.NET Core

Overview of creating .NET Core functions

Getting and publishing a function

The following shows how to get, edit, and pack your template for upload.

Versions	Template
.NET Core 2.1	Download

• After you have downloaded the template project, unzip it and navigate to ./LambdaFunction directory and open LambdaFunction.csproj project (if you are not using an IDE with automated restore functionality, run dotnet restore in command-line tool inside this folder).

• Your entry (main) method will be inside Function.cs file called Handler.

• After you are done editing your function, open command-line tool inside of ./LambdaFunction

  directory and rundotnet publish -o lambda.

• Navigate to a newly created folder ./lambda and zip all the contents inside of the directory.

• Upload zipped file to CodeMash.

For the handler, you have to specify your entry function location. Handler follows such format - assembly::namespace.className::methodName. Following the structure given in the initial template, the handler would be LambdaFunction::LambdaFunction.Function::Handler. You can edit any of these parameters for your own function.

Template overview

The following explains how to use provided template to create your own functions.

Main method

You define your main function in the handler field. In this case, the main method is Handler. It takes two parameters - input from CodeMash and function configuration.

public async Task<APIGatewayProxyResponse> Handler(CustomEventRequest<BasicInput> lambdaEvent, ILambdaContext context)
{
    ...
}

Inputs

CodeMash will always return CustomEventRequest as an input object. This class takes in generic parameter defining one of the possible input type. The following table explains when to use each of the provided inputs.

Class	Description
BasicInput	Use when executing function through API or using this function in a scheduler task.
CollectionTriggerInput	Use when using this function as a trigger for collections.
FileTriggerInput	Use when using this function as a trigger for files.
UserTriggerInput	Use when using this function as a trigger for users.

Getting environment variables

A line below shows how to get the environment variables that you have set up near your function.

var envVariable = Environment.GetEnvironmentVariable("myVariableName");

Getting app settings

If you want to userappsettings.jsonfile the following shows how to read a file. In this case, file is in root directory of a project.

public static class AppSettings
{
    private static IConfigurationRoot instance;

    // Method to get a string from settings
    public static string GetString(string key)
    {
        if (instance == null)
        {
            // Create an instance with settings
            instance = new ConfigurationBuilder()
                .SetBasePath(Directory.GetCurrentDirectory())
                .AddJsonFile("appsettings.json")
                .Build();
        }
        
        // Get value by key
        return instance[key];
    }
}

Example of a appsettings.json file:

{
    "Parameter1": "First parameter.",
    "NestedParams": {
        "NestedParam1": "First nested parameter."
    }
}

Then to get a string from settings:

// First level parameter
var settings = AppSettings.GetString("Parameter1");

// Second level parameter
var nestedSettings = AppSettings.GetString("NestedParams:NestedParam1");

Constructors

Lambda executor will call your default constructor (without parameters). If you want to add dependency injection to your services, you will have to add a default constructor which calls your wanted constructor.

public class Function
{
    private readonly IExampleService _exampleService;
    
    // (Required if adding other constructors. Otherwise, optional.) A default constructor
    // called by Lambda. If you are adding your custom constructors,
    // default constructor with no parameters must be added
    public Function() : this (new ExampleService()) {}

    // (Optional) An example of injecting a service. As a default constructor is called by Lambda
    // this constructor has to be called from default constructor
    public Function(IExampleService exampleService)
    {
        _exampleService = exampleService;
    }
    
    public async Task<APIGatewayProxyResponse> Handler(CustomEventRequest<BasicInput> lambdaEvent, ILambdaContext context)
    {
        ...
        
        // - Call example service
        var helloWorldMessage = await _exampleService.GetHelloWorld();
        
        ...
    }
}