Tutorial by Examples: ce

db.posts.find().forEach(function(doc){ if(doc.commenters){ var firstCommenter = db.users.findOne({'_id': doc.commenters[0]._id }); db.clients.update({_id: doc._id}, {$set:{'firstPost': firstCommenter }}, false, true); var firstCommenter = db.users.findOne({'_id': do...

Purpose Use the CREATE SEQUENCE statement to create a sequence, which is a database object from which multiple users may generate unique integers. You can use sequences to automatically generate primary key values. When a sequence number is generated, the sequence is incremented, independent of th...

Using Dynamic Arrays in VBA can be quite clunky and time intensive over very large data sets. When storing simple data types in a dynamic array (Strings, Numbers, Booleans etc.), one can avoid the ReDim Preserve statements required of dynamic arrays in VBA by using the Split() function with some cl...

Using generics to define the type in instanceof Consider the following generic class Example declared with the formal parameter <T>: class Example<T> { public boolean isTypeAString(String s) { return s instanceof T; // Compilation error, cannot use T as class type here ...

The following might have undefined behavior due to incorrect pointer alignment: char *memory_block = calloc(sizeof(uint32_t) + 1, 1); uint32_t *intptr = (uint32_t*)(memory_block + 1); /* possible undefined behavior */ uint32_t mvalue = *intptr; The undefined behavior happens as the pointer...

While there are many different control sequences for io:format and io_lib:format, most of the time you'll use only three different ones: ~s, ~p and ~w. ~s The ~s is for strings. It prints strings, binaries and atoms. (Anything else will cause a badarg error.) It doesn't quote or escape anything...

import scala.util.parsing.combinator._ class SimpleParser extends RegexParsers { // Define a grammar rule, turn it into a regex, and apply it the input. def word: Parser[String] = """[A-Z][a-z]+""".r ^^ { _.toString } } object SimpleParser extends SimplePar...

$ git show @{1} # uses reflog for current branch $ git show master@{1} # uses reflog for branch 'master' $ git show HEAD@{1} # uses 'HEAD' reflog A ref, usually a branch or HEAD, followed by the suffix @ with an ordinal specification enclosed in a brace pair (e.g. {1}, {1...

$ git show master@{yesterday} $ git show HEAD@{5 minutes ago} # or HEAD@{5.minutes.ago} A ref followed by the suffix @ with a date specification enclosed in a brace pair (e.g. {yesterday}, {1 month 2 weeks 3 days 1 hour 1 second ago} or {1979-02-26 18:30:00}) specifies the value of the ref at ...

$ git reset --hard HEAD^ # discard last commit $ git rebase --interactive HEAD~5 # rebase last 4 commits A suffix ^ to a revision parameter means the first parent of that commit object. ^<n> means the <n>-th parent (i.e. <rev>^ is equivalent to <rev>^1). A...

It is possible to change Code Folding preference to suit your need. Thus code folding can be set enable/unable for specific constructs (ex: if block, for loop, Sections ...). To change folding preferences, go to Preferences -> Code Folding: Then you can choose which part of the code can be f...

Suppose the following generic interface has been declared: public interface MyGenericInterface<T> { public void foo(T t); } Below are listed the possible ways to implement it. Non-generic class implementation with a specific type Choose a specific type to replace the formal type ...

Drag a gesture recognizer from the object library onto your view. Control drag from the gesture in the Document Outline to your View Controller code in order to make an Outlet and an Action. Notes This example comes from this fuller sample project demonstrating gesture recognizers.

Preconnect The preconnect relationship is similar to dns-prefetch in that it will resolve the DNS. However, it will also make the TCP handshake, and optional TLS negotiation. This is an experimental feature. <link rel="preconnect" href="URL"> DNS-Prefetch Informs bro...

An SKView does not need to fill the whole screen and can share space with other UI controls. You can even have more than one SKView displayed at once if you wish. To create a smaller SKView amongst other controls with Interface Builder, first create a normal ViewController, then drag and drop a new...

When a function returns an object (as opposed to using one that's passed in by the caller), be careful an exception doesn't cause the object to leak. function MakeStrings: TStrings; begin // Create a new object before entering the try-block. Result := TStringList.Create; try // Execu...

A try-finally block may be nested inside a try-except block. try AcquireResources; try UseResource; finally ReleaseResource; end; except on E: EResourceUsageError do begin HandleResourceErrors; end; end; If an exception occurs inside UseResource, then execution...

A try-except block may be nested inside a try-finally block. AcquireResource; try UseResource1; try UseResource2; except on E: EResourceUsageError do begin HandleResourceErrors; end; end; UseResource3; finally ReleaseResource; end; If an EResourceUsageE...

The tr method returns a copy of a string where the characters of the first argument are replaced by the characters of the second argument. "string".tr('r', 'l') # => "stling" To replace only the first occurrence of a pattern with with another expression use the sub method ...

This example describes how to create a SurfaceView with a dedicated drawing thread. This implementation also handles edge cases such as manufacture specific issues as well as starting/stopping the thread to save cpu time. import android.content.Context; import android.graphics.Canvas; import and...