Category Archives: Guides

Create DynamoDB Table – AWS CLI

Hi everyone,

A quick example of how to create a dynamodb table using the AWS CLI:

aws dynamodb create-table --table-name CatBreeds --attribute-definitions AttributeName=CatBreedId,AttributeType=S --key-schema AttributeName=CatBreedId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

For more info the following AWS page helped me: https://docs.aws.amazon.com/cli/latest/reference/dynamodb/create-table.html

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Update Wireless Info on Raspberry Pi

Hi everyone,

Just a quick post on how to configure wireless info on a raspberry pi. To start with, open the config file:

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

You can then add any number of connections to the file with varying priorities:

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=AU

network={
        ssid="Mobile Network"
        psk="YOUR_PASSWORD"
        key_mgmt=WPA-PSK
        priority=2
}

network={
        ssid="Home Network"
        psk="YOUR_PASSWORD"
        key_mgmt=WPA-PSK
        priority=10
}

Then save the file. Your raspberry pi will now connect to the network with the highest priority first (home network), when that’s not available it will use the network with the lower priority (mobile network).

The official doco is actually pretty good for this use case if you need more info: https://www.raspberrypi.org/documentation/configuration/wireless/wireless-cli.md

Fetch As Google Error – ReactJs

Hi everyone,

I ran into the following error while using “fetch as Google” and none of my pages were being indexed correctly:

Uncaught TypeError: undefined is not a function

It took a while to find a solution but after some Googling I found that GoogleBot currently uses Chrome v41. You can download the mini installer of Chromium v41 which will run in parallel with your existing Chrome version: https://www.googleapis.com/download/storage/v1/b/chromium-browser-snapshots/o/Win%2F310958%2Fmini_installer.exe?generation=1420864313749000&alt=media

After downloading Chromium you can just debug normally via the console. In my case, Chrome v41 didn’t like the following command:

document.head.append(script);

If you’re using a front-end framework like ReactJS, AngularJS or Vue you’ll often just need to add babel polyfill:


npm install babel-core --save-dev

Then add this as the first line in your entry point e.g. index.js:

import 'babel-core/polyfill';

It’s important that the polyfill import is added as the first line otherwise anything added before it won’t work.

If you’re getting an error about Headers, you may also need to install the following:

npm install whatwg-fetch --save

Add then add this import just below your babel polyfill:

import 'whatwg-fetch'

Thanks to tomekrudzki on Reddit for the link to Chromium v41: Chrome 41 the key to successful website rendering

 

 

.NET Core 2.1 is Returning JSON with Lowercase Properties

Hi everyone,

Just testing out .Net Core 2.1 and noticed that all of my JSON properties are being returned in lowercase despite being defined as uppercase. It turns out that this is configurable:


// Change from this
services.AddMvc();

// To this
services
        .AddMvc()
        .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver());

Check out these links for more info:
https://stackoverflow.com/a/38202543/522859
https://github.com/aspnet/Announcements/issues/194

Dynamic Robots.txt with Web Api 2

Hi everyone,

For a project I’m currently working on I needed a dynamic robots.txt. Because our test environment is public facing we want to keep it from being indexed by Google etc. It took a bit of Googling to find a solution that worked, but in the end it was actually pretty simple.

Here’s the action in one of the API Controllers:

    public class UtilitiesController : CustomBaseApiController
    {
        [Route("Robots.txt")]
        [HttpGet]
        public HttpResponseMessage GetRobotsFile()
        {
            var resp = new HttpResponseMessage(HttpStatusCode.OK);
            var stringBuilder = new StringBuilder();

            if (Helpers.IsProduction())
            {
                // Allow bots in production
                stringBuilder.AppendLine("user-agent: *");
                stringBuilder.AppendLine("disallow: ");
            }
            else
            {
                // Don't allow bots in non-production environments
                stringBuilder.AppendLine("user-agent: *");
                stringBuilder.AppendLine("disallow: *");
            }

            resp.Content = new StringContent(stringBuilder.ToString());

            return resp;
        }
    }

Also need to add the following to your web.config so that the robots.txt file can processed by the routing handler. Without this IIS will attempt to serve it as a static file and will return a 404 when it’s not found:


    
    
        
        
        
    
    

In production you’ll end up with the following:

user-agent: *
disallow:

And any other environments:

user-agent: *
disallow: *

Thanks to these answers on stackoverflow for the info:
https://stackoverflow.com/a/52270877/522859
https://stackoverflow.com/a/17037935/522859

Including an Externally Hosted Script in ReactJs

Hi everyone,

Just a quick example of how to include an externally hosted js file in a reactjs app. In index.html add your script tag as you would in a normal app:

  
    https://js.prelive.promisepay.com/PromisePay.js
  

Then in the file you plan to use the library you can add a const and reference it normally:

const promisepay = window.promisepay;

Thanks to this link for the info: https://stackoverflow.com/a/44877953/522859