resultMap

ResultMap is a configuration construct used by MyBatis to describe how the columns of a SQL query map to properties of Java objects. It defines a mapping between a result set and an object graph, enabling both simple and complex mappings, including nested objects and collections, as well as polymorphic mappings.

A resultMap is identified by an id and specifies a result type with the type attribute. It can extend another resultMap to reuse mappings, and it may enable automatic mapping with the autoMapping attribute. ResultMaps are referenced by select statements or other mappings to drive the translation from SQL results to domain objects.

Common child elements include:

- id: maps a primary key column to a property.

- result: maps a column to a simple property.

- constructor: maps columns to constructor parameters for constructor-based mapping.

- association: maps a nested object, using its own mappings.

- collection: maps a collection or list of nested objects, using ofType to indicate the element type.

- case and discriminator: support conditional or polymorphic mappings to vary the mapped type based on column values.

Usage examples involve mapping to single objects, nested objects (such as an object with a nested address), and one-to-many relationships (such as an employee with multiple roles). ResultMaps are declared in MyBatis XML configuration and referenced from select statements to ensure precise control over how query results are materialized into Java objects, especially when the table structure does not directly align with the domain model.