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# Model validation & API Design ---
marp: true
paginate: true
math: mathjax
theme: buutti
title: 5. Model Validation & API Design
---
# Model Validation # Model Validation & API Design
ASP.NET has a built-in system for validating whether the data sent in requests fits the model set in the code <!-- headingDivider: 5 -->
<!-- class: invert -->
Additional requirements can be set with attributes ## Model validation in ASP.NET
* ASP.NET has a built-in system for validating whether the data sent in requests fits the model set in the code
* Additional requirements can be set with attributes
```csharp
public class Contact public class Contact
{ {
public int Id { get; set; } public int Id { get; set; }
[Required] [Required]
[MaxLength(50)] [MaxLength(50)]
public string Name { get; set; } public string Name { get; set; }
[MaxLength(100)] [MaxLength(100)]
public string Email { get; set; } public string Email { get; set; }
} }
```
# Model Validation (continued) ### `TryValidateModel`
An object can be validated at any time with TryValidateModel method:
* An object can be validated at any time with `TryValidateModel` method:
```csharp
[HttpPost] [HttpPost]
public IActionResult Post([FromBody] Contact contact) public IActionResult Post([FromBody] Contact contact)
{ {
if (!TryValidateModel(contact)) if (!TryValidateModel(contact))
{ {
return BadRequest(ModelState); return BadRequest(ModelState);
} }
Contacts.Add(contact); Contacts.Add(contact);
return Created(Request.Path, contact); return Created(Request.Path, contact);
} }
```
The attributes set a corresponding error message and information to the ModelState which is sent with the bad request result ---
![](imgs/6-model-validation-and-designing-apis_0.png) * The attributes set a corresponding error message and information to the `ModelState` which is sent with the bad request result
<div class='columns23' markdown='1'>
<div markdown='1'>
![](imgs/6-model-validation-and-designing-apis_1.png) ![](imgs/6-model-validation-and-designing-apis_1.png)
Sometimes you might have custom requirements and the action should, according to the standard, return a bad request if the action does not fit those requirements </div>
<div markdown='1'>
For example, the simplest possible way to validate the format of an email is to check whether it contains the '@' symbol and with AddModelError add an error if it does not: ![](imgs/6-model-validation-and-designing-apis_0.png)
if (!contact.Email.Contains('@')) </div>
</div>
{ ---
* Sometimes you might have custom requirements and the action should, according to the standard, return a bad request if the action does not fit those requirements
* For example, the simplest possible way to validate the format of an email is to check whether it contains the `@` symbol
* Add an error with `AddModelError` if it does not contain the symbol:
```csharp
if (!contact.Email.Contains('@'))
{
ModelState.AddModelError("Description", "The email is not in valid form."); ModelState.AddModelError("Description", "The email is not in valid form.");
} }
```
Then check the model state: * Then check the model state:
```csharp
if (!ModelState.IsValid) if (!ModelState.IsValid)
{ {
return BadRequest(ModelState); return BadRequest(ModelState);
} }
```
# Exercise 1: ## Exercise 1: Add validation
<!--_class: "exercise invert" -->
Continue working on CourseAPI. Continue working on CourseAPI.
Mark all the properties of the Course class with the [Required] attribute 1) Mark all the properties of the Course class with the `[Required]` attribute
2) Create an endpoint for `POST` requests with the URI `api/courses`
Create an endpoint for POST requests with the URI api/courses 3) All the contents of the new course should come from the request body and the new course should be added to the `Courses` list
4) The maximum number of credits should be 20 and minimum 1 (Tip: Use `Range`)
All the contents of the new course should come from the request body and the new course should be added to the Courses list 5) Return an appropriate response
The maximum number of credits should be 20 and minimun 1 (Tip: Range)
Return an appropriate response
# Model Validation - Limiting PATCH ## Limiting `PATCH` with validation
* If we only want to allow the PATCH operation to affect Name and Email properties of Contact class * Suppose we only want to allow the `PATCH` operation to affect `Name` and `Email` properties of the `Contact` class
* Begin by declaring a class with only those fields: * Begin by declaring a class with only those fields:
* public class ContactPatch ```csharp
* { // Models/ContactPatch.cs
* public string Name { get; set; } public class ContactPatch
* public string Email { get; set; } {
* } public string Name { get; set; }
public string Email { get; set; }
# Model Validation - Limiting PATCH (continued) }
```
Use the ContactPatch class instead of the actual class for patching: ---
* Use the `ContactPatch` class instead of the actual class for patching:
```csharp
// Controllers/ContactsController.cs
[HttpPatch("{id}")] [HttpPatch("{id}")]
public IActionResult Patch(int id, [FromBody] JsonPatchDocument<ContactPatch> patchDocument) public IActionResult Patch(int id, [FromBody] JsonPatchDocument<ContactPatch> patchDocument)
{ {
Contact initialContact = _contactRepository.GetContact(id); Contact initialContact = _contactRepository.GetContact(id);
ContactPatch patchContact = new ContactPatch ContactPatch patchContact = new ContactPatch
{ Name = initialContact.Name, Email = initialContact.Email }; { Name = initialContact.Name, Email = initialContact.Email };
patchDocument.ApplyTo(patchContact, ModelState); patchDocument.ApplyTo(patchContact, ModelState);
if (!ModelState.IsValid) if (!ModelState.IsValid)
{ {
return BadRequest(); return BadRequest();
} }
initialContact.Name = patchContact.Name; initialContact.Name = patchContact.Name;
initialContact.Email = patchContact.Email; initialContact.Email = patchContact.Email;
_contactRepository.UpdateContact(id, initialContact); _contactRepository.UpdateContact(id, initialContact);
return Ok(initialContact); return Ok(initialContact);
} }
```
# Designing APIs
## Designing APIs
It's useful to get a good overview of the API for yourself and others before getting to work
* It can be useful to sketch an overview of the API before starting to implement it.
| __Method__ | __Endpoint__ | __Description__ | __Success__ | __Failure__ | * Write a table with all the endpoints, writing out the
| :-: | :-: | :-: | :-: | :-: | * HTTP method
| __GET__ | __/api/contacts__ | __Return all contacts__ | __200 Ok__ | __400 Bad request__ __404 Not found__ | * Description of the method
| __POST__ | __/api/contacts__ | __Add a new contact__ | __201 Created__ | __400 Bad request__ | * HTTP code on success
| __PUT__ | __/api/contacts/{id}__ | __Update a contact__ | __204 No content__ | __400 Bad request__ __404 Not found__ | * HTTP codes on different failure states
| __PATCH__ | __/api/contacts/{id}__ | __Partially update a contact__ | __204 No content__ | __400 Bad request__ __404 Not found__ | * See the following example!
| __DELETE__ | __/api/contacts/{id}__ | __Remove a contact__ | __200 OK__ | __404 Not found__ |
---
| Method | Endpoint | Description | Success | Failure |
|:---------|:---------------------|:---------------------------|:-----------------|:-----------------------------------|
| `GET` | `/api/contacts` | Return all contacts | `200 OK` | `400 Bad Request`, `404 Not Found` |
| `POST` | `/api/contacts` | Add a new contact | `201 Created` | `400 Bad Request` |
| `PUT` | `/api/contacts/{id}` | Update a contact | `204 No Content` | `400 Bad Request`, `404 Not Found` |
| `PATCH` | `/api/contacts/{id}` | Partially update a contact | `204 No Content` | `400 Bad Request`, `404 Not Found` |
| `DELETE` | `/api/contacts/{id}` | Remove a contact | `200 OK` | `404 Not Found` |

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