Step 2: Create the Siddhi Application¶

Let's create your first Siddhi application.

For this purpose, you can consider an example where production information is published in a database table. This information needs to be captured as and when it is published in the database, and published in a file after changing the case of the product name.

The following image depicts the procedure to be followed by the Siddhi application you create.

Siddhi Application Flow

Install Visual Studio Code editor, if not already installed.
Install the WSO2 Integrator: SI extension in Visual Studio Code. To do this, follow the steps below:
1. Open Visual Studio Code and click on the Extensions icon in the left pane.
2. Search for WSO2 Integrator: SI in the marketplace and install it.
Access the WSO2 Integrator: SI Welcome page by typing and selecting SI: Open SI Welcome in the command palette. You can open the command palette by pressing Ctrl + Shift + P (or Cmd + Shift + P on macOS).

Welcome Page

Create a new Siddhi file by clicking on + Create New Siddhi Application.

The new file opens as follows.
Specify a name for the new Siddhi application via the @App:name annotation.
```
@App:name("SweetFactoryApp")
```
First, let's define the stream that receives the input data.

define stream InsertSweetProductionStream (name string,amount double);
To allow the InsertSweetProductionStream stream to capture inserts from the productions database, connect a source of the cdc type to it as shown below.
```
@source(type='cdc',url = "jdbc:mysql://localhost:3306/production",username = "wso2si",password = "wso2",table.name = "SweetProductionTable",operation = "insert",
    @map(type='keyvalue'))
define stream InsertSweetProductionStream (name string,amount double);
```
8. To publish the captured data into a file, define an output stream as follows.

define stream ProductionUpdatesStream (name string,amount double);

To publish the output events to a file, connect a file source to the stream as shown below:

@sink(type='file',file.uri = "/Users/foo/productioninserts.csv",
@map(type='csv'))
define stream ProductionUpdatesStream (name string,amount double);

Here, you are publishing the output in the text format to a file named productioninserts.csv in the /Users/foo directory.

To convert the case of the product name from lower case to title case, and then publish the converted events to the file, write a query as follows.
```
@info(name='query1')
from InsertSweetProductionStream 
select str:upper(name) as name, amount 
group by name 
insert  into ProductionUpdatesStream;
```
This query gets the information inserted into the productions database table from the InsertSweetProductionStreamstream. The str:upper() function included in the select clause converts the product name from lower case to title case. Once this conversion is done, the converted events are directed to the ProductionUpdatesStream stream. These events are written into the /Users/foo/productioninserts.csv file because it is configured via the file source you previously annotated to the ProductionUpdatesStream stream.
Save the Siddhi application.

The completed Siddhi application looks as follows:

@App:name('SweetFactoryApp')

@source(type='cdc',url = "jdbc:mysql://localhost:3306/production",username = "wso2si",password = "wso2",table.name = "SweetProductionTable",operation = "insert",
    @map(type='keyvalue'))
define stream InsertSweetProductionStream (name string,amount double);

@sink(type='file',file.uri = "/Users/foo/productioninserts.csv",
    @map(type='csv'))
define stream ProductionUpdatesStream (name string,amount double);

@info(name='query1')
from InsertSweetProductionStream 
select str:upper(name) as name, amount 
group by name 
insert  into ProductionUpdatesStream;

Installing the required extensions¶

The WSO2 Integrator: SI is by default shipped with most of the available Siddhi extensions by default. If a Siddhi extension you require is not shipped by default, you can download and install it via the Extension Installer tool. The SweetFactoryApp Siddhi application you created uses a source of the cdc type. The cdc-mysql extension that is required for this source is not shipped with WSO2 Integrator: SI by default. Therefore, let's install it as follows.

In the VSCode editor, open the command palette by pressing Ctrl + Shift + P (or Cmd + Shift + P on macOS) and type SI: Open Extension Installer. Then select the SI: Extension Installer option.

Click Install for Change Data Capture - MySQL.
Reload VSCode.

Testing the Siddhi application¶

Before deploying the SweetFactoryApp Siddhi application to the WSO2 Integrator: SI Server, you need to test it to check whether the Siddhi queries you wrote work as expected. For this purpose, you can simulate events via the Event Simulator in WSO2 Integrator: SI as follows:

Tip

Although you are using the Event Simulator instead of performing an insert operation in the MySQL database table you created, you need to start the MySQL server before following the steps below.

In the VSCode editor, click the Run button to start the Event Simulator.

It opens the left panel for event simulation as follows.
Enter Information in the Single Simulation panel as described below.
1. In the Siddhi App Name field, select SweetFactoryApp.
2. In the Stream Name field, select InsertSweetProductionStream.
3. Under Attributes, enter values as follows:
  
  Attribute Value
  
  name (STRING) gingerbread
  
  amount (DOUBLE) 100
Click Start and Send.
Open the /Users/foo/productioninserts.csv. It should contain the following row.

GINGERBREAD,100.0

What's Next?

Now you can deploy the SweetFactoryApp Siddhi application you created. To do this, proceed to Step 3: Deploy the Siddhi Application.

Attribute	Value
name (STRING)	`gingerbread`
amount (DOUBLE)	`100`