diff --git a/hydro/error.js b/hydro/error.js
index 3447ac18f..d0daa7184 100644
--- a/hydro/error.js
+++ b/hydro/error.js
@@ -1,7 +1,6 @@
 class UserFacingError extends Error {
     constructor(type) {
         super(type);
-        this.template = 'error';
         this.code = 500;
         //this.stack = '';
         this.params = [];
diff --git a/hydro/handler/judge.js b/hydro/handler/judge.js
index d8e7af38c..4f6d68695 100644
--- a/hydro/handler/judge.js
+++ b/hydro/handler/judge.js
@@ -2,6 +2,7 @@ const
     { requirePerm } = require('./tools'),
     { PERM_JUDGE } = require('../permission'),
     record = require('../model/record'),
+    problem = require('../model/problem'),
     bus = require('../service/bus'),
     queue = require('../service/queue'),
     { GET, POST } = require('../service/server');
@@ -15,11 +16,12 @@ GET('/judge/fetch', requirePerm(PERM_JUDGE), async ctx => {
     let rid = await queue.get('judge', false);
     if (rid) {
         let rdoc = await record.get(rid);
+        let pdoc = await problem.getById(rdoc.pid);
         let task = {
             event: 'judge',
             rid, type: 0,
             pid: rdoc.pid,
-            data: rdoc.data,
+            data: pdoc.data,
             lang: rdoc.lang,
             code: rdoc.code
         };
@@ -28,6 +30,7 @@ GET('/judge/fetch', requirePerm(PERM_JUDGE), async ctx => {
     else ctx.body = {};
 });
 POST('/judge/next', requirePerm(PERM_JUDGE), async ctx => {
+    console.log(ctx.request.body);
     let body = ctx.request.body;
     let rdoc = await record.get(body.rid);
     let $set = {};
@@ -40,7 +43,7 @@ POST('/judge/next', requirePerm(PERM_JUDGE), async ctx => {
         $set.judgeTexts = rdoc.judgeTexts;
     }
     if (body.compiler_text) {
-        rdoc.compilerTexts.push(body.compilerTexts);
+        rdoc.compilerTexts.push(body.compiler_text);
         $set.compilerTexts = rdoc.compilerTexts;
     }
     if (body.status) $set.status = body.status;
diff --git a/hydro/handler/problem.js b/hydro/handler/problem.js
index e448cbc52..b4f98c177 100644
--- a/hydro/handler/problem.js
+++ b/hydro/handler/problem.js
@@ -80,11 +80,12 @@ GET('/p/:pid/submit', requirePerm(PERM_SUBMIT_PROBLEM), async ctx => {
     };
 });
 POST('/p/:pid/submit', requirePerm(PERM_SUBMIT_PROBLEM), async ctx => {
+    let pdoc = await problem.get({ pid: ctx.params.pid });
     let rid = await record.add({
         uid: ctx.state.user._id,
         lang: ctx.request.body.lang,
         code: ctx.request.body.code,
-        pid: ctx.params.pid
+        pid: pdoc._id
     });
     await queue.push('judge', rid);
     ctx.state.user.nSubmit++;
@@ -94,7 +95,7 @@ POST('/p/:pid/submit', requirePerm(PERM_SUBMIT_PROBLEM), async ctx => {
 GET('/p/:pid/settings', async ctx => {
     ctx.templateName = 'problem_settings.html';
     let pdoc = await problem.get({ pid: ctx.params.pid, uid: ctx.state.user._id });
-    if (pdoc.hidden) ctx.checkPerm(PERM_VIEW_PROBLEM_HIDDEN);
+    if (pdoc.owner != ctx.state.user._id) ctx.checkPerm(PERM_EDIT_PROBLEM);
     ctx.body = {
         path: [
             ['Hydro', '/'],
@@ -109,12 +110,36 @@ POST('/p/:pid/settings', async ctx => {
     // TODO(masnn)
     ctx.back();
 });
+GET('/p/:pid/edit', async ctx => {
+    ctx.templateName = 'problem_edit.html';
+    let pdoc = await problem.get({ pid: ctx.params.pid, uid: ctx.state.user._id });
+    if (pdoc.owner != ctx.state.user._id) ctx.checkPerm(PERM_EDIT_PROBLEM);
+    ctx.body = {
+        path: [
+            ['Hydro', '/'],
+            ['problem_main', '/p'],
+            [pdoc.title, `/p/${ctx.params.pid}`, true],
+            ['problem_edit', null]
+        ],
+        pdoc, page_name: 'problem_edit'
+    };
+});
+POST('/p/:pid/edit', async ctx => {
+    let title = validator.checkTitle(ctx.request.body.title);
+    let content = validator.checkContent(ctx.request.body.content);
+    let pid = validator.checkPid(ctx.request.body.pid);
+    let pdoc = await problem.get({ pid: ctx.params.pid });
+    await problem.edit(pdoc._id, {
+        title, content, pid
+    });
+    ctx.setRedirect = `/p/${pid}`;
+});
 GET('/p/:pid/upload', async ctx => {
     ctx.templateName = 'problem_upload.html';
     let pdoc = await problem.get({ pid: ctx.params.pid, uid: ctx.state.user._id });
     if (pdoc.owner != ctx.state.user._id) ctx.checkPerm(PERM_EDIT_PROBLEM);
     let md5;
-    if (typeof pdoc.data == 'object') {
+    if (pdoc.data && typeof pdoc.data == 'object') {
         let files = await gridfs.find({ _id: pdoc.data }).toArray();
         md5 = files[0].md5;
     }
@@ -133,11 +158,14 @@ POST('/p/:pid/upload', async ctx => {
         f.once('error', reject);
     });
     let md5;
-    if (typeof pdoc.data == 'object') {
+    if (pdoc.data && typeof pdoc.data == 'object') {
+        gridfs.delete(pdoc.data);
+    }
+    pdoc = await problem.edit(pdoc._id, { data: f.id });
+    if (pdoc.data && typeof pdoc.data == 'object') {
         let files = await gridfs.find({ _id: pdoc.data }).toArray();
         md5 = files[0].md5;
     }
-    pdoc = await problem.edit(ctx.params.pid, { data: f.id });
     ctx.body = { pdoc, md5 };
 });
 GET('/p/:pid/data', async ctx => {
diff --git a/hydro/handler/ui.js b/hydro/handler/ui.js
index 174d85ee7..520b6f8c9 100644
--- a/hydro/handler/ui.js
+++ b/hydro/handler/ui.js
@@ -128,7 +128,10 @@ MIDDLEWARE(async (ctx, next) => {
             } else {
                 throw new NotFoundError();
             }
-        } catch (error) {
+        } catch (e) {
+            let error;
+            if (ctx.body && ctx.body.error) error = ctx.body.error;
+            else error = e;
             if (error instanceof NotFoundError) ctx.status = 404;
             if (error.toString().startsWith('NotFoundError')) console.log(error);
             if (error.toString().startsWith('Template render error')) throw error;
diff --git a/hydro/lib/validator.js b/hydro/lib/validator.js
index f11326366..d67c43bdd 100644
--- a/hydro/lib/validator.js
+++ b/hydro/lib/validator.js
@@ -7,21 +7,21 @@ const
 
 const
     isTitle = s => s && s.length < 64,
-    checkTitle = s => { if (!isTitle(s)) throw new ValidationError('title'); },
+    checkTitle = s => { if (!isTitle(s)) throw new ValidationError('title'); else return s; },
     isUid = s => RE_UID.test(s),
-    checkUid = s => { if (!isUid(s)) throw new ValidationError('uid'); },
+    checkUid = s => { if (!isUid(s)) throw new ValidationError('uid'); else return s; },
     isUname = s => RE_UNAME.test(s),
-    checkUname = s => { if (!isUname(s)) throw new ValidationError('uname'); },
+    checkUname = s => { if (!isUname(s)) throw new ValidationError('uname'); else return s; },
     isPassword = s => s.length >= 5,
-    checkPassword = s => { if (!isPassword(s)) throw new ValidationError('password'); },
+    checkPassword = s => { if (!isPassword(s)) throw new ValidationError('password'); else return s; },
     isEmail = s => RE_MAIL.test(s),
-    checkEmail = s => { if (!isEmail(s)) throw new ValidationError('mail'); },
+    checkEmail = s => { if (!isEmail(s)) throw new ValidationError('mail'); else return s; },
     isContent = s => s && s.length < 65536,
-    checkContent = s => { if (!isContent(s)) throw new ValidationError('content'); },
+    checkContent = s => { if (!isContent(s)) throw new ValidationError('content'); else return s; },
     isName = s => s && s.length < 256,
-    checkName = s => { if (!isName(s)) throw new ValidationError('name'); },
+    checkName = s => { if (!isName(s)) throw new ValidationError('name'); else return s; },
     isPid = s => RE_PID.test(s.toString()),
-    checkPid = s => { if (!RE_PID.test(s)) throw new ValidationError('pid'); };
+    checkPid = s => { if (!RE_PID.test(s)) throw new ValidationError('pid'); else return s; };
 
 module.exports = {
     isTitle, checkTitle,
diff --git a/hydro/model/problem.js b/hydro/model/problem.js
index 7155d344a..a78216d2c 100644
--- a/hydro/model/problem.js
+++ b/hydro/model/problem.js
@@ -1,6 +1,7 @@
 const
-    validator = require('../lib/validator'),
+    { ObjectID } = require('bson'),
     { ProblemNotFoundError } = require('../error'),
+    validator = require('../lib/validator'),
     db = require('../service/db.js'),
     coll = db.collection('problem'),
     coll_status = db.collection('problem.status');
@@ -42,23 +43,32 @@ async function add({
     return pid;
 }
 async function get({ pid, uid }) {
-    pid = parseInt(pid) || pid;
-    let pdoc = await coll.findOne({ pid });
+    let query = {};
+    if (pid.generationTime || pid.length == 24) query = { _id: new ObjectID(pid) };
+    else query = { pid: parseInt(pid) || pid };
+    let pdoc = await coll.findOne(query);
     if (!pdoc) throw new ProblemNotFoundError(pid);
-    pdoc.psdoc = uid ?
-        await coll_status.findOne({ pid, uid }) :
-        null;
+    if (uid) {
+        query.uid = uid;
+        pdoc.psdoc = await coll_status.findOne(query);
+    }
+    return pdoc;
+}
+async function getById(_id) {
+    _id = new ObjectID(_id);
+    let pdoc = await coll.findOne({ _id });
+    if (!pdoc) throw new ProblemNotFoundError(_id);
     return pdoc;
 }
 async function getMany(query, sort, page, limit) {
     return await coll.find(query).sort(sort).skip((page - 1) * limit).limit(limit).toArray();
 }
-async function edit(pid, $set) {
+async function edit(_id, $set) {
     if ($set.title) validator.checkTitle($set.title);
     if ($set.content) validator.checkContent($set.content);
-    await coll.findOneAndUpdate({ pid }, { $set });
-    let pdoc = await coll.findOne({ pid });
-    if (!pdoc) throw new ProblemNotFoundError(pid);
+    await coll.findOneAndUpdate({ _id }, { $set });
+    let pdoc = await getById(_id);
+    if (!pdoc) throw new ProblemNotFoundError(_id);
     return pdoc;
 }
 async function count(query) {
@@ -80,5 +90,6 @@ module.exports = {
     getMany,
     edit,
     count,
-    random
+    random,
+    getById
 };
\ No newline at end of file
diff --git a/templates/partials/path.html b/templates/partials/path.html
index b669c3ed9..d6b57b449 100644
--- a/templates/partials/path.html
+++ b/templates/partials/path.html
@@ -8,7 +8,7 @@
           / {% if c[1] %}<a href="{{ c[1] }}">{{ c[0] if c[2] else _(c[0]) }}</a>{% endif %}
         {%- endfor %}
         </div>
-        <h1 class="location-current" data-emoji-enabled>{{ path[path.length - 1][0] if path[path.length - 1][0] else _(path[path.length - 1][0]) }}</h1>
+        <h1 class="location-current" data-emoji-enabled>{{ path[path.length - 1][0] if path[path.length - 1][2] else _(path[path.length - 1][0]) }}</h1>
       </div>
       <div class="media__right">
         {% include "partials/hamburger.html" %}
diff --git a/templates/partials/problem_list.html b/templates/partials/problem_list.html
index 398b4df06..93af487fd 100644
--- a/templates/partials/problem_list.html
+++ b/templates/partials/problem_list.html
@@ -3,7 +3,7 @@
 {% import "components/problem.html" as problem with context %}
 {% import "components/nothing.html" as nothing with context %}
 <div data-fragment-id="problem_list">
-{% if not pdocs %}
+{% if not pdocs.length %}
   {{ nothing.render('Sorry, there is no problem in the problem set') }}
 {% else %}
   <table class="data-table">
diff --git a/templates/problem_upload.html b/templates/problem_upload.html
index 10736d767..c9edb37a2 100644
--- a/templates/problem_upload.html
+++ b/templates/problem_upload.html
@@ -4,8 +4,8 @@
     {% if (typeof(pdoc.data) == 'string') %}
         <p><b>{{ _('Current dataset comes from') }} <a href="{{ pdoc.data.split('from:')[1] }}" target="_blank">{{ pdoc.data.split('from:')[1] }}</a></b></p>
     {% else %}
-        <p>{{ _('Current dataset: {0}').format(pdoc['data'].toString()|default(_('(None)'))) }}</p>
-        <p>{{ _('MD5: {0}').format(md5|default(_('(None)'))) }}</p>
+        <p>{{ _('Current dataset: {0}').format((pdoc['data'] or _('(None)')).toString()) }}</p>
+        <p>{{ _('MD5: {0}').format(md5 or _('(None)')) }}</p>
     {% endif %}
     <p>{{ _('New dataset') }}:
         <input type="hidden" name="csrf_token" value="{{ handler.csrf_token }}">