Recently a development team met some difficulties in data source computation when developing iReport reports. After the use of esProc for cross database computation, the problem is resolved.
This is a project payment progress report, as part of a project management system. It’s based on an Oracle database. The reports needs to present the project name, payment amount, contract value, payment progress (in percentage), and name of the project manager, etc., for all ongoing projects. Amount these the first 3 items contributes to the difficulties met by the development team.
Note that the project payment record is stored in accounting system, rather than the Oracle database used by the development team. The accounting system is built on MSSQL database. The contract value information is also stored in a separate MSSQL database, used by contract management system. After analysis to the database, the project information record has an one-to-many relationship with payment record, and an one-to-one relationship with contract information.
By simplifying the table and fields other than the hardest part of the problem, the issue can then be described as: we need to join table project，payProcess and contract from three heterogeneous databases.
It’s fairly easy to write the SQL statements if the three tables are in the same database. However they now belong to three heterogeneous databases, the join is then difficult. Meanwhile, the two MSSQL databases are used by two independent commercial software, which the development team can load data from, but not able to modify or administrate. This adds to the difficulty of the development. Although iReport support simple cross database computation with two tables, it’s very difficult to do this with three tables. The development team cannot leverage iReport to meet this requirement.
The use of new reporting tool that supports multiple data sources might help. However as iReport is the only one used in the development process so far, a sudden change is not realistic. iReport supports user-defined JavaBean as data source, this can also be used to handle cross database computation. But JAVA is not a language for computation. The “join” computation between multiple sets requires a lot of coding. The workload makes it a non-sense. ETL tool is also a possible way to consolidate tables from multiple databases into one. The ETL approach normally requires incremental update to databases, which means timestamp and triggers need to be used in payProcess and contract table. As we know, commercial software does not allow databases to be modified in this way. ETL cannot provide the real time updates required for payment progress monitoring, which means it’s not suitable for this report.
Under such condition, the use of esProc for cross database computation is a handy approach. Here are the codes：
A1, A2, A3 are for loading data from different databases, which are native syntax for each database. Note the difference in SQL for each heterogeneous database.
A4 is an association statement. From here on the syntax has nothing to do with certain database. The “join” function associate A1, A2, A3 according to projectID. Note that this is inner join. If it’s left join, the syntax of “join@1” should be used, whereas for full join, the syntax is “join@f”.
A5 is to output the required fields from the join, which could be part or all fields from A1, A2 and A3.
The statement of result A5 means to output the computation result by JDBC, so that iReport could rerieve them directly through JDBC. It’s also possible for esProc to be used in JAVA codes directly by means of JDBC call.
The above codes are just a prototype, which can actually run successfully. In reality more table association and data fields need to be added, plus some and parameter filters.