estimate if no complex query

* handlign variables correctly

* Trying again because it was casting to lowercase table names which doesnt work for us/

* syntax error

* Adding quotations to pg query

* hopefully final pg fix

* Postgres will now use an approximate count unless there is a more complex query specified

* handling edge case

* Fix for count being very slow on large Parse Classes' collections in Postgres. Replicating fix for Mongo in issue 5264

* Fixed silly spelling error resulting from copying over notes

* Lint fixes

* limiting results to 1 on approximation

* suppress test that we can no longer run for postgres

* removed tests from Postgres that no longer apply

* made changes requested by dplewis

* fixed count errors

* updated package.json

* removed test exclude for pg

* removed object types from method

* test disabled for postgres

* returned type

* add estimate count test

* fix mongo test

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -152,10 +152,7 @@ export class MongoStorageAdapter implements StorageAdapter {
     // encoded
     const encodedUri = formatUrl(parseUrl(this._uri));
 
-    this.connectionPromise = MongoClient.connect(
-      encodedUri,
-      this._mongoOptions
-    )
+    this.connectionPromise = MongoClient.connect(encodedUri, this._mongoOptions)
       .then(client => {
         // Starting mongoDB 3.0, the MongoClient.connect don't return a DB anymore but a client
         // Fortunately, we can get back the options and use them to select the proper DB.
@@ -385,8 +382,8 @@ export class MongoStorageAdapter implements StorageAdapter {
   deleteAllClasses(fast: boolean) {
     return storageAdapterAllCollections(this).then(collections =>
       Promise.all(
-        collections.map(
-          collection => (fast ? collection.deleteMany({}) : collection.drop())
+        collections.map(collection =>
+          fast ? collection.deleteMany({}) : collection.drop()
         )
       )
     );
@@ -952,6 +949,8 @@ export class MongoStorageAdapter implements StorageAdapter {
         readPreference = ReadPreference.NEAREST;
         break;
       case undefined:
+      case null:
+      case '':
         break;
       default:
         throw new Parse.Error(