# Query builder: DB() and NEWDB() with your own database driver

> Build queries with DB().find().where().sort() and let a driver registered with NEWDB() run them, while a registered driver implements supported database operations.

Framework: total5
Product: Total.js 5 (total5@0.0.19)
Language: en
Content-SHA256: 4bef065e707876cf8653fcd1df4979bebd7327aa58465f355fefd40b2d4ca631
Snapshot: c0700e321579725c5cf4f5ace1ad7d2866d1b4f93c24a63c0b41b6b7998e976c
Sources: total5-installed@total5@0.0.19
Review: not-recorded

`DB()` builds a query without knowing which database will run it, and `NEWDB()` registers the **driver** that runs it. `total5` itself has no SQL driver: the query builder collects what you ask for into an `options` object and calls your driver with it, and the driver (yours, or one that comes in a module) translates `options` into SQL, a NoSQL call or anything else.

- `NEWDB(driver)` registers the default driver and `NEWDB('name', driver)` a named one. The driver is `function(options, callback)`: answer with `callback(error, response)`. A table written as `name/table` (`DB().find('audit/log')`) uses the driver `name` and the table `log`; without a prefix the driver is `default`.
- The operations start the query: `find(table)` (an array), `read(table)` (one object, or `null` when there is none), `list(table)` (a page of an array: `response.page`, `limit` and `pages` are added to what the driver returns, so the driver should set `count`) and `insert(table, data)`. The builder also has `count`, `update`, `remove` and `query`; they work the same way (the driver gets `options.exec` with that name).
- Refine the query with: `where(name, [comparer], value)` (`=` when there is no comparer), `fields('a,b')`, `sort(name, [true])` (`true` for descending), `take(n)` and `page(page, limit)`. Other modifiers include `id`, `in`, `skip`, `between` and `search`.
- Finish with `.callback($)`: the result goes to the response of the action `$`, or to a function `(err, response)` that you pass instead.

For the complete native operation catalogue, upsert/error behavior and filter shapes, see [query-builder-contract](/en/total5/query-builder-contract/). For SQL CRUD, commit and rollback, see [query-builder-sqlite](/en/total5/query-builder-sqlite/). The options the driver receives are plain data. The example driver stores records in memory and exposes the last `options` object received.

```js definitions/db.js
const users = [
	{ id: 1, name: 'Ann', age: 31 },
	{ id: 2, name: 'Bob', age: 17 },
	{ id: 3, name: 'Cy', age: 45 }
];

F.seen = [];

// The default driver: it understands only "age >= value" and "id = value", which is all this example asks
NEWDB(function(options, callback) {

	F.seen.push(JSON.parse(JSON.stringify(options)));

	let rows = users.slice();

	for (let f of options.filter) {
		if (f.type === 'where' && f.name === 'age' && f.comparer === '>=')
			rows = rows.filter(n => n.age >= f.value);
		else if (f.type === 'where' && f.name === 'id')
			rows = rows.filter(n => n.id === f.value);
	}

	switch (options.exec) {
		case 'find':
		case 'read':
			if (options.sort && options.sort[0] === 'name_desc')
				rows.sort((a, b) => a.name < b.name ? 1 : -1);
			if (options.take)
				rows = rows.slice(0, options.take);
			return callback(null, rows);
		case 'list':
			rows.count = rows.length;
			return callback(null, rows);
		case 'insert':
			users.push(Object.assign({ id: users.length + 1 }, options.payload));
			return callback(null, users[users.length - 1]);
		default:
			return callback('The driver does not know ' + options.exec);
	}
});

// A second driver, used by the tables that start with "audit/"
NEWDB('audit', function(options, callback) {
	F.seen.push({ driver: 'audit', table: options.table });
	callback(null, [{ event: 'login' }]);
});
```

```js controllers/users.js
exports.install = function() {
	ROUTE('GET /adults/', adults);
	ROUTE('GET /user/{id}/', user);
	ROUTE('POST /users/', create);
	ROUTE('GET /page/', page);
	ROUTE('GET /audit/', audit);
	ROUTE('GET /seen/', seen);
};

function adults($) {
	DB().find('users').where('age', '>=', 18).fields('id,name').sort('name', true).take(5).callback($);
}

function user($) {
	DB().read('users').where('id', +$.params.id).callback($);
}

function create($) {
	DB().insert('users', { name: $.body.name, age: $.body.age }).callback($);
}

function page($) {
	DB().list('users').page(1, 2).callback(function(err, response) {
		$.json({ err: err, count: response.count, page: response.page, limit: response.limit, pages: response.pages });
	});
}

function audit($) {
	DB().find('audit/log').callback($);
}

function seen($) {
	$.json(F.seen);
}
```