pre-save hooks doesn't make sense when use db.load()

```js
//db.js
import Database from "warehouse";
import path from "path";
import fs from "fs";

const dbpath = path.resolve("./db.json");

const db = new Database({ path: dbpath });

await db.load();

console.log("db loaded...");

export default db;
```

```js
//category.js
import Database from "warehouse";
import db from "./db.js";

const { Schema } = Database;

const schema = new Schema({
name: { type: String, required: true },
});

schema.pre("save", async (data) => {
const { name, parent } = data;
if (!name) return;
const categories = db.model("categories");
const cat = await categories.findOne({ name });
if (cat) {
throw new Error(`Category \`${name}\` has already existed!`);
}
});

const Category = db.model("categories", schema);

export default Category;

```
```js
// cli.js
import Category from "./category.js";
import db from "./db.js";

const cat = await Category.save({ name: "Javascript" });

console.log("saved:", cat);

db.save();
```
```json
//db.json repeat so much!!!
{
"meta": { "version": 0, "warehouse": "4.0.0" },
"models": {
"posts": [],
"categories": [
{ "name": "Javascript", "_id": "ckwkujczh0000587nh75rhpcl" },
{ "name": "Javascript", "_id": "ckwkuqnr10000io7nb3ocey48" },
{ "name": "Javascript", "_id": "ckwkuqqpm0000u07n4gxg94r1" },
{ "name": "Javascript", "_id": "ckwkus0pb0000887nal5m0mxh" },
{ "name": "Javascript", "_id": "ckwkus2op0000dw7n5twndlvm" },
{ "name": "Javascript", "_id": "ckwkus3ko0000x07n36056e7i" },
{ "name": "Javascript", "_id": "ckwkus48c0000w47n962sfmfo" },
{ "name": "Javascript", "_id": "ckwkusz930000bg7n2rsm792b" }
]
}
}

```