Return values to the controller in the model from the ASP.NET MVC view

When we create an ASP.NET MVC web application, the model (an object) is the easiest way to return values from the view to the controller.

For the view to be able to return the values in the model, make sure the model contains properties, not fields, for every value with { get; set; }

public class MyViewModel
{
    public string ID { get; set; }
}

Add the model to the view at the top of the .cshtml file

IMPORTANT!!! To return values for properties that do not have controls on the page, like IDs that are not displayed, add a hidden field to the view.

@model MyViewModel
<form  asp-action="Index" asp-controller="My">
    <input asp-for=@Model.ID type="hidden" >
</form>

Send the data in the model to the view from the get method in the controller

public class MyController : Controller
{
    public IActionResult Index()
    {
         MyViewModel model = new MyViewModel();
         model.ID = "MY_ID";
         return View(model);
    }
}

Read the value from the model in the post method of the controller and send the model back

public class MyController : Controller
{
    [HttpPost, ValidateAntiForgeryToken]
    public IActionResult Index(MyViewModel model)
    {
        string ID = model.ID;
...
        return View(model);
    }
}

 

Error loading table definition of a PostgreSQL table

When a PostgreSQL table name contains uppercase letters there is no known way to get the table definition SQL script.

When we right-click a table name in SQLPro for Postgres the has an uppercase letter and select Script as, CREATE to, New query window

we get the error message

/*
* Error loading table definition.
* ERROR: relation “public.users” does not exist
*/

As the error message tells us, PostgreSQL is looking for the table name with all lowercase letters.


The pg_dump utility acts the same way.

pg_dump -s -h MY_SERVER_ADDRESS -U M_USERNAME -t Users MY_DATABASE

The error message is

pg_dump: no matching tables were found


The same process works if the table name only contains lowercase letters.

Convert an existing PostgreSQL database to all lowercase table and column names

To avoid similar errors caused by upper case letters in table and column names, convert the existing database definition to all lowercase

    1. Backup your database from the command prompt
      PGPASSWORD=MY_PASSWORD pg_dump -h MY_DATABASE_ADDRESS -U MY_DATABSE_USER -f MY_BACKUP_FILENAME.bak MY_DATABASE_NAME
    2. Open the backup file in a text editor
    3. Add underscores to the table and column names to match the .NET entity framework user identity processes.
      1. The PostgreSQL driver converts the first letter of all lowercase table and column names to upper-case and the letter that follows an underscore. For example, asp_net_users will be converted to AspNetUsers.
        1. Replace the table names with TableName -> table_name ( leave __EFMigrationsHistory as is)
        2. Replace the column names with “ColumnName” -> “column_name”
        3. Replace the primary key names with PK_ -> pk_
        4. Replace the index names with IX_ -> ix_
        5. Replace the foreign key names with FK_ -> fk_
    4. Drop the database. In SQL Pro for Postgres
      1. Right-click the database and select Drop database
    5. Re-create the database. In SQL Pro for Postgres
      1. Rith-click the server name and select Create database
    6. Import the modified backup file from the command prompt
      PGPASSWORD=MY_PASSWORD psql -h MY_DATABASE_ADDRESS -U MY_DATABSE_USER -d MY_DATABASE_NAME -f MY_BACKUP_FILENAME.bak
    7. Reverse engineer the database back to the .NET data layer project
      1. Delete the class files that correspond to the database tables
      2. Delete the MY_DATABSEContext.cs file
      3. Import execute the command in the data layer project directory
        dotnet ef dbcontext scaffold --force "Host=MY_DATABASE_ADDRESS;Database=MY_DATABASE_NAME;Username=MY_DATABSE_USER;Password=MY_PASSWORD" Npgsql.EntityFrameworkCore.PostgreSQL

Reverse engineer a database with AspNetCore in Visual Studio

For some reason the .NETCore designers did not think, that developers want to follow best practices by separating the data layer from the presentation layer.

The Entity framework out of the box only works if the database is accessed from the main application project.

When we try to reverse engineer a PostgreSQL database from a class library with the command:

cd MY_CLASS_LIBRARY_DIRECTORY
dotnet ef dbcontext scaffold "Host=localhost;Database=MY_DATABASE_NAME;Username=MY_USERNAME;Password=MY_PASSWORD" Npgsql.EntityFrameworkCore.PostgreSQL

we get the error message:

The specified framework version ‘2.1’ could not be parsed
The specified framework ‘Microsoft.NETCore.App’, version ‘2.1’ was not found.
– Check application dependencies and target a framework version installed at:
/usr/local/share/dotnet/
– Installing .NET Core prerequisites might help resolve this problem:
http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
– The .NET Core framework and SDK can be installed from:
https://aka.ms/dotnet-download
– The following versions are installed:
2.0.0 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
2.1.2 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
2.1.3 at [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

The problem is, that the …runtimeconfig.json files are only automatically generated in the bin/netcoreapp2.1 directory of the main application project, those are missing from all class libraries.

To enable the automatic generation of the …runtimeconfig.json files, add a line to the <PropertyGroup> section of the data layer class library project (.csproj) file.

<PropertyGroup>
...
<GenerateRuntimeConfigurationFiles>True</GenerateRuntimeConfigurationFiles>
...
</PropertyGroup>

 

Use two GitHub accounts on the same computer

Many developers have multiple GitHub accounts. One for personal projects, and another one for their work or business. There is a way to access multiple accounts simultaneously from the same computer. Only one account at a time can be configured using the HTTP connection, but we can configure the rest of the accounts using SSH.

There are many great articles on this topic, but most of them only provide partial instructions on how to set up multiple GitHub accounts on the same computer. In this post, I will document all the necessary steps to set up two accounts.

Usually, you don’t have much control over what GitHub connectivity is used for the company account, it can be dictated by the customer or your workplace, but you can always control what to use for your personal account. With SSH you can specify all aspects of your personal account, so you can leave the default SSH or HTTP connection for the business or company account.

In this post, we will set up two accounts with SSH connection. Even if the business account currently uses HTTP, it makes sense to set up SSH for that account too, in case they will switch to SSH at a later time.

Create two keys

    1. Open a terminal window and start the authentication agent to avoid the “Could not open a connection to your authentication agent” error later
       eval `ssh-agent -s`
    2. Create the personal SSH key
      ssh-keygen -t rsa -C "MY_PERSONAL_EMAIL@ADDRESS"

      when asked for the file name by the “Enter file in which to save the key“prompt, save the key as id_rsa_pers

    3. Add the personal key to the authentication agent
      ssh-add ~/.ssh/id_rsa_pers
    4. Create the business SSH key
      ssh-keygen -t rsa -C "MY_COMPANY_EMAIL@ADDRESS"

      when asked for the file name by the “Enter file in which to save the key“prompt, save the key as id_rsa_COMPANY_NAME

    5. Add the business key to the authentication agent
      ssh-add ~/.ssh/id_rsa_COMPANY_NAME

Configure SSH to use the two new keys

  1. Create the SSH config file
    touch ~/.ssh/config
  2. Open the ~/.ssh/config file with a text editor
  3. Add the following lines
    #Personal GitHub
    Host github-pers
      HostName github.com
      User MY_PERSONAL_GITHUB_USERNAME
      IdentityFile ~/.ssh/id_rsa_pers
    
    #Company GitHub
    Host github.com
      HostName github.com
      User MY_COMPANY_GITHUB_USERNAME
      IdentityFile ~/.ssh/id_rsa_COMPANY_NAME
    

Upload the keys to your GitHub accounts

  1. Log into the GitHub website with your personal credentials
  2. In the upper right corner click the down arrow next to your icon, and select Settings
  3. On the left side select SSH and GPG keys
  4. Click the New SSH key button
  5. Type a name for the key,  paste the contents of the ~/.ssh/id_rsa_pers.pub public key file into the text area, and click the Add SSH key button
  6. Log into Github with your company credentials
  7. Upload the id_rsa_COMPANY_NAME.pub public key file as explained above.

Create a personal repository

  1. Create a new folder, personal-test, and add a file to it on your computer
  2. Initialize the Git repository in the folder
    git init
    git add .
    git commit -m "Initial commit"
  3. Log into your personal GitHub account
  4. Create a new repository, and name it personal-test
  5. On the confirmation page click the SSH button
  6. Copy the …or push an existing… code to a text editor
  7. Edit the origin address to match the “Host” of the personal section in the ~/.ssh/config file, and execute the commands
    git remote add origin git@github-pers:MY_PERSONAL_GITHUB_USERNAME/personal-test.git
    git push -u origin master

Company repositories

For your company account use the default HTTP or SSH GitHub repository address without any modifications.

Change the AWS account to launch instances with Chef Test Kitchen

The Chef SDK contains Test Kitchen, that can launch server instances to test your Chef cookbooks. Test Kitchen uses the “chef_zero” provisioner to use your workstation as the virtual Chef server.

To switch Test Kitchen to launch instances in another AWS account

  1. In the .kitchen.yml file update the
    1. availability_zone
    2. subnet_id
    3. aws_ssh_key_id
    4. security_group_ids
    5. ssh_key
  2. In the default.rb attribute file update the
    1. …[‘aws_profile’]
  3. In the ~/.aws/credentials file update the
    1. [default] section

Copy files between Linux machines

The rsync command allows you to copy files using SSH connection, between your workstation and another Linux machine. You have to be logged into one of the machines, this command cannot copy files between two remote machines.

To copy a file from a remote server to your local workstation, execute

rsync -avz -e "ssh -i SSH_KEY_NAME" USER_NAME@SOURCE_IP:/SOURCE_DIRECTORY/SOURCE_FILE_NAME TARGET_DIRECTORY

To copy a file to a remote server, swap the source and target definitions after the SSH_KEY_NAME option.

Using tmux terminal multiplexer

The tmux terminal multiplexer allows us to open multiple terminal windows in the same SSH session and continue the command execution even when we log out of the SSH session. This way we can execute long-running copy commands overnight without keeping the SSH session open.

Install tmux

On CentOS family Linux

yum install tmux

To start tmux and attach to the last session

tmux a

To keep the current session active

To continue the session execution even when you log out of the server, detach from the session before closing the connection. See the commands below.

Commands

To switch to binding mode

ctrl-b

Commands in binding mode

d detach
% vertical split
horizontal split
arrows move between panes
c new window
p previous window
n next window
l last used pane
q display pane numbers
[ enable scroll with arrow keys or pgup, pgdown
q quit scroll mode
x close the pane (will ask you to press “y” to confirm)

Zooming

cmd-shift + zoom in
cmd-shift – zoom out
cmd-shift 0 (zero) 100% zoom

Add SSH key access to a GitHub repository

Generate an SSH key pair

  1. In a terminal execute
ssh-keygen

Generating public/private rsa key pair.
Enter file in which to save the key : /Users/MY_USERNAME/Git/_Keys/MY_PROJECT/MY_PROJECT_rsa_ci
Enter passphrase (empty for no passphrase):
Enter same passphrase again:

Leave the passphrase empty, many systems cannot work with password protected key pairs.

This process will save the key-pair in two files. The private key with no extension, and the public key with the .pub extension.

Create a new service GitHub user account which will have access to the repository

  1. Create a new email address (GitHub requires unique email addresses for every user)
  2. Register a new user which will have access to the repository

Upload the public key to the service GitHub account

    1. Log into the GitHub account and select Settings in the drop-down in the upper right corner
    2. On the left side select SSH and GPG keys
    3. In the upper right corner select the New SSH key button
    4. Copy the above generated public key to your clipboard.
      On a Mac copy the public key to your clipboard with the command

      pbcopy < /Users/MY_USERNAME/Git/_Keys/MY_PROJECT/MY_PROJECT_rsa_ci.pub
    5. Paste the public key into the textbox

Add the service user as a collaborator to the GitHub repository

  1. Log into the GitHub account that has admin access to the repository
  2. Navigate to the repository and select Settings
  3. Select COllaborators & teams
  4. Enter the username into the search box and click Add collaborator

If you use two-factor authentication in Github

If you use two-factor authentication in your GitHub account, and you need automated access to it, create a Personal Access Token and use it instead of your password. GitHub will not ask you to verify your identity.

Generate a Personal Access Token

    1. Log into your GitHub account
    2. On the left side select Developer settings
    3. Select Personal access tokens
    4. Click the Generate new token button
    5. Select the repo checkbox
    6. Copy the token to your clipboard. This is the last time you are able to see the token.
    7. Save the token at a secure location, and use it instead of your password when you need automated access to your GitHub account.

Creating CentOS server images with Packer

The CentOS images are not available on the AWS Quick Start tab.

CentOS publishes official images on the AWS Marketplace, but you need to subscribe to the image to be able to launch it with an automation software, like Terraform.

Find the latest available CentOS image in the AWS Marketplace

  1. Execute this command to display the list of available images
    aws --region us-east-1 ec2 describe-images --owners aws-marketplace --filters Name=product-code,Values=aw0evgkw8e5c1q413zgy5pjce
  2. Select the latest AMI from the list. The images are NOT ordered by date!
  3. If you try to launch the image before you subscribe to it, the error message is displayed

    Error launching source instance: OptInRequired: In order to use this AWS Marketplace product you need to accept terms and subscribe. To do so please visit http://aws.amazon.com/marketplace/pp?sku=…
    amazon-ebs: status code: 401, request id: []

  4. Follow the link in the error message to http://aws.amazon.com/marketplace/pp?sku=…
  5. Click the Continue to Subscribe button
  6. Once the new image has been created, share it with all the accounts you use.