Tutorial by Examples: nd

If index name is known, db.collection.dropIndex('name_of_index'); If index name is not known, db.collection.dropIndex( { 'name_of_field' : -1 } );

db.collection.getIndexes(); Output [ { "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "documentation_db.transactions" }, { "v&quo...

db.collection.createIndex( { "user_id": 1 }, { unique: true } ) enforce uniqueness on the defined index (either single or compound). Building the index will fail if the collection already contains duplicate values; the indexing will fail also with multiple entries missing the field (sin...

This solution uses the ora:tokenize XQuery function that is available from Oracle 11. Sample Data: CREATE TABLE table_name ( id, list ) AS SELECT 1, 'a,b,c,d' FROM DUAL UNION ALL -- Multiple items in the list SELECT 2, 'e' FROM DUAL UNION ALL -- Single item in the list SELECT 3, NULL ...

Useful information The very beginning of the text field text: let startPosition: UITextPosition = textField.beginningOfDocument The very end of the text field text: let endPosition: UITextPosition = textField.endOfDocument The currently selected range: let selectedRange: UITextRange? = tex...

Rust tuples, as in most other languages, are fixed-size lists whose elements can all be of different types. // Tuples in Rust are comma-separated values or types enclosed in parentheses. let _ = ("hello", 42, true); // The type of a tuple value is a type tuple with the same number of el...

This example discusses extending the below type class. trait Show[A] { def show: String } To make a class you control (and is written in Scala) extend the type class, add an implicit to its companion object. Let us show how we can get the Person class from this example to extend Show: class...

Considering the following document : <?xml version='1.0' encoding='UTF-8' ?> <library> <book id='1'>Effective Java</book> <book id='2'>Java Concurrency In Practice</book> </library> One can use the following code to build a DOM tree out of a St...

Method references make excellent self-documenting code, and using method references with Streams makes complicated processes simple to read and understand. Consider the following code: public interface Ordered { default int getOrder(){ return 0; } } public interface Valued&lt...

$ cat ip.txt address range substitution pattern sample Add Sub Mul Div Line number to line matching pattern $ sed -n '2,/pat/p' ip.txt range substitution pattern Line matching pattern to line number $ sed '/pat/,$d' ip.txt address range substitution GNU sed ...

General overview The background-size property enables one to control the scaling of the background-image. It takes up to two values, which determine the scale/size of the resulting image in vertical and and horizontal direction. If the property is missing, its deemed auto in both width and height....

There are a few ways to determine the current shell echo $0 ps -p $$ echo $SHELL

package { import flash.events.TimerEvent; import flash.events.TimerEvent; import flash.utils.Timer; public class RandomTimer extends Timer { public var minimumDelay:Number; public var maximumDelay:Number; private var _count:uint = 0; privat...

If we want to get the x-cordinate of origin of the view, then we need to write like: view.frame.origin.x For width, we need to write: view.frame.size.width But if we add a simple extension to an UIView, we can get all the attributes very simply, like: view.x view.y view.width view.height...

This is very useful when setting indent of your code if condition1 if condition2 # some commands here endif endif move your cursor to the 2nd line, then >>, the code will indent to right. Now you can repeat your action by continue to 3rd line, then hit . twice, the result will be if ...

If you use the paste command from your terminal emulator program, Vim will interpret the stream of characters as if they were typed. That will cause all kind of undesirable effects, particularly bad indendation. To fix that, from command mode: :set paste Then move on to insert mode, with i, for...

$ read -r foo <<EOF > this is a line >EOF $ printf '%s\n' "$foo" this is a line

The AND keyword is used to add more conditions to the query. NameAgeGenderSam18MJohn21MBob22MMary23F SELECT name FROM persons WHERE gender = 'M' AND age > 20; This will return: NameJohnBob using OR keyword SELECT name FROM persons WHERE gender = 'M' OR age < 20; This will return: n...

ggplot(data = diamonds, aes(x = cut, fill =color)) + geom_bar(stat = "count", position = "dodge") it is possible to obtain an horizontal bar chart simply adding coord_flip() aesthetic to the ggplot object: ggplot(data = diamonds, aes(x = cut, fill =color)) + geom_ba...

async.series(tasks, afterTasksCallback) will execute a set of tasks. Each task are executed after another. If a task fails, async stops immediately the execution and jump into the main callback. When tasks are finished successfully, async call the "master" callback with all errors and all...