ASP.NET.in.a.Nutshell.Second.Edition [Electronic resources] نسخه متنی

Chapter 20. web.config Reference

ASP.NET
provides a completely new model for configuring web applications.
This greatly simplified process makes it considerably easier to
deploy application configuration settings, the
application's content, and its components. Central
to this new configuration model is

web.config ,
an XML-based file that contains the configuration settings for your
application. Because the file is written in XML, it is both human-
and machine-readable.

web.config files configure applications
hierarchicallyi.e., an application can contain more than one

web.config file, with each file residing in a
separate folder of the application. Settings in a

web.config file in a child folder of the
application root override the settings of
the

web.config file
in the parent folder. Settings not defined in the child

web.config file inherit the settings from the
parent

web.config file. Figure 20-1 demonstrates these rules of precedence.

Figure 20-1. Inheriting and overriding web.config settings

In addition to inheriting settings from a

web.config file defined in a parent folder, all
applications on a given machine inherit settings from a file called

machine.config . The

machine.config file contains default ASP.NET
configuration settings, as well as settings for other .NET
application types. Thus, in Figure 20-1, the

Chapter20 folder inherits the

machine.config setting for the
enableSessionState attribute of the
<pages> element, which is
True by default. The

web.config file in the

Chapter20 folder overrides the

machine.config default settings for the
<authorization> element, denying access to
any anonymous user (any user who has not logged in). The

Sub1 subfolder inherits this setting (as well as
all settings defined in

machine.config ) and adds
a setting to override the

machine.config setting
for the <pages> element, disabling session
state for all pages contained in the

Sub1
folder.

web.config is made up of one or more of the
elements listed in Section 20.2 later in this
section. The <configuration> element is
required, as is its child, <system.web>. All
child elements of <system.web> (i.e., the
elements that actually provide the configuration information) are
optional; however, the use of certain elements may require you to
include other elements or child elements. Each element may also
contain one or more attributes that affect the behavior of that
element.

Certain elements are limited in the scope at which they can be used.
Some elements can be used only at the Application level (in the

web.config file at the root of the application),
some only at the machine level (in

machine.config ), and some can be used at any
scope (in

machine.config or in any

web.config file, whether at application root or
subfolder level).

The elements in Table 20-1 are organized both
functionally and hierarchically. That is, elements with related
functions, such as <authentication> and
<authorization>, are grouped together, and
child elements immediately follow their parent elements. Thus, the
<credentials> element immediately follows
the <forms> element, which is its parent,
and is immediately followed by <user>, which
is a child of <credentials>. Table 20-1 summarizes the

web.config
elements covered in this chapter.