第十九章 数据访问(In .net4.5) 之 处理数据
1. 概述
本章介绍 数据库、Json和Xml、web services 三种介质上的数据操作。
2. 主要内容
2.1 数据库
① 建立连接
.net平台中的数据连接类都继承自DbConnection。DbConnection实现了IDisposable接口。
using (SqlConnection connection = new SqlConnection(connectionString)) { connection.Open(); // Execute operations against the database
} // Connection is automatically closed.
使用ConnectionStringBuilder 可以构建连接字符串。但是把连接字符串放到配置文件中是更好的选择。
var sqlConnectionStringBuilder = new SqlConnectionStringBuilder(); sqlConnectionStringBuilder.DataSource = @”(localdb)\v11.0”; sqlConnectionStringBuilder.InitialCatalog = “ProgrammingInCSharp”; string connectionString = sqlConnectionStringBuilder.ToString();
.net平台使用连接池来优化数据库连接操作。
② 读取数据 : 可以使用async/await来异步操作。
public async Task SelectDataFromTable() { string connectionString = ConfigurationManager. ConnectionStrings[“ProgrammingInCSharpConnection”].ConnectionString; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand(“SELECT * FROM People”, connection); await connection.OpenAsync(); SqlDataReader dataReader = await command.ExecuteReaderAsync(); while (await dataReader.ReadAsync()) { string formatStringWithMiddleName = “Person ({0}) is named {1} {2} {3}”; string formatStringWithoutMiddleName = “Person ({0}) is named {1} {3}”; if ((dataReader[“middlename”] == null)) { Console.WriteLine(formatStringWithoutMiddleName, dataReader[“id”], dataReader[“firstname”], dataReader[“lastname”]); } else { Console.WriteLine(formatStringWithMiddleName, dataReader[“id”], dataReader[“firstname”], dataReader[“middlename”], dataReader[“lastname”]); } } dataReader.Close(); } }
使用DataReader的NextResultAsync，可以处理多个结果集。
public async Task SelectMultipleResultSets() { string connectionString = ConfigurationManager. ConnectionStrings[“ProgrammingInCSharpConnection”].ConnectionString; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand(“SELECT * FROM People; SELECT TOP 1 * FROM People ORDER BY LastName”, connection); await connection.OpenAsync(); SqlDataReader dataReader = await command.ExecuteReaderAsync(); await ReadQueryResults(dataReader); await dataReader.NextResultAsync(); // Move to the next result set
await ReadQueryResults(dataReader); dataReader.Close(); } } private static async Task ReadQueryResults(SqlDataReader dataReader) { while (await dataReader.ReadAsync()) { string formatStringWithMiddleName = “Person ({0}) is named {1} {2} {3}”; string formatStringWithoutMiddleName = “Person ({0}) is named {1} {3}”; if ((dataReader[“middlename”] == null)) { Console.WriteLine(formatStringWithoutMiddleName, dataReader[“id”], dataReader[“firstname”], dataReader[“lastname”]); } else { Console.WriteLine(formatStringWithMiddleName, dataReader[“id”], dataReader[“firstname”], dataReader[“middlename”], dataReader[“lastname”]); } } }
③ 更新数据
public async Task UpdateRows() { string connectionString = ConfigurationManager. ConnectionStrings[“ProgrammingInCSharpConnection”].ConnectionString; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand( “UPDATE People SET FirstName=’John’”, connection); await connection.OpenAsync(); int numberOfUpdatedRows = await command.ExecuteNonQueryAsync(); Console.WriteLine(“Updated {0} rows”, numberOfUpdatedRows); } }
④ 使用参数
public async Task InsertRowWithParameterizedQuery() { string connectionString = ConfigurationManager. ConnectionStrings[“ProgrammingInCSharpConnection”].ConnectionString; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand( “INSERT INTO People([FirstName], [LastName], [MiddleName]) VALUES(@ firstName, @lastName, @middleName)”, connection); await connection.OpenAsync(); command.Parameters.AddWithValue(“@firstName”, “John”); command.Parameters.AddWithValue(“@lastName”, “Doe”); command.Parameters.AddWithValue(“@middleName”, “Little”); int numberOfInsertedRows = await command.ExecuteNonQueryAsync(); Console.WriteLine(“Inserted {0} rows”, numberOfInsertedRows); } }
⑤ 使用事务
string connectionString = ConfigurationManager. ConnectionStrings[“ProgrammingInCSharpConnection”].ConnectionString; using (TransactionScope transactionScope = new TransactionScope()) { using (SqlConnection connection = new SqlConnection(connectionString)) { connection.Open(); SqlCommand command1 = new SqlCommand( “INSERT INTO People ([FirstName], [LastName], [MiddleInitial]) VALUES(‘John’, ‘Doe’, null)”, connection); SqlCommand command2 = new SqlCommand( “INSERT INTO People ([FirstName], [LastName], [MiddleInitial]) VALUES(‘Jane’, ‘Doe’, null)”, connection); command1.ExecuteNonQuery(); command2.ExecuteNonQuery(); } transactionScope.Complete(); }
*TransactionScope支持三种类型：Required, RequiresNew, Supress.
⑥ 使用 Object Relational Mapper(ORM)
数据记录和表不符合面向对象的结构，手动写数据对象，创建和维护成本都很高。为了解决这个问题，出现了ORM。
微软提供的ORM工具是 Entiry Framework(EF)。EF支持三种模式：数据库先行、模型先行、代码先行。
public class Person { public int Id { get; set; } public string Name { get; set; } } public class PeopleContext : DbContext { public IDbSet<Person> People { get; set; } } using (PeopleContext ctx = new PeopleContext()) { ctx.People.Add(new Person() { Id = 1, Name = “John Doe” }); ctx.SaveChanges(); } using (PeopleContext ctx = new PeopleContext()) { Person person = ctx.People.SingleOrDefault(p => p.Id == 1); Console.WriteLine(person.Name); }
2.2 使用 web services
创建一个Windows Comunication Service(WCF)服务
WCF的ABC模型：
① Address：服务公开的终结点，实际调用的物理地址。
② Binding：配置了通信的协议和传输类型。
③ Contract：合约，定义了服务公开的操作。
2.3 使用XML
System.Xml下比较重要的类包括：
① XmlReader：速度较快
string xml = @”<?xml version=””1.0”” encoding=””utf-8”” ?> <people> <person firstname=””john”” lastname=””doe””> <contactdetails> <emailaddress>[email protected]</emailaddress> </contactdetails> </person> <person firstname=””jane”” lastname=””doe””> <contactdetails> <emailaddress>[email protected]</emailaddress> <phonenumber>001122334455</phonenumber> </contactdetails> </person> </people>”; using (StringReader stringReader = new StringReader(xml)) { using (XmlReader xmlReader = XmlReader.Create(stringReader, new XmlReaderSettings() { IgnoreWhitespace = true })) { xmlReader.MoveToContent(); xmlReader.ReadStartElement(“People”); string firstName = xmlReader.GetAttribute(“firstName”); string lastName = xmlReader.GetAttribute(“lastName”); Console.WriteLine(“Person: {0} {1}”, firstName, lastName); xmlReader.ReadStartElement(“Person”); Console.WriteLine(“ContactDetails”); xmlReader.ReadStartElement(“ContactDetails”); string emailAddress = xmlReader.ReadString(); Console.WriteLine(“Email address: {0}”, emailAddress); } }
② XmlWriter：速度较快
StringWriter stream = new StringWriter(); using (XmlWriter writer = XmlWriter.Create( stream, new XmlWriterSettings() { Indent = true })) { writer.WriteStartDocument(); writer.WriteStartElement(“People”); writer.WriteStartElement(“Person”); writer.WriteAttributeString(“firstName”, “John”); writer.WriteAttributeString(“lastName”, “Doe”); writer.WriteStartElement(“ContactDetails”); writer.WriteElementString(“EmailAddress”, “[email protected]”); writer.WriteEndElement(); writer.WriteEndElement(); writer.Flush(); } Console.WriteLine(stream.ToString());
③ XmlDocument：灵活性高
XmlDocument doc = new XmlDocument(); doc.LoadXml(xml); XmlNodeList nodes = doc.GetElementsByTagName(“Person”); // Output the names of the people in the document
foreach (XmlNode node in nodes) { string firstName = node.Attributes[“firstName”].Value; string lastName = node.Attributes[“lastName”].Value; Console.WriteLine(“Name: {0} {1}”, firstName, lastName); } // Start creating a new node
XmlNode newNode = doc.CreateNode(XmlNodeType.Element, “Person”, “”); XmlAttribute firstNameAttribute = doc.CreateAttribute(“firstName”); firstNameAttribute.Value = “Foo”; XmlAttribute lastNameAttribute = doc.CreateAttribute(“lastName”); lastNameAttribute.Value = “Bar”; newNode.Attributes.Append(firstNameAttribute); newNode.Attributes.Append(lastNameAttribute); doc.DocumentElement.AppendChild(newNode); Console.WriteLine(“Modified xml...”); doc.Save(Console.Out); //Displays: //Name: john doe //Name: jane doe //Modified xml... //<?xml version=”1.0” encoding=”ibm850”?> //<people> // <person firstname=”john” lastname=”doe”> // <contactdetails> // <emailaddress>[email protected]</emailaddress> // </contactdetails> // </person> // <person firstname=”jane” lastname=”doe”> // <contactdetails> // <emailaddress>[email protected]</emailaddress> // <phonenumber>001122334455</phonenumber> // </contactdetails> // </person> // <person firstname=”Foo” lastname=”Bar” /> //</people>
*XmlDocument实现了IXPathNavigable接口，可以使用XPathNavigator 对象遍历xml.
XmlDocument doc = new XmlDocument(); doc.LoadXml(xml); // Can be found in Listing 4-43
XPathNavigator nav = doc.CreateNavigator(); string query = “//People/Person[@firstName=’Jane’]”;
XPathNodeIterator iterator = nav.Select(query); Console.WriteLine(iterator.Count); // Displays 1
while(iterator.MoveNext()) { string firstName = iterator.Current.GetAttribute(“firstName”,””); string lastName = iterator.Current.GetAttribute(“lastName”,””); Console.WriteLine(“Name: {0} {1}”, firstName, lastName); }
2.4 使用Json
可以使用第三方组件Newtonsoft.Json来处理Json数据。
3. 总结
① ADO.NET提供了provider模型来实现连接不同类型的数据源。
② 使用DbConnection对象来创建数据库连接。
③ 使用参数化的查询方式，可以避免sql注入。
④ 通过创建代理，可以使你的程序对外发布 web service 接口。
⑤ .net平台提供了处理Xml的相关类(XmlReader, XmlWriter, XPathNavigator, XmlDocument)。
⑥ 处理Json数据可以使用第三方的Newtonsoft.Json。