Implement findAndDelete in MongoCollection and move SchemasRouter to it.

src/Adapters/Storage/Mongo/MongoCollection.js

@@ -46,6 +46,17 @@ export default class MongoCollection {
   count(query, { skip, limit, sort } = {}) {
     return this._mongoCollection.count(query, { skip, limit, sort });
   }
+  
+  // Atomically find and delete an object based on query.
+  // The result is the promise with an object that was in the database before deleting.
+  // Postgres Note: Translates directly to `DELETE * FROM ... RETURNING *`, which will return data after delete is done.
+  findOneAndDelete(query) {
+    // arguments: query, sort
+    return this._mongoCollection.findAndRemove(query, []).then(document => {
+      // Value is the object where mongo returns multiple fields.
+      return document.value;
+    });
+  }
 
   drop() {
     return this._mongoCollection.drop();

src/Routers/SchemasRouter.js

@@ -164,14 +164,14 @@ function deleteSchema(req) {
     .then(() => {
       // We've dropped the collection now, so delete the item from _SCHEMA
       // and clear the _Join collections
-      return req.config.database.collection('_SCHEMA')
-        .then(coll => coll.findAndRemove({_id: req.params.className}, []))
-        .then(doc => {
-          if (doc.value === null) {
+      return req.config.database.adaptiveCollection('_SCHEMA')
+        .then(coll => coll.findOneAndDelete({_id: req.params.className}))
+        .then(document => {
+          if (document === null) {
             //tried to delete non-existent class
             return Promise.resolve();
           }
-          return removeJoinTables(req.config.database, doc.value);
+          return removeJoinTables(req.config.database, document);
         });
     })
     .then(() => {