Move field deletion logic into mongo adapter (#1471)

src/Adapters/Storage/Mongo/MongoStorageAdapter.js

@@ -1,7 +1,7 @@
-
-import MongoCollection from './MongoCollection';
-import MongoSchemaCollection from './MongoSchemaCollection';
+import MongoCollection                          from './MongoCollection';
+import MongoSchemaCollection                    from './MongoSchemaCollection';
 import {parse as parseUrl, format as formatUrl} from '../../../vendor/mongodbUrl';
+import _                                        from 'lodash';
 
 let mongodb = require('mongodb');
 let MongoClient = mongodb.MongoClient;
@@ -78,6 +78,52 @@ export class MongoStorageAdapter {
       });
     });
   }
+
+  // Remove the column and all the data. For Relations, the _Join collection is handled
+  // specially, this function does not delete _Join columns. It should, however, indicate
+  // that the relation fields does not exist anymore. In mongo, this means removing it from
+  // the _SCHEMA collection.  There should be no actual data in the collection under the same name
+  // as the relation column, so it's fine to attempt to delete it. If the fields listed to be
+  // deleted do not exist, this function should return successfully anyways. Checking for
+  // attempts to delete non-existent fields is the responsibility of Parse Server.
+
+  // Pointer field names are passed for legacy reasons: the original mongo
+  // format stored pointer field names differently in the database, and therefore
+  // needed to know the type of the field before it could delete it. Future database
+  // adatpers should ignore the pointerFieldNames argument. All the field names are in
+  // fieldNames, they show up additionally in the pointerFieldNames database for use
+  // by the mongo adapter, which deals with the legacy mongo format.
+
+  // This function is not obligated to delete fields atomically. It is given the field
+  // names in a list so that databases that are capable of deleting fields atomically
+  // may do so.
+
+  // Returns a Promise.
+
+  // This function currently accepts the collectionPrefix and adaptive collection as a paramater because it isn't
+  // actually capable of determining the location of it's own _SCHEMA collection without having
+  // the collectionPrefix. Also, Schemas.js, the caller of this function, only stores the collection
+  // itself, and not the prefix. Eventually Parse Server won't care what a SchemaCollection is and
+  // will just tell the DB adapter to do things and it will do them.
+  deleteFields(className: string, fieldNames, pointerFieldNames, collectionPrefix, adaptiveCollection) {
+    const nonPointerFieldNames = _.difference(fieldNames, pointerFieldNames);
+    const mongoFormatNames = nonPointerFieldNames.concat(pointerFieldNames.map(name => `_p_${name}`));
+    const collectionUpdate = { '$unset' : {} };
+    mongoFormatNames.forEach(name => {
+      collectionUpdate['$unset'][name] = null;
+    });
+
+    const schemaUpdate = { '$unset' : {} };
+    fieldNames.forEach(name => {
+      schemaUpdate['$unset'][name] = null;
+    });
+
+    return adaptiveCollection.updateMany({}, collectionUpdate)
+    .then(updateResult => {
+      return this.schemaCollection(collectionPrefix)
+    })
+    .then(schemaCollection => schemaCollection.updateSchema(className, schemaUpdate));
+  }
 }
 
 export default MongoStorageAdapter;