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• ValueConverter not being invoked in DataTemplate binding

  - by unforgiven3

  I have a ComboBox that uses a DataTemplate. The DataTemplate contains a binding which uses an IValueConverter to convert an enumerated value into a string. The problem is that the value converter is never invoked. This is my XAML: <ComboBox ItemsSource="{Binding Path=StatusChoices, Mode=OneWay}"> <ComboBox.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding Converter={StaticResource StatusToTextConverter}}"/> </DataTemplate> </ComboBox.ItemTemplate> </ComboBox> Is my binding not correct? I thought this is how one implicitly binds to the value a DataTemplate is presenting. Am I wrong?

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• How to figure out which key was pressed on a BlackBerry

  - by Skrud

  What I want: To know when the user has pressed the button that has the number '2' on it, for example. I don't care whether "Alt" or "Shift" has been pressed. The user has pressed a button, and I want to evaluate whether this button has '2' printed on it. Naturally, if I switch devices this key will change. On a Bold 9700/9500 this is the 'E' key. On a Pearl, this is the 'T'/'Y' key. I've managed to get this working in what appears to be a roundabout way, by looking up the keycode of the '2' character with the ALT button enabled and using Keypad.key() to get the actual button: // figure out which key the '2' is on: final int BUTTON_2_KEY = Keypad.key(KeypadUtil.getKeyCode('2', KeypadListener.STATUS_ALT, KeypadUtil.MODE_EN_LOCALE)); protected boolean keyDown(int keycode, int time) { int key = Keypad.key(keycode); if ( key == BUTTON_2_KEY ) { // do something return true; } return super.keyDown(keycode,time); } I can't help but wonder if there is a better way to do this. I've looked at the constants defined in KeypadListener and Keypad but I can't find any constants mapped to the actual buttons on the device. Would any more experienced BlackBerry devs care to lend a helping hand? Thanks!

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• How do you assign commands to keys in Terminal?

  - by NES

  Is there a solution to assign special key combinations to words in terminal use. For example the less command is very usefull and i use i a lot to pipe the output of another process through it. The idea would be to set up special key combinations that are only active in terminal use assigned to write different commands? So pressing CTRL + l in terminal window could write | less or CTRL + G could stand for | grep Note: i just mean adding the letters to commandline not execute the finally. A similar way what's tabcompletion but more specific.

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• Learn Fundamentals of Silverlight 4 Data Binding

  - by Eric J.

  I'm just starting to work with Silverlight (no WPF experience either) and am having a difficult time finding a source that provides a full explanation of Data Binding. There is absolutely no lack of tutorials (starting with the ones on Silverlight.net or Scott Gu's blogs), but everything I have found is "by example". Is there a resource that explains how data binding works in Silverlight, from a Fundamental/Conceptual perspective, and provides end-to-end coverage of data binding features? The desire for a more fundamental source of information is driven by a number of questions that came up this afternoon in reviewing tutorials and writing sample apps, such as: Why can't I bind the value of a slider like this?: Value="{Binding=Age, Mode=TwoWay}" where Age refers to an int property in the object data context I bind in code-behind (the Visual Studio error message is Expected '[]'. How do I use the DataContext property in VS 2010? What's a Path, Relative Source, Static Source, ...?

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• Integrated message queue binding does not work with Message class

  - by user80855

  I am trying to use the integrated message queue binding with the class Message. void HandleMessage(Message msg) However the binding does not work, this works with other bindings. Is this a limitation on this specific binding?

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• android: consume key press, bypassing framework processing

  - by user360024

  What I want android to do: when user presses a single key, have the view respond, but do so without opening a text area and displaying the character associated with the key that was pressed, and without requiring that the Enter key be pressed, and without requiring that the user press Esc to make the text area go away. For example, when user presses "u" (and doesn't press Enter), that means "undo the last action", so the controller and model immediately undo the last action, then the view does an invalidate() and user sees that their last action has been undone. In other words the "u" key press should be silently processed, such that the only visual result is that user's last action has been undone. I've implemented OnKeyListener and provided an onKey() method: the class: public class MyGameView extends View implements OnKeyListener{ in the constructor: //2010jun06, phj: With onKey(), helps let this View consume key presses // before the framework gets a chance to consume the key press. setOnKeyListener((View.OnKeyListener)this); the onKey() method: public boolean onKey(View v, int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_R) { Log.d("BWA", "In onKey received keycode associated with R."); } return true; // meaning the event (key press) has been consumed, so // the framework should not handle this event. } but when user presses "u" key on the emulator keypad, a textarea is opened at the bottom of the screen, the "u" charater is displayed there, and the onKey() method doesn't execute until user presses the Enter key. Is there a way to make android do what I want? Thanks,

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• Getting value of "System.Windows.Controls.TextBlock" when binding to Silverlight ComboBox

  - by sipwiz

  I'm attempting to use a Silverlight ComboBox with a static list of elements in a very simple binding scenario. The problem is the selected item is not returning me the Text of the TextBlock within the ComboBox and is instead returning "System.Windows.Controls.TextBlock". My XAML is: <ComboBox SelectedValue="{Binding Country, Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnExceptions=True}"> <TextBlock FontSize="11" Text="Afghanistan" /> <TextBlock FontSize="11" Text="Albania" /> <TextBlock FontSize="11" Text="Algeria" /> </ComboBox> In my C# file I'm binding to the ComboBox using: Customer customer = new Customer() { Country = "Albania" }; DataContext = customer; The binding does not result in Albania as the selected country and updating the ComboBox choice results in the Country being set to "System.Windows.Controls.TextBlock". I've tried fiddling around with DisplayMemberPath and SelectedValuePath but haven't found the answer. I suspect it's something really simple I'm missing.

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• Stored procedures vs. parameter binding

  - by Gagan

  I am using SQL server and ODBC in visual c++ for writing to the database. Currently i am using parameter binding in SQL queries ( as i fill the database with only 5 - 6 queries and same is true for retrieving data). I dont know much about stored procedures and I am wondering how much if any performance increase stored procedures have over parameter binding as in parameter binding we prepare the query only once and just execute it later in the program for diferent set of values of variables.

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• Tag property null when data binding

  - by rotary_engine

  Can anyone see what is wrong with this? The Tag property is returning null however the Binding for Id property is definately returning an int value. <ListBox ItemsSource="{Binding ElementName=myDomainDataSource, Path=Data}"> <ListBox.ItemTemplate> <DataTemplate> <StackPanel Orientation="Horizontal"> <TextBlock Text="{Binding Path=Id, Mode=OneWay}" /> <HyperlinkButton Content="Edit" Tag="{Binding ElementName=Id, Mode=OneWay}" Click="Edit_Click" /> </StackPanel> </DataTemplate> </ListBox.ItemTemplate> </ListBox> and then... private void Edit_Click(object sender, RoutedEventArgs e) { ContentControl c = sender as ContentControl; // exception - c.Tag is null int id = (int)c.Tag; } The Id property is showing a value on the UI, but doesn't seem to be getting stored in the buttons Tag property.

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• Silverlight: Why doesn't this binding expression work?

  - by Rosarch

  I'm having difficulty with a binding expression in Silverlight 3 for the Windows Phone 7. <Grid x:Name="LayoutRoot" Background="Transparent"> <controls:Pivot ItemsSource="{Binding SectionViewModels}"> <!-- ... --> <controls:Pivot.ItemTemplate> <DataTemplate> <Grid> <!-- this is the troublesome binding --> <TextBlock Style="{StaticResource disabledText}" Visibility="{Binding ElementName=LayoutRoot, Path=DataContext.NoStoryContent}"> Do you have a network connection? </TextBlock> <!-- ... --> The style, in app.xaml: <Style x:Key="disabledText" TargetType="TextBlock"> <Setter Property="Foreground" Value="{StaticResource PhoneDisabledBrush}" /> <Setter Property="TextWrapping" Value="Wrap" /> <Setter Property="FontSize" Value="{StaticResource PhoneFontSizeLarge}" /> </Style> Code behind: public Visibility NoStoryContent { get { // trivial return value for debugging // no breakpoint here is hit return Visibility.Collapsed; } } public Sections() { InitializeComponent(); LayoutRoot.DataContext = this; } What am I doing wrong here? I suspect I have a mistake in the binding expression, but I'm not sure where.

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• WPF Binding to a viewmodel

  - by user832747

  I'm simply binding a WPF DataGridTextColumn with a binding to my grid rows. <DataGridTextColumn Header="Name" Binding="{Binding Name}" /> I've bound to my row view models. The Name property has a PRIVATE setter. public string Name { get { return _name; } private set { _name = value; } } Shouldn't the datagrid prevent me from accessing the private setter? The grid allows me to access it. I swear it never used to, unless I'm forgetting something?

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• OpenSSH does not accept public key?

  - by Bob

  I've been trying to solve this for a while, but I'm admittedly quite stumped. I just started up a new server and was setting up OpenSSH to use key-based SSH logins, but I've run into quite a dilemma. All the guides are relatively similar, and I was following them closely (despite having done this once before). I triple checked my work to see if I would notice some obvious screw up - but nothing is apparent. As far as I can tell, I haven't done anything wrong (and I've checked very closely). If it's any help, on my end I'm using Cygwin and the server is running Ubuntu 12.04.1 LTS. Anyways, here is the output (I've removed/censored some parts for privacy (primarily anything with my name, website, or its IP address), but I can assure you that nothing is wrong there): $ ssh user@host -v OpenSSH_5.9p1, OpenSSL 0.9.8r 8 Feb 2011 debug1: Connecting to host [ipaddress] port 22. debug1: Connection established. debug1: identity file /home/user/.ssh/id_rsa type 1 debug1: identity file /home/user/.ssh/id_rsa-cert type -1 debug1: identity file /home/user/.ssh/id_dsa type -1 debug1: identity file /home/user/.ssh/id_dsa-cert type -1 debug1: identity file /home/user/.ssh/id_ecdsa type -1 debug1: identity file /home/user/.ssh/id_ecdsa-cert type -1 debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1 debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1 pat OpenSSH* debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_5.9 debug1: SSH2_MSG_KEXINIT sent debug1: SSH2_MSG_KEXINIT received debug1: kex: server->client aes128-ctr hmac-md5 none debug1: kex: client->server aes128-ctr hmac-md5 none debug1: sending SSH2_MSG_KEX_ECDH_INIT debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug1: Server host key: ECDSA 24:68:c3:d8:13:f8:61:94:f2:95:34:d1:e2:6d:e7:d7 debug1: Host 'host' is known and matches the ECDSA host key. debug1: Found key in /home/user/.ssh/known_hosts:2 debug1: ssh_ecdsa_verify: signature correct debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: SSH2_MSG_NEWKEYS received debug1: Roaming not allowed by server debug1: SSH2_MSG_SERVICE_REQUEST sent debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey debug1: Next authentication method: publickey debug1: Offering RSA public key: /home/user/.ssh/id_rsa debug1: Authentications that can continue: publickey debug1: Trying private key: /home/user/.ssh/id_dsa debug1: Trying private key: /home/user/.ssh/id_ecdsa debug1: No more authentication methods to try. Permission denied (publickey). What can I do to resolve my problem?

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• WPF: Is it possible to add or modify bindings via styles or something similar?

  - by Eamon Nerbonne

  I'm still learning the WPF ropes, so if the following question is trivial or my approach wrong-headed, please do speak up... I'm trying to reduce boilerplate and it sounds like styles are a common way to do so. In particular: I've got a bunch of fairly mundane data-entry fields. The controls for these fields have various properties I'd like to set based on the target of the binding - pretty normal stuff. However, I'd also like to set properties of the binding itself in the style to avoid repetitiveness. For example: <TextBox Style="{StaticResource myStyle}"> <TextBox.Text> <Binding Path="..." Source="..." ValidatesOnDataErrors="True" ValidatesOnExceptions="True" UpdateSourceTrigger="PropertyChanged"> </Binding> </TextBox.Text> </TextBox> Now, is there any way to use styling - or some other technique to write the previous example somewhat like this: <TextBox Style="{StaticResource myStyle}" Text="{Binding Source=... Path=...}/> That is, is there any way to set all bindings that match a particular selection (here, on controls with the myStyle style) to validate data and to use a particular update trigger? Is it possible to template or style bindings themselves? Alternatively, is it possible to add the binding in the style itself? Clearly, the second syntax is much, much shorter and more readable, and I'd love to be able to get rid of other similar boilerplate to keep my UI code comprehensible to myself :-).

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• wpf error template - red box still visible on collapse of an expander

  - by Andy Clarke

  Hi, I'm doing some validation on the DataSource of TextBox that's within an Expander and have found that once a validation error has been triggered, if I collapse the Expander, the red box stays where the TextBox would have been. <Expander Header="Blah Blah Blah"> <TextBox Name="TextBox" Validation.ErrorTemplate="{DynamicResource TextBoxErrorTemplate}" Text="{Binding Path=Blah, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" /> </Expander> I've tried to get round this by binding the visibility of the Error Template to the Expander, however I think there's something wrong with the binding. <local:NotVisibleConverter x:Key="NotVisibleConverter" /> <ControlTemplate x:Key="TextBoxErrorTemplate"> <DockPanel> <Border BorderBrush="Red" BorderThickness="2" Visibility="{Binding Path=IsExpanded, Converter={StaticResource NotVisibleConverter}, RelativeSource={RelativeSource AncestorType=Expander}}" > <AdornedElementPlaceholder Name="MyAdorner" /> </Border> </DockPanel> <ControlTemplate.Triggers> <Trigger Property="Validation.HasError" Value="true"> <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> I guess I've gone wrong with my binding, can someone put me back on track please? Alternatively does anyone know another solution to the ErrorTemplate still being visible on the collapse of an Expander?

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• DataGrid calculate difference between values in two databound cells

  - by justMe

  Hello! In my small application I have a DataGrid (see screenshot) that's bound to a list of Measurement objects. A Measurement is just a data container with two properties: Date and CounterGas (float). Each Measurement object represents my gas consumption at a specific date. The list of measurements is bound to the DataGrid as follows: <DataGrid ItemsSource="{Binding Path=Measurements}" AutoGenerateColumns="False"> <DataGrid.Columns> <DataGridTextColumn Header="Date" Binding="{Binding Path=Date, StringFormat={}{0:dd.MM.yyyy}}" /> <DataGridTextColumn Header="Counter Gas" Binding="{Binding Path=ValueGas, StringFormat={}{0:F3}}" /> </DataGrid.Columns> </DataGrid> Well, and now my question :) I'd like to have another column right next to the column "Counter Gas" which shows the difference between the actual counter value and the last counter value. E.g. this additional column should calculate the difference between the value of of Feb. 13th and Feb. 6th = 199.789 - 187.115 = 15.674 What is the best way to achieve this? I'd like to avoid any calculation in the Measurement class which should just hold the data. I'd rather more like the DataGrid to handle the calculation. So is there a way to add another column that just calculates the difference between to values? Maybe using some kind of converter and extreme binding? ;D P.S.: Maybe someone with a better reputation could embed the screenshot. Thanks :)

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• Query for model by key

  - by Jason Hall

  What I'm trying to do is query the datastore for a model where the key is not the key of an object I already have. Here's some code: class User(db.Model): partner = db.SelfReferenceProperty() def text_message(self, msg): user = User.get_or_insert(msg.sender) if not user.partner: # user doesn't have a partner, find them one # BUG: this line returns 'user' himself... :( other = db.Query(User).filter('partner =', None).get() if other: # connect users else: # no one to connect to! The idea is to find another User who doesn't have a partner, that isn't the User we already know. I've tried filter('key !=, user.key()), filter('__key__ !=, user.key()) and a couple others, and nothing returns another User who doesn't have a partner. filter('foo !=, user.key()) also returns nothing, for the record.

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• foreign key and index issue

  - by George2

  Hello everyone, I am using SQL Server 2008 Enterprise. I have a table and one of its column is referring to another column in another table (in the same database) as foreign key, here is the related SQL statement, in more details, column [AnotherID] in table [Foo] refers to another table [Goo]'s column [GID] as foreign key. [GID] is primary key and clustered index on table [Goo]. My question is, in this way, if I do not create index on [AnotherID] column on [Foo] explicitly, will there be an index created automatically for [AnotherID] column on [Foo] -- because its foreign key reference column [GID] on table [Goo] already has primary clustered key index? CREATE TABLE [dbo].[Foo]( [ID] [bigint] IDENTITY(1,1) NOT NULL, [AnotherID] [int] NULL, [InsertTime] [datetime] NULL CONSTRAINT DEFAULT (getdate()), CONSTRAINT [PK_Foo] PRIMARY KEY CLUSTERED ( [ID] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] ALTER TABLE [dbo].[Foo] WITH CHECK ADD CONSTRAINT [FK_Foo] FOREIGN KEY([Goo]) REFERENCES [dbo].[Goo] ([GID]) ALTER TABLE [dbo].[Foo] CHECK CONSTRAINT [FK_Foo] thanks in advance, George

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• Referencing surrogate key

  - by Arman

  I have a table that has an autoincrement surrogate key. I want to use it as a foreign key of my other table. The thing is, I cant figure out how I can reference it to that table, because it is nearly impossible to determine what I have to reference(the actual value of the surrogate key). Please be noted that what I am trying to do is adding a tuple/record through my program(outside the dbms). The process is: Add a new record in Table1 and generate an autoincrement key. Update Add a new record in Table2 and reference its foreign key to the primary key of Table1. Update My question is : HOW do I store the foreign key if I didnt know what is it?

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• OS X Terminal: Meta key + alt functionality at the same time

  - by abababa22

  Is there a way to use "alt/option" key as a meta key but still be able to use the key to make some characters which need it? For example in my local keyboard layout: @ is alt-2 \ is alt-shift-7 | is alt-7 etc. So if I set alt as meta key, I can't make those characters. On the other hand using "press esc, release esc, press a key" to make meta key sequences makes my hands hurt. Any emacs users with international keyboards who have solved this, please give any tips you might have! :) edit: It appears that I can set alt as meta key and then add these kind of settings in inputrc: "\e2": "@" This works in bash shell but it still won't work with emacs though, so no good.

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• Parent key of type encoded string?

  - by user246114

  Hi, How do we create a parent key which is an encoded string? Example: class Parent { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String mEncKey; } class Child { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String mEncKey; // In the doc examples, they have Key as the type here. @Persistent @Extension(vendorName="datanucleus", key="gae.parent-pk", value="true") private String mParentEncKey; } yeah I'm not sure how to make mParentEncKey an encoded string type, because the 'key' label is already being used? I would need something like?: key="gae.parent-pk.encoded-pk" not sure - is that possible? Thanks

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• SQL Server PIVOT on key-value table

  - by Zenox

  I have a table that has attributes based on a key-value. Example: CREATE TABLE ObjectAttributes ( int objectId, key nvarchar(64), value nvarchar(512) ) When I select from this I get: objectId key value ---------------------------- 1 Key 1 Value 1 1 Key 2 Value 2 I was wondering if I could use the PIVOT syntax to turn this into: objectId Key 1 Key 2 --------------------------- 1 Value 1 Value 2 I know all of my tables will have the same keys. (Unfortunately I cannot easily change the table structure. This is what is leading me to attempt using PIVOTS). The big issue here though is that pivots require an aggression function to be used. Is there a way to avert this? Am I completely wrong attempting this? Or is there a better solution?

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• Key repeat on Windows

  - by Rolle

  When you hold a key on the keyboard under Windows XP, the keyboard seems to send Key Down, Key Up repeatedly. However I am developing for a device where holding a key generates a "proper" key repeat, that is, lots of Key Down and then one Key Up when you release the button. I want to get the same behaviour under Windows to get our emulator to work as on he device. Is there anyway to acheive this? Do I need to get another keyboard driver? Thanks!

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• sftp and public keys

  - by Lizard

  I am trying to sftp into an a server hosted by someone else. To make sure this worked I did the standard sftp [email protected] i was promted with the password and that worked fine. I am setting up a cron script to send a file once a week so have given them our public key which they claim to have added to their authorized_keys file. I now try sftp [email protected] again and I am still prompted for a password, but now the password doesn't work... Connecting to [email protected]... [email protected]'s password: Permission denied, please try again. [email protected]'s password: Permission denied, please try again. [email protected]'s password: Permission denied (publickey,password). Couldn't read packet: Connection reset by peer I did notice however that if I simply pressed enter (no password) it logged me in fine... So here are my questions: Is there a way to check what privatekey/pulbickey pair my sftp connection is using? Is it possible to specify what key pair to use? If all is setup correctly (using correct key pair and added to authorized files) why am I being asked to enter a blank password? Thanks for your help in advance! UPDATE I have just run sftp -vvv [email protected] .... debug1: Authentications that can continue: publickey,password debug3: start over, passed a different list publickey,password debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password debug3: authmethod_lookup publickey debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: Next authentication method: publickey debug1: Offering public key: /root/.ssh/id_rsa debug3: send_pubkey_test debug2: we sent a publickey packet, wait for reply debug1: Server accepts key: pkalg ssh-rsa blen 277 debug2: input_userauth_pk_ok: SHA1 fp 45:1b:e7:b6:33:41:1c:bb:0f:e3:c1:0f:1b:b0:d5:e4:28:a3:3f:0e debug3: sign_and_send_pubkey debug1: read PEM private key done: type RSA debug1: Authentications that can continue: publickey,password debug1: Trying private key: /root/.ssh/id_dsa debug3: no such identity: /root/.ssh/id_dsa debug2: we did not send a packet, disable method debug3: authmethod_lookup password debug3: remaining preferred: ,password debug3: authmethod_is_enabled password debug1: Next authentication method: password It seems to suggest that it tries to use the public key... What am I missing?

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• How to Make Your Computer Press a Key Every X Seconds

  - by The Geek

  Have you ever needed to press a key every couple of seconds, or every few minutes? Perhaps you’re playing a video game and you’re waiting for an item, or you’ve got some other reason. Either way, here’s how to make your PC do it automatically. You’ll need to start by downloading and installing AutoHotkey, which is a simple scripting language that allows you to create easy scripts. Once you do that, right-click anywhere and choose New –> AutoHotkey Script. Once you’ve done that, paste the following into the script: #PersistentSetTimer, PressTheKey, 1800000Return HTG Explains: How Hackers Take Over Web Sites with SQL Injection / DDoS Use Your Android Phone to Comparison Shop: 4 Scanner Apps Reviewed How to Run Android Apps on Your Desktop the Easy Way

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• Big Data – Operational Databases Supporting Big Data – Key-Value Pair Databases and Document Databases – Day 13 of 21

  - by Pinal Dave

  In yesterday’s blog post we learned the importance of the Relational Database and NoSQL database in the Big Data Story. In this article we will understand the role of Key-Value Pair Databases and Document Databases Supporting Big Data Story. Now we will see a few of the examples of the operational databases. Relational Databases (Yesterday’s post) NoSQL Databases (Yesterday’s post) Key-Value Pair Databases (This post) Document Databases (This post) Columnar Databases (Tomorrow’s post) Graph Databases (Tomorrow’s post) Spatial Databases (Tomorrow’s post) Key Value Pair Databases Key Value Pair Databases are also known as KVP databases. A key is a field name and attribute, an identifier. The content of that field is its value, the data that is being identified and stored. They have a very simple implementation of NoSQL database concepts. They do not have schema hence they are very flexible as well as scalable. The disadvantages of Key Value Pair (KVP) database are that they do not follow ACID (Atomicity, Consistency, Isolation, Durability) properties. Additionally, it will require data architects to plan for data placement, replication as well as high availability. In KVP databases the data is stored as strings. Here is a simple example of how Key Value Database will look like: Key Value Name Pinal Dave Color Blue Twitter @pinaldave Name Nupur Dave Movie The Hero As the number of users grow in Key Value Pair databases it starts getting difficult to manage the entire database. As there is no specific schema or rules associated with the database, there are chances that database grows exponentially as well. It is very crucial to select the right Key Value Pair Database which offers an additional set of tools to manage the data and provides finer control over various business aspects of the same. Riak Rick is one of the most popular Key Value Database. It is known for its scalability and performance in high volume and velocity database. Additionally, it implements a mechanism for collection key and values which further helps to build manageable system. We will further discuss Riak in future blog posts. Key Value Databases are a good choice for social media, communities, caching layers for connecting other databases. In simpler words, whenever we required flexibility of the data storage keeping scalability in mind – KVP databases are good options to consider. Document Database There are two different kinds of document databases. 1) Full document Content (web pages, word docs etc) and 2) Storing Document Components for storage. The second types of the document database we are talking about over here. They use Javascript Object Notation (JSON) and Binary JSON for the structure of the documents. JSON is very easy to understand language and it is very easy to write for applications. There are two major structures of JSON used for Document Database – 1) Name Value Pairs and 2) Ordered List. MongoDB and CouchDB are two of the most popular Open Source NonRelational Document Database. MongoDB MongoDB databases are called collections. Each collection is build of documents and each document is composed of fields. MongoDB collections can be indexed for optimal performance. MongoDB ecosystem is highly available, supports query services as well as MapReduce. It is often used in high volume content management system. CouchDB CouchDB databases are composed of documents which consists fields and attachments (known as description). It supports ACID properties. The main attraction points of CouchDB are that it will continue to operate even though network connectivity is sketchy. Due to this nature CouchDB prefers local data storage. Document Database is a good choice of the database when users have to generate dynamic reports from elements which are changing very frequently. A good example of document usages is in real time analytics in social networking or content management system. Tomorrow In tomorrow’s blog post we will discuss about various other Operational Databases supporting Big Data. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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