A PostgreSQL Interface for MongoDB Data

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

Connect to MongoDB Data as a JDBC Data Source

To connect to MongoDB 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.mongodb.MongoDBDriver

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

  Set the Server, Database, User, and Password connection properties to connect to MongoDB. To access MongoDB collections as tables you can use automatic schema discovery or write your own schema definitions. Schemas are defined in .rsd files, which have a simple format. You can also execute free-form queries that are not tied to the schema.

  Built-in Connection String Designer

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

  java -jar cdata.jdbc.mongodb.jar

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

  A typical JDBC URL is below:

  jdbc:mongodb:Server=MyServer;Port=27017;Database=test;User=test;Password=Password;

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 (downloadable here).

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 MongoDB Data as a PostgreSQL Database

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

1. Log into your database.
2. Load the extension for the database: CREATE EXTENSION jdbc2_fdw;
3. Create a server object for MongoDB: CREATE SERVER MongoDB FOREIGN DATA WRAPPER jdbc2_fdw OPTIONS ( drivername 'cdata.jdbc.mongodb.MongoDBDriver', url 'jdbc:mongodb:Server=MyServer;Port=27017;Database=test;User=test;Password=Password;', querytimeout '15', jarfile '/home/MyUser/CData/CData\ JDBC\ Driver\ for\ Salesforce MyDriverEdition/lib/cdata.jdbc.mongodb.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 MongoDB OPTIONS ( username 'admin', password 'test');
5. Create a foreign table in your local database: postgres=# CREATE FOREIGN TABLE restaurants ( restaurants__id text, restaurants_borough text, restaurants_cuisine numeric) SERVER MongoDB OPTIONS ( table_name 'restaurants');