Handling Distributed Transactions

WSO2 Data Services Server supports data federation, which means that a single data service can expose data from multiple datasources. However, if you have multiple RDBMSs connected to your data service, and if you need to perform IN-ONLY operations (operations that can insert data and modify data in the datasource) in a coordinated manner, the RDBMSs need to be defined as XA datasources. Consider a scenario where you have two MySQL databases. You can define a single data service for these databases and insert data into both as explained below.

Setting up distributed MySQL databases

Follow the steps given below to set up a MySQL database for this tutorial.

1. Install the MySQL server.
2. Download the JDBC driver for MySQL from here and copy it to your <DSS_HOME>/repository/components/lib directory.
   
3. Set up a database for storing information of offices:

   1. Create a database called OfficeDetails: CREATE DATABASE OfficeDetails;

   2. Create the Offices table:
      

      USE OfficeDetails;
      CREATE TABLE `Offices` (`OfficeCode` int(11) NOT NULL, `AddressLine1` varchar(255) NOT NULL, `AddressLine2` varchar(255) DEFAULT NULL, `City` varchar(255) DEFAULT NULL, `State` varchar(255) DEFAULT NULL, `Country` varchar(255) DEFAULT NULL, `Phone` varchar(255) DEFAULT NULL, PRIMARY KEY (`OfficeCode`));

4. Set up a database for storing information of employees:
   1. Create a database called EmployeeDetails: CREATE DATABASE EmployeeDetails;

   2. Create the Employees table:
      

      USE EmployeeDetails;
      CREATE TABLE `Employees` (`EmployeeNumber` int(11) NOT NULL, `FirstName` varchar(255) NOT NULL, `LastName` varchar(255) DEFAULT NULL, `Email` varchar(255) DEFAULT NULL, `JobTitle` varchar(255) DEFAULT NULL, `OfficeCode` int(11) NOT NULL, PRIMARY KEY (`EmployeeNumber`));

Adding the datasources to a data service

Let's create a data service using the Create Data Service wizard:

1. Log into the management console of WSO2 DSS and click Create in the Data Service menu.
2. Add a name for the data service and go to the next step.
3. Select the Enable Boxcarring check box.
4. Click Next to go to the Datasources screen.
5. Create a datasource connection for the CompanyDetails database follows:
   1. Enter XAoffices as the datasource ID.
   2. Select RDBMS as the datasource type.
   3. Select External Datasource from the adjoining field.
   4. Select MySQL as the database engine.
   5. Enter the following database class corresponding to MySQL: com.mysql.jdbc.jdbc2.optional.MysqlXADataSource

   6. Click Add Properties and specify the following connection settings for the OfficeDetails database:

      PropertyName	Value
      url	jdbc:mysql://localhost:3306/OfficeDetails
      user	root

      The New Datasource screen will now look as follows:

   
   
6. Save the XAoffices datasource.
7. Create a datasource connection for the EmployeeDetails database as follows:
   1. Enter XAemployees as the datasource ID.
   2. Select RDBMS as the datasource type.
   3. Select External Datasource from the adjoining field.
   4. Select MySQL as the database engine.
   5. Enter the following database class corresponding to MySQL: com.mysql.jdbc.jdbc2.optional.MysqlXADataSource
      
   6. Click Add Properties and specify the following connection settings for the EmployeeDetails database:
      

      Property Name	Value
      url	jdbc:mysql://localhost:3306/EmployeeDetails
      user	root

      The New Datasource screen will now look as follows:
   
8. Save the XAemployees datasource.

Defining queries for the datasources

1. Click Add New Query to specify an insert query for the XAoffices datasource:

   1. Enter InsertOfficeQuery as the query ID.

   2. Enter the following SQL dialect:

      insert into Offices (OfficeCode,AddressLine1,AddressLine2,City,State,Country,Phone) values(:OfficeCode,:AddressLine1,'test','test','test','USA','test')

2. Click Generate Input Mapping and an input mapping will be generated automatically for the fields in the datsource:
   
3. Save the query.
4. Click Add New Query to specify an insert query for the XAemployees datasource:

   1. Enter InsertEmployeeQuery as the query ID.

   2. Enter the following SQL dialect:

      insert into EMPLOYEES (employeeNumber,firstName,lastName,email,jobtitle,OfficeCode) values(:employeeNumber,:firstName,:lastName,'test@gmail.com','test',:OfficeCode)

5. Click Generate Input Mapping and an input mapping will be generated automatically for the fields in the datsource:
   
6. Save the query.
7. Click Next to go to the Operations section. Define operations to invoke the two queries defined above.
   • Create the InsertOfficeOp for the InsertOfficeQuery.
   • Create the InsertEmployeeOp for the InsertEmployeeQuery.
8. Finish creating the data service.

Inserting data into the distributed RDBMs

1. Go to the Deployed Services page and you will see the data service listed.
2. Click Try this service to open the TryIt tool.
3. Select the batch operation that is created by default (request_box_operation).
4. Specify the values that should be inserted to the OfficeDetails database and EmployeeDetails database respectively.
5. Invoke the operation.
6. See that the data is successfully inserted into the two databases.
7. Now, enter another set of values for the two operations. However, you can make one operation erroneous. For example, leave the OfficeCode field of the InsertEmployeesOp blank.
8. Invoke the operation.
9. See that no records have been entered into either database.