Factor sessionDestruction as part of Session creation flow in RestWrite

Author: flovilmart

src/RestWrite.js

@@ -81,6 +81,8 @@ RestWrite.prototype.execute = function() {
     return this.transformUser();
   }).then(() => {
     return this.expandFilesForExistingObjects();
+  }).then(() => {
+    return this.destroyDuplicatedSessions();
   }).then(() => {
     return this.runDatabaseOperation();
   }).then(() => {
@@ -588,17 +590,31 @@ RestWrite.prototype.createSessionToken = function() {
     this.response.response.sessionToken = token;
   }
 
+  return new RestWrite(this.config, Auth.master(this.config), '_Session', null, sessionData).execute();
+}
+
+RestWrite.prototype.destroyDuplicatedSessions = function() {
+  // Only for _Session, and at creation time
+  if (this.className != '_Session' || this.query) {
+    return;
+  }
   // Destroy the sessions in 'Background'
+  const {
+    user,
+    installationId,
+    sessionToken,
+  } = this.data;
+  if (!user || !installationId)  {
+    return;
+  }
+  if (!user.objectId) {
+    return;
+  }
   this.config.database.destroy('_Session', {
-    user: {
-      __type: 'Pointer',
-      className: '_User',
-      objectId: this.objectId()
-    },
-    installationId: this.auth.installationId,
-    sessionToken: { '$ne': token },
+    user,
+    installationId,
+    sessionToken: { '$ne': sessionToken },
   });
-  return new RestWrite(this.config, Auth.master(this.config), '_Session', null, sessionData).execute();
 }
 
 // Handles any followup logic