app.config 中的嵌套自定义元素 (C#)

Question

大家好，

几个小时以来，我一直在尝试弄清楚如何从 app.config 文件中读取设置：

<?xml version="1.0"?>
<configuration>

  <configSections>
    <section name="Databases" type="McFix.DatabaseSection, McFix"/>
  </configSections>

  <Databases>
    <Database name="database">
      <Tables>
        <Table name="be_sessions">
          <Columns>
            <Column name="sess_id">
            </Column>
          </Columns>
        </Table>
      </Tables>
    </Database>
  </Databases>

  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
  </startup>
</configuration>

自定义处理程序类的代码位于此处，也复制如下：

public class DatabaseSection : ConfigurationSection
{
    [ConfigurationProperty("Databases", IsDefaultCollection = false)]
    public DatabaseInstanceCollection Databases
    {
        get { return (DatabaseInstanceCollection)this["Databases"]; }
        set { this[""] = value; }
    }
}
[ConfigurationCollection(typeof(DatabaseElement), AddItemName = "add", CollectionType = ConfigurationElementCollectionType.BasicMap )]
public class DatabaseInstanceCollection : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new DatabaseElement();
    }
    protected override object GetElementKey(ConfigurationElement element)
    {
        return ((DatabaseElement)element).Name;
    }
}
public class DatabaseElement : ConfigurationElement
{
    [ConfigurationProperty("name", IsKey = true, IsRequired = true)]
    public string Name
    {
        get { return (string)base["name"]; }
        set { base["name"] = value; }
    }
}

public class TableSection : ConfigurationSection
{
    [ConfigurationProperty("Tables", IsDefaultCollection = true)]
    public TableInstanceCollection Tables
    {
        get { return (TableInstanceCollection)this["Tables"]; }
        set { this[""] = value; }
    }
}

[ConfigurationCollection(typeof(TableElement), AddItemName = "Table", CollectionType = ConfigurationElementCollectionType.BasicMap)]
public class TableInstanceCollection : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new TableElement();
    }
    protected override object GetElementKey(ConfigurationElement element)
    {
        return ((TableElement)element).Name;
    }
}

public class TableElement : ConfigurationElement
{
    [ConfigurationProperty("name", IsKey = true, IsRequired = true)]
    public string Name
    {
        get { return (string)base["name"]; }
        set { base["name"] = value; }
    }
}

public class ColumnSection : ConfigurationSection
{
    [ConfigurationProperty("Columns", IsDefaultCollection = true)]
    public ColumnInstanceCollection Columns
    {
        get { return (ColumnInstanceCollection)this["Columns"]; }
        set { this[""] = value; }
    }
}

[ConfigurationCollection(typeof(ColumnElement), AddItemName = "Column", CollectionType = ConfigurationElementCollectionType.BasicMap)]
public class ColumnInstanceCollection : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new ColumnElement();
    }
    protected override object GetElementKey(ConfigurationElement element)
    {
        return ((ColumnElement)element).Name;
    }
}

public class ColumnElement : ConfigurationElement
{
    [ConfigurationProperty("name", IsKey = true, IsRequired = true)]
    public string Name
    {
        get { return (string)base["name"]; }
        set { base["name"] = value; }
    }
}

问题是当我尝试获取“数据库”时通过 GetSection 方法获取节：

Configuration Config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
DatabaseSection DbConfig = Config.GetSection("Databases") as DatabaseSection;

程序抛出 ConfigurationErrorsException，报告​​“无法识别的元素‘数据库’”，尽管它在执行 DatabaseSection 的 get 方法后执行此操作，即使我将 DatabaseInstanceCollection 的 AddItemName 定义为“数据库”。我是否缺少一些可以让底层代码正确读取 app.config 的属性？

Answer 1

必填链接：

• 揭开 .NET 2.0 配置的神秘面纱
• 解密 .NET 2.0 配置的奥秘
• 破解.NET 2.0 配置之谜

粗略查看后，您的问题似乎出在这一行：

[ConfigurationCollection(typeof(DatabaseElement), AddItemName = "add", CollectionType = ConfigurationElementCollectionType.BasicMap )]

这表明 .config 文件应如下所示：

<Databases>
    <add><!-- Database goes here --></add>
</Databases>

即您的 Databases 元素正在期待一个“add”子项，指示要将项目添加到集合中。

您应该尝试将 AddItemName 属性从“add”更改为“Database”：（

[ConfigurationCollection(typeof(DatabaseElement), AddItemName = "Database", CollectionType = ConfigurationElementCollectionType.BasicMap )]

我没有机会测试这一点，可能还有其他问题）

Answer 2

你是对的，Kragen，我必须删除 Table/ColumnSection 并将 Table/ColumnInstanceCollection 添加到 Database/TableElement。 DatabaseSection 的 Databases 属性必须类似于：

[ConfigurationProperty("", IsDefaultCollection = true)]
        public DatabaseInstanceCollection Databases
        {
            get { return (DatabaseInstanceCollection)this[""]; }
        }