48 lines
1.3 KiB
Markdown
48 lines
1.3 KiB
Markdown
---
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tags:
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- node-js
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- REST
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- APIs
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---
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# Creating a RESTful API: Validation
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We can provide server-side validation for our projects by using a **schema
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validator**. This is a program that declaratively parses the JSON values
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received as requests from the client. This makes it easy to systematically
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validate the data that we receive from any HTTP requests where the client sends
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a body to the endpoint.
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One of the most popular schema validators for NodeJS is
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[joi](joi).
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## Demonstration
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Let's say we have a POST request that expects a single field as the body that
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must be a string and greater than two characters long. First we define our
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schema:
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```js
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const schema = Joi.object({
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name: Joi.string().min(3).required(),
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});
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const { error } = schema.validate(req.body);
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```
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The `schema` variable is an object whose keys should match those of the intended
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request body. Instead of actual values we provide Joi's in-built validators,
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concatenated as necessary. We then store the results of the validation in a
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variable.
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Next we add handling in the case of errors:
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```js
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if (error) {
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error.details.map((joiErr) => res.status(400).send(joiErr.message));
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return;
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}
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```
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We loop through the error array and return 400s as the response if they are
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found. If there are no errors, the Joi object will return `undefined`.
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