iBATIS Data Mapper Developer Guide详解：从入门到高级优化

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《iBATIS.NET指南》是一份全面的文档，专为开发者设计，旨在帮助理解、运用和优化iBATIS框架在.NET环境中的数据访问和映射。该手册分为多个章节，深入解析了iBATIS的核心概念和技术细节。首先，第1章“iBATIS DataMapper”介绍了手册的主要内容和免责声明，让读者对接下来的讨论有清晰的预期。iBATIS作为一个持久层框架，它的工作原理是将应用程序与数据库交互的复杂性抽象出来，使开发者能够专注于业务逻辑，而非SQL语句的编写。第二部分“The Big Picture”深入探讨了iBATIS的优势和适用场景。它解答了“iBATIS是否适合我的项目”的问题，强调了其易用性、性能优化以及处理复杂查询的能力，特别是如何通过避免“N+1问题”（通过减少不必要的数据库查询）来提升效率。第三章“Working with Data Maps”是核心内容，讲解了数据映射的实质。数据映射定义文件包含<parameterMap>、<parameter>元素以及<resultMap>，用于指定参数绑定和结果集结构。这里详细解释了不同类型的Statement（存储过程调用和自定义SQL），并列出了相关属性的使用方法。例如，<parameterMap>的属性用于定义参数集合，<parameter>元素用于定义单个参数，而inlineParameterMaps则支持直接在SQL语句中嵌入参数。在处理参数和结果时，手册涵盖了多种类型，如标准类型参数、Map或IDictionary类型参数，以及如何处理不同类型的返回值，如基本类型（如String、Integer和Boolean）和复杂的数据结构，如复合键和多对多关系。 3.4节特别关注了避免“N+1 Selects”策略，针对1:1、1:M和M:N关系提供了具体的优化建议。通过精心设计数据映射和查询策略，可以显著减少数据库查询次数，提高应用性能。《iBATIS.NET指南》提供了一套详尽的教程，从基础到高级，无论是初次接触iBATIS的开发者，还是希望深入理解并优化其使用的专业人员，都能从中找到所需的知识。通过阅读和实践手册中的内容，开发者将能更好地利用iBATIS在.NET项目中实现高效的数据操作。

</parameterMap>

insert into PRODUCT (PRD_ID, PRD_DESCRIPTION) values (?,?);

</statement>

In Example 11, the Parameter Map describes two parameters that will match, in order, two placeholders in the

SQL statement. The first “?” is replaced by the value of the id property. The second is replaced with the de-

scription property.

iBATIS also supports named, inline parameters, which most developers seem to prefer. However, Parameter

Maps are useful when the SQL must be kept in a standard form or when extra information needs to be provided.

For more about Parameter Maps see Section 3.4.

3.2.4.3. parameterClass

If a parameterMap attribute is not specified (see Section 3.2.4.2), you may specify a parameterClass instead and

use inline parameters (see Section 3.3.3 ). The value of the parameterClass attribute can be a Type Alias or the

fully qualified name of a class. Example 12 shows a statement using a fully-qualified name versus an alias.

Example 12. Ways to specify a parameterClass

insert into PRODUCT values (#id#, #description#, #price#)

</statement>

insert into PRODUCT values (#id#, #description#, #price#)

</statement>

3.2.4.4. resultMap

A Result Map lets you control how data is extracted from the result of a query, and how the columns are

mapped to object properties. Example 13 shows a <resultMap> element and a corresponding <statement> ele-

ment.

Example 13. A <resultMap> and corresponding <statement>

</resultMap>

select * from PRODUCT

</statement>

In Example 13, the result of the SQL query will be mapped to an instance of the Product class using the "select-

product-result" <resultMap>. The <resultMap> says to populate the id property from the PRD_ID column, and

to populate the description property from the PRD_DESCRIPTION column.

Tip

In Example 13, note that using “ select * ” is supported. If you want all the columns, you don't

iBATIS Data Mapper Developer

Guide

need to map them all individually. (Though many developers consider it a good practice to always

specify the columns expected.)

For more about Result Maps, see Section 3.4.

3.2.4.5. resultClass

If a resultMap is not specified, you may specify a resultClass instead. The value of the resultClass attribute can

be a Type Alias or the fully qualified name of a class. The class specified will be automatically mapped to the

columns in the result, based on the result metadata. Example 14 shows a <statement> element with a resultClass

attribute.

Example 14. A <statement >element with resultClass attribute

SELECT

ER_ID as id,

PER_FIRST_NAME as firstName,

PER_LAST_NAME as lastName,

PER_BIRTH_DATE as birthDate,

PER_WEIGHT_KG as weightInKilograms,

PER_HEIGHT_M as heightInMeters

FROM PERSON

WHERE PER_ID = #value#

</statement>

In Example 14, the Person class has properties including: id, firstName, lastName, birthDate, weightInKilo-

grams and heightInMeters. Each of these corresponds with the column aliases described by the SQL select state-

ment (using the “as” keyword –a standard SQL feature). When executed, a Person object is instantiated and

populated by matching the object property names to the (aliased) column names from the query.

Using SQL aliases to map columns to properties saves defining a <parameterMap> element, but there are limita-

tions. There is no way to specify the types of the output columns (if necessary), there is no way to automatically

load related data (complex properties), and there is a slight performance consequence (from accessing the result

metadata). Architecturally, using aliases this way mixes "database logic" with "reporting logic", making the

query harder to read and maintain. You can overcome these limitations with an explicit Result Map (Section

3.4).

3.2.4.6. cacheModel

If you want to cache the result of a query, you can specify a Cache Model as part of the <statement> element.

Example 15 shows a <cacheModel> element and a corresponding <statement>.

Example 15. A <cacheModel> element with its corresponding <statement>

</cacheModel>

select * from PRODUCT where PRD_CAT_ID = #value#

</statement>

In Example 15, a cache is defined for products that uses a LRU reference type and flushes every 24 hours or

whenever associated update statements are executed. For more about Cache Models, see Section 3.6.

iBATIS Data Mapper Developer

Guide

3.2.4.7. xmlResultName (Java only)

If you prefer results returned as XML, you can use the XMLResultName to specify the enclosing element. Ex-

ample 16 shows a <select> that specifies a xmlResultName.

Example 16. A <select> element with <xmlResultName> attribute

SELECT

ER_ID as id,

PER_FIRST_NAME as firstName,

PER_LAST_NAME as lastName,

PER_BIRTH_DATE as birthDate,

PER_WEIGHT_KG as weightInKilograms,

PER_HEIGHT_M as heightInMeters, only one of which is required

FROM PERSON

WHERE PER_ID = #value#

</select>

Example 17 shows a XML object that might be returned by the <select> statement shown by Example 16.

Example 17. A result XML object

<firstName>Clinton</firstName>

<lastName>Begin</lastName>

</person>

3.3. Parameter Maps and Inline Parameters

Most SQL statements are useful because we can pass them values at runtime. Someone wants a database record

with the ID 42, and we need to merge that ID number into a select statement. Both JDBC and ADO.NET sup-

port using question marks ("?") as replaceable parameters. A list of one or more parameters are passed at run-

time, and each placeholder is replaced in turn. Simple, but labor intensive, since developers spend a lot of time

counting symbols to make sure everything is in sync.

Note

Sections 3.0 and 3.1.2 introduce the iBATIS inline parameters, which automatically map properties to

named parameters. Many, if not most, iBATIS developers prefer this approach. But others do prefer to

stick to the standard, anonymous approach to SQL parameters. Sometimes people need to retain the pu-

rity of the SQL statements, other times because extra information needs to be passed.

A Parameter Map defines an ordered list of values that match up with the placeholders of a parameterized query

statement. While the attributes specified by the map still need to be in the correct order, each parameter is

named. You can populate the underlying class in any order, and the Parameter Map ensures each value is passed

in the correct order.

Note

Dynamic Mapped Statements (Section 3.7) can't use Parameter Maps. Being dynamic, the number of

parameters will change and defeat the purpose of a Parameter Map.

iBATIS Data Mapper Developer

Guide

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