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Run Custom Code Event
This article looks at how you can write a custom function and add this to your actions and events.
The run custom code event allows you to add custom code into your Dittofi backend. Your custom backend code must be written in Google GO.
You can write to types of custom code (1) custom functions and (2) custom endpoints. In this user guide we are going to look at how to write and run custom functions inside Dittofi.
To learn how to write a custom endpoint read the article, how to write a custom endpoint in Dittofi.
WHY CUSTOM CODE?
There are two main reasons that you might want to use custom code in the Dittofi no-code platform:
  1. 1.
    To add functionality to your backend where, using custom code would be easier than using the out of the box event types
  2. 2.
    To create some functionality that is very specific to your app and where the event type does not already exist inside Dittofi. For example, many clients use the custom code section to write custom analytics.
You can add custom code to your app in 5 quick and easy steps.
  • Step 1. Add a new backend template
  • Step 2. Code your custom function
  • Step 3. Add a run custom code endpoint
  • Step 4. Add a run custom code action
  • Step 5. Build and test your code

Step 1. Add a new backend template

Custom code can be input into the system using the templates tab inside the Dittofi Design Studio. The templates tab is under the wrench icon in the purple side panel, as shown below.
From inside the templates tab, you must first add a new template into the folder Backend > Templates.
In the next step we are going to add in some custom code and add a custom function to add together two numbers.

Step 2. Code your custom function

After you've created your template you need to add the comment into your code "// @custom" at the top of the file, as shown below.
The "// @custom" comment tells the system that this is a custom file, rather than one of Dittofi's automatically generated ones.
NOTE
Automatically generated code for your backend is found in the folder Generated Code. All of this code can be exported from Dittofi, customized and debugged locally and the re-imported into Dittofi.
You also need to import the package "main" as shown below.
Finally, you can add any custom function written in GO. In this example we create the following function to add together two integers. Note that we need to tag this function "// @custom" as well.
// Custom function for addition
// @custom
func Add(left int, right int) (sum int, err error){
​
return left + right, nil
}
** IMPORTANT **
The final parameter of the function must always be of type error. You can see this above where we return a variable err of type error.
Save your custom code by clicking on
. This completes this step.

Step 3. Add a run custom code endpoint

Next, we are going to add an endpoint. To do this head over to the endpoints tab, click
and fill in the parameters for the endpoint as below.
Remember to save your endpoint and then head over to the actions tab.

Step 4. Add a run custom code action

Next, inside the actions tab, add a run custom code action. To do this, start by creating a new action. This can be done by clicking on
in the top right of the screen.
Inside the action, give your action a name and link the action to the Run Custom Code Endpoint that we created in Step 3 of this article.
Next, add the Run Custom Code Event to your action as below.
In the parameters for the event, select your custom function from the list of dropdown options.
As you can see, the custom code event will update to show the function arguments that are available for the custom function and the return value that we wrote in Step 2. of this guide. You can see this below.
For the purpose of this example, we can create two new variables inside our event, and map these variables into our custom code event. The GIF below shows us adding the second of these variables which we call "Two" and will store the number "2".
Our other variable is the number one and is stored inside the Variable "One", as show below. This can be added in the same way as the variable above.
Next, we add map these variables into our custom Add function as shown below and set a return value.
Finally, under our Trigger Component we can set the Response Variable that will be returned to our Action. In this case we choose the variable "ReturnSum" that we set above.

Step 5. Build and test your code

The final step is to build your code and test it. To do this click
. Next, head over to your endpoints tab, open your Run custom code endpoint and click run in the top right hand corner.
If you've set everything up correctly, you will get the response code 200 and will see the number 3 returned in the endpoint response body. This is because our addition function is adding up the numbers 1 and 2 that we input into in Step 4. of this article.
Endpoint Response Body

(Optional) review code documentation

Dittofi auto generates real source code for your apps. To help stress this point, if you open up the help panel by clicking on the question mark icon inside your help panel, you will see the option for "Code Documentation".
Opening this up, you can see that the code that has generated now include the custom function "Add". This is the custom function that we just wrote.
If you scroll down the code documentation, you can see the custom code that has been injected.
You can also use the Dittofi code export function to get your full stack code and read and add to your go code directly in there.