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• Dealing with SQLException with spring,hibernate & Postgres

  - by mad

  Hi im working on a project using HibernateDaoSUpport from my Daos from Spring & spring-ws & hibernate & postgres who will be used in a national application (means a lot of users) Actually, every exception from hibernate is automatically transformed into some specific Spring dataAccesException. I have a table with a keyword on the dabatase & a unique constraint on the keywords : no duplicate keywords is allowed. I have found twows ways to deal with with that in the Insert Dao: 1- Check for the duplicate manually (with a select) prior to doing your insert. I means that the spring transaction will have a SERIALIZABLE isolation level. The obvious drawback is that we have now 2 queries for a simple insert.Advantage: independent of the database 2-let the insert gone & catch the SqlException & convert it to a userfriendly message & errorcode to the final consumer of our webservices. Solution 2: Spring has developped a way to translate specific exeptions into customized exceptions. see http://www.oracle.com/technology/pub/articles/marx_spring.html In my case i would have a ConstraintViolationException. Ideally i would like to write a custom SQLExceptionTranslator to map the duplicate word constraint in the database with a DuplicateWordException. But i can have many unique constraints on the same table. So i have to get the message of the SQLEXceptions in order to find the name of the constraint declared in the create table "uq_duplicate-constraint" for example. Now i have a strong dependency with the database. Thanks in advance for your answers & excuse me for my poor english (it is not my mother tongue)

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• In MVC framworks (such as Ruby on Rails), does usually Model spell as singular and controller and vi

  - by Jian Lin

  I usually see Ruby on Rails books using script/generate model Story name:string link:string which is a singular Story, while when it is controller script/generate controller Stories index then the Story now is Stories, which is plural. Is this a standard on Ruby on Rails? Is it true in other MVC frameworks too, like CakePHP, Symfony, Django, or TurboGears? I see that in the book Rails Space, the controller is also called User, which is the same as the model name, and it is the only exception I see. Update: also, when scaffold is done on Ruby on Rails, then automatically, the model is singular and the controller and view are both plural.

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• confusion about using types instead of gtts in oracle

  - by Omnipresent

  I am trying to convert queries like below to types so that I won't have to use GTT: insert into my_gtt_table_1 (house, lname, fname, MI, fullname, dob) (select house, lname, fname, MI, fullname, dob from (select 'REG' house, mbr_last_name lname, mbr_first_name fname, mbr_mi MI, mbr_first_name || mbr_mi || mbr_last_name fullname, mbr_dob dob from table_1 a, table_b where a.head = b.head and mbr_number = '01' and mbr_last_name = v_last_name) c above is just a sample but complex queries are bigger than this. the above is inside a stored procedure. So to avoid the gtt (my_gtt_table_1). I did the following: create or replace type lname_row as object ( house varchar2(30) lname varchar2(30), fname varchar2(30), MI char(1), fullname VARCHAR2(63), dob DATE ) create or replace type lname_exact as table of lname_row Now in the SP: type lname_exact is table of <what_table_should_i_put_here>%rowtype; tab_a_recs lname_exact; In the above I am not sure what table to put as my query has nested subqueries. query in the SP: (I am trying this for sample purpose to see if it works) select lname_row('', '', '', '', '', '', sysdate) bulk collect into tab_a_recs from table_1; I am getting errors like : ORA-00913: too many values I am really confused and stuck with this :(

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• Non-normalized association with legacy tables in Rails and ActiveRecord

  - by Thomas Holmström

  I am building a Rails application accessing a legacy system. The data model contains Customers which can have one or more Subscriptions. A Subscription always belong to one and only one Customer. Though not needed, this association is represented through a join table "subscribes", which do not have an id column: Column | Type | Modifiers -----------------+---------+----------- customer_id | integer | not null subscription_id | integer | not null I have this coded as a has_and_belongs_to_many declarations in both Customer and Subscription class Customer < Activerecord::Base has_and_belongs_to_many :subscriptions, :join_table => "subscribes", :foreign_key => "customer_id", :association_foreign_key => "subscription_id" end class Subscription < Activerecord::Base has_and_belongs_to_many :customers, :join_table => "subscribes", :foreign_key => "subscription_id", :association_foreign_key => "customer_id" end The problem I have is that there can only ever be one customer for each subscription, not many, and the join table will always contain at most one row with a certain customer_id. And thus, I don't want the association "customers" on a Subscription which returns an array of (at most one) Customer, I really do want the relation "customer" which returns the Customer associated. Is there any way to force ActiveRecord to make this a 1-to-N relation even though the join table itself seems to make it an N-to-M relation? --Thomas

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• For a set of sql-queries, how do you determine which result-set contains a certain row?

  - by ManBugra

  I have a set of sql - queries: List<String> queries = ... queries[0] = "select id from person where ..."; ... queries[8756] = "select id from person where ..."; Each query selects rows from the same table 'person'. The only difference is the where-clause. Table 'person' looks like this: id | name | ... many other columns How can i determine which queries will contain a certain person in their subset? For example: List<Integer> matchingQueries = magicMethod(queries, [23,45]); The list obtained by 'magicMethod' filters all sql queries present in the list 'queries' (defined above) and returns only those that contain either the person with id 23 OR a person with id 45. Why i need it: I am dealing with an application that contains products and categories where the categories are sql queries that define which products belong to them (queries stored in a table also). Now i have a requirement where an admin has to see all categories an item belongs to immediately after the item was created. Btw, over 8.000 categories defined (so far, more to come). language and db: java && postgreSQL Thanks,

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• NHibernate mapping with two special cases

  - by brainimus

  I am using NHibernate to map a class to a database table. The Part table has an ID column (primary key) and a ParentPart column (along with a few others). class Part { public virtual long ID{ get; set; } public virtual Part ParentPart { get; set; } } The ParentPart is normally another valid part in the part table but I have two special cases. I have a case where the ParentPart column can be 0 (zero) and another case where it can be -1. Neither of these cases currently represent another valid Part object. I was thinking I could make 2 subclasses of Part (ZeroPart and NegativeOnePart) that would never persist. I want the zero and -1 values to be entered in the column but not persist the entire ZeroPart or NegativeOnePart objects. I am unsure how to map this (I'm using hbm files) or if this even the correct approach. How can I map this so that normal valid parts are persisted but I can also handle the special cases? As an aside: My current hbm file has the Part.ID's unsaved value as zero but I think I can just change this in the mapping to something different and default it in the class.

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• LINQ Joins - Performance

  - by Meiscooldude

  I am curious on how exactly LINQ (not LINQ to SQL) is performing is joins behind the scenes in relation to how Sql Server performs joins. Sql Server before executing a query, generates an Execution Plan. The Execution Plan is basically an Expression Tree on what it believes is the best way to execute the query. Each node provides information on whether to do a Sort, Scan, Select, Join, ect. On a 'Join' node in our execution plan, we can see three possible algorithms; Hash Join, Merge Join, and Nested Loops Join. Sql Server will choose which algorithm to for each Join operation based on expected number of rows in Inner and Outer tables, what type of join we are doing (some algorithms don't support all types of joins), whether we need data ordered, and probably many other factors. Join Algorithms: Nested Loop Join: Best for small inputs, can be optimized with ordered inner table. Merge Join: Best for medium to large inputs sorted inputs, or an output that needs to be ordered. Hash Join: Best for medium to large inputs, can be parallelized to scale linearly. LINQ Query: DataTable firstTable, secondTable; ... var rows = from firstRow in firstTable.AsEnumerable () join secondRow in secondTable.AsEnumerable () on firstRow.Field<object> (randomObject.Property) equals secondRow.Field<object> (randomObject.Property) select new {firstRow, secondRow}; SQL Query: SELECT * FROM firstTable fT INNER JOIN secondTable sT ON fT.Property = sT.Property Sql Server might use a Nested Loop Join if it knows there are a small number of rows from each table, a merge join if it knows one of the tables has an index, and Hash join if it knows there are a lot of rows on either table and neither has an index. Does Linq choose its algorithm for joins? or does it always use one?

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• how do i insert html file that have hebrew text and read it back in sql server 2008 using the filest

  - by gadym

  hello all, i am new to the filestream option in sql server 2008, but i have already understand how to open this option and how to create a table that allow you to save files. let say my table contains: id,name, filecontent i tried to insert an html file (that has hebrew chars/text in it) to this table. i'm writing in asp.net (c#), using visual studio 2008. but when i tried to read back the content , hebrew char becomes '?'. the actions i took were: 1. i read the file like this: // open the stream reader System.IO.StreamReader aFile = new StreamReader(FileName, System.Text.UTF8Encoding.UTF8); // reads the file to the end stream = aFile.ReadToEnd(); // closes the file aFile.Close(); return stream; // returns the stream i inserted the 'stream' to the filecontent column as binary data. i tried to do a 'select' to this column and the data did return (after i coverted it back to string) but hebrew chars become '?' how do i solve this problem ? what I should pay attention to ? thanks, gadym

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• customer.name joining transactions.name vs. customer.id [serial] joining transactions.id [integer]

  - by Frank Computer

  INFORMIX-SQL 7.32 Pawnshop Application: one-to-many relationship where each customer (master) can have many transactions (detail). customer( id serial, pk_name char(30), {PATERNAL-NAME MATERNAL-NAME, FIRST-NAME MIDDLE-NAME} [...] ); unique index on id; unique cluster index on name; transaction( fk_name char(30), ticket_number serial, [...] ); dups cluster index on fk_name; unique index on ticket_number; Several people have told me this is not the correct way to join master to detail. They said I should always join customer.id[serial] to transactions.id[integer]. When a customer pawns merchandise, clerk queries the master using wildcards on name. The query usually returns several customers, clerk scrolls until locating the right name, enters a 'D' to change to detail transactions table, all transactions are automatically queried, then clerk enters an 'A' to add a new transaction. The problem with using customer.id joining transaction.id is that although the customer table is maintained in sorted name order, clustering the transaction table by fk_id groups the transactions by fk_id, but they are not in the same order as the customer name, so when clerk is scrolling through customer names in the master, the system has to jump allover the place to locate the clustered transactions belonging to each customer. As each new customer is added, the next id is assigned to that customer, but new customers dont show up in alphabetical order. I experimented using id joins and confirmed the decrease in performance. How can I use id joins instead of name joins and still preserve the clustered transaction order by name if transactions has no name column?

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• Does a Postgresql dump create sequences that start with - or after - the last key?

  - by bennylope

  I recently created a SQL dump of a database behind a Django project, and after cleaning the SQL up a little bit was able to restore the DB and all of the data. The problem was the sequences were all mucked up. I tried adding a new user and generated the Python error IntegrityError: duplicate key violates unique constraint. Naturally I figured my SQL dump didn't restart the sequence. But it did: DROP SEQUENCE "auth_user_id_seq" CASCADE; CREATE SEQUENCE "auth_user_id_seq" INCREMENT 1 START 446 MAXVALUE 9223372036854775807 MINVALUE 1 CACHE 1; ALTER TABLE "auth_user_id_seq" OWNER TO "db_user"; I figured out that a repeated attempt at creating a user (or any new row in any table with existing data and such a sequence) allowed for successful object/row creation. That solved the pressing problem. But given that the last user ID in that table was 446 - the same start value in the sequence creation above - it looks like Postgresql was simply trying to start creating rows with that key. Does the SQL dump provide the wrong start key by 1? Or should I invoke some other command to start sequences after the given start ID? Keenly curious.

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• jQuery re-checking check boxes

  - by Jacob

  Hi, I having problems with re-checking some checkboxes after and ajax call updates a table. I have a table of what the project calls 'shares'. I want to: 1) check for and save any checked shares to an array 2) Do my ajax call to update the table of shares 3) Re-check any there we checked before the ajax update. My code is not working and I can't see why? Any tips, help or advise much appreciated. // Array to hold our checked share ids var savedShareIDs = new Array(); // Add checked share ids into array $("input:checkbox[name=share_ids]:checked").each(function() { savedShareIDs.push($(this).val()); }); // Do ajax update Dajaxice.pagination_shares('Dajax.process',{'id':1, 'page':1}) // Re-check any that were checked before ajax update $("input:checkbox[name=share_ids]").each(function() { if ( $.inArray( $(this).val(), savedShareIDs) > -1 ) { $(this).attr('checked',true) } }); The problem is the checkboxes are not checking. I'm pretty sure the loop is working and the inArray check works. Just not checking the checkboxes. Can anyone see where I'm going wrong? Thanks.

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• Hibernate mapping Problem

  - by Geln Yang

  Hi, There is a table Item like, code,name 01,parent1 02,parent2 0101,child11 0102,child12 0201,child21 0202,child22 Create a java object and hbm xml to map the table.The Item.parent is a Item whose code is equal to the first two characters of its code : class Item{ String code; String name; Item parent; List<Item> children; .... setter/getter.... } <hibernate-mapping> <class name="Item" table="Item"> <id name="code" length="4" type="string"> <generator class="assigned" /> </id> <property name="name" column="name" length="50" not-null="true" /> <many-to-one name="parent" class="Item" not-found="ignore"> <formula> <![CDATA[ (select i.code,r.name from Item i where (case length(code) when 4 then i.code=SUBSTRING(code,1,2) else false end)) ]]> </formula> </many-to-one> <bag name="children"></bag> </class> </hibernate-mapping> I try to use formula to define the many-to-one relationship,but it doesn't work!Is there something wrong?Or is there other method? Thanks! ps,I use mysql database.

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• What noncluster index would be better to create on SQL Server?

  - by Junior Mayhé

  Here I am studying nonclustered indexes on SQL Server Management Studio. I've created a table with more than 1 million records. This table has a primary key. SELECT CustomerName FROM Customers Which leads the execution plan to show me: I/O cost = 3.45646 Operator cost = 4.57715 For the first attempt to improve performance, I've created a nonclustered index for this table: CREATE NONCLUSTERED INDEX [IX_CustomerID_CustomerName] ON [dbo].[Customers] ( [CustomerId] ASC, [CustomerName] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this first try, I've executed the select statement and the execution plan shows me: I/O cost = 2.79942 Operator cost = 3.92001 Now the second try, I've deleted this nonclustered index in order to create a new one. CREATE NONCLUSTERED INDEX [IX_CategoryName] ON [dbo].[Categories] ( [CategoryId] ASC ) INCLUDE ( [CategoryName]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO With this second try, I've executed the select statement and the execution plan shows me the same result: I/O cost = 2.79942 Operator cost = 3.92001 Am I doing something wrong or this is expected? Shall I use the first nonclustered index with two fields, or the second nonclustered with one field (CategoryID) including the second field (CategoryName)?

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• [C#] Linq doesn't insert associated entity on insert.

  - by Tomek

  Hello! I have simple mapping: [Table(Name="Person")] public class Person { private int id; private int state_id; private EntityRef<PersonState> state = new EntityRef<PersonState>(); [Column(IsPrimaryKey = true, Storage = "id", Name="id", IsDbGenerated = true, CanBeNull = false)] public int ID { get { return id; } set { id = value; } } [Column(Storage="state_id", Name="state_id")] public int StateID { get{ return state_id;} set{ state_id = value;} } [Association( Storage = "state", ThisKey = "StateID", IsForeignKey=true)] public PersonState State { get { return state.Entity; } set { state.Entity = value; } } } [Table(Name = "PersonState")] public class PersonState { private int id; private State state; [Column(Name="id", Storage="id", IsDbGenerated=true, IsPrimaryKey=true)] public int ID { get { return id; } set { id = value; } } [Column(Name = "date", Storage = "date")] public DateTime Date { get { return date; } set { date = value; } } [Column(Name = "type", Storage = "state")] public State State { get { return state; } set { state = value; } } } I use this code to insert new person with default state: private static Person NewPerson() { Person p = new Person(); p.State = DefaultState(p); return p; } private static PersonState DefaultState() { PersonState state = new PersonState(); state.Date = DateTime.Now; state.State = State.NotNotified; state.Comment = "Default State!"; return state; } Leater in code: db.Persons.InsertOnSubmit(NewPerson()); db.SubmitChanges(); In database(sqlite) I have all new persons, but state_id of all persons is set to 0, and PersonState table is empty. Why Linq did not insert any State object to database?

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• Draw a comparison between an integer in a specific row and a count

  - by XCoderX

  This is a follow-up question to this one: Check for specific integer in a row WHERE user = $name I want a user to be able to comment on my site for exactly five times a day. After this five times, the user has to wait 24 hours. In order to accomplish that I raise a counter in my MYSQL database, right next to the user. So where the name of the user is, there is where the counter gets raised. When it reaches 5 it should stop counting and reset after 24 hours. In order to check the time I use a timestamp. I check if the timestamp is older than 24 hours. If that is the case, the counter gets reseted (-5) and the user can comment again. In order to do that, I use the following code, however it never stops at five, my guess is that my comparison is wrong somehow: $counter = "SELECT FROM table VALUES CommentCounterReset WHERE Name = '$name'"; if(!isset($_SESSION['ts'])); { $_SESSION['ts'] = time(); } if ($counter >= 5) { if (time() - $_SESSION['ts'] <= 60*60*24){ echo "You already wrote five comments."; } else { $sql = "UPDATE table SET CommentCounterReset = CommentCounterReset-5 WHERE Name = '$name'"; } } else { $sql = "UPDATE table SET CommentCounterReset = CommentCounterReset+1 WHERE Name = '$name'"; echo "Your comment has been added."; }

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• Kohana 3.2 - Database Session losing data on new Page Request

  - by reado

  I've setup my dev Kohana server to use an encrypted database as the default Session type. I'm also using this in combination with Auth to implement user authentication. Right now my user's are able to authenticate correctly and the authentication keys are being stored in the session. I'm also storing additional data like the user's firstname and businessname during the login procedure. When my login function is ready to redirect the user to the user dashboard, I'm able to see all the data correctly when I do $session::instance()->as_array(); (Array ( [auth_user] => NRyk6lA8 [businessname] => Dudetown [firstname] => Matt )) As soon as I redirect the user to another page, $session::instance()->as_array(); is empty. By dumping out the Session::instance() object, I can see that the Session id's are still the same. When I look at my database table though, i dont see any session records being saved and my session table is empty. My bootstrap.php contains: Session::$default = 'database'; Cookie::$salt = 'asdfasdf'; Cookie::$expiration = 1209600; Cookie::$domain = FALSE; and my session.php config file looks like: return array( 'database' => array( 'name' => 'auth_user', 'encrypted' => TRUE, 'lifetime' => 24 * 3600, 'group' => 'default', 'table' => 'sessions', 'columns' => array( 'session_id' => 'session_id', 'last_active' => 'last_active', 'contents' => 'contents' ), 'gc' => 500, ), ); I've looked high and low for an answer.. if anyone has any suggestions, i'm all ears! Thanks!

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• What are the best practices for storing PHP session data in a database?

  - by undefined

  I have developed a web application that uses a web server and database hosted by a web host (on the ground) and a server running on Amazon Web Services EC2. Both servers may be used by a user during a session and both will need to know some session information about a user. I don't want to POST the information that is needed by both servers because I dont want it to be visible to browsers / Firebug etc. So I need my session data to persist across servers. And I think that this means that the best option is to store all / some of the data that I need in the database rather than in a session. The easiest thing to do seems to be to keep the sessions but to POST the session_id between servers and use this as the key to lookup the data I need from a 'user_session_data' table in the database. I have looked at Tony Marston's article "Saving PHP Session Data to a database" - should I use this or will a table with the session data that I need and session_id as key suffice? What would be the downside of creating my own table and set of methods for storing the data I need in the database?

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• Breadcrumbs in Fusebox 4/5

  - by Jordan Reiter

  I'm wondering if anyone has come up with a clean way to generate a breadcrumbs trail in Fusebox. Specifically, is there a way of keeping track of "where you are" and having that somehow generate the breadcrumbs for you? So, for example, if you're executing /index.cfm?fuseaction=Widgets.ViewWidget&widget=1 and the circuit structure is something like /foo/bar/widgets/ then somehow the system automatically creates an array like: [ { title: 'Foo', url: '#self#?fuseaction=Foo.Main' }, { title: 'Bar', url: '#self#?fuseaction=Bar.Main' }, { title: 'Widgets', url: '#self#?fuseaction=Widgets.Main' }, { title: 'Awesome Widget', url: '' } ] Which can then be rendered as Foo Bar Widgets Awesome Widget Right now it seems the only way to really do this is to create the structure for each fuseaction in a fuse of some kind (either the display fuse or a fuse dedicated to creating the crumbtrail).

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• Django Generating RSS feed with description

  - by Issy

  Hey Guys, I am trying to generate a full rss feed, however when loading the feed in Mail, it just shows the title, with a read more link at the bottom. I have tried several different options. But none seem to work. I would like to generate the feed with a combination of several feeds in my modl. Here is the code i have tried: class LatestEvents(Feed): description_template = "events_description.html" def title(self): return "%s Events" % SITE.name def link(self): return '/events/' def items(self): events = list(Event.objects.all().order_by('-published_date')[:5]) return events author_name = 'Latest Events' def item_pubdate(self, item): return item.published_date And in my template which is stored in TEMPLATE_ROOT/feeds/ {{ obj.description|safe }} <h1>Event Location Details</h1> {{ obj.location|safe }} Even if i hard code the description it does not work.

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• Coupling an MFC CListCtrl and CTreeCtrl to get a view of the whole tree, not just one node at a time

  - by omatai

  Consider Windows Explorer (or regedit or similar). To the left side, there is a tree view, and to the right, a list view. In all cases I know of, the contents of the right view reflect the attributes of the selected node from the left pane. This is all well and good... but just not what I want. The nodes of the tree I want to display have a very few attributes (2-3) associated with each node - a reasonable amount to display horizontally as a row in a table. Rather than waste all that list view space on a single node with very few properties, I would like to have my list view display a table of the whole tree's properties (as the part of the tree currently expanded). So the nth line in the left view (tree) will correspond directly to the nth line in the right view (list/table), and I will get a decent overview of the properties of my tree. Does anyone know of code that does this? I am guessing that slaving a CListCtrl to a CTreeCtrl would be the way to go, and somehow overriding the vertical scrolling functions so that they are locked together. I'm just not sure that it is possible to lock the scrolls together like this... among other things! All advice gratefully welcomed :-)

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• Align div inline

  - by Rajeev

  How to make the second div inline to the first div.I need the flash swf to appear next to the tds <html> <div style="display: inline"> <table style="table-layout:fixed;width:100%;"> <tr> <td width ="20%"> </td> </tr> <tr> <td width="20%"> 1.Can you view the image? </td> <td width="20%"> 1.Can you upload the image? </td> </tr> </table> </div> <div style="display: inline;"> <object width="100" height="100"> <embed src="image_tr.swf" width="250" height="250"> </embed> </object> </div>

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• Mysql partitioning: Partitions outside of date range is included

  - by Sturlum

  Hi, I have just tried to configure partitions based on date, but it seems that mysql still includes a partition with no relevant data. It will use the relevant partition but also include the oldest for some reason. Am I doing it wrong? The version is 5.1.44 (MyISAM) I first added a few partitions based on "day", which is of type "date" ALTER TABLE ptest PARTITION BY RANGE(TO_DAYS(day)) ( PARTITION p1 VALUES LESS THAN (TO_DAYS('2009-08-01')), PARTITION p2 VALUES LESS THAN (TO_DAYS('2009-11-01')), PARTITION p3 VALUES LESS THAN (TO_DAYS('2010-02-01')), PARTITION p4 VALUES LESS THAN (TO_DAYS('2010-05-01')) ); After a query, I find that it uses the "old" partition, that should not contain any relevant data. mysql> explain partitions select * from ptest where day between '2010-03-11' and '2010-03-12'; +----+-------------+------------+------------+-------+---------------+------+---------+------+------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+------------+-------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | ptest | p1,p4 | range | day | day | 3 | NULL | 79 | Using where | +----+-------------+------------+------------+-------+---------------+------+---------+------+------+-------------+ When I select a single day, it works: mysql> explain partitions select * from ptest where day = '2010-03-11'; +----+-------------+------------+------------+------+---------------+------+---------+-------+------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+------------+------------+------+---------------+------+---------+-------+------+-------+ | 1 | SIMPLE | ptest | p4 | ref | day | day | 3 | const | 39 | | +----+-------------+------------+------------+------+---------------+------+---------+-------+------+-------+

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• Planning a competition

  - by Jérôme

  I need to produce the schedule of a sport-event. There are 30 teams. Each team has to play 8 matches. This means that it is not possible for each team to compete again all other teams, but I need to avoid that two team compete more than once against each other. My idea was to generate all possible matches (for 30 teams: (30*29)/2 = 435 matches) and select from this list 120 matches (8 match for each team: 8 * 30 / 2 = 120 matches). This is where I'm having a hard time: how can I select these 120 matches? I tried some simple solutions (take first match of the list, then the last, and so on) but they don't seem to work with 30 teams. I also tried to generate all possible match combination and find which one is working but with 30 team, this is too much calculation time. Is there an existing algorithm that I could implement?

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• WCF data services (OData), query with inheritance limitation?

  - by Mathieu Hétu

  Project: WCF Data service using internally EF4 CTP5 Code-First approach. I configured entities with inheritance (TPH). See previous question on this topic: Previous question about multiple entities- same table The mapping works well, and unit test over EF4 confirms that queries runs smoothly. My entities looks like this: ContactBase (abstract) Customer (inherits from ContactBase), this entity has also several Navigation properties toward other entities Resource (inherits from ContactBase) I have configured a discriminator, so both Customer and Resource map to the same table. Again, everythings works fine on the Ef4 point of view (unit tests all greens!) However, when exposing this DBContext over WCF Data services, I get: - CustomerBases sets exposed (Customers and Resources sets seems hidden, is it by design?) - When I query over Odata on Customers, I get this error: Navigation Properties are not supported on derived entity types. Entity Set 'ContactBases' has a instance of type 'CodeFirstNamespace.Customer', which is an derived entity type and has navigation properties. Please remove all the navigation properties from type 'CodeFirstNamespace.Customer'. Stacktrace: at System.Data.Services.Serializers.SyndicationSerializer.WriteObjectProperties(IExpandedResult expanded, Object customObject, ResourceType resourceType, Uri absoluteUri, String relativeUri, SyndicationItem item, DictionaryContent content, EpmSourcePathSegment currentSourceRoot) at System.Data.Services.Serializers.SyndicationSerializer.WriteEntryElement(IExpandedResult expanded, Object element, ResourceType expectedType, Uri absoluteUri, String relativeUri, SyndicationItem target) at System.Data.Services.Serializers.SyndicationSerializer.<DeferredFeedItems>d__b.MoveNext() at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteItems(XmlWriter writer, IEnumerable`1 items, Uri feedBaseUri) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeedTo(XmlWriter writer, SyndicationFeed feed, Boolean isSourceFeed) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteFeed(XmlWriter writer) at System.ServiceModel.Syndication.Atom10FeedFormatter.WriteTo(XmlWriter writer) at System.Data.Services.Serializers.SyndicationSerializer.WriteTopLevelElements(IExpandedResult expanded, IEnumerator elements, Boolean hasMoved) at System.Data.Services.Serializers.Serializer.WriteRequest(IEnumerator queryResults, Boolean hasMoved) at System.Data.Services.ResponseBodyWriter.Write(Stream stream) Seems like a limitation of WCF Data services... is it? Not much documentation can be found on the web about WCF Data services (OData) and inheritance specifications. How can I overpass this exception? I need these navigation properties on derived entities, and inheritance seems the only way to provide mapping of 2 entites on the same table with Ef4 CTP5... Any thoughts?

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• vb.net sqlite how to loop through selected records and pass each record as a parameter to another fu

  - by mazrabul

  Hi, I have a sqlite table with following fields: Langauge level hours German 2 50 French 3 40 English 1 60 German 1 10 English 2 50 English 3 60 German 1 20 French 2 40 I want to loop through the records based on language and other conditions and then pass the current selected record to a different function. So I have the following mixture of actual code and psudo code. I need help with converting the psudo code to actual code, please. I am finding it difficult to do so. Here is what I have: Private sub mainp() Dim oslcConnection As New SQLite.SQLiteConnection Dim oslcCommand As SQLite.SQLiteCommand Dim langs() As String = {"German", "French", "English"} Dim i as Integer = 0 oslcConnection.ConnectionString = "Data Source=" & My.Settings.dbFullPath & ";" oslcConnection.Open() oslcCommand = oslcConnection.CreateCommand Do While i <= langs.count If langs(i) = "German" Then oslcCommand.CommandText = "SELECT * FROM table WHERE language = '" & langs(i) & "';" For each record selected 'psudo code If level = 1 Then 'psudo code update level to 2 'psudo code minorp(currentRecord) 'psudo code: calling minorp function and passing the whole record as a parameter End If 'psudo code If level = 2 Then 'psudo code update level to 3 'psudo code minorp(currentRecord) 'psudo code: calling minorp function and passing the whole record as a parameter End If 'psudo code Next 'psudo code End If If langs(i) = "French" Then oslcCommand.CommandText = "SELECT * FROM table WHERE language = '" & langs(i) & "';" For each record selected 'psudo code If level = 1 Then 'psudo code update level to 2 'psudo code minorp(currentRecord) 'psudo code: calling minorp function and passing the whole record as a parameter End If 'psudo code If level = 2 Then 'psudo code update level to 3 'psudo code minorp(currentRecord) 'psudo code: calling minorp function and passing the whole record as a parameter End If 'psudo code Next 'psudo code End If Loop End Sub Many thanks for your help.

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