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A PostgreSQL Interface for Cosmos DB Data

Use the Remoting features of the Cosmos DB JDBC Driver to create a PostgreSQL entry-point for data access.

There are a vast number of PostgreSQL clients available on the Internet. From standard Drivers to BI and Analytics tools, PostgreSQL is a popular interface for data access. Using our JDBC Drivers, you can now create PostgreSQL entry-points that you can connect to from any standard client.

To access Cosmos DB data as a PostgreSQL database, use the CData JDBC Driver for Cosmos DB and a JDBC foreign data wrapper (FDW). In this article, we compile the FDW, install it, and query Cosmos DB data from PostgreSQL Server.

Connect to Cosmos DB Data as a JDBC Data Source

To connect to Cosmos DB as a JDBC data source, you will need the following:

  • Driver JAR path: The JAR is located in the lib subfolder of the installation directory.
  • Driver class: cdata.jdbc.cosmosdb.CosmosDBDriver

  • JDBC URL: The URL must start with "jdbc:cosmosdb:" and can include any of the connection properties in name-value pairs separated with semicolons.

    To obtain the connection string needed to connect to a Cosmos DB account using the SQL API, log in to the Azure Portal, select Azure Cosmos DB, and select your account. In the Settings section, click Connection String and set the following values:

    • AccountEndpoint: The Cosmos DB account URL from the Keys blade of the Cosmos DB account
    • AccountKey: In the Azure portal, navigate to the Cosmos DB service and select your Azure Cosmos DB account. From the resource menu, go to the Keys page. Find the PRIMARY KEY value and set AccountKey to this value.

    Built-in Connection String Designer

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

    java -jar cdata.jdbc.cosmosdb.jar

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

    A typical JDBC URL is below:

    jdbc:cosmosdb:AccountEndpoint=myAccountEndpoint;AccountKey=myAccountKey;

Build the JDBC Foreign Data Wrapper

The Foreign Data Wrapper can be installed as an extension to PostgreSQL, without recompiling PostgreSQL. The jdbc2_fdw extension is used as an example.

  1. Add a symlink from the shared object for your version of the JRE to /usr/lib/libjvm.so. For example: ln -s /usr/lib/jvm/java-6-openjdk/jre/lib/amd64/server/libjvm.so /usr/lib/libjvm.so
  2. Start the build: make install USE_PGXS=1

Query Cosmos DB Data as a PostgreSQL Database

After you have installed the extension, follow the steps below to start executing queries to Cosmos DB data:

  1. Log into your database.
  2. Load the extension for the database: CREATE EXTENSION jdbc2_fdw;
  3. Create a server object for Cosmos DB: CREATE SERVER CosmosDB FOREIGN DATA WRAPPER jdbc2_fdw OPTIONS ( drivername 'cdata.jdbc.cosmosdb.CosmosDBDriver', url 'jdbc:cosmosdb:AccountEndpoint=myAccountEndpoint;AccountKey=myAccountKey;', querytimeout '15', jarfile '/home/MyUser/CData/CData\ JDBC\ Driver\ for\ Salesforce MyDriverEdition/lib/cdata.jdbc.cosmosdb.jar');
  4. Create a user mapping for the username and password of a user known to the MySQL daemon. CREATE USER MAPPING for postgres SERVER CosmosDB OPTIONS ( username 'admin', password 'test');
  5. Create a foreign table in your local database: postgres=# CREATE FOREIGN TABLE customers ( customers_id text, customers_City text, customers_CompanyName numeric) SERVER CosmosDB OPTIONS ( table_name 'customers');
You can now execute read/write commands to Cosmos DB: postgres=# SELECT * FROM customers;