This is the official [Gel](https://www.geldata.com) client library
for JavaScript and TypeScript.
If you're just getting started with Gel, we recommend going through the
[Gel Quickstart](https://docs.geldata.com/learn/quickstart/overview/nextjs) first. This walks
you through the process of installing Gel, creating a simple schema, and
writing some simple queries.
### Requirements
- Node.js 18+
- For TypeScript users:
- TypeScript 4.4+ is required
## Basic usage
> The examples below demonstrate only the most fundamental use cases for this
> library. **[Go to the complete documentation site. >](https://docs.geldata.com/reference/clients/js#gel-js-intro)**
### Create a client
A _client_ is an instance of the `Client` class, which maintains a pool of
connections to your database and provides methods for executing queries.
```ts
import * as gel from "gel";
const client = gel.createClient();
```
### Configuring the connection
The call to `gel.createClient()` doesn't require arguments, as the library
can determine how to connect to your database using the following mechanisms.
1. _For local development_: initialize a project with the `gel project init`
command. As long as the file is within a project directory, `createClient`
will be able to auto-discover the connection information of the project's
associated instance. For more information on projects, follow the
[Using projects](https://docs.geldata.com/learn/projects) guide.
2. _In production_: configure the connection using **environment variables**.
(This can also be used during local development if you prefer.) The easiest
way is to set the `GEL_DSN` variable; a DSN (also known as a "connection
string") is a string of the form
`gel://USERNAME:PASSWORD@HOSTNAME:PORT/DATABASE`.
For advanced cases, see the
[DSN specification](https://docs.geldata.com/database/reference/dsn) and
[Reference > Connection Parameters](https://docs.geldata.com/database/reference/connection).
### Run a query
```ts
import * as gel from "gel";
const client = gel.createClient();
await client.query("select 2 + 2"); // => [4]
```
Note that the result is an _array_. The `.query()` method always returns an
array, regardless of the result cardinality of your query. If your query returns
_zero or one elements_, use the `.querySingle()` method instead. If your query
is guaranteed to return exactly one element, use the `.queryRequiredSingle()`
method.
```ts
// empty set, zero elements
const q1 = await client.querySingle("select {}");
// ^? string | null
// one element
const q2 = await client.querySingle("select 2 + 2");
// ^? number | null
// one element
const q3 = await client.querySingle<{ title: string }>(
// ^? { title: string } | null
`select Movie { title }
filter .id = '2eb3bc76-a014-45dc-af66-2e6e8cc23e7e';`,
);
// exactly one element
const q4 = await client.queryRequiredSingle("select 42;");
// ^? number
```
## Generators
Install the `@gel/generate` package as a dev dependency to take advantage of Gel's built-in code generators.
```bash
npm install @gel/generate --save-dev
```
Then run a generator with the following command:
```bash
$ npx @gel/generate [FLAGS]
```
The following ``s are currently supported:
- `queries`: Generate typed functions from `*.edgeql` files
- `interfaces`: Generate interfaces for your schema types
- `edgeql-js`: Generate the query builder
### `queries`
Run the following command to generate a source file for each `*.edgeql` system in your project.
```bash
$ npx @gel/generate queries
```
Assume you have a file called `getUser.edgeql` in your project directory.
```
// getUser.edgeql
select User {
name,
email
}
filter .email = $email;
```
This generator will generate a `getUser.query.ts` file alongside it that exports a function called `getUser`.
```ts
import { createClient } from "gel";
import { getUser } from "./getUser.query";
const client = createClient();
const user = await getUser(client, { name: "Timmy" });
// ^? { name: string; email: string }
```
The first argument is a `Client`, the second is the set of _parameters_. Both the parameters and the returned value are fully typed.
### `edgeql-js` (query builder)
The query builder lets you write queries in a code-first way. It automatically infers the return type of your queries.
To generate the query builder, install the `gel` package, initialize a project (if you haven't already), then run the following command:
```bash
$ npx @gel/generate edgeql-js
```
This will generate an EdgeQL query builder into the `./dbschema/edgeql-js`
directory, as defined relative to your project root.
For details on generating the query builder, refer to the [complete documentation](https://docs.geldata.com/reference/clients/js/querybuilder#generation). Below is a simple `select` query as an example.
```ts
import { createClient } from "gel";
import e from "./dbschema/edgeql-js";
const client = createClient();
const query = e.select(e.Movie, (movie) => ({
id: true,
title: true,
actors: { name: true },
num_actors: e.count(movie.actors),
filter_single: e.op(movie.title, "=", "Dune"),
}));
const result = await query.run(client);
result.actors[0].name; // => Timothee Chalamet
```
For details on using the query builder, refer to the full [query builder docs](https://docs.geldata.com/reference/clients/js/querybuilder).
## Contribute
Contributing to this library requires a local installation of Gel. Install
Gel from [here](https://docs.geldata.com/learn/cli) or
[build it from source](https://docs.geldata.com/resources/guides/contributing/code).
```bash
$ git clone git@github.com:geldata/gel-js.git
$ cd gel-js
$ yarn # install dependencies
$ yarn run build # build all packages
$ yarn run test # run tests for all packages
```
> In order to be able to run all tests you need to have `gel-server` in your
> path. This can be done by either running tests from within a Python 3.12
> virtual environment (you will have it if you built Gel locally), or by
> [installing](https://docs.geldata.com/reference/cli/gel_server/gel_server_install)
> specific Gel version and then adding its binary path to the `GEL_SERVER_BIN` environment variable.
> Check [here](https://docs.geldata.com/reference/cli/gel_server/gel_server_info)
> to find how to get the binary path.
## License
`gel-js` is developed and distributed under the Apache 2.0 license.
