How to Build a MVP REST API Using Low-Code Approach

Build and host and API in 15 minutes? Crazy? No, really!

REST APIs are pretty much everywhere. They are the standard method to expose databases to clients and knowing how to develop a REST API is a necessity at all layers of the stack.

By using one of the many public APIs out there, you can expand the functionality of your application or enrich it with the necessary data.

But what if you have created your own unique functionality that you want to share with the community?

The answer is to create your own API.

I’m going to show you how to do this in Linx, a low-code development tool for IT pros.

Let's Get Started

This tutorial will demonstrate how to build a minimally viable REST Web service integrated with a SQL Database using Linx to both build (Linx Designer) and host the web service (Linx Application Server). 

The REST web service will involve an operation related to the creation of a ‘user’ record in the database.

What is Linx?  Linx enables the rapid development and deployment of back-end applications like APIs, integrations and automations. Developers design and debug solutions in a familiar procedural style using a drag and drop interface with access to 1000s of ready made functions. Solutions are deployed with one click to servers running in the cloud or on-premise.

Prerequisites

This tutorial assumes:

1. Basic understanding of REST Web services
2. A database instance  and some basic familiarity with SQL 
3. Linx Application Designer (download here)
4. An active Linx Application Server*
5.  Web service request tool (e.g. Postman)

*The Linx application Server is available on a trial basis. 

Linx Solution Specification

The sample application will contain a REST Web service containing a single operation.  The operation will execute a custom process flow which results in a submitted ‘user’ being added to a database and the results returned in the response.

API Specification

The REST WebService will contain a single ‘AddUser’ operation. The ‘AddUser’ operation involves a POST request made to the ‘/users’ endpoint. 

HTTP Request

A JSON request body is submitted containing a ‘user’ object.

Request Body
{
      "username" 	: "string",
      "firstname"	: "string",
      "lastname"	: "string",
      "password"	: "string",
      "email"	: "string"
}

A JSON response body is then returned containing a ‘user’ object.

Response Body
{
      "id":0,
      "username" : "string",
      "firstname"	: "string",
      "lastname"	: "string",
      "email"	: "string"
}

NOTE:  For the purpose of this demonstration - creating a minimally viable REST API - I will only be creating a single operation and will not be applying any security to the operation. Extending the API functionality and adding security is simple enough.

Database Specification

Here is a SQL database containing a [User] table consisting of the following fields:

• [ID] – Primary Key
• [Username] – Username of user
• [Password] - Password (encrypted)
• [FirstName] - First name of user
• [LastName] - Last name of user
• [email] - email of user

The ‘user’ details that are submitted with the request will be added to this table. The newly generated ID and additional fields of the new record will then be returned.

You can use the sample SQL below to create the table:

SQL
CREATE TABLE [dbo].[User](
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[Username] [varchar](50) NOT NULL,
	[Password] [varchar](50) NOT NULL,
	[FirstName] [varchar](50) NULL,
	[LastName] [varchar](50) NULL,
	[email] [varchar](50) NULL,
        CONSTRAINT [PK_User] PRIMARY KEY (ID)
)

Create the Linx Application

Creating a REST Web service and adding custom functionality with Linx involves the following broad stages:

1. Creating a new solution
2. Adding Plugins (functionality)
3. Create custom logic flow
4. Configure REST Web service and Operations
5. Link custom logic to REST operations
6. Debug & deploy 

Creating a New Solution

To create a new Linx solution is easy - with just a single click, the base skeleton of the application is created for you. Your solution is created with a blank ‘process’ and you can add as many processes and services as you require.

Plugin Configuration

Linx is based upon a plugin architecture.  To build the application, I require functionality related to the following areas:

1. REST Web Services (to generate a REST API)
2. Encryption (for the user’s password)
3. Database integration (executes a query against a database instance and returns any results)  

Plugins contain types, functions, and services;   which are higher-level components that reduce complex programming functionality into simple visual elements. For example, the File plugin contains functions relating to file operations such as writing and reading files (TextFileWrite, TextFileRead, CopyFile etc) as well as automated services such as Directory monitoring (DirectoryWatch).

Create custom logic flow

The custom logic flow will result in a ‘user’ object being added to a database and the results returned.

To start, create a single process which will take in an input parameter of a ‘user’ object. The ‘user.password’ ‘ will then be encrypted and added to the database along with the rest of the user’s details. The newly created record details will then be returned from the database and will be set as the result of the process.

Once this process has been built, it will then link to the REST endpoint operation.

Building a custom process

1. Configure a ‘user’ Custom Type. 
2. Configure the ‘user’ Custom Type to be an input and output of the process.
3. Add an Encrypt function to encrypt the ‘user.password’.
4. Connect to the database and execute SQL function that will insert the ‘user’ object and the encrypted password into the database.
5. Add a SetValue function to return the user’s details as the output of the process.

Configure a ‘user’ Custom Type

To create a ‘user’ object to use in the application you can create a Custom Type.

Custom Types are customizable objects containing basic types (integers, string etc) as well as nested objects. These Custom Types are automatically stored as JSON format and can be converted into a number of other formats using Linx functions.

To create a Custom Type, simply select the option from the menu bar.   Create a ‘user’ custom type with the following fields to resemble the [user] table in the database.

With the ‘user’ Custom Type, you can

• Set it as the input and output type of the process that adds the user details to the database.
• Set it as the format of the request body and response body of the operation.
  

Configure process input and output

By default, a single process is created when a new solution is created, The default name of ‘Process’ can be easily changed by editing the ‘name’ property. in this case, it has been renamed ‘AddUserToDatabase’.

Set the ‘user’ Custom Type as the input and the output of the ‘AddUserToDatabase’ process by using the field editor in the properties.

Encrypt password

To encrypt the incoming user’s password using a passphrase, drag on the ‘Encrypt’ function from the cryptography plugin onto the ‘AddUserToDatabase’ process. Linx  will automatically validate the properties for errors and indicate that there are required properties that need to be configured.

All the available data objects that are in scope of the process are available for selection. It is important to reference which data object is going to be encrypted and supply a passphrase or key depending on the algorithm chosen.

In this case it will be the input ‘user’ password. The result of the ‘Encrypt’ function will be a base64 encoded string that can be used when inserting the user details into the database.

Configure database connection and SQL

Select the ExecuteSQL function from the Database plugin to connect your database instance. Using the built-in connection editor, you can easily add a ‘connection string’ property which will allow access to your database instance.

Optional: By storing the Database connection string as a setting, you can access the value from anywhere in the solution.  The advantage of this is that you can have a single property source and reference this for multiple service or function properties.

Once connected,  add the SQL that will insert the details passed in from the user object and return the results. Using the SQL editor, you can use the built-in query generator to create an INSERT statement template for the [user] table.

Set the process output

The ‘user’ has been inserted into the database and the new details returned from the query.

You can set the output ‘user’ of the process equal to the ‘user’ returned from the database. To do this, simply use a SetValue function which allows you to assign the output of the ‘AddUserToDatabase’ process.

Configure REST Web Service and Operations

By now, you should have a custom process that:

1. Takes in a ‘user’ object
2. Inserts the details into a database 
3. Returns the updated details

Next, you can expose this functionality by linking the relevant custom logic to a specific REST operation which is contained in the REST host service. To do this;

1. Add a SimpleRESTHost service to your Solution
2. Configure properties and operation
3. Link your custom process to the operation
4. Debug and test
5. Deploy

Add a SimpleRESTHost service to your Solution

To add and initiate a SimpleRESTHost service to your solution, drag the ‘SimpleRESTHost’ service from the REST Plugin. This will create the base skeleton for the REST service.

Configure properties and operation.

First configure the Base URI, this is where the REST service will be hosted on.

Next, create the operations needed for the REST service by expanding the ‘Operations’ property wizard. Here you can quickly define operations, endpoints and parameters. In this case I want to:

1. Create an ‘AddUser’ operation (Name)
2. Configure the endpoint path to be ‘/users’ (Path)
3. Configure this operation as a POST method
4. For the request body, configure the operation to have a request body of a ‘user’ object that you created earlier
5. For the response body, it will also be a ‘user’ object
6. For the demo, you can bypass any security 
   

Click save to create your AddUser operation. Linx will provide all the necessary input and output structures in place.

Linking your custom process to the operation

You now have a 

1. Custom process
2. REST Operation

To link the two, in the  ‘AddUser’ operation, drag in the ‘AddUserToDatabase’ process. This will mean that when the ‘AddUsers’ operation is executed, it will execute the ‘AddUserToDatabase’ custom sub-process.

However, you first need to configure the inputs for the ‘AddUserToDatabase’ custom process to reference the ‘user’ passed in with the request body. Do so by simply referencing the input request body:

Finally, you can set the response body of the operation equal to the output returned from the ‘AddUserToDatabase’, which is done as follows:

SQL expression

Debug and test

The Linx IDE allows you to debug your operations in order to simulate the run time functionality.

To debug, initialize the debugger on the ‘AddUser’ operation. 

In the ‘Debug Values’ panel, input test data for the ‘request body’ property. 

By adding a ‘breakpoint’ to the ‘AddUserToDatabase’ operation, you can step through and pause on each function in the logic flow and see their runtime values.

Next, step into the ‘AddUserToDatabase’ process which will where you should see that the request body is then assigned as the input.user to the ‘AddUserToDatabase’

You can see the encrypted string as the output of the ‘Encrypt’ function.

The ‘user’ is inserted into the database and the new details are returned from the ExecuteSQL function. If you step over until you return to the parent operation, you can see the ‘AddUserToDatabase’ process has returned a ‘user’. Finally, you can see the operation’s response body being set to the values returned from the ‘AddUserToDatabase’ process.

Deploy

With the functionality of the REST service tested,  you are ready for deployment. This is done by simply clicking the ‘deploy’ button, directly from the IDE.

Linx Applications require a Linx Application Server to run. Deploy your Linx Applications directly from the Linx Designer - in the cloud or on-premise - to host and run your application.

Once deployed, and since it's the first time the application is uploaded,  you will need to ‘start’ the service. Once activated, the SimpleRESTHost service can begin to make requests against the API.

The Linx Server:

Testing with POSTMAN

To test, make a request to the ‘/users’ endpoint to add some user details to the database. In the database I currently have a [User] table with no records.

When a request is made to the Linx REST web service, details passed in with the request will be added to the database and an auto-generated ID along with the inserted details will be returned in the response.

Using Postman, you can setup a ‘POST request made to your REST service endpoint.

In the database a new record has been added along with an auto-generated ID.

In the response body you can see this ID as well as the user details returned with some having text manipulation being performed.

{
"id": 5,
"username": "linx",
"password": "",
"firstanme": "LinxDemo",
"lastname": "TEST",
"email": "[email protected]"
}

You’re done!

An end to end example fo building an API using Linx.

Watch this tutorial in a video format: