Question

Consider the following situation. I have 3 tables in a resource planning project(created using mysql)

1. raw_materials (stores details about all raw materials)

2. procurement_orders (stores details about all details about requests sent to vendors for sending us the quotations. This table references the raw_materials table.)

3. quotations (contains details about all quotations sent by vendors to us. This table references the procurement_orders table).

I have created dbManagers for each of them using java which specialize in storing,retrieving,deleting data from respective tables.

My question is if i want to retrieve data which has to needs data from other tables, what is the best way to do it. eg:I want quotations of all raw_materials having stock below x. then according to me there are two ways

1. i write it in dbManager for rawMaterials. The flaw with this technique is it tries to access data out of its domain directly.
2. in dbManager of of raw_Materials create instances of other dbManagers. The flaw here is the iterations will large. As in if there are 300 raw materials, i will have to call method of the procurement_request’s dbManager 300 times. If it returns multiple values we will again have to call dbMnager of quatations many no. of times(many of them will be unwanted) affecting performance.

My question is what is the best way to design it in a proper oo way without hitting the performance.

Answer 1

This is a rather larger question than can easily be handled quickly, but aligning java classes to tables is not necessarily a good approach, precisely because as you note, some things naturally involve multiple tables in complex relations.

I’d recommend starting by looking at Martin Fowler’s book Patterns of Enterprise Application Architecture.

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There are also some notes on the patterns in this book at his website.

Your usage most nearly resembles Table Data Gateway. Following this pattern, it would be perfectly reasonable to have methods in each of your dbManager classes that retrieves data from its associated table but involves another table as part of a where clause.

You might also want to consider Object-relational mapping as implemented for instance by Hibernate.