mirror of https://gitee.com/bigwinds/arangodb
302 lines
18 KiB
Plaintext
302 lines
18 KiB
Plaintext
!CHAPTER Getting Started
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We're going to start with an empty folder. This will be the root folder of our services. You can name it something clever but for the course of this guide we'll assume it's called the name of your service: `getting-started`.
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First we need to create a manifest. Create a new file called `manifest.json` and add the following content:
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```json
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{
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"engines": {
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"arangodb": "^3.0.0"
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}
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}
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```
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This just tells ArangoDB the service is compatible with versions 3.0.0 and later (all the way up to but not including 4.0.0), allowing older versions of ArangoDB to understand that this service likely won't work for them and newer versions what behavior to emulate should they still support it.
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The little hat to the left of the version number is not a typo, it's called a "caret" and indicates the version range. Foxx uses semantic versioning (also called "semver") for most of its version handling. You can find out more about how semver works at the [official semver website](http://semver.org).
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Next we'll need to specify an entry point to our service. This is the JavaScript file that will be executed to define our service's HTTP endpoints. We can do this by adding a "main" field to our manifest:
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```json
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{
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"engines": {
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"arangodb": "^3.0.0"
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},
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"main": "index.js"
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}
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```
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That's all we need in our manifest for now, so let's next create the `index.js` file:
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```js
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'use strict';
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const createRouter = require('@arangodb/foxx/router');
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const router = createRouter();
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module.context.use(router);
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```
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The first line causes our file to be interpreted using [strict mode](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode). All examples in the ArangoDB documentation assume strict mode, so you might want to familiarize yourself with it if you haven't encountered it before.
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The second line imports the `@arangodb/foxx/router` module which provides a function for creating new Foxx routers. We're using this function to create a new `router` object which we'll be using for our service.
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The `module.context` is the so-called Foxx context or service context. This variable is available in all files that are part of your Foxx service and provides access to Foxx APIs specific to the current service, like the `use` method, which tells Foxx to mount the `router` in this service (and to expose its routes to HTTP).
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Next let's define a route that prints a generic greeting:
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```js
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// continued
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router.get('/hello-world', function (req, res) {
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res.send('Hello World!');
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})
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.response(['text/plain'], 'A generic greeting.')
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.summary('Generic greeting')
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.description('Prints a generic greeting.');
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```
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The `router` provides the methods `get`, `post`, etc corresponding to each HTTP verb as well as the catch-all `all`. These methods indicate that the given route should be used to handle incoming requests with the given HTTP verb (or any method when using `all`).
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These methods take an optional path (if omitted, it defaults to `"/"`) as well as a request handler, which is a function taking the `req` ([request](Router/Request.md)) and `res` ([response](Router/Response.md)) objects to handle the incoming request and generate the outgoing response. If you have used the express framework in Node.js, you may already be familiar with how this works, otherwise check out [the chapter on routes](Router/Endpoints.md).
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The object returned by the router's methods provides additional methods to attach metadata and validation to the route. We're using `summary` and `description` to document what the route does -- these aren't strictly necessary but give us some nice auto-generated documentation. The `response` method lets us additionally document the response content type and what the response body will represent.
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!SECTION Try it out
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At this point you can upload the service folder as a zip archive from the web interface using the *Services* tab.
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<!-- TODO [Screenshot of the Services tab with no services listed] -->
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Click *Add Service* then pick the *Zip* option in the dialog. You will need to provide a *mount path*, which is the URL prefix at which the service will be mounted (e.g. `/getting-started`).
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<!-- TODO [Screenshot of the Add Service dialog with the Zip tab active] -->
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Once you have picked the zip archive using the file picker, the upload should begin immediately and your service should be installed. Otherwise press the *Install* button and wait for the dialog to disappear and the service to show up in the service list.
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<!-- TODO [Screenshot of the Services tab with the getting-started service listed] -->
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Click anywhere on the card with your mount path on the label to open the service's details.
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<!-- TODO [Screenshot of the details for the getting-started service] -->
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In the API documentation you should see the route we defined earlier (`/hello-world`) with the word `GET` next to it indicating the HTTP method it supports and the `summary` we provided on the right. By clicking on the route's path you can open the documentation for the route.
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<!-- TODO [Screenshot of the API docs with the hello-world route open] -->
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Note that the `description` we provided appears in the generated documentation as well as the description we added to the `response` (which should correctly indicate the content type `text/plain`, i.e. plain text).
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Click the *Try it out!* button to send a request to the route and you should see an example request with the service's response: "Hello World!".
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<!-- TODO [Screenshot of the API docs after the request] -->
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Congratulations! You have just created, installed and used your first Foxx service.
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!SECTION Parameter validation
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Let's add another route that provides a more personalized greeting:
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```js
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// continued
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const joi = require('joi');
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router.get('/hello/:name', function (req, res) {
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res.send(`Hello ${req.pathParams.name}`);
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})
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.pathParam('name', joi.string().required(), 'Name to greet.')
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.response(['text/plain'], 'A personalized greeting.')
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.summary('Personalized greeting')
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.description('Prints a personalized greeting.');
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```
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The first line imports the [`joi` module from npm](https://www.npmjs.com/package/joi) which comes bundled with ArangoDB. Joi is a validation library that is used throughout Foxx to define schemas and parameter types.
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**Note**: You can bundle your own modules from npm by installing them in your service folder and making sure the `node_modules` folder is included in your zip archive. For more information see the section on [module dependencies in the chapter on dependencies](Dependencies.md).
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The `pathParam` method allows us to specify parameters we are expecting in the path. The first argument corresponds to the parameter name in the path, the second argument is a joi schema the parameter is expected to match and the final argument serves to describe the parameter in the API documentation.
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The path parameters are accessible from the `pathParams` property of the request object. We're using a template string to generate the server's response containing the parameter's value.
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Note that routes with path parameters that fail to validate for the request URL will be skipped as if they wouldn't exist. This allows you to define multiple routes that are only distinguished by the schemas of their path parameters (e.g. a route taking only numeric parameters and one taking any string as a fallback).
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<!-- TODO [Screenshot of the API docs after a request to /hello/world] -->
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Let's take this further and create a route that takes a JSON request body:
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```js
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// continued
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router.post('/sum', function (req, res) {
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const values = req.body.values;
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res.send({
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result: values.reduce(function (a, b) {
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return a + b;
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}, 0)
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});
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})
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.body(joi.object({
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values: joi.array().items(joi.number().required()).required()
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}).required(), 'Values to add together.')
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.response(joi.object({
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result: joi.number().required()
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}).required(), 'Sum of the input values.')
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.summary('Add up numbers')
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.description('Calculates the sum of an array of number values.');
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```
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Note that we used `post` to define this route instead of `get` (which does not support request bodies). Trying to send a GET request to this route's URL (in the absence of a `get` route for the same path) will result in Foxx responding with an appropriate error response, indicating the supported HTTP methods.
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As this route not only expects a JSON object as input but also responds with a JSON object as output we need to define two schemas. We don't strictly need a response schema but it helps documenting what the route should be expected to respond with and will show up in the API documentation.
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Because we're passing a schema to the `response` method we don't need to explicitly tell Foxx we are sending a JSON response. The presence of a schema in the absence of a content type always implies we want JSON. Though we could just add `["application/json"]` as an additional argument after the schema if we wanted to make this more explicit.
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The `body` method works the same way as the `response` method except the schema will be used to validate the request body. If the request body can't be parsed as JSON or doesn't match the schema, Foxx will reject the request with an appropriate error response.
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<!-- TODO [Screenshot of the API docs after a request with an array of numbers] -->
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!SECTION Creating collections
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The real power of Foxx comes from interacting with the database itself. In order to be able to use a collection from within our service, we should first make sure that the collection actually exists. The right place to create collections your service is going to use is in [a *setup* script](Scripts.md), which Foxx will execute for you when installing or updating the service.
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First create a new folder called "scripts" in the service folder, which will be where our scripts are going to live. For simplicity's sake, our setup script will live in a file called `setup.js` inside that folder:
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```js
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// continued
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'use strict';
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const db = require('@arangodb').db;
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const collectionName = 'myFoxxCollection';
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if (!db._collection(collectionName)) {
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db._createDocumentCollection(collectionName);
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}
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```
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The script uses the [`db` object](../Appendix/References/DBObject.md) from the `@arangodb` module, which lets us interact with the database the Foxx service was installed in and the collections inside that database. Because the script may be executed multiple times (i.e. whenever we update the service or when the server is restarted) we need to make sure we don't accidentally try to create the same collection twice (which would result in an exception); we do that by first checking whether it already exists before creating it.
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The `_collection` method looks up a collection by name and returns `null` if no collection with that name was found. The `_createDocumentCollection` method creates a new document collection by name (`_createEdgeCollection` also exists and works analogously for edge collections).
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**Note**: Because we have hardcoded the collection name, multiple copies of the service installed alongside each other in the same database will share the same collection. Because this may not always be what you want, the [Foxx context](Context.md) also provides the `collectionName` method which applies a mount point specific prefix to any given collection name to make it unique to the service. It also provides the `collection` method, which behaves almost exactly like `db._collection` except it also applies the prefix before looking the collection up.
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Next we need to tell our service about the script by adding it to the manifest file:
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```json
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{
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"engines": {
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"arangodb": "^3.0.0"
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},
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"main": "index.js",
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"scripts": {
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"setup": "scripts/setup.js"
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}
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}
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```
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The only thing that has changed is that we added a "scripts" field specifying the path of the setup script we just wrote.
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Go back to the web interface and update the service with our new code, then check the *Collections* tab. If everything worked right, you should see a new collection called "myFoxxCollection".
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<!-- TODO [Screenshot of the Collections tab with "myFoxxCollection" in the list] -->
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!SECTION Accessing collections
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Let's expand our service by adding a few more routes to our `index.js`:
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```js
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// continued
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const db = require('@arangodb').db;
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const errors = require('@arangodb').errors;
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const foxxColl = db._collection('myFoxxCollection');
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const DOC_NOT_FOUND = errors.ERROR_ARANGO_DOCUMENT_NOT_FOUND.code;
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router.post('/entries', function (req, res) {
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const data = req.body;
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const meta = foxxColl.save(req.body);
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res.send(Object.assign(data, meta));
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})
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.body(joi.object().required(), 'Entry to store in the collection.')
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.response(joi.object().required(), 'Entry stored in the collection.')
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.summary('Store an entry')
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.description('Stores an entry in the "myFoxxCollection" collection.');
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router.get('/entries/:key', function (req, res) {
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try {
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const data = foxxColl.document(req.pathParams.key);
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res.send(data)
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} catch (e) {
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if (!e.isArangoError || e.errorNum !== DOC_NOT_FOUND) {
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throw e;
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}
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res.throw(404, 'The entry does not exist', e);
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}
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})
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.pathParam('key', joi.string().required(), 'Key of the entry.')
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.response(joi.object().required(), 'Entry stored in the collection.')
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.summary('Retrieve an entry')
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.description('Retrieves an entry from the "myFoxxCollection" collection by key.');
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```
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We're using the `save` and `document` methods of the collection object to store and retrieve documents in the collection we created in our setup script. Because we don't care what the documents look like we allow any attributes on the request body and just accept an object.
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Because the key will be automatically generated by ArangoDB when one wasn't specified in the request body, we're using `Object.assign` to apply the attributes of the metadata object returned by the `save` method to the document before returning it from our first route.
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The `document` method returns a document in a collection by its `_key` or `_id`. However when no matching document exists it throws an `ArangoError` exception. Because we want to provide a more descriptive error message than ArangoDB does out of the box, we need to handle that error explicitly.
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All `ArangoError` exceptions have a truthy attribute `isArangoError` that helps you recognizing these errors without having to worry about `instanceof` checks. They also provide an `errorNum` and an `errorMessage`. If you want to check for specific errors you can just import the `errors` object from the `@arangodb` module instead of having to memorize numeric error codes.
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Instead of defining our own response logic for the error case we just use `res.throw`, which makes the response object throw an exception Foxx can recognize and convert to the appropriate server response. We also pass along the exception itself so Foxx can provide more diagnostic information when we want it to.
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!SECTION Writing database queries
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Storing and retrieving entries is fine, but right now we have to memorize each key when we create an entry. Let's add a route that gives us a list of the keys of all entries so we can use those to look an entry up in detail.
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The naïve approach would be to use the `toArray()` method to convert the entire collection to an array and just return that. But we're only interested in the keys and there might potentially be so many entries that first retrieving every single document might get unwieldy. Let's write a short AQL query to do this instead:
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```js
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// continued
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const aql = require('@arangodb').aql;
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router.get('/entries', function (req, res) {
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const keys = db._query(aql`
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FOR entry IN ${foxxColl}
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RETURN entry._key
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`);
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res.send(keys);
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})
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.response(joi.array().items(
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joi.string().required()
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).required(), 'List of entry keys.')
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.summary('List entry keys')
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.description('Assembles a list of keys of entries in the collection.');
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```
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Here we're using two new things:
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The `_query` method executes an AQL query in the active database.
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The `aql` template string handler allows us to write multi-line AQL queries and also handles query parameters and collection names. Instead of hardcoding the name of the collection we want to use in the query we can simply reference the `foxxColl` variable we defined earlier -- it recognizes the value as an ArangoDB collection object and knows we are specifying a collection rather than a regular value even though AQL distinguishes between the two.
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**Note**: If you aren't used to JavaScript template strings and template string handlers just think of `aql` as a function that receives the multiline string split at every `${}` expression as well as an array of the values of those expressions -- that's actually all there is to it.
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Alternatively, here's a version without template strings (notice how much cleaner the `aql` version will be in comparison when you have multiple variables):
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```js
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const keys = db._query(
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'FOR entry IN @@coll RETURN entry._key',
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{'@coll': foxxColl}
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);
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```
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!SECTION Next steps
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You now know how to create a Foxx service from scratch, how to handle user input and how to access the database from within your Foxx service to store, retrieve and query data you store inside ArangoDB. This should allow you to build meaningful APIs for your own applications but there are many more things you can do with Foxx:
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* Need to go faster? Turn on [development mode](AtAGlance.md) and hack on your code right on the server.
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* Concerned about security? You could add [authentication](Auth.md) to your service to protect access to the data before it even leaves the database.
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* Writing a single page app? You could [store some basic assets](Assets.md) right inside your Foxx service.
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* Need to integrate external services? You can [make HTTP requests](Modules.md) from inside Foxx and use [queued jobs](Scripts.md) to perform that work in the background.
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* Tired of reinventing the wheel? Learn about [dependencies](Dependencies.md).
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<!-- TODO * Everything broken? You can [write tests](Testing.md) to make sure your logic remains sound. -->
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