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‎doc/index.html

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<ul>
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<li><a href="/doc/nhibernate-reference/index.html">The NHibernate Reference</a></li>
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<li><a href="/doc/nh/en/index.html">The NHibernate Reference - single page</a></li>
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<li><a href="/doc/nhibernate-features.html">NHibernate Features</a></li>
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<li><a href="/doc/tutorials/first-nh-app/your-first-nhibernate-based-application.html">Tutorial: Your first NHibernate based application</a></li>
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</ul>
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<h2>Previous Reference</h2>
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<ul>
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<li><a href="/previous-doc/v4.1/ref/index.html">The NHibernate Reference, v4.1</a></li>
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<li><a href="/previous-doc/v4.1/single/index.html">The NHibernate Reference, v4.1 - single page</a></li>
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</ul>
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<h2>Patterns &amp; Practices</h2>
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<ul>
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<li><a href="/doc/patternsandpractices/identity-field-equality-and-hash-code.html">Identity Field, Equality and Hash Code</a></li>

‎previous-doc/v4.1/ref/architecture.html

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<html><head>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1" />
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta http-equiv="content-type" content="text/html;charset=utf-8" />
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<link rel="canonical" href="http://nhibernate.info/doc/nhibernate-reference/architecture.html" />
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<title>Chapter&nbsp;2.&nbsp;Architecture</title><link rel="stylesheet" href="../shared/css/html.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.65.1"><link rel="home" href="index.html" title="NHibernate - Relational Persistence for Idiomatic .NET"><link rel="up" href="index.html" title="NHibernate - Relational Persistence for Idiomatic .NET"><link rel="previous" href="quickstart.html" title="Chapter&nbsp;1.&nbsp;Quickstart with IIS and Microsoft SQL Server"><link rel="next" href="session-configuration.html" title="Chapter&nbsp;3.&nbsp;ISessionFactory Configuration"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter&nbsp;2.&nbsp;Architecture</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="quickstart.html">Prev</a>&nbsp;</td><th width="60%" align="center">&nbsp;</th><td width="20%" align="right">&nbsp;<a accesskey="n" href="session-configuration.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="architecture"></a>Chapter&nbsp;2.&nbsp;Architecture</h2></div></div><div></div></div>{% include google_adsense.html %}<div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="architecture-overview"></a>2.1.&nbsp;Overview</h2></div></div><div></div></div><p>
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A (very) high-level view of the NHibernate architecture:
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</p><div class="mediaobject" align="center"><img src="../shared/images/overview.png" align="middle"></div><p>
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This diagram shows NHibernate using the database and configuration data to
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provide persistence services (and persistent objects) to the application.
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</p><p>
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We would like to show a more detailed view of the runtime architecture.
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Unfortunately, NHibernate is flexible and supports several approaches. We will
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show the two extremes. The "lite" architecture has the application
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provide its own ADO.NET connections and manage its own transactions. This approach
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uses a minimal subset of NHibernate's APIs:
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</p><div class="mediaobject" align="center"><img src="../shared/images/lite.png" align="middle"></div><p>
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The "full cream" architecture abstracts the application away from the
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underlying ADO.NET APIs and lets NHibernate take care of the details.
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</p><div class="mediaobject" align="center"><img src="../shared/images/fullcream.png" align="middle"></div><p>
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Heres some definitions of the objects in the diagrams:
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</p><div class="variablelist"><dl><dt><span class="term">ISessionFactory (<tt class="literal">NHibernate.ISessionFactory</tt>)</span></dt><dd><p>
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A threadsafe (immutable) cache of compiled mappings for a single database.
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A factory for <tt class="literal">ISession</tt> and a client of
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<tt class="literal">IConnectionProvider</tt>. Might hold an optional (second-level)
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cache of data that is reusable between transactions, at a
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process- or cluster-level.
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</p></dd><dt><span class="term">ISession (<tt class="literal">NHibernate.ISession</tt>)</span></dt><dd><p>
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A single-threaded, short-lived object representing a conversation between
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the application and the persistent store. Wraps an ADO.NET connection. Factory
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for <tt class="literal">ITransaction</tt>. Holds a mandatory (first-level) cache
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of persistent objects, used when navigating the object graph or looking up
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objects by identifier.
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</p></dd><dt><span class="term">Persistent Objects and Collections</span></dt><dd><p>
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Short-lived, single threaded objects containing persistent state and business
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function. These might be ordinary POCOs, the only special thing about
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them is that they are currently associated with (exactly one)
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<tt class="literal">ISession</tt>. As soon as the <tt class="literal">Session</tt> is closed,
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they will be detached and free to use in any application layer (e.g. directly
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as data transfer objects to and from presentation).
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</p></dd><dt><span class="term">Transient Objects and Collections</span></dt><dd><p>
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Instances of persistent classes that are not currently associated with a
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<tt class="literal">ISession</tt>. They may have been instantiated by
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the application and not (yet) persisted or they may have been instantiated by a
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closed <tt class="literal">ISession</tt>.
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</p></dd><dt><span class="term">ITransaction (<tt class="literal">NHibernate.ITransaction</tt>)</span></dt><dd><p>
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(Optional) A single-threaded, short-lived object used by the application to
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specify atomic units of work. Abstracts application from underlying ADO.NET
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transaction. An <tt class="literal">ISession</tt> might span several
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<tt class="literal">ITransaction</tt>s in some cases.
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</p></dd><dt><span class="term">IConnectionProvider (<tt class="literal">NHibernate.Connection.IConnectionProvider</tt>)</span></dt><dd><p>
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(Optional) A factory for ADO.NET connections and commands. Abstracts application
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from the concrete vendor-specific implementations of <tt class="literal">IDbConnection</tt>
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and <tt class="literal">IDbCommand</tt>. Not exposed to application, but can be
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extended/implemented by the developer.
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</p></dd><dt><span class="term">IDriver (<tt class="literal">NHibernate.Driver.IDriver</tt>)</span></dt><dd><p>
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(Optional) An interface encapsulating differences between ADO.NET providers, such
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as parameter naming conventions and supported ADO.NET features.
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</p></dd><dt><span class="term">ITransactionFactory (<tt class="literal">NHibernate.Transaction.ITransactionFactory</tt>)</span></dt><dd><p>
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(Optional) A factory for <tt class="literal">ITransaction</tt> instances. Not exposed to the
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application, but can be extended/implemented by the developer.
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</p></dd></dl></div><p>
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</p><p>
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Given a "lite" architecture, the application bypasses the
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<tt class="literal">ITransaction</tt>/<tt class="literal">ITransactionFactory</tt> and/or
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<tt class="literal">IConnectionProvider</tt> APIs to talk to ADO.NET directly.
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</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="architecture-states"></a>2.2.&nbsp;Instance states</h2></div></div><div></div></div><p>
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An instance of a persistent classes may be in one of three different states,
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which are defined with respect to a <span class="emphasis"><em>persistence context</em></span>.
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The NHibernate <tt class="literal">ISession</tt> object is the persistence context:
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</p><div class="variablelist"><dl><dt><span class="term">transient</span></dt><dd><p>
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The instance is not, and has never been associated with
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any persistence context. It has no persistent identity
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(primary key value).
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</p></dd><dt><span class="term">persistent</span></dt><dd><p>
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The instance is currently associated with a persistence
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context. It has a persistent identity (primary key value)
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and, perhaps, a corresponding row in the database. For a
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particular persistence context, NHibernate
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<span class="emphasis"><em>guarantees</em></span> that persistent identity
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is equivalent to CLR identity (in-memory location of the
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object).
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</p></dd><dt><span class="term">detached</span></dt><dd><p>
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The instance was once associated with a persistence
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context, but that context was closed, or the instance
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was serialized to another process. It has a persistent
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identity and, perhaps, a corrsponding row in the database.
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For detached instances, NHibernate makes no guarantees
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about the relationship between persistent identity and
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CLR identity.
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</p></dd></dl></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="architecture-current-session"></a>2.3.&nbsp;Contextual Sessions</h2></div></div><div></div></div><p>
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Most applications using NHibernate need some form of "contextual" sessions, where a given
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session is in effect throughout the scope of a given context. However, across applications
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the definition of what constitutes a context is typically different; and different contexts
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define different scopes to the notion of current.
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</p><p>
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Starting with version 1.2, NHibernate added the <tt class="literal">ISessionFactory.GetCurrentSession()</tt>
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method. The processing behind <tt class="literal">ISessionFactory.GetCurrentSession()</tt> is pluggable.
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An extension interface (<tt class="literal">NHibernate.Context.ICurrentSessionContext</tt>) and a new
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configuration parameter (<tt class="literal">hibernate.current_session_context_class</tt>) have been added
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to allow pluggability of the scope and context of defining current sessions.
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</p><p>
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See the API documentation for the <tt class="literal">NHibernate.Context.ICurrentSessionContext</tt>
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interface for a detailed discussion of its contract. It defines a single method,
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<tt class="literal">CurrentSession()</tt>, by which the implementation is responsible for
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tracking the current contextual session. Out-of-the-box, NHibernate comes with several
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implementations of this interface:
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</p><div class="itemizedlist"><ul type="disc"><li><p>
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<tt class="literal">NHibernate.Context.CallSessionContext</tt> - current sessions are tracked
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by <tt class="literal">CallContext</tt>. You are responsible to bind and unbind an <tt class="literal">
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ISession</tt> instance with static methods of class <tt class="literal">CurrentSessionContext
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</tt>.
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</p></li><li><p>
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<tt class="literal">NHibernate.Context.ThreadStaticSessionContext</tt> - current session is
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stored in a thread-static variable. This context only supports one session factory.
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You are responsible to bind and unbind an <tt class="literal">ISession</tt> instance with
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static methods of class <tt class="literal">CurrentSessionContext</tt>.
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</p></li><li><p>
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<tt class="literal">NHibernate.Context.WebSessionContext</tt> -
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stores the current session in <tt class="literal">HttpContext</tt>.
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You are responsible to bind and unbind an <tt class="literal">ISession</tt>
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instance with static methods of class <tt class="literal">CurrentSessionContext</tt>.
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</p></li><li><p>
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<tt class="literal">NHibernate.Context.WcfOperationSessionContext</tt> - current sessions are tracked
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by WCF <tt class="literal">OperationContext</tt>. You need to register the <tt class="literal">WcfStateExtension</tt>
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extension in WCF. You are responsible to bind and unbind an <tt class="literal">ISession
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</tt> instance with static methods of class <tt class="literal">CurrentSessionContext</tt>.
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</p></li><li><p>
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<tt class="literal">NHibernate.Context.ManagedWebSessionContext</tt> - current
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sessions are tracked by <tt class="literal">HttpContext</tt>. Removed in NHibernate 4.0
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- <tt class="literal">NHibernate.Context.WebSessionContext</tt> should be used instead.
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You are responsible to bind and unbind an <tt class="literal">ISession</tt> instance with static methods
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on this class, it never opens, flushes, or closes an <tt class="literal">ISession</tt> itself.
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</p></li></ul></div><p>
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The <tt class="literal">hibernate.current_session_context_class</tt> configuration parameter
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defines which <tt class="literal">NHibernate.Context.ICurrentSessionContext</tt> implementation
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should be used. Typically, the value of this parameter would just name the implementation
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class to use (including the assembly name); for the out-of-the-box implementations, however,
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there are corresponding short names: "call", "thread_static", "web" and "wcf_operation",
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respectively.
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</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="quickstart.html">Prev</a>&nbsp;</td><td width="20%" align="center"><a accesskey="u" href="index.html">Up</a></td><td width="40%" align="right">&nbsp;<a accesskey="n" href="session-configuration.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter&nbsp;1.&nbsp;Quickstart with IIS and Microsoft SQL Server&nbsp;</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">&nbsp;Chapter&nbsp;3.&nbsp;ISessionFactory Configuration</td></tr></table></div>{% include google_analytics.html %}{% include metrika_yandex_ru.html %}</body></html>

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