Choosing an object-relational mapping tool

When developing an application, it is almost unavoidable to write data access and data manipulation code. Many object-relational mapping tools are available to help. Choosing the right one is important.

Whether you are developing a small or a big application, you always have to deal with data. It's even a critical part of an application. The Problem here is it is tedious, repetitive work, which consumes a lot of the time we would prefer to spend on other parts of the application.

Again it is a known fact that the less interesting the work is, the higher the risks of errors.
To solve these problems, multiple solutions exist. The goal is to simplify the creation of

• data access layers
• automate data access
• generate data access code.

  The main focus herer is on object-relational mapping tools (O/RM).

The principle of object-relational mapping is

• To delegate to tools the management of persistence
• To work at code-level with objects representing a domain model, and not with data structures in the same format as the relational database

Data management tasks in object-oriented (OO) programming are typically implemented by manipulating objects which are almost always non-scalar values.

For example, consider an address book entry which represents a single person along with zero or more phone numbers and zero or more addresses.

This could be modeled in an object-oriented implementation by a "person object" with "slots" to hold the data that comprise the entry: the person's name, a list (or array) of phone numbers, and a list of addresses. The list of phone numbers would itself contain "phone number objects" and so on. The address book entry is treated as a single value by the programming language (it can be referenced by a single variable, for instance). Various methods can be associated with the object, such as a method to return the preferred phone number, the home address, and so on.

The need for mapping tables into higher level data structures is at the heart of the problem which ORM tools attempt to solve. Even systems which are not labelled as ORM dependant deal with such issues: i.e. once one executes a "join" on a table, they are essentially hardcoding object relational logic into their SQL.