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Bridge JSON Connectivity with Apache Airflow



Access and process JSON services in Apache Airflow using the CData JDBC Driver.

Apache Airflow supports the creation, scheduling, and monitoring of data engineering workflows. When paired with the CData JDBC Driver for JSON, Airflow can work with live JSON services. This article describes how to connect to and query JSON services from an Apache Airflow instance and store the results in a CSV file.

With built-in optimized data processing, the CData JDBC Driver offers unmatched performance for interacting with live JSON services. When you issue complex SQL queries to JSON, the driver pushes supported SQL operations, like filters and aggregations, directly to JSON and utilizes the embedded SQL engine to process unsupported operations client-side (often SQL functions and JOIN operations). Its built-in dynamic metadata querying allows you to work with and analyze JSON services using native data types.

Configuring the Connection to JSON

Built-in Connection String Designer

For assistance in constructing the JDBC URL, use the connection string designer built into the JSON JDBC Driver. Either double-click the JAR file or execute the jar file from the command-line.

java -jar cdata.jdbc.json.jar

Fill in the connection properties and copy the connection string to the clipboard.

See the Getting Started chapter in the data provider documentation to authenticate to your data source: The data provider models JSON APIs as bidirectional database tables and JSON files as read-only views (local files, files stored on popular cloud services, and FTP servers). The major authentication schemes are supported, including HTTP Basic, Digest, NTLM, OAuth, and FTP. See the Getting Started chapter in the data provider documentation for authentication guides.

After setting the URI and providing any authentication values, set DataModel to more closely match the data representation to the structure of your data.

The DataModel property is the controlling property over how your data is represented into tables and toggles the following basic configurations.

  • Document (default): Model a top-level, document view of your JSON data. The data provider returns nested elements as aggregates of data.
  • FlattenedDocuments: Implicitly join nested documents and their parents into a single table.
  • Relational: Return individual, related tables from hierarchical data. The tables contain a primary key and a foreign key that links to the parent document.

See the Modeling JSON Data chapter for more information on configuring the relational representation. You will also find the sample data used in the following examples. The data includes entries for people, the cars they own, and various maintenance services performed on those cars.

To host the JDBC driver in clustered environments or in the cloud, you will need a license (full or trial) and a Runtime Key (RTK). For more information on obtaining this license (or a trial), contact our sales team.

The following are essential properties needed for our JDBC connection.

PropertyValue
Database Connection URLjdbc:json:RTK=5246...;URI=C:/people.json;DataModel=Relational;
Database Driver Class Namecdata.jdbc.json.JSONDriver

Establishing a JDBC Connection within Airflow

  1. Log into your Apache Airflow instance.
  2. On the navbar of your Airflow instance, hover over Admin and then click Connections.
  3. Next, click the + sign on the following screen to create a new connection.
  4. In the Add Connection form, fill out the required connection properties:
    • Connection Id: Name the connection, i.e.: json_jdbc
    • Connection Type: JDBC Connection
    • Connection URL: The JDBC connection URL from above, i.e.: jdbc:json:RTK=5246...;URI=C:/people.json;DataModel=Relational;)
    • Driver Class: cdata.jdbc.json.JSONDriver
    • Driver Path: PATH/TO/cdata.jdbc.json.jar
  5. Test your new connection by clicking the Test button at the bottom of the form.
  6. After saving the new connection, on a new screen, you should see a green banner saying that a new row was added to the list of connections:

Creating a DAG

A DAG in Airflow is an entity that stores the processes for a workflow and can be triggered to run this workflow. Our workflow is to simply run a SQL query against JSON services and store the results in a CSV file.

  1. To get started, in the Home directory, there should be an "airflow" folder. Within there, we can create a new directory and title it "dags". In here, we store Python files that convert into Airflow DAGs shown on the UI.
  2. Next, create a new Python file and title it json_hook.py. Insert the following code inside of this new file:
    	import time
    	from datetime import datetime
    	from airflow.decorators import dag, task
    	from airflow.providers.jdbc.hooks.jdbc import JdbcHook
    	import pandas as pd
    
    	# Declare Dag
    	@dag(dag_id="json_hook", schedule_interval="0 10 * * *", start_date=datetime(2022,2,15), catchup=False, tags=['load_csv'])
    	
    	# Define Dag Function
    	def extract_and_load():
    	# Define tasks
    		@task()
    		def jdbc_extract():
    			try:
    				hook = JdbcHook(jdbc_conn_id="jdbc")
    				sql = """ select * from Account """
    				df = hook.get_pandas_df(sql)
    				df.to_csv("/{some_file_path}/{name_of_csv}.csv",header=False, index=False, quoting=1)
    				# print(df.head())
    				print(df)
    				tbl_dict = df.to_dict('dict')
    				return tbl_dict
    			except Exception as e:
    				print("Data extract error: " + str(e))
                
    		jdbc_extract()
        
    	sf_extract_and_load = extract_and_load()
    
  3. Save this file and refresh your Airflow instance. Within the list of DAGs, you should see a new DAG titled "json_hook".
  4. Click on this DAG and, on the new screen, click on the unpause switch to make it turn blue, and then click the trigger (i.e. play) button to run the DAG. This executes the SQL query in our json_hook.py file and export the results as a CSV to whichever file path we designated in our code.
  5. After triggering our new DAG, we check the Downloads folder (or wherever you chose within your Python script), and see that the CSV file has been created - in this case, account.csv.
  6. Open the CSV file to see that your JSON services is now available for use in CSV format thanks to Apache Airflow.

More Information & Free Trial

Download a free, 30-day trial of the CData JDBC Driver for JSON and start working with your live JSON services in Apache Airflow. Reach out to our Support Team if you have any questions.