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Learning iBATIS - Why iBATIS?


iBATIS and Java
Dynamic SQL is currently the most popular means of accessing relational databases from modern languages.
It has the advantage of flexibility. The SQL can be manipulated at runtime based on different parameters or dynamic application functions.

The language such as Java includes a standard API for database access.  The following is a simple example of Dynamic SQL in Java:


String name;
Date hiredate;
String sql = "SELECT emp_name, hire_date" + " FROM employee WHERE emp_num = ? ";
Connection conn = dataSource.getConnection();
PreparedStatement ps = conn.prepareStatement (sql);
ps.setInt (1, 28959);
ResultSet rs = ps.executeQuery();
while (rs.next) {
name = rs.getString("emp_name");
hiredate = rs.getDate("hire_date");
}
rs.close();
conn.close();

Without a doubt, Dynamic SQL is not elegant at all. The APIs are often complex and very verbose, Using these frameworks generally results in a lot of code, which is often very repetitive. In addition, the SQL itself is often too long to be on a single line. This means that the strring has to be broken up into multiple strings that are concatenated. Concatenation results in unreadable SQL code that is difficult to maintain and work with.


iBAITS and O/RM tools
In modern object-oriented applications, one of the most compelling solutions to interacting with a relational database is through the use of an object/relational mapping tool. O/RM was designed to simplify persistence of objects by eliminating SQL from the developer's responsibility altogether. Instead, the SQL is generated. Some tools generate the SQL statically at build or compile time, while others generate it dynamically at runtime. The SQL is generated base on mappings made between application classes and the relational database tables. In addition to eliminating the SQL, the API for working with an O/RM tool s uaually a lot simpler than the typical SQL APIs. Object/Relational mapping is not a new concept and is almost as old as object-oriented programming languages. There have been a lot of advances in recent years that make object/relational mapping a compelling approach to persistence.

Modern object/relational mapping tools do more than simply generate SQL. They offer a complete persistence architecture that benefits the entire application. This includes simple APIs for dealing with both local and distributed transactions. O/RM tools also usually offer multiple caching strategies for dealing with different kinds of data to avoid needless access of the database. Another way that an O/RM tool can reduce database hits is by lazy loading of data. Lazy loading delays the retrieval of data until absolutely necessary, right at the point where the  data is used.

Despite these features, object/relational mapping tools are not a silver-bullet solution and do not work in all situations. O/RM tools are based on assumptions and rules. The most common assumption is that the database will be properly normalized. No object relational solution will ever be able to provide support for every feature, capability and design flaw of every single database available. As stated earlier, SQL is not a reliable standard. For this reason, every O/RM tool will always be a subset of the full capabilities of any particular database.

Enter the hybrid.



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