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• Multiple column foreign key contraints

  - by eugene4968

  I want to setup table constraints for the following scenario and I’m not sure how to do it or if it’s even possible in SQL Server 2005. I have three tables A,B,C. C is a child of B. B will have a optional foreign key(may be null) referencing A. For performance reasons I also want table C to have the same foreign key reference to table A. The constraint on table C should be that C must reference its parent (B) and also have the same foreign key reference to A as its parent. Anyone have any thoughts on how to do this?

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• MySQL foreign key creation with alter table command

  - by user313338

  I created some tables using MySQL Workbench, and then did forward ‘forward engineer’ to create scripts to create these tables. BUT, the scripts lead me to a number of problems. One of which involves the foreign keys. So I tried creating separate foreign key additions using alter table and I am still getting problems. The code is below (the set statements, drop/create statements I left in … though I don’t think they should matter for this): SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL'; DROP SCHEMA IF EXISTS `mydb` ; CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ; -- ----------------------------------------------------- -- Table `mydb`.`User` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User` ; CREATE TABLE IF NOT EXISTS `mydb`.`User` ( `UserName` VARCHAR(35) NOT NULL , `Num_Accts` INT NOT NULL , `Password` VARCHAR(45) NULL , `Email` VARCHAR(45) NULL , `User_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_ID`) ) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `mydb`.`User_Space` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User_Space` ; CREATE TABLE IF NOT EXISTS `mydb`.`User_Space` ( `User_UserName` VARCHAR(35) NOT NULL , `User_Space_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_Space_ID`), FOREIGN KEY (`User_UserName`) REFERENCES `mydb`.`User` (`UserName`) ON UPDATE CASCADE ON DELETE CASCADE) ENGINE = InnoDB; SET SQL_MODE=@OLD_SQL_MODE; SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS; The error this produces is: Error Code: 1005 Can't create table 'mydb.user_space' (errno: 150) Anybody know what the heck I’m doing wrong?? And anybody else have problems with the script generation done by mysql workbench? It’s a nice tool, but annoying that it pumps out scripts that don’t work for me. [As an fyi here’s the script it auto-generates: SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL'; DROP SCHEMA IF EXISTS `mydb` ; CREATE SCHEMA IF NOT EXISTS `mydb` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci ; -- ----------------------------------------------------- -- Table `mydb`.`User` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User` ; CREATE TABLE IF NOT EXISTS `mydb`.`User` ( `UserName` VARCHAR(35) NOT NULL , `Num_Accts` INT NOT NULL , `Password` VARCHAR(45) NULL , `Email` VARCHAR(45) NULL , `User_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_ID`) ) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `mydb`.`User_Space` -- ----------------------------------------------------- DROP TABLE IF EXISTS `mydb`.`User_Space` ; CREATE TABLE IF NOT EXISTS `mydb`.`User_Space` ( `User_Space_ID` INT NOT NULL AUTO_INCREMENT , PRIMARY KEY (`User_Space_ID`) , INDEX `User_ID` () , CONSTRAINT `User_ID` FOREIGN KEY () REFERENCES `mydb`.`User` () ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; SET SQL_MODE=@OLD_SQL_MODE; SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS; ** Thanks!]

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• Cocoa Key Value Bindings: What are the explanations of the various options for Controller Key?

  - by Elisabeth

  When I bind a control to an NSArrayController using Interface Builder, there are a variety of options under the "Controller Key" field in the bindings inspector. I understand what "arrangedObjects" is, and I semi-understand what "selection" is, but I'd love to see a really nice explanation of all the options and when to use each one. The list includes: selectionIndexes, selectionIndex, selectedObject, sortDescriptors, etc. I haven't been able to find a good explanation of these options. I'm having trouble with a button that's bound to target selection, so I'm hoping a much deeper understanding of these Controller Keys might help me debug my issue. Thanks!!!

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• juju -v status ERROR Invalid SSH key

  - by Captain T

  root@cloudcontrol:/storage# juju -v status 2012-06-07 11:19:47,602 DEBUG Initializing juju status runtime 2012-06-07 11:19:47,621 INFO Connecting to environment... 2012-06-07 11:19:47,905 DEBUG Connecting to environment using node-386077143930... 2012-06-07 11:19:47,906 DEBUG Spawning SSH process with remote_user="ubuntu" remote_host="node-386077143930" remote_port="2181" local_port="57004". The authenticity of host 'node-386077143930 (10.5.5.113)' can't be established. ECDSA key fingerprint is 31:94:89:62:69:83:24:23:5f:02:70:53:93:54:b1:c5. Are you sure you want to continue connecting (yes/no)? yes 2012-06-07 11:19:52,102 ERROR Invalid SSH key 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.5 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@662: Client environment:host.name=cloudcontrol 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@669: Client environment:os.name=Linux 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@670: Client environment:os.arch=3.2.0-23-generic 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@671: Client environment:os.version=#36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@679: Client environment:user.name=sysadmin 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@687: Client environment:user.home=/root 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@699: Client environment:user.dir=/storage 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=localhost:57004 sessionTimeout=10000 watcher=0x7feb11afc6b0 sessionId=0 sessionPasswd= context=0x2dc7d20 flags=0 2012-06-07 11:19:52,429:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client 2012-06-07 11:19:55,765:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client This is from a clean install with 2 nodes all running 12.04 Precise juju bootstrap - finishes with no errors and allocates the machine to the user but still no joy after juju environment-destroy and rebuild with different users and different nodes. Anyone got any ideas

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• Invalid SSH key erron in juju

  - by Captain T

  This is the output of juju from a clean install with 2 nodes all running 12.04 Precise juju bootstrap - finishes with no errors and allocates the machine to the user but still no joy after juju environment-destroy and rebuild with different users and different nodes. root@cloudcontrol:/storage# juju -v status 2012-06-07 11:19:47,602 DEBUG Initializing juju status runtime 2012-06-07 11:19:47,621 INFO Connecting to environment... 2012-06-07 11:19:47,905 DEBUG Connecting to environment using node-386077143930... 2012-06-07 11:19:47,906 DEBUG Spawning SSH process with remote_user="ubuntu" remote_host="node-386077143930" remote_port="2181" local_port="57004". The authenticity of host 'node-386077143930 (10.5.5.113)' can't be established. ECDSA key fingerprint is 31:94:89:62:69:83:24:23:5f:02:70:53:93:54:b1:c5. Are you sure you want to continue connecting (yes/no)? yes 2012-06-07 11:19:52,102 ERROR Invalid SSH key 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@658: Client environment:zookeeper.version=zookeeper C client 3.3.5 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@662: Client environment:host.name=cloudcontrol 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@669: Client environment:os.name=Linux 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@670: Client environment:os.arch=3.2.0-23-generic 2012-06-07 11:19:52,426:18541(0x7feb13b58700):ZOO_INFO@log_env@671: Client environment:os.version=#36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@679: Client environment:user.name=sysadmin 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@687: Client environment:user.home=/root 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@log_env@699: Client environment:user.dir=/storage 2012-06-07 11:19:52,428:18541(0x7feb13b58700):ZOO_INFO@zookeeper_init@727: Initiating client connection, host=localhost:57004 sessionTimeout=10000 watcher=0x7feb11afc6b0 sessionId=0 sessionPasswd=<null> context=0x2dc7d20 flags=0 2012-06-07 11:19:52,429:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client 2012-06-07 11:19:55,765:18541(0x7feb0e856700):ZOO_ERROR@handle_socket_error_msg@1579: Socket [127.0.0.1:57004] zk retcode=-4, errno=111(Connection refused): server refused to accept the client

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• POJOs for Composite Primary Key from Foreign Key

  - by Gaurav

  hi, I have table in database that has only two columns and these two colums are FK references. they have made these two colums as composite primarykey. table structure Table A [ A_id PK Description ] Table B [ B_Id PK Description ] Table A_B_Pemissiom [ A_id (FK table A) B_Id (FK table B) PrimaryKey ( A_id,B_Id ) ] Can anyone help , I tried several ways and none of them works. Can anyone tell a working Hibernate mapping solution using annotations ? Thanks, Gaurav

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• Which MySQL Frontend shows foreign rows?

  - by Jeremy Rudd

  I once came across a MySQL Frontend app that displayed foreign linked rows within the parent row, if for instance the Events table has a foreign key to the Students table: Student ID Name DOB -- ---- --------- [+] 22 Bob 25-1-1984 [-] 21 Jane 25-1-1982 Event ID Student-ID Name Time -- ---------- ---- --------- 1 21 Event A 05:50 1 21 Event B 17:20 [+] 20 Jack 25-1-1980

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• Partitioning mySQL tables that has foreign keys?

  - by Industrial

  Hi! What would be an appropriate way to do this, since mySQL obviously doesnt enjoy this. To leave either partitioning or the foreign keys out from the database design would not seem like a good idea to me. I'll guess that there is a workaround for this? Update 03/24: http://opendba.blogspot.com/2008/10/mysql-partitioned-tables-with-trigger.html http://stackoverflow.com/questions/1537219/how-to-handle-foreign-key-while-partitioning Thanks!

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• Postgresql: Implicit lock acquisition from foreign-key constraint evaluation

  - by fennec

  So, I'm being confused about foreign key constraint handling in Postgresql. (version 8.4.4, for what it's worth). We've got a couple of tables, mildly anonymized below: device: (id, blah, blah, blah, blah, blah x 50)… primary key on id whooooole bunch of other junk device_foo: (id, device_id, left, right) Foreign key (device_id) references device(id) on delete cascade; primary key on id btree index on 'left' and 'right' So I set out with two database windows to run some queries. db1> begin; lock table device in exclusive mode; db2> begin; update device_foo set left = left + 1; The db2 connection blocks. It seems odd to me that an update of the 'left' column on device_stuff should be affected by activity on the device table. But it is. In fact, if I go back to db1: db1> select * from device_stuff for update; *** deadlock occurs *** The pgsql log has the following: blah blah blah deadlock blah. CONTEXT: SQL statement "SELECT 1 FROM ONLY "public"."device" x WHERE "id" OPERATOR(pg_catalog.=) $1 FOR SHARE OF X: update device_foo set left = left + 1; I suppose I've got two issues: the first is that I don't understand the precise mechanism by which this sort of locking occurs. I have got a couple of useful queries to query pg_locks to see what sort of locks a statement invokes, but I haven't been able to observe this particular sort of locking when I run the update device_foo command in isolation. (Perhaps I'm doing something wrong, though.) I also can't find any documentation on the lock acquisition behavior of foreign-key constraint checks. All I have is a log message. Am I to infer from this that any change to a row will acquire an update lock on all the tables which it's foreign-keyed against? The second issue is that I'd like to find some way to make it not happen like that. I'm ending up with occasional deadlocks in the actual application. I'd like to be able to run big update statements that impact all rows on device_foo without acquiring a big lock on the device table. (There's a lot of access going on in the device table, and it's kind of an expensive lock to get.)

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• how to save related models with non-null foreign key

  - by Fortress

  I have a model called user which has_one email. I put the foreign key (NOT NULL) inside users table. Now I'm trying to save it in the following way: @email = Email.new(params[:email]) @email.user = User.new(params[:user]) @email.save This raises a db exception, because the foreign key constraint is not met (NULL is inserted into email_id). How can I elegantly solve this or is my data modeling wrong?

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• Phpmyadmin mysql foreign key help

  - by Alan

  Hey guys i'm using phpmyadmin (php & mysql) and i'm having alot of trouble linking the tables using foreign keys. I'm getting negative values for the field countyId (which is the foriegn key). However it is linking to my other table fine and it's cascading fine. So when I go to add data there will be a drop box for the CountyId and the vlaues will look something like this, " -1 1- " Here is my alter statement, ALTER TABLE Baronies ADD FOREIGN KEY (CountyId) REFERENCES Counties (CountyId) ON DELETE CASCADE

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• Foreign keys - temporarily bypass?

  - by Industrial

  Hi, I have just started to learn about the pros of foreign keys in database design (mySQL / innoDB) and I wonder if there's any way to temporarily bypass the foreign key when doing a specific delete query, to just delete in the parent table, and not from the linked child tables. Thanks

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• Jupiter Changes Display when using volume key bindings

  - by user87797

  I recently downloaded jupiter on ubuntu 12.04 ASUS U36JC and I noticed that my display would switch from clone to exterior to clone everytime that I used the keys that control the volume. Hit "function volume down" and the screen goes blank, hit "function volume up" and the display come back. This only happens when I am running jupiter and I assume there is a key binding issue, but I don't know how to fix it. No options other than the regular ones show up in the keyboard settings under system tools.

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• mysql foreign key problem.

  - by JP19

  Hi, What is wrong with the foreign key addition here: mysql> create table notes ( id int (11) NOT NULL auto_increment PRIMARY KEY, note_type_id smallint(5) NOT NULL, data TEXT NOT NULL, created_date datetime NOT NULL, modified_date timestamp NOT NULL on update now()) Engine=InnoDB; Query OK, 0 rows affected (0.08 sec) mysql> create table notetypes ( id smallint (5) NOT NULL auto_increment PRIMARY KEY, type varchar(255) NOT NULL UNIQUE) Engine=InnoDB; Query OK, 0 rows affected (0.00 sec) mysql> alter table `notes` add constraint foreign key(`note_type_id`) references `notetypes`.`id` on update cascade on delete restrict; ERROR 1005 (HY000): Can't create table './admin/#sql-43e_b762.frm' (errno: 150) Thanks JP

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• Foreign keys in django admin list display

  - by Olivier

  If a django model contains a foreign key field, and if that field is shown in list mode, then it shows up as text, instead of displaying a link to the foreign object. Is it possible to automatically display all foreign keys as links instead of flat text? (of course it is possible to do that on a field by field basis, but is there a general method?) Example: class Author(models.Model): ... class Post(models.Model): author = models.ForeignKey(Author) Now I choose a ModelAdmin such that the author shows up in list mode: class PostAdmin(admin.ModelAdmin): list_display = [..., 'author',...] Now in list mode, the author field will just use the __unicode__ method of the Author class to display the author. On the top of that I would like a link pointing to the url of the corresponding author in the admin site. Is that possible? Manual method: For the sake of completeness, I add the manual method. It would be to add a method author_link in the PostAdmin class: def author_link(self, item): return '<a href="../some/path/%d">%s</a>' % (item.id, unicode(item)) author_link.allow_tags = True That will work for that particular field but that is not what I want. I want a general method to achieve the same effect. (One of the problems is how to figure out automatically the path to an object in the django admin site.)

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• [Linq to SQL] Multiple foreign keys to the same table

  - by cdonner

  I have a reference table with all sorts of controlled value lookup data for gender, address type, contact type, etc. Many tables have multiple foreign keys to this reference table I also have many-to-many association tables that have two foreign keys to the same table. Unfortunately, when these tables are pulled into a Linq model and the DBML is generated, SQLMetal does not look at the names of the foreign key columns, or the names of the constraints, but only at the target table. So I end up with members called Reference1, Reference2, ... not very maintenance-friendly. Example: <Association Name="tb_reference_tb_account" Member="tb_reference" <====== ThisKey="shipping_preference_type_id" OtherKey="id" Type="tb_reference" IsForeignKey="true" /> <Association Name="tb_reference_tb_account1" Member="tb_reference1" <====== ThisKey="status_type_id" OtherKey="id" Type="tb_reference" IsForeignKey="true" /> I can go into the DBML and manually change the member names, of course, but this would mean I can no longer round-trip my database schema. This is not an option at the current stage of the model, which is still evolving. Splitting the reference table into n individual tables is also not desirable. I can probably write a script that runs against the XML after each generation and replaces the member name with something derived from ThisKey (since I adhere to a naming convention for these types of keys). Has anybody found a better solution to this problem?

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• SQL Server problems reading columns with a foreign key

  - by illdev

  I have a weird situation, where simple queries seem to never finish for instance SELECT top 100 ArticleID FROM Article WHERE ProductGroupID=379114 returns immediately SELECT top 1000 ArticleID FROM Article WHERE ProductGroupID=379114 never returns SELECT ArticleID FROM Article WHERE ProductGroupID=379114 never returns SELECT top 1000 ArticleID FROM Article returns immediately By 'returning' I mean 'in query analyzer the green check mark appears and it says "Query executed successfully"'. I sometimes get the rows painted to the grid in qa, but still the query goes on waiting for my client to time out - 'sometimes': SELECT ProductGroupID AS Product23_1_, ArticleID AS ArticleID1_, ArticleID AS ArticleID18_0_, Inventory_Name AS Inventory3_18_0_, Inventory_UnitOfMeasure AS Inventory4_18_0_, BusinessKey AS Business5_18_0_, Name AS Name18_0_, ServesPeople AS ServesPe7_18_0_, InStock AS InStock18_0_, Description AS Descript9_18_0_, Description2 AS Descrip10_18_0_, TechnicalData AS Technic11_18_0_, IsDiscontinued AS IsDisco12_18_0_, Release AS Release18_0_, Classifications AS Classif14_18_0_, DistributorName AS Distrib15_18_0_, DistributorProductCode AS Distrib16_18_0_, Options AS Options18_0_, IsPromoted AS IsPromoted18_0_, IsBulkyFreight AS IsBulky19_18_0_, IsBackOrderOnly AS IsBackO20_18_0_, Price AS Price18_0_, Weight AS Weight18_0_, ProductGroupID AS Product23_18_0_, ConversationID AS Convers24_18_0_, DistributorID AS Distrib25_18_0_, type AS Type18_0_ FROM Article AS articles0_ WHERE (IsDiscontinued = '0') AND (ProductGroupID = 379121) shows this behavior. I have no idea what is going on. Probably select is broken ;) I got a foreign key on ProductGroups ALTER TABLE [dbo].[Article] WITH CHECK ADD CONSTRAINT [FK_ProductGroup_Articles] FOREIGN KEY([ProductGroupID]) REFERENCES [dbo].[ProductGroup] ([ProductGroupID]) GO ALTER TABLE [dbo].[Article] CHECK CONSTRAINT [FK_ProductGroup_Articles] there are some 6000 rows and IsDiscontinued is a bit, not null, but leaving this condition out does not change the outcome. Anyone can tell me how to handle such a situation? More info, anyone? Additional Info: this does not seem to be restricted to this Foreign Key, but all/some referencing this entity.

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• Core data many-to-many relationship - Predicate question

  - by Garry

  In my Core Data model I have two entities: List and Patient. List has an attribute called 'name'. A List can have any number of Patients and each Patient can belong to any number of different lists. I have therefore set a relationship on List called 'patients' that has an inverse to-many relationship to Patient AND a relationship on Patient called 'lists' that has a to-many relationship to List. What I'm struggling to figure out is how to create a Predicate that will select all Patients that belong to a particular List name. How would I go about this? I have never used relationships before in Core Data. Thanks,

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• How to handle key in PhP array if the key contains japanese characters [migrated]

  - by Jim Thio

  I have this array: [ID] => ????????-???????????__35.79_139.72 [Email] => [InBuildingAddress] => [Price] => [Street] => [Title] => ???????? ??????????? [Website] => [Zip] => [Rating Star] => 0 [Rating Weight] => 0 [Latitude] => 35.7865334803033 [Longitude] => 139.716800710514 [Building] => [City] => Unknown_Japan [OpeningHour] => [TimeStamp] => 0000-00-00 00:00:00 [CountViews] => 0 Then I do something like this: $output[$info['ID']]=$info; //mess up here $tes=$info['ID']['Title']; Well guess what it messes up. Basically even though the content of an array in PhP can be Japanese. Is this true? What's wrong. The error I got is: Debug Warning: /sdfdsfdf/api/test2.php line 36 - Cannot find element ????????-???????????__35.79_139.72 in variable Debug Warning: /sdfdsfdf/api/test2.php line 36 - main() [function.main]: It is not safe to rely on the system's timezone settings. You are required to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Asia/Krasnoyarsk' for '7.0/no DST' instead So many question mark Why is this happening. What's really going on inside PhP? Where can I learn more of such things. Most importantly, what would be the best way to handle this situation. Should I tell PhP to internally always use UTF-8? Does PhP array inherenty cannot use non ascii id?

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• SQL Server: Natural Key Versus Surrogate Key

  When designing a database to support applications you need to consider how you are going to handle primary keys. This article explores natural and surrogate keys, and discusses the pros and cons of each, allowing you to determine what makes the best sense in your environment when you are designing your databases. NEW! SQL Monitor 2.0Monitor SQL Server Central's servers withRed Gate's new SQL Monitor.No installation required. Find out more.

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• Create automatically table that is composed by its primery key and 2 other foreign keys

  - by user210481

  I have table A with a primary id, a table B with a primary key id also and another table C with a primary key id and rows Aid and Bid where Aid and Bid are foreign keys of C and the primary keys of A and B respectively. One way of populating these DB would be populating table A, table B and table C separately. I would like to know if there is a more clever way of doing it, where I could populate A first and at the same time I populate B, I can indicate that an entry in C should be also created. Any idea and suggestion on how to populate them is welcome. I'm trying to take advantage of the foreign keys structure Thanks

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• Manage Foreign key and Drop downlist for optional field in .NET

  - by Brij

  What is the best way to handle following situation? A dropdown(for master table) is optional in a particular form. But, In database table the field is constrained with foreign key. If user don't select from dropdown then It creates problem because of foreign key. One solution is to create default option in master table and use it in case of blank selection. but in dropdown, we need to handle this to show on top. Is it perfect solution? Is there any other optimized solution for this? Thanks

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• T-SQL foreign key check constraint

  - by PaN1C_Showt1Me

  When you create a foreign key constraint in a table and you create the script in MS SQL Management Studio, it looks like this. ALTER TABLE T1 WITH CHECK ADD CONSTRAINT FK_T1 FOREIGN KEY(project_id) REFERENCES T2 (project_id) GO ALTER TABLE T1 CHECK CONSTRAINT FK_T1 GO What I don't understand is what purpose has the second alter with check constraint. Isn't creating the FK constraint enough? Do you have to add the check constraint to assure reference integrity ? Another question: how would it look like then when you'd write it directly in the column definition? CREATE TABLE T1 ( my_column INT NOT NULL CONSTRAINT FK_T1 REFERENCES T2(my_column) ) Isn't this enough?

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• linq to sql using foreign keys returning iqueryable(of myEntity]

  - by Gern Blandston

  I'm trying to use Linq to SQL to return an IQueryable(of Project) when using foreign key relationships. Using the below schema, I want to be able to pass in a UserId and get all the projects created for the company the user is associated with. DB tables: Projects Projid ProjCreator FK (UserId from UserInfo table) Companyid FK (CompanyID from Companies table) UserInfo UserID PK Companyid FK Companies CompanyId PK Description I can get the iqueryable(of project) when simply getting the ProjectCreator with this: Return (From p In db.Projects _ Where p.ProjectCreator = Me.UserId) But I'm having trouble getting the syntax to get a iqueryable(of projects) when using foreign keys. Below gives me an IQueryable(of anonymous) but I can't seem to convince it to give me an IQueryable(of project) even if I try to cast it: Dim retval = (From p In db.Projects _ Join c In db.Companies On p.CompanyId Equals c.CompanyId _ Join u In db.UserInfos On u.CompanyId Equals c.CompanyId _ Where u.Login = UserId)

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• Rails Nested Attributes, Relationship for Shared or Common Object

  - by SooDesuNe

  This has to be a common problem, so I'm surprised that Google didn't turn up more answers. I'm working on a rails app that has several different kinds of entities, those entities by need a relation to a different entity. For example: Address: a Model that stores the details of a street address (this is my shared entity) PersonContact: a Model that includes things like home phone, cell phone and email address. This model needs to have an address associated with it DogContact: Obviously, if you want to contact a dog, you have to go to where it lives. So, PersonContact and DogContact should have foreign keys to Address. Even, though they are really the "owning" object of Address. This would be fine, except that accepts_nested_attributes_for is counting on the foreign key being in Address to work correctly. What's the correct strategy to keep the foreign key in Address, but have PersonContact and DogContact be the owning objects?

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