I want to create a default value for an attribute by defining it in ActiveRecord. By default everytime the record is created, I want to have a default value for attribute :status. I tried to do this:  class Task &lt; ActiveRecord::Base   def status=(status)     status = 'P'     write_attribute(:status, status)   end end   But upon creation I still retrieve this error from the database:  ActiveRecord::StatementInvalid: Mysql::Error: Column 'status' cannot be null   Therefore I presume the value was not applied to the attribute.   What would be the elegant way to do this in Rails?  Many thanks.
How can I set default value in ActiveRecord?  I see a post from Pratik that describes an ugly, complicated chunk of code:   class Item &lt; ActiveRecord::Base     def initialize_with_defaults(attrs = nil, &amp;block)     initialize_without_defaults(attrs) do       setter = lambda { |key, value| self.send("#{key.to_s}=", value) unless         !attrs.nil? &amp;&amp; attrs.keys.map(&amp;:to_s).include?(key.to_s) }       setter.call('scheduler_type', 'hotseat')       yield self if block_given?     end   end   alias_method_chain :initialize, :defaults end   I have seen the following examples googling around:    def initialize      super     self.status = ACTIVE unless self.status   end   and    def after_initialize      return unless new_record?     self.status = ACTIVE   end   I've also seen people put it in their migration, but I'd rather see it defined in the model code.  Is there a canonical way to set default value for fields in ActiveRecord model?
Peggy would like to prove to Victor that she knows the discrete logarithm of $y$ based $g$; that is, she knows $x$ such that $y = g^x \bmod p$. One round of the interactive proof protocol consists of the following steps.   Peggy picks random $k \in \mathbb Z/(p−1)\mathbb Z$, computes $t = g^k \bmod p$, and sends $t$ to Victor. Victor picks random $h \in \mathbb Z/(p−1)\mathbb Z$ and sends $h$ to Peggy. Peggy computes $r = (k − hx) \bmod (p − 1)$ and sends $r$ to Victor. Victor verifies that $t = g^r y^h \bmod p$.   The interactive protocol can be converted into a noninteractive zero-knowledge proof by choosing and making public a collision-resistant hash function $H$, and changing the second step of the interactive protocol to the following: Peggy computes $h = H(y, t)$. Then the noninteractive proof consists of $(t, h, r)$, which can be verified as follows: $$h = H(y, t), \qquad t \stackrel?= g^r y^h \bmod p.$$   What is the problem if in the non-interactive proof the hash $h$ depends only on $y$? That is, $h = H(y)$, and the proof consists of $(t, h, r)$, which can be verified as follows: $$h = H(y), \qquad t \stackrel?= g^r y^h \bmod p.$$ What is the problem if in the non-interactive proof the hash $h$ depends only on $t$? That is, $h = H(t)$, and the proof consists of $(t, h, r)$, which can be verified as follows: $$h = H(t), \qquad t \stackrel?= g^r y^h \bmod p.$$ In the LoTR movies (not sure if the books are the same) but when Gollum lost the ring to Bilbo decades ago in The Hobbit, he appeared to look the same and even move the same in The Fellowship of the Ring. Bilbo on the other hand, seemed to have aged very rapidly when he passed the ring to Frodo. When Frodo met up with Bilbo in Rivendell shortly after his quest began, Bilbo appeared much older and even more much slower.  I realize that Gollum had the ring for much longer than Bilbo, but wouldn't him losing the ring have the same effect as it had on Bilbo? How to register domain for 15 years? I have heard that Google trust that website which has long expiry date. that want to know how can I register my domain for a long period. Why isn't Higgs coupling considered a fifth fundamental force? I was chatting with a friend after I saw his photos in Russia (Petersburg). He is a white British dude who has been to many, many, many countries. On the other hand, I am a pure Arab who looks like a typical Middle Easterner or North African, who has also been to many countries, but never to Russia or its neighbors.  Anyway, it seemed like he really liked Russia, so I told him it will be in my list. He told me "you do not belong".  At first, I wasn't sure what he did mean. He started explaining and told me stuff like "you will be hassled for no reason in some parts of the city" and "the police will stop you every few hundred meters asking for money". He made sure to make me believe that's all because I do not belong.  Can someone clarify this? Of course, some of this is hyperbole to help convey the point, but to what extent?  Note: The friend is . If you think the question is wrong, feel free to downvote him ;) Learning Resources on Parsers, Interpreters, and Compilers I've been wanting to play around with writing my own language for a while now (ostensibly for the learning experience) and as such need to be relatively grounded in the construction of Parsers, Interpreters, and Compilers. So:   Does anyone know of any good resources on constructing Parsers, Interpreters, and Compilers?   EDIT: I'm not looking for compiler-compilers/parser-compilers such as Lex, Yacc and Bison... Portrait for phone, landscape for Tablet (Android-Layout) The legacy tray (see the screenshot below) will be removed in GNOME 3.26. I want to wean myself off it before the change arrives in Ubuntu (17.10 or 18.04).    Can I disable the legacy tray in Ubuntu GNOME 17.04? How to Fix Broken Packages? How do I reference photographs with a separate numbering system to figures in latex? I am writing a book, and would like to be able to have the photographs labelled with an independent numbering system to my figures.  In the text I would refer to, for example, figure X and separately to photograph X, so I want them to have different numbering systems, just as equations and figures do.  Is it possible to have a different \begin{figure} environment so that the numbering can be separated? How to prove that $A_5$ has no subgroup of order 30? If I remove the heatsink from my processor temporarily, then later put it back without changing the heatsink or CPU, do I need to reapply thermal paste? Sample size for logistic regression? I want to make a logistic model from my survey data. It is a small survey of four residential colonies in which only 154 respondents were interviewed. My dependent variable is "satisfactory transition to work". I found that, of the 154 respondents, 73 said that they have satisfactorily transitioned to work, while the rest did not. So the dependent variable is binary in nature and I decided to use logistic regression. I have seven independent variables (three continuous and four nominal). One guideline suggest that there should be 10 cases for each predictor / independent variable (Agresti, 2007). Based on this guideline I feel that it is OK to run logistic regression.    Am I right? If not please let me know how to decide the number of independent variables? From :     Importantly, the DDH assumption does not hold in the multiplicative group $\mathbb {Z} _{p}^{*}$, where $p$ is prime. This is because given $g^{a}$ and $g^{b}$, one can efficiently compute the Legendre symbol of $g^{ab}$, giving a successful method to distinguish $g^{ab}$ from a random group element.   The only way I can think of to distinguish $g^c$ from $g^{ab}$ is:    If $\left(\frac{g}{p}\right)=-1$, then $\left(\frac{g^{ab}}{p}\right) = 1$ if and only if $a$ or $b$ is even (which is $3/4$ of the times). So if $\left(\frac{g^c}{p}\right) =-1$, probably $g^c\neq g^{ab}$. Nothing is certain.   How'd do you compute $\left(\frac{g^{ab}}{p}\right)$ given $g^a$ and $g^b$? How do I fix Outlook only showing the first line of every message? I'm experiencing a strange problem with Outlook 2019. When viewing a message it only shows the first line. On an HTML message, it stops at the first close paragraph tag. On a plaintext message, it stops at the first newline character. This is true if viewing a message in the reading pane as well as if double-clicking the message to open in its own window. I have the preview pane set to show 3 lines and it does show more of the message so it seems like Outlook can see more of the message than it's rendering in the reading pane. If I use View Source, the underlying data seems fine and the whole message is there. I've tried the following:  Deleting and re-creating the user's mail profile Uninstalling &amp; re-installing Office Creating a new Windows account &amp; connecting Outlook to a different Exchange account than the one that originally exhibited the problem Checked for Windows updates Checked for Office updates  Any ideas what might be causing this? I feel like I've tried everything obvious &amp; I'm striking out on Google. More options when flagging for migration I think there should be more Stack Exchange networks available when flagging a question to be migrated. For example I'd think that the following question:    ...would be a better fit on unix.stackexchange.com instead of Stack Overflow. But without the option to mark it so, I feel hesitant to mark it. I am trying to use a Bluetooth headset on an Ubuntu PC. I am able to connect phone to pc via BT. I can stream music to PC. But cannot hear call audio. I have checked in Android phone logs, and BT sco link is established. But when making a call or virtual call (play audio through sco path in Android phone) the audio is not audible in PC headset. SCO packets are NOT appearing in btmon logs either. Anyone successfully done this?  version- ubuntu 16.04 Installed- bluez, ofono, pulseaudio pactl sink: Name- bluez_sink.22_22_8E_DE_B9_2B,             Name: alsa_output.pci-0000_00_1b.0.iec958-stereo pactl source: Name-bluez_sink.22_22_8E_DE_B9_2B.monitor               Name: alsa_input.pci-0000_00_1b.0.analog-stereo How are Dementors created/born? This is inspired by some discussions in .  In the Harry Potter universe, how are Dementors born?  Or are they artificially created by some magical means? Since the latest versions (ICS+?) no longer have mass storage, is there any viable alternative to MTP?  The protocol seems inherently broken and the decision to regress to this format seems like a very 'iphone-esque' move (dumb things down, take away power from the users).  There seem to be numerous problems  with files not showing and it seems to me that transferring a file should be simpler than requiring a system reboot - I am unreasonably demanding that way.  I'm aware of tools like Wi-Fi file transfer but often I find myself in areas without wifi, with just my laptop, phone and a usb cable. The other day, for example, I was one a plane, which is an environment decidedly non-conducive to using a wireless system. Probability that no two consecutive heads occur? A fair coin is tossed $10$ times. What is the probability that no two   consecutive tosses are heads?   Possibilities are (dont mind the number of terms):  $H TTTTTTH$, $HTHTHTHTHTHTHT$.  But except for those,  let $y(n)$ be the number of sequences that start with $T$  $T _$, there are two options, $T$ and $H$ so,  $y(n) = y(n - 1) + x(n-1) = y(n - 1) + y(n - 2)$  Let $x(n)$ be the number of sequences that start with $H$,   $H _$ the next option is only $T$ hence,  $x(n) = y(n - 1)$   The total number of sequences $F(n)$ is:  $$F(n) = y(n) + x(n) = 2y(n - 1) + y(n - 2)$$  We are after $F(10)$,  $$F(10) = 2y(9) + y(8)$$  $$F(3) = 2y(2) + y(1) = 1 + 4 = 5$$  $$F(4) = 2y(3) + y(2) = 6 + 2 = 8$$  But I'm not quite sure where this will take me though.