Fix model methods to omit _id

 const mongoose = require("mongoose");
 const mongoose = require("mongoose");
+const challenge = require("../api/challenge");
 
 
 const { Schema } = mongoose;
 const { Schema } = mongoose;
 
 
@@ -42,7 +43,9 @@ ChallengeSchema.methods.getStatus=function(){
 }
 }
 
 
 ChallengeSchema.methods.serialize=function(){
 ChallengeSchema.methods.serialize=function(){
-    return this.toJSON();
+    let challengeJSON = this.toJSON();
+    delete challenge._id;
+    return challengeJSON;
 }
 }
 
 
 const Challenge = mongoose.model('Challenge', ChallengeSchema);
 const Challenge = mongoose.model('Challenge', ChallengeSchema);

@@ -3,12 +3,17 @@ const mongoose = require("mongoose");
 const { Schema } = mongoose;
 const { Schema } = mongoose;
 
 
 const GroupSchema = new Schema({
 const GroupSchema = new Schema({
+    groupName: { type: String },
     members: [{ type: Schema.Types.ObjectId, ref: 'User' }]
     members: [{ type: Schema.Types.ObjectId, ref: 'User' }]
 },{
 },{
     collection: 'group'
     collection: 'group'
 });
 });
 
 
-GroupSchema.methods.addGroupMemeber=function(user){
+GroupSchema.statics.findByGroupName=function(groupName){
+    return this.find({groupName:groupName});
+}
+
+GroupSchema.methods.addGroupMember=function(user){
     this.members.push(user._id);
     this.members.push(user._id);
     return this.save();
     return this.save();
 }
 }
@@ -18,7 +23,9 @@ GroupSchema.methods.getMembers=function(){
 }
 }
 
 
 GroupSchema.methods.serialize=function(){
 GroupSchema.methods.serialize=function(){
-    return this.toJSON();
+    let groupJSON=this.toJSON();
+    delete groupJSON._id;
+    return groupJSON;
 }
 }
 
 
 const Group = mongoose.model('Group',GroupSchema);
 const Group = mongoose.model('Group',GroupSchema);

@@ -29,5 +29,11 @@ ParticipationSchema.methods.addProblem=function(problem){
     this.problems.push({problemNum:problem.problemNum,isSolved:problem.isSolved});
     this.problems.push({problemNum:problem.problemNum,isSolved:problem.isSolved});
 }
 }
 
 
+ParticipationSchema.methods.serialize=function(){
+    let participationJSON=this.toJSON();
+    delete participationJSON._id;
+    return participationJSON;
+}
+
 const Participation = mongoose.model('Participation', ParticipationSchema);
 const Participation = mongoose.model('Participation', ParticipationSchema);
 module.exports = Participation;
 module.exports = Participation;
\ No newline at end of file

@@ -58,7 +58,9 @@ ProblemSchema.methods.getCategory=function(){
 }
 }
 
 
 ProblemSchema.methods.serialize=function(){
 ProblemSchema.methods.serialize=function(){
-    return this.toJSON();
+    let problemJSON=this.toJSON();
+    delete problemJSON._id;
+    return problemJSON;
 }
 }
 
 
 const Problem = mongoose.model('Problem',ProblemSchema);
 const Problem = mongoose.model('Problem',ProblemSchema);

@@ -28,7 +28,9 @@ SessionSchema.methods.getStatus=function(){
 }
 }
 
 
 SessionSchema.methods.serialize=function(){
 SessionSchema.methods.serialize=function(){
-    return this.toJSON();
+    let sessionJSON=this.toJSON();
+    delete sessionJSON._id;
+    return sessionJSON;
 }
 }
 
 
 const Session = mongoose.model('Session', SessionSchema);
 const Session = mongoose.model('Session', SessionSchema);

@@ -38,13 +38,14 @@ UserSchema.methods.checkPassword = async function (password) {
 UserSchema.methods.serialize = function () {
 UserSchema.methods.serialize = function () {
   const data = this.toJSON();
   const data = this.toJSON();
   delete data.hashedPassword;
   delete data.hashedPassword;
+  delete data._id;
   return data;
   return data;
 };
 };
 
 
 UserSchema.methods.generateToken = function () {
 UserSchema.methods.generateToken = function () {
   const token = jwt.sign(
   const token = jwt.sign(
     {
     {
-      _id: this.id,
+      _id: this._id,
       username: this.username,
       username: this.username,
     },
     },
     process.env.JWT_SECRET,
     process.env.JWT_SECRET,