Comprehensive Guide to MyBatis: Concepts, Configuration, SQL Mapping, and Dynamic SQL

MyBatis is a lightweight SQL mapping framework that simplifies ORM tasks while offering a rich set of features for Java applications.

1. Core Concepts

MyBatis operates on top of JDBC, using SqlSession to manage database connections and caching. The main components include SqlSessionFactoryBuilder , SqlSessionFactory , SqlSession , and mapper interfaces, each with distinct lifecycles.

When used in a Spring environment, Spring discovers the MyBatis configuration file, creates a SqlSessionFactory , injects mapper beans, and scans classpath for mapper XML files, linking them to their interfaces.

2. What MyBatis Contains

MyBatis provides two essential parts: core configuration (caching, data source, logging, etc.) and mapper interface mappings that define SQL statements for business logic.

3. SQL Mapping

Mappings can be defined via XML or annotations. Common tags include select , insert , update , delete , and the reusable <sql> fragment.

Example of a reusable SQL fragment:

<sql id="baseColumns">id, name, age</sql>

The placeholder syntax differs: #{} uses prepared‑statement parameters (safer and faster), while ${} performs direct string substitution.

Type aliases reduce verbosity, e.g., <typeAlias type="com.someapp.model.User" alias="User"/> .

ResultMap is a powerful feature that maps result sets to complex object graphs, handling nested queries and collections.

Caching can be enabled with the cache tag for second‑level cache, and cache-ref allows sharing caches between namespaces.

4. Dynamic SQL

MyBatis supports dynamic SQL tags such as:

if – conditional inclusion based on a test expression.

choose (with when and otherwise ) – mutually exclusive branches.

trim (with where and set ) – automatically adds/removes leading/trailing keywords and commas.

foreach – iterates over collections, arrays, or maps to generate repeated SQL fragments.

bind – defines a variable using an OGNL expression for later use in the statement.

These dynamic tags enable flexible, maintainable SQL generation within MyBatis mapper files.