回答：
In MyBatis, result maps are used to define how the results of a SQL query are mapped to Java objects. There are several types of result maps available in MyBatis, each serving different purposes. Here are the main types:
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Basic Result Map:
- This is the most common type of result map. It maps the columns of a result set to the properties of a Java object. You define a result map using the
<resultMap> element, specifying the mapping between the database columns and the object properties.
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Association:
- Associations are used to map relationships between objects. For example, if you have a
User object that has an associated Address object, you can define an association in your result map to indicate how to retrieve the Address for each User.
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Collection:
- Collections are used to map one-to-many relationships. For instance, if a
User can have multiple Orders, you can define a collection in your result map to retrieve all Orders associated with a User.
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Discriminator:
- A discriminator is used to handle polymorphic associations. It allows you to map a single result set to different types of objects based on a specific column value. This is useful when you have a base class and several subclasses.
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Nested Result Maps:
- You can nest result maps within each other. This is useful for complex object graphs where you want to map a parent object and its child objects using separate result maps.
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Dynamic Result Maps:
- MyBatis allows for dynamic result maps, where you can use conditional logic to include or exclude certain mappings based on the context. This is useful for scenarios where the structure of the result set may vary.
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Result Map Inheritance:
- MyBatis supports inheritance in result maps, allowing you to create a base result map and extend it in child result maps. This is useful for reducing redundancy in your mappings.
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Auto-mapping:
- MyBatis can automatically map columns to properties based on naming conventions. This feature can simplify the mapping process, especially for simple queries.
Each of these result map types can be combined and customized to fit the specific needs of your application, allowing for flexible and powerful data mapping capabilities in MyBatis.