diff --git a/package.json b/package.json
index 653bd1e7..826b2c55 100644
--- a/package.json
+++ b/package.json
@@ -12,7 +12,7 @@
         "jest": "node build/jest",
         "debug": "node --async-stack-traces --trace-deprecation --enable-source-maps build/start --debug",
         "start": "node build/start",
-        "clean": "zsh -c \"rm -rf tsconfig.build.tsbuildinfo ./packages/*/tsconfig.tsbuildinfo ./packages/*/dist ./**/tscofig.json ./.coverage\""
+        "clean": "zsh -c \"rm -rf tsconfig.build.tsbuildinfo ./packages/*/tsconfig.tsbuildinfo ./packages/*/dist ./.coverage\""
     },
     "version": "1.0.0",
     "license": "AGPL-3.0-only",
@@ -41,4 +41,4 @@
         "fs-extra": "^9.0.1",
         "yargs": "^16.0.3"
     }
-}
+}
\ No newline at end of file
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index 9a39f181..77c151a8 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -3,6 +3,7 @@ import { Readable, Writable } from 'stream';
 import { ObjectID } from 'mongodb';
 import fs from 'fs';
 import { Dictionary, NumericDictionary } from 'lodash';
+import type { Pdoc } from './model/problem';
 
 type document = typeof import('./model/document');
 
@@ -155,31 +156,32 @@ export interface RemoteProblemConfig {
 
 export type ProblemConfig = LocalProblemConfig | RemoteProblemConfig;
 
-export interface Pdoc {
-    _id: ObjectID,
-    domainId: string,
-    docType: 10,
-    docId: number,
-    pid: string,
-    owner: number,
-    title: string,
-    content: string,
-    nSubmit: number,
-    nAccept: number,
-    tag: string[],
-    category: string[],
-    data?: ProblemData,
-    hidden: boolean,
-    config: ProblemConfig,
-    acMsg?: string,
-    html?: boolean,
-
-    difficulty?: number,
-    difficultyAlgo?: number,
-    difficultyAdmin?: number,
-    difficultySetting?: any,
+declare module './model/problem' {
+    interface Pdoc {
+        domainId: string,
+        docType: 10,
+        docId: number,
+        pid: string,
+        owner: number,
+        title: string,
+        content: string,
+        nSubmit: number,
+        nAccept: number,
+        tag: string[],
+        category: string[],
+        data?: ProblemData,
+        hidden: boolean,
+        config: ProblemConfig,
+        acMsg?: string,
+        html?: boolean,
+
+        difficulty?: number,
+        difficultyAlgo?: number,
+        difficultyAdmin?: number,
+        difficultySetting?: any,
+    }
 }
-
+export type { Pdoc } from './model/problem';
 export type Pdict = NumericDictionary<Pdoc>;
 
 export interface StatusDoc {
diff --git a/packages/hydrooj/src/model/problem.ts b/packages/hydrooj/src/model/problem.ts
index 9afa1709..a6f91ebe 100644
--- a/packages/hydrooj/src/model/problem.ts
+++ b/packages/hydrooj/src/model/problem.ts
@@ -5,13 +5,57 @@ import { STATUS } from './builtin';
 import * as file from './file';
 import * as document from './document';
 import * as domain from './domain';
-import {
-    Pdoc, Pdict, ProblemDataSource, ProblemStatusDoc,
-} from '../interface';
+import { ProblemStatusDoc, ProblemDataSource, Pdict } from '../interface';
 import { NumberKeys, Projection } from '../typeutils';
 import { ProblemNotFoundError } from '../error';
 import * as testdataConfig from '../lib/testdataConfig';
 
+export interface Pdoc {
+    _id: ObjectID
+}
+export namespace Pdoc {
+    export type Field = keyof Pdoc;
+    export const fields: Field[] = [];
+    type Getter = (docId?: number, pid?: string) => Partial<Pdoc>
+    const getters: Getter[] = [];
+    export function extend(getter: Getter) {
+        getters.push(getter);
+        fields.push(...Object.keys(getter(0, '0')) as any);
+    }
+
+    extend((docId, pid) => ({
+        _id: new ObjectID(),
+        domainId: 'system',
+        docType: document.TYPE_PROBLEM,
+        docId: docId || -1,
+        pid: pid || docId.toString(),
+        owner: 1,
+        title: '*',
+        content: '',
+        html: false,
+        nSubmit: 0,
+        nAccept: 0,
+        tag: [],
+        category: [],
+        data: null,
+        hidden: true,
+        config: {},
+        acMsg: '',
+        difficulty: 0,
+        difficultyAlgo: 0,
+        difficultyAdmin: 0,
+        difficultySetting: null,
+    }));
+
+    export function create(docId?: number, pid?: string) {
+        const result = {} as Pdoc;
+        for (const getter of getters) {
+            Object.assign(result, getter(docId, pid));
+        }
+        return result;
+    }
+}
+
 export const SETTING_DIFFICULTY_ALGORITHM = 0;
 export const SETTING_DIFFICULTY_ADMIN = 1;
 export const SETTING_DIFFICULTY_AVERAGE = 2;
@@ -22,34 +66,13 @@ export const SETTING_DIFFICULTY_RANGE = [
     [SETTING_DIFFICULTY_AVERAGE, 'Use average of above'],
 ];
 
-export const pdocHidden: Pdoc = {
-    _id: new ObjectID(),
-    domainId: 'system',
-    docType: document.TYPE_PROBLEM,
-    docId: -1,
-    pid: '',
-    owner: 1,
-    title: '*',
-    content: '',
-    html: false,
-    nSubmit: 0,
-    nAccept: 0,
-    difficulty: 0,
-    tag: [],
-    category: [],
-    data: null,
-    hidden: true,
-    config: {},
-    acMsg: '',
-};
-
-export const PROJECTION_LIST: Projection<Pdoc> = [
+export const PROJECTION_LIST: Pdoc.Field[] = [
     '_id', 'domainId', 'docType', 'docId', 'pid',
     'owner', 'title', 'nSubmit', 'nAccept', 'difficulty',
     'tag', 'category', 'hidden',
 ];
 
-export const PROJECTION_PUBLIC: Projection<Pdoc> = [
+export const PROJECTION_PUBLIC: Pdoc.Field[] = [
     ...PROJECTION_LIST,
     'content', 'html', 'data', 'config', 'acMsg',
 ];
@@ -133,7 +156,7 @@ export async function getList(
         for (const pid of pids) {
             if (!(r[pid] || l[pid])) {
                 if (doThrow) throw new ProblemNotFoundError(domainId, pid);
-                else r[pid] = pdocHidden;
+                else r[pid] = Pdoc.create(undefined, pid.toString());
             }
         }
     }
@@ -173,6 +196,8 @@ export async function setTestdata(domainId: string, _id: number, filePath: strin
 }
 
 global.Hydro.model.problem = {
+    Pdoc,
+
     PROJECTION_LIST,
     PROJECTION_PUBLIC,
 
@@ -181,7 +206,6 @@ global.Hydro.model.problem = {
     SETTING_DIFFICULTY_AVERAGE,
     SETTING_DIFFICULTY_RANGE,
 
-    pdocHidden,
     add,
     inc,
     get,