throw 和 throw ex 的差別

看看你是否也寫過以下的 code:

// do something
catch (Exception ex)
// do something
throw ex;
注意 throw ex; 這一行, 它的用意只是把原來的 exception 再次的抛出去, 看起來好像沒什麼問題, 但是其實這種寫法已經改變的原來的 StackTrace, 一般的用法如果想要抛出原來的例外應該是只要寫 throw; 就可以了, 這樣才能保留原有的 StackTrace, 以下範例可以比較清楚的看出這個問題:

    void Main() {
try {
catch (Exception e) {

static void InnerCall() {
throw new Exception();

static void OuterCall() {
try    {
catch (Exception ex) {
throw; // 試著將這行改成 throw ex;

at MyTest.InnerCall() in ...
at MyTest.OuterCall() in ...
at MyTest.Main() in ...

第二種(throw ex;)執行結果為

at MyTest.OuterCall() in ...
at MyTest.Main() in ...


keywords: throw, exception, stacktrace


26G (260億) 相素巴黎美景

LINQ to SQL changes in .NET 4.0

Change list


  • Query plans are reused more often by specifically defining text parameter lengths (when connecting to SQL 2005 or later)
  • Identity cache lookups for primary key with single result now includes query.Where(predicate).Single/SingleOrDefault/First/FirstOrDefault
  • Reduced query execution overhead when DataLoadOptions specified (cache lookup considers DataLoadOptions value equivalency)


  • ITable interface for additional mocking possibilities
  • Contains with enums automatically casts to int or string depending on column type
  • Associations can now specify non-primary-key columns on the other end of the association for updates
  • Support list initialization syntax for queries
  • LinqDataSource now supports inherited entities
  • LinqDataSource support for ASP.NET query extenders added

Query stability

  • Contains now detects self-referencing IQueryable and doesn’t cause a stack overflow
  • Skip(0) no longer prevents eager loading
  • GetCommand operates within SQL Compact transactions
  • Exposing Link on a property/field is detected and reported correctly
  • Compiled queries now correctly detect a change in mapping source and throw
  • String.StartsWith, EndsWith and Contains now correctly handles ~ in the search string (regular & compiled queries)
  • Now detects multiple active result sets (MARS) better
  • Associations are properly created between entities when using eager loading with Table-Valued Functions (TVFs)
  • Queries that contain sub-queries with scalar projections now work better

Update stability

  • SubmitChanges no longer silently consumes transaction rollback exceptions
  • SubmitChanges deals with timestamps in a change conflict scenario properly
  • IsDbGenerated now honors renamed properties that don’t match underlying column name
  • Server-generated columns and SQL replication/triggers now work instead of throwing SQL exception
  • Improved binding support with the MVC model binder

General stability

  • Binary types equate correctly after deserialization
  • EntitySet.ListChanged fired when adding items to an unloaded entity set
  • Dispose our connections upon context disposal (ones passed in are untouched)

Database  control

  • DeleteDatabase no longer fails with case-sensitive database servers

SQL Metal

  • Foreign key property setter now checks all affected associations not just the first
  • Improved error handling when primary key type not supported
  • Now skips stored procedures containing table-valued parameters instead of aborting process
  • Can now be used against connections that use AttachDbFilename syntax
  • No longer crashes when unexpected data types are encountered

LINQ to SQL class designer

  • Now handles a single anonymously named column in SQL result set
  • Improved error message for associations to nullable unique columns
  • No longer fails when using clauses are added to the partial user class
  • VarChar(1) now correctly maps to string and not char
  • Decimal precision and scale are now emitted correctly in the DbType attributes for stored procedures & computed columns
  • Foreign key changes will be picked up when bringing tables back into the designer without a restart
  • Can edit the return value type of unidentified stored procedure types
  • Stored procedure generated classes do not localize the word “Result” in the class name
  • Opening a DBML file no longer causes it to be checked out of source control
  • Changing a FK for a table and re-dragging it to the designer surface will show new FK’s

Code generation (SQL Metal + LINQ to SQL class designer)

  • Stored procedures using original values now compiles when the entity and context namespaces differ
  • Virtual internal now generates correct syntax
  • Mapping attributes are now fully qualified to prevent conflicts with user types
  • KnownTypeAttributes are now emitted for DataContractSerializer with inheritance
  • Delay-loaded foreign keys now have the correct, compilable, code generated
  • Using stored procedures with concurrency no longer gets confused if entities in different namespace to context
  • ForeignKeyReferenceAlreadyHasValueException is now thrown if any association is loaded not just the first

Potentially breaking changes

We worked very hard to avoid breaking changes but of course any potential bug fix is a breaking change if your application was depending on the wrong behavior. The ones I specifically want to call out are:

Skip(0) is no longer a no-op

The special-casing of 0 for Skip to be a no-op was causing some subtle issues such as eager loading to fail and we took the decision to stop special casing this. This means if you had syntax that was invalid for a Skip greater than 0 it will now also be invalid for skip with a 0. This makes more sense and means your app would break on the first page now instead of subtlety breaking on the second page. Fail fast :)

ForeignKeyReferenceAlreadyHasValue exception

If you are getting this exception where you weren’t previously it means you have an underlying foreign key with multiple associations based on it and you are trying to change the underlying foreign key even though we have associations loaded.Best thing to do here is to set the associations themselves and if you can’t do that make sure they aren’t loaded when you want to set the foreign key to avoid inconsistencies.


在 Ubuntu Apache 下架設 Mercurial Server 筆記

  1. 確定安裝好 apache2
    dpkg –l  | grep apache2, 若沒裝則用 sudo apt-get install apache2 安裝
  2. 變身成 root
    $ sudo su
  3. 建立 hg repositories 和 cgi-bin 的存放路徑
    # mkdir /var/hg
    # mkdir /var/hg/cgi-bin
    # mkdir /var/hg/repos
  4. 複製 hgwebdir.cgi 到指定位置, 並更改權限為可執行
    # cp /usr/share/doc/mercurial/examples/hgwebdir.cgi /var/hg/cgi-bin/
    # chmod a+x /var/hg/cgi-bin/hgwebdir.cgi
  5. 建立 /var/hg/cgi-bin/hgweb.config, 寫入以下內容
    /var/hg/repos/ = /var/hg/repos/
  6. 設定 apache
    1. 建立 /etc/apache2/sites-available/hg, 寫入以下資訊, 一行而已
      ScriptAlias /hg "/var/hg/cgi-bin/hgwebdir.cgi"
    2. 啟用該設定
      # a2ensite hg
      # /etc/init.d/apache2 reload
  7. 開啟瀏覽器, 輸入 http://localhost/hg 應該就可以看到 mercurial 的畫面

若要 allow push, 有兩個設定要調整

  1. 確定 apache 有 /var/hg/repos/ 的寫入權限
    # chown –R www-data.www-data /var/hg/repos/
  2. 在 allow push 的 repository 的 .hg 目錄下編輯 hgrc 檔
    push_ssl = false
    allow_push = *

想要更進一步控制權限, 要自行設定 .htaccess!

keywords: mercurial, hg, apache, ubuntu, scm

參考資料: Serving Mercurial using Apache on Ubuntu