SQL on MongoDB using Teiid - Part 2

In the previous article SQL on MongoDB using Teiid - Part 1 I showed a simple example how one can start using SQL based queries on MongoDB using Teiid. I have showed how to install and configure the Teiid and test.

The previous example was very simple that generated a MongoDB collection for defined relational table in Teiid. One of many advantages of NoSQL based stores like MongoDB is, user's ability to de-normalize data such that data for related entities is co-located. When the data is co-located there is no requirement for defining the relationships across entities, and queries will be naturally faster to execute. However, in relational databases data is more often very normalized, the naive implementation of relational to MongoDB where one table is mapped to a collection will result in very poorly performing queries. The solution is, utilize the MongoDB's nested document feature to represent a relationships in Relational database.

In this article, I will show how to define relationships across different tables and it's representation in MongoDB document, where the performance is not compromised.

ONE-2-ONE

 CREATE FOREIGN TABLE Customer (  
   CustomerId integer PRIMARY KEY,  
   FirstName varchar(25),  
   LastName varchar(25)  
 ) OPTIONS(UPDATABLE 'TRUE');  

 CREATE FOREIGN TABLE Address (  
   CustomerId integer,  
   Street varchar(50),  
   City varchar(25),  
   State varchar(25),  
   Zipcode varchar(6),  
   FOREIGN KEY (CustomerId) REFERENCES Customer (CustomerId)  
 ) OPTIONS(UPDATABLE 'TRUE');  

When you issue INSERT statements against above tables, by default it will produce the documents like

 Customer  
 {  
  _id: 1,  
  FirstName: "John",  
  LastName: "Doe"  
 }  
 Address  
 {   
  _id: ObjectID("..."),   
   CustomerId: 1,  
   Street: "123 Lane"  
   City: "New York",  
   State: "NY"  
   Zipcode: "12345"  
 }  

You can enhance the storage in MongoDB to a single collection by using "teiid_mongo:MERGE' extension property on the table's OPTIONS clause

 CREATE FOREIGN TABLE Customer (  
   CustomerId integer PRIMARY KEY,  
   FirstName varchar(25),  
   LastName varchar(25)  
 ) OPTIONS(UPDATABLE 'TRUE');  

 CREATE FOREIGN TABLE Address (  
   CustomerId integer PRIMARY KEY,  
   Street varchar(50),  
   City varchar(25),  
   State varchar(25),  
   Zipcode varchar(6),  
   FOREIGN KEY (CustomerId) REFERENCES Customer (CustomerId)  
  ) OPTIONS(UPDATABLE 'TRUE', "teiid_mongo:MERGE" 'Customer');  

this will produce single collection in MongoDB

 Customer  
 {  
  _id: 1,  
  FirstName: "John",  
  LastName: "Doe",  
  Address:   
    {   
     Street: "123 Lane",  
     City: "New York",  
     State: "NY",  
     Zipcode: "12345"  
    }  
 }  

You can issue queries like

 SELECT * FROM Customer JOIN Address ON Customer.CustomerId = Address.CustomerId  

ONE-2-MANY

Following the similar strategy using "teiid_mongo:MERGE" property, the below shows the one to many relationship  .

 CREATE FOREIGN TABLE Customer (  
   CustomerId integer PRIMARY KEY,  
   FirstName varchar(25),  
   LastName varchar(25)  
 ) OPTIONS(UPDATABLE 'TRUE');  

 CREATE FOREIGN TABLE Order (      
   OrderID integer PRIMARY KEY,  
   CustomerId integer,  
   OrderDate date,  
   Status integer,  
   FOREIGN KEY (CustomerId) REFERENCES Customer (CustomerId)  
 ) OPTIONS(UPDATABLE 'TRUE', "teiid_mongo:MERGE" 'Customer');  

Will generate MongoDB collection like below

 {  
  _id: 1,  
  FirstName: "John",  
  LastName: "Doe",  
  Order:   
  [  
    {   
     _id: 100,   
     OrderDate: ISODate("2000-01-01T06:00:00Z")  
     Status: 2  
    },  
    {   
     _id: 101,   
     OrderDate: ISODate("2001-03-06T06:00:00Z")  
     Status: 5  
    }  
    ...  
   ]  
 }  

You can issue SQL queries like

SELECT * FROM Customer JOIN Orders ON Customer.CustomerId = Orders.CustomerId 
  WHERE OrderDate = <date>  

Note that above I showed the nesting of the documents at single level, however you can define even define deeper nesting. For example, Order table has OrderItems table

  CREATE FOREIGN TABLE Customer (   
   CustomerId integer PRIMARY KEY,   
   FirstName varchar(25),   
   LastName varchar(25)   
  ) OPTIONS(UPDATABLE 'TRUE');  
 
  CREATE FOREIGN TABLE Order (     
   OrderID integer PRIMARY KEY,   
   CustomerId integer,   
   OrderDate date,   
   Status integer,   
   FOREIGN KEY (CustomerId) REFERENCES Customer (CustomerId)   
  ) OPTIONS(UPDATABLE 'TRUE', "teiid_mongo:MERGE" 'Customer'); 
  
 CREATE FOREIGN TABLE OrderDetails (  
  OrderID integer NOT NULL,  
  UnitPrice double default '0',  
  Quantity integer default '1',  
  Discount float default '0',  
  FOREIGN KEY (OrderID) REFERENCES Orders (OrderID),  
 ) OPTIONS ("teiid_mongo:MERGE" 'Orders', UPDATABLE 'TRUE');  

after inserting some data, the result MongoDB document will look like

 {  
  _id: 1,  
  FirstName: "John",  
  LastName: "Doe",  
  Order:   
  [  
    {   
     _id: 100,   
     OrderDate: ISODate("2000-01-01T06:00:00Z")  
     Status: 2,  
     OrderDetails:  
     [  
       {  
         UnitPrice: 23.12  
         Quantity: 5  
         Discount: 34.2  
       },  
       {  
         UnitPrice: 51.17  
         Quantity: 10  
         Discount: 15.0  
       }  
       ...  
     ]  
    },  
    {   
     _id: 101,   
     OrderDate: ISODate("2001-03-06T06:00:00Z")  
     Status: 5,  
     OrderDetails:  
     [  
       {  
         UnitPrice: 78.00  
         Quantity: 4  
         Discount: 20  
       },  
       {  
         UnitPrice: 43.12  
         Quantity: 100  
         Discount: 30  
       }  
       ...  
     ]      
    }  
    ...  
   ]  
 }  

So, as you can see you can create pretty complex nested documents in MongoDB using Teiid, to save query performance, at the same time you can use your expertise in SQL to design the queries using the JOINS to  read the data that you are interested in or run BI tool on top it to generate reports etc.

For more information please read https://docs.jboss.org/author/display/TEIID/MongoDB+Translator 

If you are working with existing MongoDB database, Teiid can import the existing collections and their document structure and automatically create the relational tables in Teiid. For that please refer to article https://developer.jboss.org/wiki/ConnectToAMongoDBSource

I have showed in these articles how to create and use MongoDB database and access the MongoDB using SQL. This is great tool, if you looking to replace your relational database like Oracle, SQLServer etc with MongoDB. Most of the concepts in your relational world map one to one using Teiid.

Thank you, If you have any questions please let us know.

Ramesh..