[JAVA] Write what you thought after using mybatis for half a year

What is mybatis?

• https://github.com/mybatis/mybatis-3

It is a kind of OR mapper for Java and has the following features.

• Write SQL in annotation or xml file
• Easy to apply to non-normalized legacy systems
• Easy to tune SQL, so it is easy to apply to systems where DB tends to be a performance bottleneck.

It's been half a year since I used it in the project I'm in charge of, so I'll write down the good points and issues.

good point

The class used for SQL access is reduced

For JDBC

• As a promise, use the following classes
• DataSource
• Connection
• PreparedStatement
• ResultSet
• You need to remember to close Coneection, PreparedStatement, and ResultSet when the SQL issuance process is finished.

For mybatis

• The following two libraries are used for SQL access
• SqlSessionFactory
• SqlSession
• Only SqlSession can be closed
• Of course, you don't need to getValue () from ResultSet and set it to the object.

Can write SQL in XML

When assembling SQL in Java

StringBuffer sql = new StringBuffer();
sql.append("select * from table ");
sql.append("where id=? ");
sql.toString();

• With this, sometimes I want to extract only SQL and execute it from Workbench or pgAdmin, which is very annoying.

For Mybatis Mapper XML

<select id="selectPerson" parameterType="int" resultType="hashmap">
  SELECT * FROM PERSON WHERE ID = #{id}
</select>

• Since it can be written as the contents of the XML tag element, it is much easier to cut out only here and execute it for a while.

SQL is completely separated from logic (Java file)

• Therefore, it is easy to count the number of SQL and logic steps separately.
• In our product, SQL has as many steps as logic! DB ghost system! You can do self-deprecation

Bad point

Since it is XML, the refactoring function of eclipse cannot be used.

• When you want to rename the Model class, you need to grep the source ... and do something like a scripting language.

Since it is XML, coverage cannot be obtained.

• In my project, I use Jacoco to measure coverage, but of course I can't measure coverage in a Mapper XML file.
• In XML, you can write an if statement that adds a where clause only when a value is specified, but I don't know if it covers all of this.

Summary

• I don't have much insight, but I'm generally happy with mybatis
• Why not consider it when maintaining a legacy app?