DataSet与ado.net：数据填充与DataAdapter详解

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本文档主要探讨了ADO.NET在C#编程中的应用，特别是与数据集(DataSets)相关的知识点。ADONET是一种用于.NET框架的数据库访问技术，它允许开发人员高效地与各种类型的数据源进行交互，包括关系型数据库。 5.2 填充数据集(DataSets)：由于数据集并非局限于数据库数据，它们可以视为简单的关联数据存储库。在实际操作中，填充数据集有三种常见方法：通过DataAdapter（通常源自数据库）、从XML文件，以及手动构建数据集。DataAdapter在连接DataSet与底层数据存储（如SQL Server、Oracle等）之间起到了至关重要的作用。它是实质上的元命令对象集合，由最多四个命令对象组成： 1. 选择命令(SelectCommand)：从数据源检索数据，执行查询操作。 2. 插入命令(InsertCommand)：根据DataSet中的新记录，将数据添加到底层数据存储中。 3. 更新命令(UpdateCommand)：基于DataSet中的更改，更新底层数据存储中的现有记录。 4. 删除命令(DeleteCommand)：根据DataSet中的删除标记，从底层数据存储中移除记录。每当DataSet需要直接与数据源交互时，就会使用DataAdapter。理解并有效使用这些概念至关重要，因为它们涉及到数据的持久化、维护和同步，对于构建高性能、健壮的.NET应用程序至关重要。此外，开发者还需掌握如何配置和处理DataSet的关联性和事务性，以确保数据一致性。通过熟练运用ADO.NET和DataSet，开发人员能够编写出更高效、可维护的代码，适应复杂的数据处理需求。

5.2 Filling DataSets

Because DataSets are not tied to database data in any way, you may think of DataSets as simply

relational data stores. There is no requirement that you use database data to fill in a DataSet. In

practice, there are three ways to construct DataSets: from a DataAdapter (usually from a database),

from XML, and by constructing the DataSet manually.

5.2.1 Introducing DataAdapters

DataAdapters are the glue that connects DataSets to the underlying data stores. With DataAdapter,

you can fill the DataSet and update the data store from the DataSet. DataAdapters are essentially

meta-Command objects. The DataAdapter is composed of up to four Command objects. Each of

these Command objects does a specific job:

 SelectCommand: Retrieves data from the data store

 InsertCommand: Adds new records created in the DataSet to the underlying data store

 UpdateCommand: Changes existing records in the data store based on changes in the DataSet

 DeleteCommand: Deletes existing records in the data store based on deletions in the DataSet

The DataAdapter is used whenever the DataSet needs to interact directly with the data source. The

important concept here is that the DataAdapter holds Command objects for each of the basic

database operations, SELECT, INSERT, UPDATE, and DELETE. The idea behind the DataAdapter

is for it to be the bridge between the DataSet and the database. If the DataAdapter is that bridge, then

it must have the ability to do all the necessary database operations. As we continue to discuss the

DataSet throughout this chapter and the rest of Part 2 of this book, you will see how the DataAdapter

is used as a bridge.

One important job of the DataAdapter is to minimize the time a connection is open. You will notice

that throughout our use of DataAdapters, we never open and close the connection associated with our

DataAdapter. The DataAdapter knows that the connection needs to be as short-lived as possible and

handles all opening and closing of the connection. If we are using an already opened connection

when we use our DataAdapter, it will preserve the state of the connection (it will not open or close

the connection).

5.2.2 Creating a DataSet from a Database

In the most basic case, you would use the DataSet to hold a single table, as shown in Listing 5.1.

Listing 5.1 Creating a DataSet from the Database

...

// Create a Command object to query the entire Customer

table

SqlCommand cmd = conn.CreateCommand();

cmd.CommandText = "SELECT * FROM CUSTOMER";

// Create a DataAdapter for use with filling a DataSet

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