iBATIS.NET 数据映射器开发指南

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"这是关于IBATIS.NET的学习文档，主要涵盖了Data Access Objects Developer Guide的内容，适合开发者参考使用。文档由Ted Husted、Gilles Bayon、Clinton Begin和Roberto Rabe等人编写，受Apache Software Foundation版权保护。" 在深入探讨IBATIS.NET之前，先了解一下这个框架的基本信息。IBATIS.NET是一款数据访问对象（DAO）开发指南，主要用于帮助开发者更有效地管理和操作数据库。它提供了一种将SQL语句与应用程序代码解耦的方法，使得数据库交互更加灵活和可维护。 1. **简介** - **概述**：IBATIS.NET是用于.NET平台的数据持久层解决方案，它简化了数据库操作，允许开发者通过配置文件来定义SQL语句，而不是硬编码到代码中。 - **覆盖内容**：文档包括了框架的介绍、工作原理、适用场景、数据映射的详细使用方法等。 - **版本历史**：这里提到的是版本1.6.1，发布于2007年3月，可能会包含该版本的更新日志，但具体内容未给出。 - **许可信息**：遵循Apache Software Foundation的开源许可，允许自由使用和分发，但要求保留版权信息。 - **支持**：可能提供了获取技术支持的途径，具体信息未详述。 - **免责声明**：文档可能包含免责声明，提醒用户自行承担使用风险。 2. **整体概念** - **介绍**：这部分介绍了IBATIS.NET的背景和目标，以及它在项目中的作用。 - **它能做什么？**：IBATIS.NET能够帮助开发者构建数据访问层，通过数据映射实现动态SQL，处理存储过程，提高代码的可读性和可维护性。 - **如何工作？**：通过XML配置文件定义数据映射，将SQL语句与.NET代码分离，提供参数映射和结果集映射功能。 - **是否适合你的项目？**：文档可能讨论了选择IBATIS.NET作为数据访问解决方案的各种考虑因素，比如项目的规模、需求复杂性等。 3. **工作与数据映射** - **数据映射定义文件**：详细解释了数据映射文件的结构，包括映射语句、参数映射等元素。 - **映射语句**：分为不同的类型，如简单SQL语句和存储过程，以及如何在映射文件中定义它们。 - **SQL语句**：如何在映射文件中编写和管理SQL，包括动态SQL的实现。 - **声明类型属性**：描述了与声明相关的各种属性，如SQL语句类型、是否缓存等。 - **参数映射**：包括了<parameterMap>和<parameter>元素的使用，以及内联参数映射的方法。 - **标准类型参数**：讨论了不同数据类型的参数处理，例如日期、字符串等。文档还可能继续深入讲解结果集映射、事务管理、错误处理和性能优化等方面的内容，帮助开发者全面理解和应用IBATIS.NET。通过这份指南，开发者可以更好地理解如何利用IBATIS.NET构建高效、灵活的数据访问层，提高代码的可维护性和数据库操作的便利性。

The <include> tag is namespace aware so you can refer to fragments even when they are located in

another map (however, due to the way iBATIS loads the SqlMaps, the included fragment should be

loaded before the including statement). The fragments are included and processed on

query-execution so parameters can be used too :

FROM items

WHERE parentid = #value#

</sql>

SELECT COUNT(*) AS total

</select>

SELECT id, name

</select>

Note

In many case, you can also use the extends attribute on statement tag to achieve the same goal.

3.3.3.2. Escaping XML symbols

Because you are combining SQL and XML in a single document, conflicts can occur. The most

common conflict is the greater-than and less-than symbols (><). SQL statements use these symbols

as operators, but they are reserved symbols in XML. A simple solution is to escape the SQL

statements that uses XML reserved symbols within a CDATA element. Example 3.6 demonstrates

this.

Example 3.8. Using CDATA to "escape" SQL code

<![CDATA[

SELECT * FROM PERSON WHERE AGE > #value#

]]>

</statement>

3.3.3.3. Auto-Generated Keys

Many database systems support auto-generation of primary key fields, as a vendor extension. Some

vendors pre-generate keys (e.g. Oracle), some vendors post-generate keys (e.g. MS-SQL Server and

MySQL). In either case, you can obtain a pre-generated key using a <selectKey> stanza within an

<insert> element. Example 3.7 shows an <insert> statement for either approach.

Example 3.9. <insert> statements using <selectKey> stanzas

<!—Oracle SEQUENCE Example using .NET 1.1 System.Data.OracleClient -->

SELECT STOCKIDSEQUENCE.NEXTVAL AS VALUE FROM DUAL

</selectKey>

insert into PRODUCT (PRD_ID,PRD_DESCRIPTION) values (#id#,#description#)

</insert>

<!— Microsoft SQL Server IDENTITY Column Example -->

insert into PRODUCT (PRD_DESCRIPTION)

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DataMapper Guide Version 1.6.1 13

values (#description#)

select @@IDENTITY as value

</selectKey>

</insert>

insert into PRODUCT (PRD_DESCRIPTION)

values (#description#)

select LAST_INSERT_ID() as value

</selectKey>

</insert>

3.3.3.4. <generate> tag

You can use iBATIS to execute any SQL statement your application requires. When the

requirements for a statement are simple and obvious, you may not even need to write a SQL

statement at all. The <generate> tag can be used to create simple SQL statements automatically,

based on a <parameterMap> element. The four CRUD statement types (insert, select, update, and

delete) are supported. For a select, you can select all or select by a key (or keys). Example 3.8 shows

an example of generating the usual array of CRUD statements.

Example 3.10. Creating the "usual suspects" with the <generate> tag

</parameterMap>

</parameterMap>

</parameterMap>

</parameterMap>

</parameterMaps>

</update>

</delete>

<select id="SelectByPKCategoryGenerate" resultClass="Category" parameterClass="Category"

parameterMap="select-generate-params">

</select>

<select id="SelectAllCategoryGenerate" resultClass="Category"

parameterMap="select-generate-params">

</select>

Working with Data Maps

DataMapper Guide Version 1.6.1 14

standard, parameterized query statement. Example 3.9 shows a <parameterMap> and a

corresponding <statement>.

Example 3.11. A parameterMap and corresponding statement

</parameterMap>

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

</statement>

In Example 3.9, 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 description 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.

3.3.4.3. parameterClass

If a parameterMap attribute is not specified, you may specify a parameterClass instead and use inline

parameters (see Section 3.4.3 ). The value of the parameterClass attribute can be a Type Alias or the

fully qualified name of a class. Example 3.10 shows a statement using a fully-qualified name versus

an alias.

Example 3.12. Ways to specify a parameterClass

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

</statement>

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

</statement>

3.3.4.4. 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 3.11 shows a <resultMap> element and a corresponding

<statement> element.

Example 3.13. A <resultMap> and corresponding <statement>

</resultMap>

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DataMapper Guide Version 1.6.1 16

select * from PRODUCT

</statement>

In Example 3.11, 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 3.11, note that using " select * " is supported. If you want all the columns, you don't

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 3.5.

3.3.4.5. 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. The following

example shows a <statement> element with a resultClass attribute.

Example 3.14. A <statement >element with resultClass attribute

SELECT

PER_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 3.12, the Person class has properties including: Id, FirstName, LastName, BirthDate,

WeightInKilograms, and HeightInMeters. Each of these corresponds with the column aliases

described by the SQL select statement 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 <resultMap> element, but there are

limitations. There is no way to specify the types of the output columns (if needed), there is no way to

automatically load related data such as 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 3.5).

3.3.4.6. listClass

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DataMapper Guide Version 1.6.1 17

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