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.NET Forum / ASP.NET / General / December 2007Very quick question: What's the difference between Close() and Dispose()?
You know, a SqlConnection object, a SqlCommand object, a SqlDataReader object and many other data access objects, have a Close() method and a Dispose() method. What are their differences? Q1: Should we call both Close() and Dispose() on an object in finally block? If not, then which one should we call and why? Q2: If it makes sense to call both, does the order of calling them matter? Q3: Does the order of calling either Close() or Dispose() or both matter on a SqlConnection object, a SqlCommand object which contains this connection, a SqlDataReader object which is a result of ExecuteReader of this SqlCommand object? Thank you. > What are their differences? Close() closes the connection and returns it to the pool, leaving the object in memory until the garbage collector decides it can destroy it - Dispose() removes it from memory by first calling Close: http://blog.devstone.com/aaron/archive/2004/06/03/184.aspx > Q1: Should we call both Close() and Dispose() on an object in finally > block? No. > If not, then which one should we call and why? Neither - use the "using (.......) {.....}" syntax as described in the above article. > Q2: If it makes sense to call both, does the order of calling them > matter? See above - Dispose calls Close anyway...  SignatureMark Rae ASP.NET MVP http://www.markrae.net > > What are their differences? > > Close() closes the connection and returns it to the pool, leaving the object > in memory until the garbage collector decides it can destroy it - Dispose() > removes it from memory by first calling Close:http://blog.devstone.com/aaron/archive/2004/06/03/184.aspx Thank you. So, I guess if the connection object is gonna be used soon, we better simply call Close() to improve the performance. > > Q1: Should we call both Close() and Dispose() on an object in finally > > block? [quoted text clipped - 5 lines] > Neither - use the "using (.......) {.....}" syntax as described in the above > article. I am aware of the using syntax, but have never seriously used it. I read the article which you referred to above. Very nice, but I am sorta confused by this: <quote> When Close() is called (or Dispose() by virtue of what it does) the connection is not actually closed but is returned to the database connection pool - remember that the connection pool is a collection of SQL Connections, not SqlConnection objects. </quote> Does the author imply (by way of the parenthesized part) that Close() and Dispose makes no difference in terms of returning the connection object to the conection pool? > Thank you. So, I guess if the connection object is gonna be used > soon, we better simply call Close() to improve the performance. No - use the using syntax... > I am aware of the using syntax, but have never seriously used it. I recommend that you do... > I read the article which you referred to above. Very nice, but I am > sorta confused by this: [quoted text clipped - 9 lines] > and Dispose makes no difference in terms of returning the connection > object to the conection pool? Yes. SignatureMark Rae ASP.NET MVP http://www.markrae.net > "gnewsgroup" <gnewsgroup@gmail.com> wrote in message > Neither - use the "using (.......) {.....}" syntax as described in the > above article. This is a bit misleading, as the following are functionally equivalent: using(SqlConnection conn = new SqlConnection()) { // work here } SqlConnection conn = new SqlConnection(); try { conn.Open(); // work here } finally { conn.Dispose(); } The main advantage of using, here, is it is more succinct and therefore faster to code. The advantage of the try ... finally is you have the option of adding a catch without recoding the entire instantiation and use. SignatureGregory A. Beamer MVP, MCP: +I, SE, SD, DBA ************************************************* | Think outside the box! ************************************************* > This is a bit misleading, as the following are functionally equivalent: True. > The main advantage of using, here, is it is more succinct and therefore > faster to code. Indeed, which is why I recommended it... :-) SignatureMark Rae ASP.NET MVP http://www.markrae.net >> This is a bit misleading, as the following are functionally equivalent: > [quoted text clipped - 4 lines] > > Indeed, which is why I recommended it... :-) I find too many cases where I temporary have to add a catch, so I am a creature of habit. ;-) SignatureGregory A. Beamer MVP, MCP: +I, SE, SD, DBA ************************************************* | Think outside the box! ************************************************* > I find too many cases where I temporary have to add a catch, so I am a > creature of habit. ;-) Yeah, me too... I have a DAL that I use for everything, so I don't really need to think about this on a daily basis... SignatureMark Rae ASP.NET MVP http://www.markrae.net > You know, a SqlConnection object, a SqlCommand object, a SqlDataReader > object and many other data access objects, have a Close() method and a [quoted text clipped - 4 lines] > Q1: Should we call both Close() and Dispose() on an object in finally > block? If not, then which one should we call and why? I generally use this pattern: try { conn.Open(); //work here } finally { conn.Dispose(); } The Dispose() will call Close on the object and mark it for cleanup. As connections are returned to the pool, for reuse, they are dead from your perspective, but still have an underlying lifetime. Not a big deal. The other option is using: using(SqlConnection conn = new SqlConnection()) { //work here } This automatically disposes the object for you and makes for very clean syntax. I generally go to the extra work of setting up the try ... finally, however, as it allows me to add a catch. > Q2: If it makes sense to call both, does the order of calling them > matter? It doesn't make sense, but you have to call Close() first if you do. > Q3: Does the order of calling either Close() or Dispose() or both > matter on a SqlConnection object, a SqlCommand object which contains > this connection, a SqlDataReader object which is a result of > ExecuteReader of this SqlCommand object? Try to clean up any objects as they are on the stack. With the command, there really is no clean up as killing connection will solve it. You have the option on the DataReader, if you so desire. SignatureGregory A. Beamer MVP, MCP: +I, SE, SD, DBA ************************************************* | Think outside the box! ************************************************* Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. 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