Firebird sample with WSO2 DSS

I'm going to provide instructions to showcase how we can use Firebird data-source with WSO2 DSS.

Note:
I will be using the employee database(/opt/firebird/examples/empbuild/employee.fdb) which is available by-default with the Firebird 2.5.7  in this post.

Following are the Firebird/JDBC driver and WSO2 DSS versions which I have tried.

• Firebird: 2.5.X
• JDBC Driver: jaybird-full-2.2.12
• WSO2 DSS: 3.5.1

Steps:

1. Download the JDBC driver for Firebird and copy into the <DSS_HOME>/repository/components/lib/ directory.
2. Start the DSS node.(or restart if it's already started)
3. Add a new Data Service with the following configuration.

Datasource type: RDBMS

Database Engine: Generic

Driver Class: org.firebirdsql.jdbc.FBDriver

URL: jdbc:firebirdsql://localhost:3050//opt/firebird/examples/empbuild/employee.fdb

* Provide Host, Port, Database Path, User Name, Password accordingly.

Create and test the Datasource connection.

Save and proceed next, to add the query

select EMP_NO,FIRST_NAME,
LAST_NAME,PHONE_EXT,HIRE_DATE,DEPT_NO,SALARY from employee where EMP_NO=:EMP_NO

Add Input/Output mappings accordingly.

Save and proceed next, to add the operation.

 

Save and finish.

Now if you go to the Home> Manage> Services> List> firebirdTest> Edit Data Source(XML Edit) you can see the following Data Service definition.

<data disableStreaming="true" name="firebirdTest" transports="http https local">
   <config enableOData="false" id="emp">
      <property name="driverClassName">org.firebirdsql.jdbc.FBDriver</property>
      <property name="url">jdbc:firebirdsql://localhost:3050//opt/firebird/examples/empbuild/employee.fdb</property>
      <property name="username">SYSDBA</property>
      <property name="password">admin</property>
   </config>
   <query id="select" useConfig="emp">
      <sql>select EMP_NO,FIRST_NAME,&#xd;LAST_NAME,PHONE_EXT,HIRE_DATE,DEPT_NO,SALARY from employee where EMP_NO=:EMP_NO</sql>
      <result element="Entries" rowName="Entry">
         <element column="EMP_NO" name="EMP_NO" xsdType="string"/>
         <element column="FIRST_NAME" name="FIRST_NAME" xsdType="string"/>
         <element column="LAST_NAME" name="LAST_NAME" xsdType="string"/>
         <element column="PHONE_EXT" name="PHONE_EXT" xsdType="string"/>
         <element column="HIRE_DATE" name="HIRE_DATE" xsdType="string"/>
         <element column="DEPT_NO" name="DEPT_NO" xsdType="string"/>
         <element column="SALARY" name="SALARY" xsdType="string"/>
      </result>
      <param name="EMP_NO" sqlType="STRING"/>
   </query>
   <operation disableStreaming="true" name="getEmp">
      <call-query href="select">
         <with-param name="EMP_NO" query-param="EMP_NO"/>
      </call-query>
   </operation>
</data>

How to test the data-service(Try-it tool)

Go to Home> Manage> Services> List> firebirdTest> Try this service.

Provide the EMP_NO and press send.

Further information on query/input and output mappings/operation can be found here.

Cross database pagination problem and how we solved it

When we are developing a webapp with any type of listing, pagination is a must have feature. From the UI perspective we can use infinite scrolling or pages approach.

If you are familiar with google search this is how google uses the second approach,

Now the problem is how we generate listing for a particular page?
Lets take a hypothetical library application where we need to list down existing books, assume we need to list 10 books per page.

This is how we query books to generate the 1st page,

SELECT * FROM BOOKS LIMIT 10;

to generate the 2nd page,

SELECT * FROM BOOKS LIMIT 10 OFFSET 10;

So easy,  by providing the offset value we can dynamically generate our pages.

BUT can we use the same across database types?

If you know the exact backend DB type you gonna use in production, lucky you!
But if you are developing a product which needs to support multiple DB types (MySQL, Oracle, Postgres, H2 ....) above query will fail in some of them. For example above will work in MySQL, H2 and Postgres but will not work in Oracle.

In Oracle 11g you can run following but not in 12c

SELECT *
FROM (
  SELECT b.*, ROWNUM RN
  FROM (
    SELECT *
    FROM BOOKS
    ORDER BY ID ASC
  ) b
  WHERE ROWNUM <= 10
)
WHERE RN > 10

Now let's discuss how we solved this problem. Following is high-level architecture of the solution.







In this scenario we have exposed all CRUD operations as OSGI services to the outside world. This component may or may not have DB specific logic. But for sure we don't have any DB type specific logic within our main OSGI component. We have delegated all those DB type specific logic to the DB Adapter.

What are the DB type specific things we can have?

1. Above pagination related stuff (LIMIT, OFFSET)
2. Auto generate key usage(getGenaratedKeys)

How to load correct DB Adapter class through reflection

We can maintain a configuration file where we state the DB Adapter class. Then read that class name within our main component and use/call through reflection.

Reference

http://www.jooq.org/doc/3.5/manual/sql-building/sql-statements/select-statement/limit-clause/