Create Trigger

In the previous step, we created an empty project and described it in the project.yml file.

Now to add a trigger to the project we need to go to the triggers directory and create an empty .yml file there.

cd ./triggers
echo > my-first-trigger.yml

Open the created file in any text editor.

The first step in configuring the trigger is to give it a unique name.

name: my-first-trigger

Next, we can specify a trigger labels, for example specifying which group the trigger belongs to. If this label is not specified, the trigger defaults to the other group.

labels:
  group: first

We can also describe the trigger metadata in the corresponding field.

meta:
  title: My First Trigger
  description: My first trigger

After describing the trigger, it is necessary to describe the initial parameters (values) that are required for the trigger to work. If the trigger does not need initial parameters, values field can be left empty.

values: {}

More information about the types of values can be found here.

The last but the most important part is to describe the core of our trieger - pipeline. Pipeline consists of a list of nodes and a pointer to the final output node. All nodes are described in blocks. There are many different blocks for different tasks. You can find the list of basic blocks here.

Let's look at a simple example. Suppose we want to create a trigger that will output some random number from 0 to 100 every 10 minutes. We'll need two blocks for this:

• scheduler, which will be responsible for initiating the pipeline once every 10 minutes; (link)

• transform, with the help of which we will be able to get a random value. (link) Learn more about how to use javascript when describing output transformation logic here. It is important to note that the output data of the node must be an object or an array of objects.

pipeline:
  output: rnd
  nodes:
    - name: start
      block: schedule
      options:
        interval: 10m
    - name: rnd
      block: transform
      input: start
      params:
        output: 
          value: "{{ Math.floor(Math.random() * 100) }}"

That's it. As a result, the full contents of the trigger config file will look like this:

name: my-first-trigger
labels:
  group: first
meta:
  title: My First Trigger
  description: My first trigger
values: {}
pipeline:
  output: rnd
  nodes:
    - name: start
      block: schedule
      options:
        interval: 10m
    - name: rnd
      block: transform
      input: start
      params:
        output: 
          value: "{{ Math.floor(Math.random() * 100) }}"

If we want to allow the user to customize the range of random numbers, we can set a two parameters of type number in values and use it in the Pipeline. It will look like this:

name: my-first-trigger
labels:
  group: first
meta:
  title: My First Trigger
  description: My first trigger
values: 
  lower: { type: number }
  upper: { type: number }
pipeline:
  output: rnd
  nodes:
    - name: start
      block: schedule
      options:
        interval: 10m
    - name: rnd
      block: transform
      input: start
      values: 
        lower: "{{ values.lower }}"
        upper: "{{ values.upper }}"
      params:
        output: 
          value: "{{ Math.floor( Math.random() * (values.upper - values.lower) + values.lower ) }}"

To save the created trigger, you need to repeat the command push for the project from the root folder of the project.

After that, the trigger will appear in the service and you can subscribe to it and receive data for example in Telegram or Discord.

Next we will study how to test our trigger before push it to the Web3alert.