spring-net/doc/reference/src/dbprovider.xml

<?xml version="1.0" encoding="UTF-8"?>
<chapter id="dbprovider">
  <title>DbProvider</title>

  <section id="dbprovider-introduction">
    <title>Introduction</title>

    <para>Spring provides a generic factory for creating ADO.NET API artifacts
    such as <code><classname>IDbConnection</classname></code> and
    <code><classname>IDbCommand</classname></code>. The factory API is very
    similar to the one introduced in .NET 2.0 but adds extra metadata needed
    by Spring to support features provided by its DAO/ADO.NET framework such
    as error code translation to a DAO exception hierarchy. The factory itself
    is configured by using a standard Spring XML based configuration file
    though it is unlikely you will need to modify those settings yourself, you
    only need be concerned with using the factory. Out of the box several
    popular databases are supported and an extension mechanism is available
    for defining new database providers or modifying existing ones. A custom
    database namespace for configuration aids in making terse XML based
    declarations of Spring's database objects you wish to use.</para>

    <para>The downside of Spring's factory as compared to the one in .NET 2.0
    is that the types returned are lower level interfaces and not the abstract
    base classes in System.Data.Common. However, there are still 'holes' in
    the current .NET 2.0 provider classes that are 'plugged' with Spring's
    provider implementation. One of the most prominent is the that the top
    level DbException exposes the HRESULT of the remote procedure call, which
    is not what you are commonly looking for when things go wrong. As such
    Spring's provider factory exposes the vendor sql error code and also maps
    that error code onto a consistent data access exception hierarchy. This
    makes writing portable exception handlers much easier. In addition, the
    DbParameter class doesn't provide the most common convenient methods you
    would expect as when using say the SqlServer provider. If you need to
    access the BCL provider abstraction, you still can through Spring's
    provider class. Furthermore, a small wrapper around the standard BCL
    provider abstraction allows for integration with Spring's transaction
    management facilities, allowing you to create a DbCommand with its
    connection and transaction properties already set based on the transaction
    calling context.</para>
  </section>

  <section id="dbprovider-dbprovider">
    <title>IDbProvider and DbProviderFactory</title>

    <para>The <code><interfacename>IDbProvider</interfacename></code> API is
    shown below and should look familiar to anyone using .NET 2.0 data
    providers. Note that Spring's DbProvider abstraction can be used on .NET
    1.1 in addition to .NET 2.0</para>

    <programlisting>    public interface IDbProvider
    {
        IDbCommand CreateCommand();

        object CreateCommandBuilder();        
        
        IDbConnection CreateConnection();

        IDbDataAdapter CreateDataAdapter();
        
        IDbDataParameter CreateParameter();
        
        string CreateParameterName(string name);

        string CreateParameterNameForCollection(string name);

        IDbMetadata DbMetadata
        {
            get;
        }               

        string ConnectionString
        {
            set;
            get;
        }
        
        string ExtractError(Exception e);

        bool IsDataAccessException(Exception e);
        
    }</programlisting>

    <para>ExtractError is used to return an error string for translation into
    a DAO exception. On .NET 1.1 the method IsDataAccessException is used to
    determine if the thrown exception is related to data access since in .NET
    1.1 there isn't a common base class for database exceptions.
    CreateParameterName is used to create the string for parameters used in a
    CommandText object while CreateParameterNameForCollection is used to
    create the string for a IDataParameter.ParameterName, typically contained
    inside a IDataParameterCollection.</para>

    <para>The class <classname>DbProviderFactory</classname> creates
    IDbProvider instances given a provider name. The connection string
    property will be used to set the IDbConnection returned by the factory if
    present. The provider names, and corresponding database, currently
    configured are listed below.</para>

    <itemizedlist>
      <listitem>
        <para><code>SqlServer-1.1</code> - Microsoft SQL Server, provider
        V1.0.5000.0 in framework .NET V1.1</para>
      </listitem>

      <listitem>
        <para><code>SqlServer-2.0</code> (aliased to
        <code>System.Data.SqlClient</code>) - Microsoft SQL Server, provider
        V2.0.0.0 in framework .NET V2.0</para>
      </listitem>

      <listitem>
        <para><literal>SqlServerCe-3.1</literal> - Microsoft SQL Server
        Compact Edition, provider V9.0.242.0</para>
      </listitem>

      <listitem>
        <para><literal>SqlServerCe-3.5.1</literal> (aliased to
        <literal>System.Data.SqlServerCe</literal>) - Microsoft SQL Server
        Compact Edition, provider V3.5.1.0</para>
      </listitem>

      <listitem>
        <para><code>OleDb-1.1</code> - OleDb, provider V1.0.5000.0 in
        framework .NET V1.1</para>
      </listitem>

      <listitem>
        <para><code>OleDb-2.0</code> (aliased to
        <code>System.Data.OleDb</code>) - OleDb, provider V2.0.0.0 in
        framework .NET V2.0</para>
      </listitem>

      <listitem>
        <para><code>OracleClient-2.0</code> (aliased to
        <code>System.Data.OracleClient</code>) - Oracle, Microsoft provider
        V2.0.0.0</para>
      </listitem>

      <listitem>
        <para><code>OracleODP-2.0</code> (aliased to
        <code>System.DataAccess.Client</code>) - Oracle, Oracle provider
        V2.102.2.20</para>
      </listitem>

      <listitem>
        <para><code>MySql</code> - MySQL, MySQL provider 1.0.10.1</para>
      </listitem>

      <listitem>
        <para><literal>MySql-1.0.9</literal> - MySQL, MySQL provider
        1.0.9</para>
      </listitem>

      <listitem>
        <para><literal>MySql-5.0</literal> - MySQL, MySQL provider
        5.0.7.0</para>
      </listitem>

      <listitem>
        <para><literal>MySql-5.0.8.1</literal> - MySQL, MySQL provider
        5.0.8.1</para>
      </listitem>

      <listitem>
        <para><literal>MySql-5.1 </literal>- MySQL, MySQL provider
        5.1.2.2</para>
      </listitem>

      <listitem>
        <para><literal>MySql-5.1.4</literal> - (aliased to
        <literal>MySql.Data.MySqlClient</literal>) MySQL, MySQL provider
        5.1.2.2</para>
      </listitem>

      <listitem>
        <para><literal>Npgsql-1.0</literal> - Postgresql provider 1.0.0.0 (and
        1.0.0.1 - were build with same version info)</para>
      </listitem>

      <listitem>
        <para><literal>Npgsql-2.0-beta1</literal> - Postgresql provider
        1.98.1.0 beta 1</para>
      </listitem>

      <listitem>
        <para><literal>DB2-9.0.0-1.1</literal> - IBM DB2 Data Provider 9.0.0
        for .NET Framework 1.1</para>
      </listitem>

      <listitem>
        <para><literal>DB2-9.0.0-2.0 </literal>- (aliased to
        <literal>IBM.Data.DB2</literal>) - IBM DB2 Data Provider 9.0.0 for
        .NET Framework 2.0</para>
      </listitem>

      <listitem>
        <para><literal>DB2-9.1.0-1.1</literal> - IBM DB2 Data Provider 9.1.0
        for .NET Framework 1.1</para>
      </listitem>

      <listitem>
        <para><literal>DB2-9.1.0.2</literal> - (aliased to
        <literal>IBM.Data.DB2.9.1.0</literal>) - IBM DB2 Data Provider 9.1.0
        for .NET Framework 2.0</para>
      </listitem>

      <listitem>
        <para><literal>SQLite-1.0.43 </literal>SQLite provider 1.0.43 for .NET
        Framework 2.0</para>
      </listitem>

      <listitem>
        <para><literal>SQLite-1.0.47 </literal>- (aliased to
        System.Data.SQLite) - SQLite provider 1.0.43 for .NET Framework
        2.0</para>
      </listitem>

      <listitem>
        <para><literal>SybaseAse-12</literal> - Sybase ASE provider for ASE
        12.x</para>
      </listitem>

      <listitem>
        <para><literal>SybaseAse-15</literal> - Sybase ASE provider for ASE
        15.x</para>
      </listitem>

      <listitem>
        <para><literal>SybaseAse-AdoNet2</literal> - Sybase ADO.NET 2.0
        provider for ASE 12.x and 15.x</para>
      </listitem>

      <listitem>
        <para><literal>Odbc-1.1</literal> - ODBC provider V1.0.5000.0 in
        framework .NET V1.1</para>
      </listitem>

      <listitem>
        <para><literal>Odbc-2.0</literal> - ODBC provider V2.0.0.0 in
        framework .NET V2</para>
      </listitem>
    </itemizedlist>

    <para>An example using DbProviderFactory is shown below</para>

    <programlisting>IDbProvider dbProvider = DbProviderFactory.GetDbProvider("System.Data.SqlClient");</programlisting>

    <para>The default definitions of the providers are contained in the
    assembly resource
    <code>assembly://Spring.Data/Spring.Data.Common/dbproviders.xml</code>.
    Future additions to round out the database coverage are forthcoming. The
    current crude mechanism to add additional providers, or to apply any
    standard Spring <interfacename>IApplicationContext</interfacename>
    functionality, such as applying AOP advice, is to set the public static
    property DBPROVIDER_ADDITIONAL_RESOURCE_NAME in
    <classname>DbProviderFactory</classname> to a Spring resource location.
    The default value is <code>file://dbProviders.xml</code>. (That isn't a
    typo, there is a difference in case with the name of the embedded
    resource). This crude mechanism will eventually be replaced with one based
    on a custom configuration section in App.config/Web.config.</para>

    <para>It may happen that the version number of an assembly you have
    downloaded is different than the one listed above. If it is a point
    release, i.e. the API hasn't changed in anyway that is material to your
    application, you should add an assembly redirect of the form shown
    below.</para>

    <programlisting>&lt;dependentAssembly&gt;
  &lt;assemblyIdentity name="MySql.Data" 
                           publicKeyToken="c5687fc88969c44d" 
                           culture="neutral"/&gt;
  &lt;bindingRedirect oldVersion="0.0.0.0-65535.65535.65535.65535"
                         newVersion="1.0.10.1"/&gt;
&lt;/dependentAssembly&gt;</programlisting>

    <para>This redirects any reference to an older version of the assembly
    MySql.Data to the version 1.0.10.1.</para>
  </section>

  <section>
    <title>XML based configuration</title>

    <para>Creating a DbProvider in Spring's XML configuration file is shown
    below in the typical case of using it to specify the DbProvider property
    on an AdoTemplate.</para>

    <programlisting>&lt;objects xmlns='http://www.springframework.net'
         xmlns:db="http://www.springframework.net/database"&gt;

  &lt;db:provider id="DbProvider" 
                provider="System.Data.SqlClient" 
                connectionString="Data Source=(local);Database=Spring;User ID=springqa;Password=springqa;Trusted_Connection=False"/&gt;
  
  &lt;object id="adoTemplate" type="Spring.Data.AdoTemplate, Spring.Data"&gt;  
    &lt;property name="DbProvider" ref="DbProvider"/&gt;                
  &lt;/object&gt;

&lt;/objects&gt;</programlisting>

    <para>A custom namespace should be registered in the main application
    configuration file to use this syntax. This configuration, only for the
    parsers, is shown below. Additional section handlers are needed to specify
    the rest of the Spring configuration locations as described in previous
    chapters.</para>

    <programlisting>&lt;configuration&gt;

  &lt;configSections&gt;
    &lt;sectionGroup name="spring"&gt;
      &lt;section name="parsers" type="Spring.Context.Support.NamespaceParsersSectionHandler, Spring.Core" /&gt;
    &lt;/sectionGroup&gt;
  &lt;/configSections&gt;

  &lt;spring&gt;
    &lt;parsers&gt;
      &lt;parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" /&gt;
    &lt;/parsers&gt;
  &lt;/spring&gt;

&lt;/configuration&gt;</programlisting>
  </section>

  <section>
    <title>Connection String management</title>

    <para>There are a few options available to help manage your connection
    strings.</para>

    <para>The first option is to leverage the Spring property replacement
    functionality, as described in <xref
    linkend="objects-factory-placeholderconfigurer" />. This lets you insert
    variable names as placeholders for values in a Spring configuration file.
    In the following example specific parts of a connection string have been
    parameterized but you can also use a variable to set the entire connection
    string.</para>

    <para>An example of such a setting is shown below</para>

    <programlisting>&lt;configuration&gt;
  &lt;configSections&gt;
    &lt;sectionGroup name="spring"&gt;
      &lt;section name='context' type='Spring.Context.Support.ContextHandler, Spring.Core'/&gt;
    &lt;/sectionGroup&gt;

    &lt;section name="databaseSettings" type="System.Configuration.NameValueSectionHandler, System, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" /&gt;
       
  &lt;/configSections&gt;

  &lt;spring&gt;
    &lt;context&gt;      
      &lt;resource uri="Aspects.xml" /&gt;
      &lt;resource uri="Services.xml" /&gt;
      &lt;resource uri="Dao.xml" /&gt;
    &lt;/context&gt;
  &lt;/spring&gt;

  &lt;!-- These properties are referenced in Dao.xml --&gt;
  &lt;databaseSettings&gt;
    &lt;add key="db.datasource" value="(local)" /&gt;
    &lt;add key="db.user" value="springqa" /&gt;
    &lt;add key="db.password" value="springqa" /&gt;
    &lt;add key="db.database" value="Northwind" /&gt;
  &lt;/databaseSettings&gt;


&lt;/configuration&gt;</programlisting>

    <para>Where <literal>Dao.xml</literal> has a connection string as shown
    below</para>

    <programlisting>&lt;objects xmlns='http://www.springframework.net'
         xmlns:db="http://www.springframework.net/database"&gt;

  &lt;db:provider id="DbProvider" 
                provider="System.Data.SqlClient" 
                connectionString="${db.datasource};Database=${db.database};User ID=${db.user};Password=${db.password};Trusted_Connection=False"/&gt;
  
  &lt;object id="adoTemplate" type="Spring.Data.AdoTemplate, Spring.Data"&gt;  
    &lt;property name="DbProvider" ref="DbProvider"/&gt;                
  &lt;/object&gt;

  &lt;!-- configuration of what values to substitute for ${ } variables listed above --&gt;
  &lt;object name="appConfigPropertyHolder"
          type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core"&gt;
    &lt;property name="configSections" value="DatabaseConfiguration"/&gt;
  &lt;/object&gt; 

&lt;/objects&gt;</programlisting>

    <para>Please refer to the Section <xref
    linkend="objects-factory-placeholderconfigurer" /> for more
    information.</para>
  </section>

  <section id="dbprovider-additional">
    <title>Additional IDbProvider implementations</title>

    <para>Spring provides some convenient implementations of the IDbProvider
    interface that add addtional behavior on top of the standard
    implementation.</para>

    <section id="dbprovider-usercredentials">
      <title>UserCredentialsDbProvider</title>

      <para>This <classname>UserCredentialsDbProvider</classname> will allow
      you to change the username and password of a database connection at
      runtime. The API contains the properties <literal>Username</literal> and
      <literal>Password</literal> which are used as the default strings
      representing the user and password in the connection string. You can
      then change the value of these properties in the connection string by
      calling the method <literal>SetCredentialsForCurrentThread</literal> and
      fall back to the default values by calling the method
      <literal>RemoveCredentialsFromCurrentThread</literal>. You call the
      <literal>SetCredentialsForCurrentThread</literal> method at runtime,
      before any data access occurs, to determine which database user should
      be used for the current user-case. Which user to select is up to you.
      You may retrieve the user information from an HTTP session for example.
      Example configuration and usage is shown below</para>

      <programlisting>&lt;object id="DbProvider" type="Spring.Data.Common.UserCredentialsDbProvider, Spring.Data"&gt;
  &lt;property name="TargetDbProvider" ref="targetDbProvider"/&gt;
  &lt;property name="Username" value="User ID=defaultName"/&gt;
  &lt;property name="Password" value="Password=defaultPass"/&gt;
&lt;/object&gt;
 
&lt;db:provider id="targetDbProvider" provider="SqlServer-2.0"
    connectionString="Data Source=MARKT60\SQL2005;Database=Spring;Trusted_Connection=False"/&gt;</programlisting>

      <para>If you use dependency injection to configure a class with a
      property of the type <literal>IDbProvider</literal>, you will need to
      downcast to the subtype or you can change your class to have a property
      of the type <literal>UserCredentialsDbProvider</literal> instead of
      <literal>IDbProvider</literal>.</para>

      <programlisting>userCredentialsDbProvider.SetCredentialsForCurrentThread("User ID=springqa", "Password=springqa");</programlisting>

      <para><literal>UserCredentialsDbProvider's</literal> has a base class,
      <literal>DelegatingDbProvider</literal>, and is intended for you to use
      in your own implementations that delegate calls to a target
      <literal>IDbProvider</literal> instance. This class in meant to be
      subclassed with subclasses overriding only those methods, such as
      <literal>CreateConnection()</literal>, that should not simply delegate
      to the target <literal>IDbProvider</literal>.</para>
    </section>

    <section id="dbprovider-multidelegating">
      <title>MultiDelegatingDbProvider</title>

      <para>There are use-cases in which there will need to be a runtime
      selection of the database to connect to among many possible candidates.
      This is often the case where the same schema is installed in separate
      databases for different clients. The
      <classname>MultiDelegatingDbProvider</classname> implements the
      <classname>IDbProvider</classname> interface and provides an abstraction
      to the multiple databases and can be used in DAO layer such that the DAO
      layer is unaware of the switching between databases.
      <classname>MultiDelegatingDbProvider</classname> does its job by looking
      into thread local storage under the key dbProviderName. This storage
      location stores the name of the dbProvider that is to be used for
      processing the request. <classname>MultiDelegatingDbProvider</classname>
      is configured using the dictionary property
      <literal>TargetDbProviders</literal>. The key of this dictionary
      contains the name of a dbProvider and its value is a dbProvider object.
      (You can also provide this dictionary as a constructor argument.) During
      request processing, once you have determined which target dbProvider
      should be use, in this example database1ProviderName, you should execute
      the following code
      <literal>LogicalThreadContext.SetData("dbProviderName",
      "database1ProviderName")</literal> and then call the data access
      layer.</para>

      <para></para>
    </section>
  </section>
</chapter>