Consider this code:

    &gt;&gt;&gt; x = &quot;google&quot;
    &gt;&gt;&gt; x is &quot;google&quot;
    True
    &gt;&gt;&gt; x = &quot;google.com&quot;
    &gt;&gt;&gt; x is &quot;google.com&quot;
    False
    &gt;&gt;&gt;

Why is it like that?

To make sure the above is correct, I have just tested on Python 2.5.4, 2.6.5, 2.7b2, Python 3.1 on windows and Python 2.7b1 on Linux.

It looks like there is consistency across all of them, so it&#39;s by design. Am I missing something?

I just find it out that from some of my personal domain filtering script failing with that.


Why does the &quot;is&quot; keyword have a different behavior when there is a dot in the string?

Two variables in Python have the same `id`:

    a = 10
    b = 10
    a is b
    &gt;&gt;&gt; True

If I take two `list`s:

    a = [1, 2, 3]
    b = [1, 2, 3]
    a is b
    &gt;&gt;&gt; False

according to [this link][1] Senderle answered that immutable object references have the same id and mutable objects like lists have different ids.

So now according to his answer, tuples should have the same ids - meaning:

    a = (1, 2, 3)
    b = (1, 2, 3)
    a is b
    &gt;&gt;&gt; False

Ideally, as tuples are not mutable, it should return `True`, but it is returning `False`!

What is the explanation?

  [1]: https://stackoverflow.com/questions/27460234/two-variables-with-the-same-list-have-different-ids-why-is-that?answertab=votes#tab-top



Two variables in Python have same id, but not lists or tuples

I don&#39;t work with Microsoft but I&#39;m struggling understanding conceptually how AD, ADFS and LDAP work together.

Let&#39;s say I have an application that needs an Identity Provider. How does AD and LDAP come into play?

My googling hasn&#39;t come up with a clear summary of these concepts for me, but if there is a resource that exists, please do point me towards it.



AD vs ADFS vs LDAP: Explain it like I&#39;m 5

I have installed the Windows Identity Foundation but can&#39;t find the Microsoft.IdentityModel dll. According to the Azure Hands-on-Labs it should just be in Add Reference in VS2010. However it&#39;s not there.

I also looked in c:\Program Files(x86)\Windows Identity Foundation\* and it&#39;s not in there (or the 64 bit program files folder).

Help!

Where is the Microsoft.IdentityModel dll

Two string variables are set to the same value. `s1 == s2` always returns `True`, but `s1 is s2` sometimes returns `False`.

If I open my Python interpreter and do the same `is` comparison, it succeeds:

    &gt;&gt;&gt; s1 = &#39;text&#39;
    &gt;&gt;&gt; s2 = &#39;text&#39;
    &gt;&gt;&gt; s1 is s2
    True

Why is this?

Why does comparing strings using either &#39;==&#39; or &#39;is&#39; sometimes produce a different result?

When a class in Java doesn&#39;t override **hashCode()**, 
printing an instance of this class gives a nice unique number.

The Javadoc of Object says about **hashCode()**:
&gt; *As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects.*

But when the class overrides **hashCode()**, how can I get
its unique number?

How to get the unique ID of an object which overrides hashCode()?

I have an Article entity in my project which has the `ApplicationUser` property named `Author`. How can I get the full object of currently logged `ApplicationUser`? While creating a new article, I have to set the `Author` property in `Article` to the current `ApplicationUser`.

In the old Membership mechanism it was simple, but in the new Identity approach I don&#39;t know how to do this.

I tried to do it this way:

 - Add using statement for Identity extensions: `using Microsoft.AspNet.Identity;`
 - Then I try to get the current user: `ApplicationUser currentUser = db.Users.FirstOrDefault(x =&gt; x.Id == User.Identity.GetUserId());`


But I get the following exception:

&gt; LINQ to Entities does not recognize the method &#39;System.String GetUserId(System.Security.Principal.IIdentity)&#39; method, and this method cannot be translated into a store expression.
  Source=EntityFramework



ASP.NET MVC 5 - Identity. How to get current ApplicationUser

I know `Scope_Identity()`, `Identity()`, `@@Identity`, and `Ident_Current()` all get the value of the identity column, but I would love to know the difference.

Part of the controversy I&#39;m having is what do they mean by scope as applied to these functions above?

I would also love a simple example of different scenarios of using them?

What is the difference between Scope_Identity(), Identity(), @@Identity, and Ident_Current()?

I wanted to clarify if I understand this correctly:

- `==` is a reference comparison, i.e. both objects point to the same memory location
- `.equals()` evaluates to the comparison of values in the objects

What is the difference between == and equals() in Java?

I have a MS SQL 2005 database with a table `Test` with column `ID`. `ID` is an identity column. 

I have rows in this table and all of them have their corresponding ID auto incremented value.

Now I would like to change every ID in this table like this:

   ` ID = ID + 1`

But when I do this I get an error:

 &gt;   Cannot update identity column &#39;ID&#39;.

I&#39;ve tried this:
```
    ALTER TABLE Test NOCHECK CONSTRAINT ALL 
    set identity_insert ID ON
```
But this does not solve the problem.

I need to have identity set to this column, but I need to change values as well from time to time. So my question is how to accomplish this task.

How to change identity column values programmatically?

I have a strange scenario in which the auto identity int column in my SQL Server 2012 database is not incrementing properly.

Say I have a table which uses an int auto identity as a primary key it is sporadically skipping increments, for example:

1,
2,
3,
4,
5,
1004,
1005

This is happening on a random number of tables at very random times, can not replicate it to find any trends.

How is this happening?
Is there a way to make it stop?

SQL Server 2012 column identity increment jumping from 6 to 1000+ on 7th entry

Why does the following behave unexpectedly in Python?

    &gt;&gt;&gt; a = 256
    &gt;&gt;&gt; b = 256
    &gt;&gt;&gt; a is b
    True           # This is an expected result
    &gt;&gt;&gt; a = 257
    &gt;&gt;&gt; b = 257
    &gt;&gt;&gt; a is b
    False          # What happened here? Why is this False?
    &gt;&gt;&gt; 257 is 257
    True           # Yet the literal numbers compare properly

I am using Python 2.5.2. Trying some different versions of Python, it appears that Python 2.3.3 shows the above behaviour between 99 and 100.

Based on the above, I can hypothesize that Python is internally implemented such that &quot;small&quot; integers are stored in a different way than larger integers and the `is` operator can tell the difference. Why the leaky abstraction? What is a better way of comparing two arbitrary objects to see whether they are the same when I don&#39;t know in advance whether they are numbers or not?


&quot;is&quot; operator behaves unexpectedly with integers

 * Need to handle &gt; 1000 but &lt; 10000 new records per day 

 * Cannot use GUID/UUIDs, auto increment numbers etc.

 * Ideally should be 5 or 6 chars long, can be alpha of course

 * Would like to reuse existing, well-known algos, if available

Anything out there ?



Generating human-readable/usable, short but unique IDs

How do I `auto increment` the `primary key` in a `SQL Server` database table? I&#39;ve had a look through the forum but can&#39;t see how to do this.

I&#39;ve looked at the properties but can&#39;t see an option. I saw an answer where you go to the `Identity` specification property and set it to yes and set the `Identity increment` to **1**, but that section is grayed out and I can&#39;t change the *no* to *yes*.

There must be a simple way to do this but I can&#39;t find it.

Auto increment primary key in SQL Server Management Studio 2012

I write websocket chat.
How to generate unique id for user?

now i use this code:

&lt;!-- language: lang-dart --&gt;

    id = new DateTime.now().millisecondsSinceEpoch;

is there any more neat solution?

How to generate unique id in Dart

(Came up with this question in the course of trying to answer [this other one][1])  

Consider the following MS-SQL table, called GroupTable:

&lt;pre&gt;
GroupID
-------
1  
2  
3  
&lt;/pre&gt;

where GroupID is the primary key and is an Identity column.

How do you insert a new row into the table (and hence generate a new ID) **without** using IDENTITY_INSERT ON?

Note that this:  

    INSERT INTO GroupTable() Values ()   
... won&#39;t work.

edit: we&#39;re talking SQL 2005 or SQL 2008 here.


  [1]: https://stackoverflow.com/questions/850017/how-to-manage-groups-in-the-database/850049#850049

How to insert into a table with just one IDENTITY column?

What is the purpose of the `ConcurrencyStamp` column in the `AspNetUsers` table in the new ASP.NET MVC 6 identity?

This is the database schema of the `AspNetUsers` table:

[![enter image description here][1]][1]

It is also there in the `AspNetRoles` table:

[![enter image description here][2]][2]

As I remember it wasn&#39;t there in the ASP.NET MVC 5 identity.

What I&#39;ve noticed so far is that it seems to have GUID values as it is defined with the following code:

    /// &lt;summary&gt;
    /// A random value that must change whenever a user is persisted to the store
    /// &lt;/summary&gt;
    public virtual string ConcurrencyStamp { get; set; } = Guid.NewGuid().ToString();

But this documentation is not sufficient for me to understand in which situations it is used.


  [1]: http://i.stack.imgur.com/Zr319.png
  [2]: http://i.stack.imgur.com/6Lbwx.png

What is the purpose of the ConcurrencyStamp column in the AspNetUsers table in the new ASP.NET MVC 6 identity?

Trying to see if a UIViewController or UIView can identify its Storyboard ID.  So was hoping for:

    UIViewController *aViewController;
    NSString *storyboardID = aViewController.storyboard.id;  //not an actual property

or:

    NSString *storyboardID = [aViewController.storyboard valueForKey:@&quot;storyboardId&quot;];  //also not a working call

But no joy and couldn&#39;t find a similar solution online.  Does anyone know if this is even possible?


Programmatically get a Storyboard ID?

Why do ranges which are initialized with different values compare equal to one another in Python 3?  

When I execute the following commands in my interpreter:

    &gt;&gt;&gt; r1 = range(0)
    &gt;&gt;&gt; r2 = range(2, 2, 2)
    &gt;&gt;&gt; r1 == r2
    True

The result is `True`. Why is this so? Why are two different `range` objects with different parameter values treated as equal?

Why is range(0) == range(2, 2, 2) True in Python 3?

Is it using some kind of byte codes modification to the original classes?

Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version?

I&#39;m having a problem with `hashCode()` and `equals()` methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem.

If Hibernate won&#39;t use `hashCode()`/`equals()` to check the dirty state, I guess I should not use `equals()`/`hashCode()` for the entity object (not value object), but I&#39;m also afraid if the same operator (`==`) is not enough.

So, the questions are:

1. How does Hibernate know if a property of an object is changed?

2. Do you suggest to override the `hashCode()`/`equals()` methods for complicated objects? What if they contains cyclic references?

    And, also, 

3. Would `hashCode()`/`equals()` with only the `id` field be enough?


How does Hibernate detect dirty state of an entity object?

There have been [some][1] [discussions][2] here about JPA entities and which `hashCode()`/`equals()` implementation should be used for JPA entity classes.  Most (if not all) of them depend on Hibernate, but I&#39;d like to discuss them JPA-implementation-neutrally (I am using EclipseLink, by the way).

All possible implementations are having their own **advantages** and **disadvantages** regarding:

- **`hashCode()`/`equals()`** contract **conformity** (immutability) for `List`/`Set` operations
- Whether **identical** objects (e.g. from different sessions, dynamic proxies from lazily-loaded data structures) can be detected
- Whether entities behave correctly in **detached (or non-persisted) state** 
&lt;br&gt;

As far I can see, there are **three options**: 

1. Do not override them; rely on `Object.equals()` and `Object.hashCode()`
   - `hashCode()`/`equals()` work
   - cannot identify identical objects, problems with dynamic proxies
   - no problems with detached entities
2. Override them, based on the **primary key**
   - `hashCode()`/`equals()` are broken
   - correct identity (for all managed entities)
   - problems with detached entities
3. Override them, based on the **Business-Id** (non-primary key fields; what about foreign keys?)
   - `hashCode()`/`equals()` are broken
   - correct identity (for all managed entities)
   - no problems with detached entities

**My questions are:**

1. Did I miss an option and/or pro/con point?&lt;br&gt;
2. What option did you choose and why?

&lt;br&gt;&lt;br&gt;
**UPDATE 1:**

By &quot;`hashCode()`/`equals()` are broken&quot;, I mean that successive `hashCode()` invocations may return differing values, which is (when correctly implemented) not broken in the sense of the `Object` API documentation, but which causes problems when trying to retrieve a changed entity from a `Map`,  `Set` or other hash-based `Collection`.  Consequently, JPA implementations (at least EclipseLink) will not work correctly in some cases.

**UPDATE 2:**

Thank you for your answers -- most of them have remarkable quality.&lt;br&gt;
Unfortunately, I am still unsure which approach will be the best for a real-life application, or how to determine the best approach for my application.  So, I&#39;ll keep the question open and hope for some more discussions and/or opinions.

  [1]: https://stackoverflow.com/questions/4762573/should-embeddable-jpa-class-implement-equals-and-hashcode
  [2]: https://stackoverflow.com/questions/3147166/how-to-implement-equals-and-hashcode-methods-in-baseentity-of-jpa

The JPA hashCode() / equals() dilemma

I need numeric IDs for human readability. How do I get it in Firebase? 


I want numeric ID for keys, e.g. &quot;000000001&quot;, &quot;000000002&quot;,&quot;00000003&quot;,&quot;00000004&quot;.

The reason I need it is because these IDs will become the permanent object ID both online and offline. I want users to be able to browse that object page by just entering URL &quot;/objects/00000001&quot; without efforts. 

I am asking here, because I want to know if this can be done without using `.priority`, sub-properties, etc. I guess `set` method can do it somehow. If it is not possible, just tell me no, I can accept that answer. 

Firebase: how to generate a unique numeric ID for key?

I have seen various methods used when retrieving the value of a primary key identity field after insert.

    declare @t table (
    	id int identity primary key,
    	somecol datetime default getdate()
    )
    insert into @t
    default values
    
    select SCOPE_IDENTITY() --returns 1
    select @@IDENTITY --returns 1
    
Returning a table of identities following insert:

    Create Table #Testing (  
    	id int identity,  
    	somedate datetime default getdate()  
    )  
    insert into #Testing  
    output inserted.*  
    default values   

What method is proper or better? Is the OUTPUT method scope-safe?

The second code snippet was borrowed from [SQL in the Wild][1]


  [1]: http://sqlinthewild.co.za/index.php/2008/12/31/on-the-output-of-a-data-modification/#more-124

@@IDENTITY, SCOPE_IDENTITY(), OUTPUT and other methods of retrieving last identity

I would like to have a nice template for doing this in development. How do I reset an increment identity&#39;s starting value in SQL Server?

How do I reset an increment identity&#39;s starting value in SQL Server

Why does `&quot;hello&quot; is &quot;hello&quot;` produce `True` in Python?

I read the following [here](http://zetcode.com/tutorials/pythontutorial/keywords/):

 &gt; If two string literals are equal, they have been put to same
 memory location. A string is an immutable entity. No harm can
 be done.

So there is one and only one place in memory for every Python string? Sounds pretty strange. What&#39;s going on here?

Python: Why does (&quot;hello&quot; is &quot;hello&quot;) evaluate as True?

In `Ruby 1.9.2` on `Rails 3.0.3`, I&#39;m attempting to test for object equality between two `Friend` (class inherits from `ActiveRecord::Base`) objects.

The objects are equal, but the test fails:

    Failure/Error: Friend.new(name: &#39;Bob&#39;).should eql(Friend.new(name: &#39;Bob&#39;))
  
    expected #&lt;Friend id: nil, event_id: nil, name: &#39;Bob&#39;, created_at: nil, updated_at: nil&gt;
         got #&lt;Friend id: nil, event_id: nil, name: &#39;Bob&#39;, created_at: nil, updated_at: nil&gt;
  
    (compared using eql?)

Just for grins, I also test for object identity, which fails as I&#39;d expect:

    Failure/Error: Friend.new(name: &#39;Bob&#39;).should equal(Friend.new(name: &#39;Bob&#39;))
  
    expected #&lt;Friend:2190028040&gt; =&gt; #&lt;Friend id: nil, event_id: nil, name: &#39;Bob&#39;, created_at: nil, updated_at: nil&gt;
         got #&lt;Friend:2190195380&gt; =&gt; #&lt;Friend id: nil, event_id: nil, name: &#39;Bob&#39;, created_at: nil, updated_at: nil&gt;
  
    Compared using equal?, which compares object identity,
    but expected and actual are not the same object. Use
    &#39;actual.should == expected&#39; if you don&#39;t care about
    object identity in this example.

Can someone explain to me why the first test for object equality fails, and how I can successfully assert those two objects are equal?

How to test for (ActiveRecord) object equality

I need to integrate Asp.Net latest MVC version with an *existing* database which has an additional column `String Address` to table `dbo.AspNetUsers`


I need to create an instance `ApplicationUser` which has property Address.


Any idea how to do it?




All Identity Solutions on Gang of Coders

Total of 27 Identity Solutions

Why does the "is" keyword have a different behavior when there is a dot in the string?