部分公共代码db和const放到shared目录

shared/db/Counter.ts

@@ -0,0 +1,23 @@
+import BaseModel from './BaseModel';
+import { index, getModelForClass, prop } from '@typegoose/typegoose';
+
+/**
+  * 自增 ID
+*/
+@index({ name: 1 })
+export default class Counter extends BaseModel {
+
+  @prop({ required: true })
+  name: string;
+
+  @prop({ required: true, default: 1 })
+  seq: number;
+
+  public static async getNewCounter(name: string, lean = true) {
+    const counter = await CounterModel.findOneAndUpdate({ name }, { $inc: { seq: 1 } }, { new: true, upsert: true }).lean(lean);
+    return counter?.seq;
+  }
+
+}
+
+export const CounterModel = getModelForClass(Counter);