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    jinfeng_wang

    G-G-S,D-D-U!

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    http://groups.google.com/group/microsoft.public.dotnet.framework.adonet/browse_frm/thread/eca73047adca7edb/12f1ae6ae176afe1?lnk=raot#12f1ae6ae176afe1



    1. jinfeng_W...@msn.com
     1月20日 上午9時56分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: jinfeng_W...@msn.com - 查找此作者的帖子 
    日期:19 Jan 2006 17:56:57 -0800
    當地時間:2006年1月20日(星期五) 上午9時56分 
    主題:the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    hi, I have a question about the difference between
    SqlConnection.IDisposable.Dispose()  and  SqlConnection.Dispose(). Both
     of them realize the function of releasing the connection to the
    ConnectionPool?  Do they have the same effection source code?  If they
    are different, who can tell me the differences? If they are same, why
    MS gives the SqlConnection.IDisposable.Dispose, but  only
    SqlConnection.Dispose() method?


    In the MSDN, there are following description about the
    SqlConnection.IDisposable.Dispose Method:
      "This member supports the .NET Framework infrastructure and is not
    intended to be used directly from your code."  what's the meaning of
    it?


    If the user has called the SqlConnection.IDisposable.Dispose() in the
    client application, what probem results in?  and if there are some
    problem becomes, then why did MS give us such a method?


    in the same, who can tell me the using of
    "SqlConnection.ICloneable.Clone ",
    "SqlConnection.IDbConnection.BeginTransaction" and
    "SqlConnection.IDbConnection.CreateCommand"?


    Anybody can help me to solve my question? thanks a lot.


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       2. Cor Ligthert [MVP]
     1月20日 下午3時10分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "Cor Ligthert [MVP]" <notmyfirstn...@planet.nl> - 查找此作者的帖子 
    日期:Fri, 20 Jan 2006 08:10:00 +0100
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    JinFeng,


    Both of them are removing the connectionstring from the connectionobject.
    They both have nothing to do direct with the ConnectionPool, although you
    should close a connection either by close or dispose to let the
    ConnectionPool do its job.


    Every Interface can be used to get its members (in the implementing
    contract) from the implementing class. Therefore it is an interface. A good
    programmer start the name of his interfaces all with a capital I.


    I hope that this gives an idea


    Cor


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       3. jinfeng_Wang@msn.com
     1月20日 下午5時52分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "jinfeng_W...@msn.com" <jinfeng_W...@msn.com> - 查找此作者的帖子 
    日期:20 Jan 2006 01:52:12 -0800
    當地時間:2006年1月20日(星期五) 下午5時52分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    hello, Cor . thanks for you answer. but it's not what i want.


    please read the following URL and look at the left frame:
    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpre...


    there are two methods in the SQLConnection:
     "Dispose"  and  "SqlConnection.IDisposable.Dispose" Method.


    and in MSDN , the description about the
    "SqlConnection.IDisposable.Dispose" is:  "This member supports the .NET
    Framework infrastructure and is not intended to be used directly from
    your code".
    can you help to tell me, what's the meaning of the above setence? MS
    advice me that i should not call the
    "SqlConnection.IDisposable.Dispose", yeah?


    if there is a client code, like this  (copied from  MSDN, and i have
    modified it):
    public void ReadMyData()
    {
        String      myConnString = "Persist Security Info=False;User
    ID=sa;Initial Catalog=Northwind;Data Source=DTK-S-SVR;User
    ID=sa;Pwd=sa";
       string mySelectQuery = "SELECT OrderID, CustomerID FROM Orders";
       SqlConnection myConnection = new SqlConnection(myConnString);
       SqlCommand myCommand = new SqlCommand(mySelectQuery,myConnection);
       myConnection.Open();
       SqlDataReader myReader;
       myReader = myCommand.ExecuteReader();
       while (myReader.Read())
          {
            Console.WriteLine(myReader.GetInt32(0) + ", " +
    myReader.GetString(1));
         }
        myReader.Close();


         //myConnection.Close();  // old source code.
         IDisposable disposable =myConnection as IDisposable;   // new
    source code.
         disposable.Dispose();   // new source code.


    }


    will it cause some problem when cast the myConnection  to IDisposable
    and call  disposable.Dispose() ?
    Does the "new souce code" have the same effect as the "old source code"
    ??
    if they are, why MS implements the method of "IDisposable.Disp­ose()"
    explicity. I means: there is only the SqlConnection.Dispose() method.

    if there is no problem here, then can you why MS said that "This member
    supports the .NET Framework infrastructure and is not intended to be
    used directly from your code."??
    if there is some problem, then why MS does not make the methods of
    SqlConnection.IDisposable.Disp­­ose() and SqlConnection.Dispose()
    shared the same source code? and why MS tell us that there exists a
    "SqlConnection.IDisposable.Disp­­ose()" method, but warn us not to
    call it??


    in the same, how about the "SqlConnection.ICloneable.Clone ",
    "SqlConnection.IDbConnection.BeginTransaction" and
    "SqlConnection.IDbConnection.CreateCommand"?


    i do not whether you have understand my question for my poor english
    and expression.
    can you help me? anyway, thanks to all of you.


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       4. Cor Ligthert [MVP]
     1月20日 下午6時29分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "Cor Ligthert [MVP]" <notmyfirstn...@planet.nl> - 查找此作者的帖子 
    日期:Fri, 20 Jan 2006 11:29:36 +0100
    當地時間:2006年1月20日(星期五) 下午6時29分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    JinFeng,


    Both Frans and me are not first language English speakers (AFAIK is Frans
    born where the native language is Fries and I where it is Dutch). In my
    opinion should you never excuse you for your English in these newsgroups.
    Almost everybody, no matter how good he can speak a language, will make
    errors in email messages (even in his own). I assume that you are using the
    English version of Visual Studio so that tells enough.


    I thought that the protected dispose is used by component (don't mix this up
    with the rest from what I write about component). If you open a form or a
    component (by the designer), than you see the implementation of IDisposable
    direct. That part is used to do the most of the disposing.


    Nice pages about Idisposable are these new ones


    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpre...


    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpre...


    As I said, be aware that if you use a form or a component the code is
    already in the designer created part.


    However as long discussions has be done in this newsgroup. Disposing and
    Closing have the same effect on the connection pool.


    I hope this gives some information.


    Cor


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       5. Frans Bouma [C# MVP]
     1月20日 下午4時22分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "Frans Bouma [C# MVP]" <perseus.usenetNOS...@xs4all.nl> - 查找此作者的帖子 
    日期:Fri, 20 Jan 2006 00:22:50 -0800
    當地時間:2006年1月20日(星期五) 下午4時22分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    - 隱藏被引用文字 -
    - 顯示引用的文字 -

    jinfeng_W...@msn.com wrote:
    > hi, I have a question about the difference between
    > SqlConnection.IDisposable.Dispose()  and  SqlConnection.Dispose().
    > Both  of them realize the function of releasing the connection to the
    > ConnectionPool?  Do they have the same effection source code?  If they
    > are different, who can tell me the differences? If they are same, why
    > MS gives the SqlConnection.IDisposable.Dispose, but  only
    > SqlConnection.Dispose() method?

    > In the MSDN, there are following description about the
    > SqlConnection.IDisposable.Dispose Method:
    >   "This member supports the .NET Framework infrastructure and is not
    > intended to be used directly from your code."  what's the meaning of
    > it?


    > If the user has called the SqlConnection.IDisposable.Dispose() in the
    > client application, what probem results in?  and if there are some
    > problem becomes, then why did MS give us such a method?


    > in the same, who can tell me the using of
    > "SqlConnection.ICloneable.Clone ",
    > "SqlConnection.IDbConnection.BeginTransaction" and
    > "SqlConnection.IDbConnection.CreateCommand"?


    > Anybody can help me to solve my question? thanks a lot.

     

            what does 'SqlConnection.IDisposable.Dispose' mean? 'IDisposable'
    isn't a property or something of SqlConnection. 'Dispose()' is a method
    in Component, the base class of SqlConnection. SqlConnection overrides
    Dispose(true), which is called from Dispose(), and therefore whatever
    Dispose() you call, it doesnt matter.

                    FB


    --
    ------------------------------------------------------------------------
    Get LLBLGen Pro, productive O/R mapping for .NET: http://www.llblgen.com
    My .NET blog: http://weblogs.asp.net/fbouma
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       6. jinfeng_Wang@msn.com
     1月20日 下午5時55分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "jinfeng_W...@msn.com" <jinfeng_W...@msn.com> - 查找此作者的帖子 
    日期:20 Jan 2006 01:55:46 -0800
    當地時間:2006年1月20日(星期五) 下午5時55分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    FB, i know that 'IDisposable'  is not one property of the
    SQLConnection. please read my answer to Cor.
    'SqlConnection.IDisposable.Dispose'  is copied from MSDN.    :-)
    I think it means that SQLConnection has implemnt the Dispose() method
    of the IDisposable explicity.


    I want to know the difference between the two method of
    SqlConnection.IDisposable.Disp­­ose() and SqlConnection.Dispose().


    Thanks to you!!! thanks!


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       7. Frans Bouma [C# MVP]
     1月21日 下午6時54分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "Frans Bouma [C# MVP]" <perseus.usenetNOS...@xs4all.nl> - 查找此作者的帖子 
    日期:Sat, 21 Jan 2006 02:54:24 -0800
    當地時間:2006年1月21日(星期六) 下午6時54分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    jinfeng_W...@msn.com wrote:
    > FB, i know that 'IDisposable'  is not one property of the
    > SQLConnection. please read my answer to Cor.
    > 'SqlConnection.IDisposable.Dispose'  is copied from MSDN.    :-)
    > I think it means that SQLConnection has implemnt the Dispose() method
    > of the IDisposable explicity.


            I thought that it meant that, but checking SqlConnection in reflector
    I couldn't find IDisposable explicit implementations :D Hence my
    question :)


    > I want to know the difference between the two method of
    > SqlConnection.IDisposable.Disp­­ose() and SqlConnection.Dispose().


            I have no idea.

                    FB


    --
    ------------------------------------------------------------------------
    Get LLBLGen Pro, productive O/R mapping for .NET: http://www.llblgen.com
    My .NET blog: http://weblogs.asp.net/fbouma
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       8. jinfeng_Wang@msn.com
     1月23日 上午9時17分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "jinfeng_W...@msn.com" <jinfeng_W...@msn.com> - 查找此作者的帖子 
    日期:22 Jan 2006 17:17:00 -0800
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    :-)


    copied from Reflector:


    System.Data.SqlClient.SqlConnection.System.Data.IDbConnection.BeginTransact­ion()
    : IDbTransaction
    IDbTransaction IDbConnection.BeginTransaction()
    {
          return this.BeginTransaction();

     

    }


    I think that the disposable is same as here .
    but, but  why MS does such a foolish action :-(

    this folliwing is copied from MSDN  in the
    SqlConnection.IDbConnection.BeginTransaction Method ():
    "This member supports the .NET Framework infrastructure and is not
    intended to be used directly from your code."
    faint to death. ~


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       9. William (Bill) Vaughn
     1月22日 上午2時55分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "William \(Bill\) Vaughn" <billvaRemoveT...@nwlink.com> - 查找此作者的帖子 
    日期:Sat, 21 Jan 2006 10:55:46 -0800
    當地時間:2006年1月22日(星期日) 上午2時55分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    Ok... if you're that curious, use Reflector to walk through the .Net
    Framework code to see what it does. You must have a lot more time on your
    hands that we do.


    Frankly, it does not matter what they do. You don't need to call
    them--either of them. As long as you use Close on the Connection you're
    fine. Sure, you can call Dispose if you want to, but it won't help the
    problem you're trying to solve.


    --
    ____________________________________
    William (Bill) Vaughn
    Author, Mentor, Consultant
    Microsoft MVP
    INETA Speaker
    www.betav.com/blog/billva
    www.betav.com
    Please reply only to the newsgroup so that others can benefit.
    This posting is provided "AS IS" with no warranties, and confers no rights.
    __________________________________


    "Frans Bouma [C# MVP]" <perseus.usenetNOS...@xs4all.nl> wrote in message
    news:xn0ehgc512v14b001@news.microsoft.com...

     

    - 隱藏被引用文字 -
    - 顯示引用的文字 -

    > jinfeng_W...@msn.com wrote:

    >> hi, I have a question about the difference between
    >> SqlConnection.IDisposable.Dispose()  and  SqlConnection.Dispose().
    >> Both  of them realize the function of releasing the connection to the
    >> ConnectionPool?  Do they have the same effection source code?  If they
    >> are different, who can tell me the differences? If they are same, why
    >> MS gives the SqlConnection.IDisposable.Dispose, but  only
    >> SqlConnection.Dispose() method?


    >> In the MSDN, there are following description about the
    >> SqlConnection.IDisposable.Dispose Method:
    >>   "This member supports the .NET Framework infrastructure and is not
    >> intended to be used directly from your code."  what's the meaning of
    >> it?


    >> If the user has called the SqlConnection.IDisposable.Dispose() in the
    >> client application, what probem results in?  and if there are some
    >> problem becomes, then why did MS give us such a method?


    >> in the same, who can tell me the using of
    >> "SqlConnection.ICloneable.Clone ",
    >> "SqlConnection.IDbConnection.BeginTransaction" and
    >> "SqlConnection.IDbConnection.CreateCommand"?


    >> Anybody can help me to solve my question? thanks a lot.


    > what does 'SqlConnection.IDisposable.Dispose' mean? 'IDisposable'
    > isn't a property or something of SqlConnection. 'Dispose()' is a method
    > in Component, the base class of SqlConnection. SqlConnection overrides
    > Dispose(true), which is called from Dispose(), and therefore whatever
    > Dispose() you call, it doesnt matter.


    > FB


    > --
    > ------------------------------------------------------------------------
    > Get LLBLGen Pro, productive O/R mapping for .NET: http://www.llblgen.com
    > My .NET blog: http://weblogs.asp.net/fbouma
    > Microsoft MVP (C#)
    > ------------------------------------------------------------------------

     

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       10. Frans Bouma [C# MVP]
     1月22日 下午6時52分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "Frans Bouma [C# MVP]" <perseus.usenetNOS...@xs4all.nl> - 查找此作者的帖子 
    日期:Sun, 22 Jan 2006 02:52:11 -0800
    當地時間:2006年1月22日(星期日) 下午6時52分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    William (Bill) Vaughn wrote:
    > Ok... if you're that curious, use Reflector to walk through the .Net
    > Framework code to see what it does. You must have a lot more time on
    > your hands that we do.

    > Frankly, it does not matter what they do. You don't need to call
    > them--either of them. As long as you use Close on the Connection
    > you're fine. Sure, you can call Dispose if you want to, but it won't
    > help the problem you're trying to solve.

     

            On a side note: not all ADO.NET providers' connection objects can
    live without a Dispose call. For example the Firebird .NET provider and
    the ODP.NET providers do need a call to Dispose to properly clean up.
    (especially firebird, for cleaning up on the server side!).

            FB, who still couldn't find an explicit IDisposable implementation on
    SqlConnection...


    --
    ------------------------------------------------------------------------
    Get LLBLGen Pro, productive O/R mapping for .NET: http://www.llblgen.com
    My .NET blog: http://weblogs.asp.net/fbouma
    Microsoft MVP (C#)
    ------------------------------------------------------------------------


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    11. jinfeng_Wang@msn.com
     1月23日 上午8時55分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "jinfeng_W...@msn.com" <jinfeng_W...@msn.com> - 查找此作者的帖子 
    日期:22 Jan 2006 16:55:26 -0800
    當地時間:2006年1月23日(星期一) 上午8時55分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    thanks all of you.


    If i was just a client programmer, i think all the information from you
    and MSDN is enough.
    but,...  now i am trying  to develop one new .NET Data Provider for own
    database.
    so i want  to know what has happened in SQL .NET Data Provider.
    it give me a dozens of puzzling interface.
    here is "SqlConnection.IDisposable.Disp­­ose() " and
    "SqlConnection.Dispose()".


    In fact, the SQLConnection is inherited from Compnent, which has
    implemented the IDisposable.
    This is very like the question of "deadly diamond", that one Class
    inherits one Interface from TWO path.
                 IDisposable
                  /                \
                  |                 |
    Component       IDBConnection
                  |                 |
                  \                /
                SQLConnection


    if there is no difference between the
    SqlConnection.IDisposable.Disp­­ose() and SqlConnection.Dispose(),
    then MS has no need to implement the
    SqlConnection.IDisposable.Disp­­ose() explicitly. But, it has done
    it, that means there are some differences between them. What's that?
    MSDN has not told us, it just warn us not to call  the
    SqlConnection.IDisposable.Disp­­ose() in the client program.    :(


    In the  Oracle? Data Provider for .NET,
         public sealed class OracleConnection : Component, IDbConnection,
    ICloneable
    but, OracleConnection has not implement the
    IDbConnection.IDisposable.Disposable() explicity.


    MS, :-(


     14. Frans Bouma [C# MVP]
     1月23日 下午5時54分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "Frans Bouma [C# MVP]" <perseus.usenetNOS...@xs4all.nl> - 查找此作者的帖子 
    日期:Mon, 23 Jan 2006 01:54:56 -0800
    當地時間:2006年1月23日(星期一) 下午5時54分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
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    jinfeng_W...@msn.com wrote:
    > If i was just a client programmer, i think all the information from
    > you and MSDN is enough.
    > but,...  now i am trying  to develop one new .NET Data Provider for
    > own database.


            there are guidelines for that if I'm not mistaken. And I think you
    should relax a little. I work with a lot of ADO.NET providers and none
    of them works the same as the others. So 'what should be done' is what
    you think is the easiest for your users :).

            So, 'Close()' should clean up, and for example connection.Dispose()
    should also dispose commands, parameters etc.


            In general derive a class from DbConnection, and override the specific
    methods to add your own code.

     

    > so i want  to know what has happened in SQL .NET Data Provider.
    > it give me a dozens of puzzling interface.
    > here is "SqlConnection.IDisposable.Disp­­ose() " and
    > "SqlConnection.Dispose()".


            Have you looked into the code with reflector ? I think you should do
    that. :)

     

    - 隱藏被引用文字 -
    - 顯示引用的文字 -

    > In fact, the SQLConnection is inherited from Compnent, which has
    > implemented the IDisposable.
    > This is very like the question of "deadly diamond", that one Class
    > inherits one Interface from TWO path.
    >              IDisposable
    >               /                \
    >               |                 |
    > Component       IDBConnection
    >               |                 |
    >               \                /
    >             SQLConnection

    > if there is no difference between the
    > SqlConnection.IDisposable.Disp­­ose() and SqlConnection.Dispose(),
    > then MS has no need to implement the
    > SqlConnection.IDisposable.Disp­­ose() explicitly. But, it has done
    > it, that means there are some differences between them. What's that?
    > MSDN has not told us, it just warn us not to call  the
    > SqlConnection.IDisposable.Disp­­ose() in the client program.    :(

     

            I looked up the page, and I can only get to that page through the
    index. So I think it's a mistake in the MSDN. As said by others in this
    thread, look at the code through reflector first, then come back here
    with questions.

            Also, inherited interfaces are simply type definitions, not
    implementations. So 1 routine can serve the Dispose() method of
    multiple interfaces.

     

    > In the  Oracle? Data Provider for .NET,
    >      public sealed class OracleConnection : Component, IDbConnection,
    > ICloneable
    > but, OracleConnection has not implement the
    > IDbConnection.IDisposable.Disposable() explicity.

    > MS, :-(

     

            Neither has sqlconnection!!! Look into the code! Just because it's an
    error in the MSDN doesn't mean it's true. Why do you ignore what we
    said and keep believing an errorous page in the msdn?

                    FB


    --
    ------------------------------------------------------------------------
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    My .NET blog: http://weblogs.asp.net/fbouma
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    ------------------------------------------------------------------------


    回復
                 
         

     
       15. jinfeng_Wang@msn.com
     1月23日 下午10時15分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "jinfeng_W...@msn.com" <jinfeng_W...@msn.com> - 查找此作者的帖子 
    日期:23 Jan 2006 06:15:59 -0800
    當地時間:2006年1月23日(星期一) 下午10時15分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
    回復 | 答復作者 | 轉發 | 打印 | 顯示個別帖子 | 顯示原始郵件 | 刪除 | 報告濫用行為 

    :-)


    MSDN Error?
    why the MS make such an Error .
    I have said that  now i am developing one .NET Data Provider for my own
    database, so i should know the everything what have happened in the SQL
    .NET  Data Provider, and learning something from the MS's code.


    now i have realized why MS  give us such a SQL .NET  Data Provider.
    wait a minute, and i  will write it clearly.


    回復
                 
         

     
       16. jinfeng_Wang@msn.com
     1月23日 下午11時10分   顯示選項

    新聞論壇:microsoft.public.dotnet.framework.adonet
    發件人: "jinfeng_W...@msn.com" <jinfeng_W...@msn.com> - 查找此作者的帖子 
    日期:23 Jan 2006 07:10:37 -0800
    當地時間:2006年1月23日(星期一) 下午11時10分 
    主題:Re: the difference between SqlConnection.IDisposable.Disp­ose() and SqlConnection.Dispose()
    回復 | 答復作者 | 轉發 | 打印 | 顯示個別帖子 | 顯示原始郵件 | 刪除 | 報告濫用行為 

    firstly, let's take a look at the following code.


    ///--------------
            public interface myInterface
            {
                    Object getobject();
            }


            public class MyImplement : myInterface
            {
                    public String getobject()    //override.
                    {
                            return "str";
                    }
            }///---------------
    the code above can not be compiled, the compiler will have give us an
    error.  Because the method of MyImplement.getobject() has a wrong
    return type, which is "String", but the method of
    MyInterface.getobject() declared that the return type is "Object:. Here
    the compiler take the "return type" into the "override" compile
    progregess. If MyImplement.getobject() returns "String",  this is not
    the implementation of MyInterface.getobject().


    now let's take a look at another code.
    ///---------------
            public class AnotherImplement
            {
                    public object getobject()
                    {
                            return new object();
                    }


                    public string getobject()  //overload
                    {
                            return new string("");
                    }


            }
    ///---------------
    Here I want to overload the method of "getobject()", but the compiler
    give us an error. Here the compiler DOES NOT take the "return type"
    into the "overload" compile progregess (DIFFERENCE WITH THE OVERRIDE).


    Now let's go back to the IDBConnection and SQLConnection.
    In the interface of IDbConnection, it declares one method of
    "createcomand".
    ///----------
    IDbConnection {
        ....
        IDbCommand CreateCommand();
       ....


    }


    ///----------
    When design the interface of IDBConnection, the designer does not
    what's kind of "Command" will be returned, for example
    "SQLCommand","OracleCommand". so in the IDbConnection.CreateCommand(),
    it only return an interface of "IDbCommand".

    Now we are design the SQLConnection which implements the interface of
    "IDbConnection". if in the SQLConnection, it only write :
    ///---------
      SQLConnection:IDbConnection {
       ....
          SQLCommand  CreateCommand() {
                  ........
          }
       ....
     }
    ///---------
    the compiler will give us an error, because  the "return type" is
    SQLCommand, but not IDbCommand(defined in the IDbConnection). THE
    COMPILER TAKE THE RETURN TYPE INTO THE COMPILE PROGRESS. so we must
    give another definition of "IDbConnection.CreateCommand()".


    if we write the code as follows:
    ///---------
      SQLConnection:IDbConnection {
       ....
          SQLCommand  CreateCommand() {
                  ........
          }


          IDBCommand CreateCommand() {
                  .......
         }
       ....
     }
    ///---------
    The compiler will give us an error. THE COMPILER DOES NOT TAKE THE
    RETURN TYPE INTO THE COMPILE PROGRESS.


    so the SQLConnection have to implement  the
    IDbConncection.CreateCommand explicyly.
    ///--------
       SQLConnection:IDbConnection {
       ....
          SQLCommand  CreateCommand() {
                  ........
          }


          IDBCommand  IDbConnection.CreateCommand() {
                  return this.CreateCommand();
         }
       ....
     }
    ///---------
    The above is the  SQLConnection.


    ============BUT============
    The MSDN told us the "we should call the
    SQLConnection.IDbConnection.CreateCommand() in the client program".
    that is, "we should use the SQLConnection.CreateCommand() in the client
    program."
    THIS will result a foolish result. In the client pogram, we will write
    such a code:
    ///------------
       void doSomething() {
             SqlConnection  conn = new SqlConnection(connectionString);
             SqlCommand command = conn.CreateCommand();
                               //  We MUST have call
    SqlConnection.CreateCommand(),
                               //  not
    SqlConnection.IDbConnection.CreateCommand(),
                               //  which is suggested by MSDN.
       }
    ///------------
    The above client code has violated the programming rule: "PROGRAMMING
    TO INTERFACE".
    According to the MSDN, we can not "PROGRAM TO IDbCommand".
    The action of  "SqlConnection.CreateCommand()"  is difference with  the
    action of"IDbConnection.CreeateCommand()".


    Now if i want to shift to the Oracle database.   All of the client code
    must be modified, because the above is "PROGRAM TO SqlCommand".  :-(
    What a foolish ADO.NET FrameWork.


    I am a java programmer. If i design the SQLConnection, i will give a
    such a implemention:
    ///--------
       SQLConnection:IDbConnection {
       ....
          IDBCommand  CreateCommand() {
                  ........
          }


          SqlCommand  CreateSqlCommand() {
                  ........
         }
       ....
     }
    ///---------
    If the client programmer want to "PROGRAM TO SqlCommand",  he will call
    the method of SqlConnection.CreateSqlCommand().  If the client
    programmer want to "PROGRAMM TO IDbConnection", he will call the
    SqlConnection.CreateCommand(). Now The action of
    "SqlConnection.CreateCommand()"  is same as   the action
    of"IDbConnection.CreeateCommand()".
    Because the client code is "PROGRAM TO IDbCommand", so if the client
    program shifts to Oracle database, the client code will not have to
    modify all the code.


    回復
     

    posted on 2006-01-23 09:35 jinfeng_wang 閱讀(956) 評論(0)  編輯  收藏 所屬分類: .Net
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