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If you need an ActiveRecord method to raise an exception instead of a false value in case of failure, you can add ! to them. This is very important. As some exceptions/failures are hard to catch if you don't use ! on them. I recommended doing this in your development cycle to write all your ActiveRe...

If you need to delete a lot of records quickly, ActiveRecord gives .delete_all method. to be called directly on a model, to delete all records in that table, or a collection. Beware though, as .delete_all does not instantiate any object hence does not provide any callback (before_* and after_destroy...

for loop: arr=(a b c d e f) for i in "${arr[@]}";do echo "$i" done Or for ((i=0;i<${#arr[@]};i++));do echo "${arr[$i]}" done while loop: i=0 while [ $i -lt ${#arr[@]} ];do echo "${arr[$i]}" i=$(expr $i + 1) done Or i=0...

Break multiple loop: arr=(a b c d e f) for i in "${arr[@]}";do echo "$i" for j in "${arr[@]}";do echo "$j" break 2 done done Output: a a Break single loop: arr=(a b c d e f) for i in "${arr[@]}";do e...

It is very rare that you'll ever want to use Select or Activate in your code, but some Excel methods do require a worksheet or workbook to be activated before they'll work as expected. If you're just starting to learn VBA, you'll often be suggested to record your actions using the macro recorder, t...

All published ISO standards are available for sale from the ISO store ( http://www.iso.org ). The working drafts of the C++ standards are publicly available for free though. The different versions of the standard: Upcoming (Sometimes referred as C++20 or C++2a): Current working draft (HTML-vers...

Symbol is a new primitive type in ES6. Symbols are used mainly as property keys, and one of its main characteristics is that they are unique, even if they have the same description. This means they will never have a name clash with any other property key that is a symbol or string. const MY_PROP_KE...

See this Q&A question if you don't know what race conditions are. The following code may be subject to race conditions : article = Article.objects.get(pk=69) article.views_count += 1 article.save() If views_count is equal to 1337, this will result in such query: UPDATE app_article SET vi...

Let's assume that we want to remove 2 upvotes from all the articles of the author with id 51. Doing this only with Python would execute N queries (N being the number of articles in the queryset): for article in Article.objects.filter(author_id=51): article.upvotes -= 2 article.save() ...

Vim supports the use of regular expressions when searching through a file. The character to indicate that you wish to perform a search is /. The simplest search you can perform is the following /if This will search the entire file for all instances of if. However, our search if is actually a r...

// You need a writable database to update a row final SQLiteDatabase database = openHelper.getWritableDatabase(); // Create a ContentValues instance which contains the up to date data for each column // Unlike when inserting data you need to specify the value for the PRIMARY KEY column as well ...

Transactions can be used to make multiple changes to the database atomically. Any normal transaction follows this pattern: // You need a writable database to perform transactions final SQLiteDatabase database = openHelper.getWritableDatabase(); // This call starts a transaction database.beginT...

Orders Table CustomerIdProductIdQuantityPrice12510013220014150021450356700 To check for customers who have ordered both - ProductID 2 and 3, HAVING can be used select customerId from orders where productID in (2,3) group by customerId having count(distinct productID) = 2 Return value:...

Following statement matches all records having FName that starts with a letter from A to F from Employees Table. SELECT * FROM Employees WHERE FName LIKE '[A-F]%'

We can destructure lists of compound objects CL-USER> (loop for (a . b) in '((1 . 2) (3 . 4) (5 . 6)) collect a) (1 3 5) CL-USER> (loop for (a . b) in '((1 . 2) (3 . 4) (5 . 6)) collect b) (2 4 6) CL-USER> (loop for (a b c) in '((1 2 3) (4 5 6) (7 8 9) (10 11 12)) collect b) (2 5 8 11...

package main import ( "fmt" "io/ioutil" ) func main() { files, err := ioutil.ReadDir(".") if err != nil { panic(err) } fmt.Println("Folders in the current directory:") for _, fileInfo := range files { ...

The equivalent to git pull is the command git svn rebase This retrieves all the changes from the SVN repository and applies them on top of your local commits in your current branch. You can also use the command git svn fetch to retrieve the changes from the SVN repository and bring them to ...

The command git svn dcommit will create a SVN revision for each of your local git commits. As with SVN, your local git history must be in sync with the latest changes in the SVN repository, so if the command fails, try performing a git svn rebase first.

Just use your local git repository as a normal git repo, with the normal git commands: git add FILE and git checkout -- FILE To stage/unstage a file git commit To save your changes. Those commits will be local and will not be "pushed" to the SVN repo, just like in a normal git reposito...

git does not recognice the concept of folders, it just works with files and their filepaths. This means git does not track empty folders. SVN, however, does. Using git-svn means that, by default, any change you do involving empty folders with git will not be propagated to SVN. Using the --rmdir fl...