`:null =&gt; false` tells your database not to accept `NULL` values. 

`:default =&gt; 0` does two things:

 1. Tell your database to use &#39;0&#39; as the default value when `NULL` or nothing is specified in a query.
 2. Tell rails to use &#39;0&#39; as a default value when creating a new object.

Point 2 makes sure that when you save your new object, you actually have a valid value in place.

To answer your question: If you don&#39;t want `NULL` values in your database, set `:null =&gt; false`, otherwise just use the `:default` parameter. Mind you, &#39;0&#39; and `NULL` are not the same things.

Not having `NULL` values might be important for indexing purposes or if you need to provide direct database access to a third party.

I am trying to develop an app on canvas,I am drawing a bitmap on the canvas. After drawing, I am trying to convert into bitmap image.

Can anyone give me a suggestion?

converting a canvas into bitmap image in android

I stumbled upon this open source project [Fake It Easy][1], and I have to admit, it looks very interesting, however I have my doubts, what are the difference between FIE fakes and say Moq Mocks? Is any one better for particular uses?

EDIT:

What is it about this new framework that would make it better than say Moq? 


  [1]: http://code.google.com/p/fakeiteasy/

Are fakes better than Mocks?

If I use a migration to update a database, and I add an integer field like this:

    t.integer :foo :default =&gt; 0, :null =&gt; false

What is the default state of existing and new records in the database?  I hoping the answer is:
- Both will read back foo as 0.

Is default =&gt; 0 necessary, if I have :null =&gt; false?

Just trying to understand the difference between the two...

How do :default =&gt; 0 and :null =&gt; false differ for integer fields in migrations?

If I use a migration to update a database, and I add an integer field like this:
<pre><code class="hljs language-php">t.integer :foo :default => 0, :null => false
</code></pre>
What is the default state of existing and new records in the database? I hoping the answer is:
<ul>
<li>Both will read back foo as 0.</li>
</ul>
Is default => 0 necessary, if I have :null => false?
Just trying to understand the difference between the two...

In my database has column names such as &#39;delete&#39; or &#39;listen-control&#39; and so on. These cannot be changed, so I would like to alias the names so as to avoid problems in my application.

I found [the following code][1] but it is outdated (05 Aug 2005) and doesn&#39;t work with Rails 3:

    module Legacy
      def self.append_features(base)
        super
        base.extend(ClassMethods)
      end
      module ClassMethods
        def alias_column(options)
          options.each do |new_name, old_name|
            self.send(:define_method, new_name) { self.send(old_name) }
            self.send(:define_method, &quot;#{new_name}=&quot;) { |value| self.send(&quot;#{old_name}=&quot;, value) }
          end
        end
      end
    end
    
    ActiveRecord::Base.class_eval do
      include Legacy
    end

How can I alias the column names? Is it possible?

  [1]: http://snippets.dzone.com/posts/show/556

Alias for column names in Rails

I added a table that I thought I was going to need, but now no longer plan on using it. How should I remove that table?

I&#39;ve already run migrations, so the table is in my database. I figure `rails generate migration` should be able to handle this, but I haven&#39;t figured out how yet.

I&#39;ve tried:  

    rails generate migration drop_tablename

but that just generated an empty migration.

What is the &quot;official&quot; way to drop a table in Rails?

Rails DB Migration - How To Drop a Table?

Given the following associations, I need to reference the `Question` that a `Choice` is attached through from the `Choice` model. I have been attempting to use `belongs_to :question, through: :answer` to perform this action.

    class User
      has_many :questions
      has_many :choices
    end

    class Question
      belongs_to :user
      has_many :answers
      has_one :choice, :through =&gt; :answer
    end

    class Answer
      belongs_to :question
    end

    class Choice
      belongs_to :user
      belongs_to :answer
      belongs_to :question, :through =&gt; :answer

      validates_uniqueness_of :answer_id, :scope =&gt; [ :question_id, :user_id ]
    end

I am getting

&gt; NameError uninitialized constant `User::Choice`

when I try to do `current_user.choices`

It works fine, if I don&#39;t include the

    belongs_to :question, :through =&gt; :answer
 
But I want to use that because I want to be able to do the `validates_uniqueness_of`

I am probably overlooking something simple. Any help would be appreciated.

belongs_to through associations

Please suggest me a way to save an image from an URL by Paperclip.

Save image from URL by paperclip

I have looked through the Ruby on Rails guides and I can&#39;t seem to figure out how to prevent someone from deleting a Parent record if it has Children.  For example.  If my database has **CUSTOMERS** and each customer can have multiple **ORDERS**, I want to prevent someone from deleting a customer if it has any orders in the database.  They should only be able to delete a customer if it has no orders.

Is there a way when defining the association between models to enforce this behavior?

How do I prevent deletion of parent if it has child records?

If I have a vararg Java method `foo(Object ...arg)` and I call `foo(null, null)`, I have both `arg[0]` and `arg[1]` as `null`s. But if I call `foo(null)`, `arg` itself is null. Why is this happening? 

How should I call `foo` such that `foo.length == 1 &amp;&amp; foo[0] == null` is `true`?



Calling Java varargs method with single null argument?

This question requires some hypothetical background. Let&#39;s consider an `employee` table that has columns `name`, `date_of_birth`, `title`, `salary`, using MySQL as the RDBMS. Since if any given person has the same name and birth date as another person, they are, by definition, the same person (barring amazing coincidences where we have two people named Abraham Lincoln born on February 12, 1809), we&#39;ll put a unique key on `name` and `date_of_birth` that means &quot;don&#39;t store the same person twice.&quot; Now consider this data:

    id name        date_of_birth title          salary
     1 John Smith  1960-10-02    President      500,000
     2 Jane Doe    1982-05-05    Accountant      80,000
     3 Jim Johnson NULL          Office Manager  40,000
     4 Tim Smith   1899-04-11    Janitor         95,000

If I now try to run the following statement, it should and will fail:

    INSERT INTO employee (name, date_of_birth, title, salary)
    VALUES (&#39;Tim Smith&#39;, &#39;1899-04-11&#39;, &#39;Janitor&#39;, &#39;95,000&#39;)

If I try this one, it will succeed:

    INSERT INTO employee (name, title, salary)
    VALUES (&#39;Jim Johnson&#39;, &#39;Office Manager&#39;, &#39;40,000&#39;)

And now my data will look like this:

    id name        date_of_birth title          salary
     1 John Smith  1960-10-02    President      500,000
     2 Jane Doe    1982-05-05    Accountant      80,000
     3 Jim Johnson NULL          Office Manager  40,000
     4 Tim Smith   1899-04-11    Janitor         95,000
     5 Jim Johnson NULL          Office Manager  40,000

This is not what I want but I can&#39;t say I entirely disagree with what happened. If we talk in terms of mathematical sets,

    {&#39;Tim Smith&#39;, &#39;1899-04-11&#39;} = {&#39;Tim Smith&#39;, &#39;1899-04-11&#39;} &lt;-- TRUE
    {&#39;Tim Smith&#39;, &#39;1899-04-11&#39;} = {&#39;Jane Doe&#39;, &#39;1982-05-05&#39;} &lt;-- FALSE
    {&#39;Tim Smith&#39;, &#39;1899-04-11&#39;} = {&#39;Jim Johnson&#39;, NULL} &lt;-- UNKNOWN
    {&#39;Jim Johnson&#39;, NULL} = {&#39;Jim Johnson&#39;, NULL} &lt;-- UNKNOWN

My guess is that MySQL says, &quot;Since I don&#39;t *know* that Jim Johnson with a `NULL` birth date isn&#39;t already in this table, I&#39;ll add him.&quot;

My question is: **How can I prevent duplicates even though `date_of_birth` is not always known?** The best I&#39;ve come up with so far is to move `date_of_birth` to a different table. The problem with that, however, is that I might end up with, say, two cashiers with the same name, title and salary, different birth dates and no way to store them both without having duplicates.

Unique key with NULLs

How do I verify the existence of an object in JavaScript?

The following works:

    if (!null)
       alert(&quot;GOT HERE&quot;);

But this throws an Error:

    if (!maybeObject)
       alert(&quot;GOT HERE&quot;);

**The Error:** 
&gt;`maybeObject` is not defined.



Check if object exists in JavaScript

The statement is

    SELECT * FROM tableA WHERE x = ?

and the parameter is inserted via java.sql.PreparedStatement &#39;stmt&#39;

    stmt.setString(1, y); // y may be null

If `y` is null, the statement returns no rows in every case because `x = null` is always false (should be `x IS NULL`).
One solution would be

    SELECT * FROM tableA WHERE x = ? OR (x IS NULL AND ? IS NULL)

But then i have to set the same parameter twice. Is there a better solution?

Thanks!

How to deal with (maybe) null values in a PreparedStatement?

&gt; **Possible Duplicate:**  
&gt; [How do I check for nulls in an ‘==’ operator overload without infinite recursion?](https://stackoverflow.com/questions/73713/how-do-i-check-for-nulls-in-an-operator-overload-without-infinite-recursion)  

&lt;!-- End of automatically inserted text --&gt;

There is probably an easy answer to this...but it seems to be eluding me.  Here is a simplified example:

    public class Person
    {
       public string SocialSecurityNumber;
       public string FirstName;
       public string LastName;
    }


Let&#39;s say that for this particular application, it is valid to say that if the social security numbers match, and both names match, then we are referring to the same &quot;person&quot;.

    public override bool Equals(object Obj)
    {
        Person other = (Person)Obj;
        return (this.SocialSecurityNumber == other.SocialSecurityNumber &amp;&amp;
            this.FirstName == other.FirstName &amp;&amp;
            this.LastName == other.LastName);
    }

To keep things consistent, we override the == and != operators, too, for the developers on the team who don&#39;t use the `.Equals` method.

    public static bool operator !=(Person person1, Person person2)
    {
        return ! person1.Equals(person2);
    }
    
    public static bool operator ==(Person person1, Person person2)
    {
        return person1.Equals(person2);
    }


Fine and dandy, right?

However, what happens when a Person object is `null`?

You can&#39;t write:

    if (person == null)
    {
        //fail!
    }

Since this will cause the == operator override to run, and the code will fail on the:

    person.Equals()

method call, since you can&#39;t call a method on a null instance.


On the other hand, you can&#39;t explicitly check for this condition inside the == override, since it would cause an infinite recursion (and a Stack Overflow [dot com])

    public static bool operator ==(Person person1, Person person2)
    {
        if (person1 == null)
        {
             //any code here never gets executed!  We first die a slow painful death.
        }
        return person1.Equals(person2);
    }


So, how do you override the == and != operators for value equality and still account for null objects?

I hope that the answer is not painfully simple. :-)

Overriding == operator. How to compare to null?

I have a web application using sqlalchemy (within Pylons). I need to effiently change the schema to be able to change the production version at least on a daily basis, maybe more, without losing the data.

I have played a little bit with sqlalchemy-migrate over the week-end and I would say that it gave me a bad impression. First **I think it cannot help with migration between two databases engines**; that&#39;s something that could probably be done with sqlalchemy alone. 
Second the docs do not seem up to date. I had to change some command-line options, like giving the repository path at each command, this could be a bug of migrate. 

But the worst thing it the &quot;manage.py **test**&quot; command. Not only it actually **modifies the database** (this point is clearly indicated in the documentation so I can&#39;t blame migrate) but my first migration script just made plain stupid schema migration, leaving the upgraded-downgraded db with a **different schema than the original**. But the &quot;manage.py test&quot; just answered something like

     success !

That is, it did not even check if the schema was left in a coherent state. 
So **is it worth using migrate?** Is there any advantage compared to the Do It Yourself method associated with good practices [as proposed by S.Lott][1] ?
Are there alternatives to sqlalchemy-migrate actually simplifying the migration process or am I just trying to use migrate with a bad a *priori* (then please show me why is&#39;t clearly superior to creating CSV columns as proposed in the link above)?

Many Thanks!


  [1]: https://stackoverflow.com/questions/4165452/how-to-efficiently-manage-frequent-schema-changes-using-sqlalchemy/4165496#4165496

Is it worth using sqlalchemy-migrate ?

How do I describe an enumeration column in a Rails 3 migration?

How do I do a `script/generate migration` to create a join table for a `has_and_belongs_to_many` relationship?

The application runs on Rails 2.3.2, but I also have Rails 3.0.3 installed.

Rails migration for has_and_belongs_to_many join table

I am working with a rather large app written in **JSF 1.2**.
JSF 1.2 is around 6 years old now. I need to upgrade to JSF 2.0. How painful will this be? I noticed that some attributes in custom tags have been changed etc. 

Migrating from JSF 1.2 to JSF 2.0

I am designing a small C# application and there is a web browser in it. I currently have all of my defaults on my computer say google chrome is my default browser, yet when I click a link in my application to open in a new window, it opens internet explorer. Is there any way to make these links open in the default browser instead? Or is there something wrong on my computer?

My problem is that I have a webbrowser in the application, so say you go to google and type in &quot;stack overflow&quot; and right click the first link and click &quot;Open in new window&quot; it opens in IE instead of Chrome. Is this something I have coded improperly, or is there a setting not correct on my computer

===EDIT===

This is really annoying. I am already aware that the browser is IE, but I had it working fine before. When I clicked a link it opened in chrome. I was using sharp develop to make the application at that time because I could not get c# express to start up. I did a fresh windows install and since I wasn&#39;t too far along in my application, I decided to start over, and now I am having this problem. That is why I am not sure if it is my computer or not. Why would IE start up the whole browser when a link is clicked rather than simply opening the new link in the default browser?

How to open in default browser in C#

In one of my first code reviews (a while back), I was told that it&#39;s good practice to include a default clause in all switch statements.  I recently remembered this advice but can&#39;t remember what the justification was.  It sounds fairly odd to me now.

1. Is there a sensible reason for always including a default statement?

2. Is this language dependent?  I don&#39;t remember what language I was using at the time - maybe this applies to some languages and not to others?

Should switch statements always contain a default clause?

While there might be valid cases where such method overloadings could become ambiguous, why does the compiler disallow code which is neither ambiguous at compile time nor at run time?

Example:

    // This fails:
    def foo(a: String)(b: Int = 42) = a + b
    def foo(a: Int)   (b: Int = 42) = a + b

    // This fails, too. Even if there is no position in the argument list,
    // where the types are the same.
    def foo(a: Int)   (b: Int = 42) = a + b
    def foo(a: String)(b: String = &quot;Foo&quot;) = a + b

    // This is OK:
    def foo(a: String)(b: Int) = a + b
    def foo(a: Int)   (b: Int = 42) = a + b    

    // Even this is OK.
    def foo(a: Int)(b: Int) = a + b
    def foo(a: Int)(b: String = &quot;Foo&quot;) = a + b

    val bar = foo(42)_ // This complains obviously ...

Are there any reasons why these restrictions can&#39;t be loosened a bit?

Especially when converting heavily overloaded Java code to Scala default arguments are a very important and it isn&#39;t nice to find out after replacing plenty of Java methods by one Scala methods that the spec/compiler imposes arbitrary restrictions.

Why does the Scala compiler disallow overloaded methods with default arguments?

Normally, default is not necessary in a switch statement. However, in the following situation the code successfully compiles only when I uncomment the default statement. Can anybody explain why?

	public enum XYZ {A,B};
	public static String testSwitch(XYZ xyz)
	{
		switch(xyz)
		{
		case A:
			return &quot;A&quot;;
		case B:
		//default:
			return &quot;B&quot;;
		}
	}


Why is default required for a switch on an enum?

What command we have to execute (from Java, but that should not matter) on Linux (different common distributions) to open a given URL in the default browser?

Content Type	Original Author	Original Content on Stackoverflow
Question	cmaughan	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Ariejan	View Answer on Stackoverflow

How do :default => 0 and :null => false differ for integer fields in migrations?

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Are fakes better than Mocks?

converting a canvas into bitmap image in android

Attributions