Implement a Rest API that manages a todo list using Azure Functions

The default route for an azure function: localhost/api/functionName

We can use Azure Functions to implement a Rest API that will have the desired routh patterns for a rest api e.g:

• get: localhost/api/todo
• post: localhost/api/todo
• getById: localhost/ap/todo/{id}
• update: localhost/api/todo/{id}
• delete: localhost/api/todo/{id}

We can customise function route by using the route and specifying the http verb in the functions parameters. When the route parameter is specified the route of the function will change to match: localhost/api/routeParamValue

That's how we can implement REST API with azure functions.

https://docs.microsoft.com/en-us/azure/azure-functions/functions-triggers-bindings

Triggers are what cause a function to run. A trigger defines how a function is invoked and a function must have exactly one trigger.

• Https Trigger: makes the function respond to an http request.
• Timer Trigger: for scheduled functions.
• Blob Trigger: responds to blobs been created in blob storage.
• Queue Trigger: responds to message on a storage queue.

Binding to a function is a way of declaratively connecting another resource to the function (allows you to connect to external bindings. e.g post message to a queue or write to a blob/ table storage.); bindings may be connected as input bindings, output bindings, or both. Data from bindings is provided to the function as parameters. Bindings are optional and a function might have one or multiple input and/or output bindings.

• Input Bindings: brings data into your function from an external servic, e.g blob binding (can read the content of a blob from a blobs storage container), cosmosDb binding (can find a document in the cosmosDb database) etc
• Output Bindings: allows you to send data to an external service e.g queue binding (you can send message to a queue), sendGrid binding (with the sendgrid output binding extension you can send an email)

Triggers and Bindings(input/ouput) are defined in the function.json file, generated automaticlly when we build.

Additional bindings are added as an extension through nuget packages e.g cosmosDb, sendGrid etc. https://docs.microsoft.com/en-us/azure/azure-functions/functions-triggers-bindings#supported-bindings https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-storage-table?tabs=csharp

• To implement Rest API with azure functions we use Http Trigger attribute to customise the route for each function.
• Multiple functions can share the same route as long has they respond to different Http methods(verbs).
• We can use the route template syntax e.g {id} to pass in the itemId that we are interested in, in a route for HttpGet(Id), HttpUpdate(Id) and HttpDeleted(Id)
• We can serilise objects in the response of our methods by using the OkObjectResult