Change and Switch nodes

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Del curso dictado por IBM

A Developer's guide to Node-RED

17 calificaciones

IBM

A Developer's guide to Node-RED

17 calificaciones

>>> By enrolling in this course you agree to the End User License Agreement as set out in the FAQ. Once enrolled you can access the license in the Resources area <<< Rapid application development using agile methodologies and processes are increasingly being used when developing applications. There is pressure on development teams to reduce the time needed to convert an idea into a working solution, be it as part of an innovation workshop or hackathon, a prototype for a new solution idea or main stream development. Developers are looking for new ways to allow them to be more production and innovations, such as Node-RED from the JS Foundation is a technology that allows a developer to rapidly create applications, taking a fraction of the time need coding write code. Node-RED is built on Node.js, so will run anywhere capable of hosting node.js applications, such as small single board computers like the Raspberry Pi or Beaglebone, on your laptop or workstation or in cloud environments, such as the IBM Cloud. Node red allows developers to compose flows using a pallet of nodes, where each node provides prebuilt functionality, that can be connected to other nodes to rapidly construct an application. This course assumes some basic knowledge of Node-RED, so if you have not used Node-RED then you may want to take a look at the Coursera course - A Developer’s Guide to the Internet of Things (https://www.coursera.org/learn/developer-iot/), which provides a beginner look at Node-RED. What you will learn: The course will improve your use of Node-RED. It will introduce some more advanced features available in key nodes, show you how to visualise data using dashboard nodes. It shows you how to create web APIs using Node-RED and how to consume web services and how to make use of different storage technologies within a Node-RED flow. The last section of the course shows how you can extend Node-RED by creating your own nodes. What technology is required to complete the course? The course requires you to have an IBM Cloud account, as some of the assignment work does make use of designated cloud services. You can create a free account on the IBM Cloud and in week 2 of the course we make a promotional code available, which unlocks some additional resources on the IBM Cloud, so you can complete the course without having to provide credit card information or pay for cloud services. If you choose to take this course and earn the Coursera course certificate, you will also earn an IBM digital badge. To find out more about IBM digital badges follow the link https://ibm.biz/badging.

De la lección

Week 2 - Useful Node-RED nodes

Week 2 is about getting to know some of the more advanced features available in Node-RED. It looks at the more advanced configuration options available in some of the key nodes, such as regular expressions and JSONata. The second part of this module looks at the dashboard nodes, which can be added to Node-RED. This module will show you how these nodes allow you to quickly create feature rich dashboards.

Change and Switch nodes6:48

Getting started with Regular expressions7:50

JSONata in Node-RED6:05

Conoce a los instructores

Brian Innes
Developer Advocate
IBM Digital Business Group
Nick O'Leary
Developer Advocate
IBM Digital Business Group
Maeve O'Reilly
IT Specialist
IBM Watson Internet of Things
John Walicki
Watson IoT Developer Advocate
Watson Internet of Things

In this lecture, I'll be looking at some of the key nodes we've not yet looked at,

and explain why using some of the nodes in the function section

of the pallet is a better option than just using the function node.

The function node is a very useful node,

as it provides a way to incorporate custom code into a flow.

But it's often used in places where one of

the other standard nodes might be a better option.

The function node runs code defined in

its configuration within a sandbox using the node.js vm package.

The Sandbox provides a level of isolation from the core node-red run time.

Each function node has its own sandbox context,

which does incur a performance penalty as

a sandbox context has to be established when the node is created,

and then each time a message arrives at the function node,

the run time has to switch into the function node's context to run the code,

and then switch back out to the context when the function node is completed.

While the function node does provide a very useful capability of running custom code,

it's often overused to do simple tasks,

such as setting a property on the message object which can be

completed in one of the standard nodes available in the pallet.

The rest of this lecture,

I'll introduce you to a couple of useful nodes.

And the first one I'll look at is the change node.

The change node can be used to modify

a message object or the flow or global context objects.

You have configuration options to set or delete properties,

you can move or rename properties,

and you can search and replace property values.

You can also make multiple changes to any of the objects within a single change node.

When setting a property, you can access any existing property on the incoming message,

or the flow or global context objects.

You can specify a string,

a number, a boolean true or false value,

set an object value from JSON,

a buffer, a timestamp,

or the output of a JSONata expression.

And I'll be discussing JSON values, what a buffer is,

and JSONata expressions later in the video.

When changing a value,

you can search for a value to be replaced.

The search value can be specified in the node configuration,

or from another property in the incoming message,

or the flow or global context objects.

Regular expressions can be used to search for patterns in the property being changed,

and we'll discuss these later in the video.

You can specify a property of the incoming message,

or the flow or global context objects to be deleted,

and the move option moves the property specified.

It can be thought of as a set operation on

the destination and delete operation on the source object.

Looking at a couple of the options on the set and change options,

a JSON value can be specified when setting or changing a value.

If you select a JSON value,

you'll see the edit field has an ellipsis character at the end,

which allows you to open up a JSON editor.

This JSON editor that will help you validate the JSON.

And it's worth noting that you need to enter valid JSON in this field,

and not a JavaScript object literal definition,

which allows things such as single quotes to be used.

I've included a link in the resources section of the course,

where you can find further details of valid JSON syntax.

A buffer allows you to create a JSON array of byte values.

You can create an array of unsigned byte values.

If the input cannot be passed as an array of unsigned byte values,

then the input is taken as a UTF-8 string.

The buffer editor indicates how the content is being handled,

and the buffer array is shown in the lower panel.

A timestamp value is the number of milliseconds since midnight at start of day,

on the 1st of January 1970 at Greenwich Mean Time.

JSONata is a lightweight query and transformation language for JSON data,

which allows you to easily query, manipulate JSON data.

I'll cover the syntax of JSONata in another video,

but there's a link to the JSONata website in the course's resources section.

Hopefully, you'll see how useful

the change node can be at manipulating object properties.

So next, I'm going to look at the switch node.

If you're more familiar with traditional programming,

the switch node can be thought of as the branch operation,

similar to an if or a switch statement.

It allows you to take a different route through a flow

depending on a specified condition or rule.

You can specify one or more rules in the switch node configuration,

and can select if you want to apply all the rules against the test property,

or stop after the first match.

Matching goes from top to bottom.

There's also an option of providing an otherwise clause.

Note, the otherwise rule only fires if one

of the other conditions above it in the list does not fire.

If you select to stop after the first match,

then no rule after the otherwise rule will ever be considered.

So, the otherwise rule should always be placed at the bottom of the list.

Rules can be reordered by dragging them in the configuration panel.

There are a number of options for specifying the rules

including regular expressions which will be discussed in another lecture.

You can specify a property from the incoming message or the flow

or global context objects to compare the rule against.

You can also supply a JSONata expression to generate the value to compare against.

And again, JSONata syntax will be discussed in another video.

Each new rule you create will add an output connector to the switch node.

You can choose to name the connectors if you want, but by default,

you can see the rule associated to the output connected by hovering over it.

If you reorder the rules,

then the output connectors will also be reordered to match the rule order.

As an exercise, you should explore the other nodes in

the function section of the pallet to become familiar with how they work and

the capabilities they offer as using one of the standard nodes is

preferrable to writing custom code in a function node that does the same task.

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