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  • privmsg system db schema

    - by Bartek
    I'm making a PM-system on my site. And I want to know ultimate db schema. I have always just used only 1 table. But my users have started complained that the messages in their outbox suddently dissapers =D Thats because if the other users deletes it, the one who sent it wont see it to. So im thinking of making another table with the same fields So im thinking something like this: privmsgs id | to | from | subject | message | date -- -- ---- ------- ------- ---- 1 76 893 blabla. blabla. 20100404 sent_msgs id | to | from | subject | message | date -- -- ---- ------- ------- ---- 1 76 893 blabla. blabla. 20100404 Whatya think? Sorry for my bad english

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  • Help Reading Binary Image Data from SQL Server into PHP

    - by Joe Majewski
    I cannot seem to figure out a way to read binary data from SQL server into PHP. I am working on a project where I need to be able to store the image directly in the SQL table, not on the file system. Currently, I have been using a query like this one: INSERT INTO myTable(Document) SELECT * FROM OPENROWSET(BULK N'C:\image.jpg', SINGLE_BLOB) as BLAH This works fine to actually insert the image into the table, but I haven't yet figured a way to retrieve it and get my image back. I am doing this with PHP, and ultimately will have to make a stored procedure out of it, but can anyone enlighten me on a way to get that binary data (varbinary(MAX)) and generate an image on the fly. I expected it to be simple to use a SELECT statement and add a content-type to the headers that indicated it was an image, but it's simply not working. Instead, the page will just display the name of the file, which I have encountered in the past and understand it to be an error with the image data.

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  • SQLite and PostgreSql longtext

    - by Nik
    Hello all, Does anyone know how to change a column in SQLite and PostgreSQL to LONGTEXT? I have done so in MySQL successfully with: "ALTER TABLE projects MODIFY description LONGTEXT;" But this clause doesn't seem to work on SQLite. I tried hard to find documentation on PostgreSQL, but that site's format really makes people puke. SQLite's website is better but the only command I find relevant, alter table, doesn't seem to support changing column data type at all. ( infact, it doesn't even allow changing column name!!!) Thanks all!

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  • Grouping Months of a particular Time span together using DateTime.

    - by Calibre2010
    public static string TimeLine2(this HtmlHelper helper, string myString2) { StringBuilder myString3 = new StringBuilder(); DateTime start = new DateTime(2010, 1, 1); DateTime end = new DateTime(2011, 12, 12); myString3.Append("<table>"); myString3.Append("<tr>"); for (DateTime date = start; date <= end; date = date.AddDays(1)) { DayOfWeek dw = date.DayOfWeek; var g = date.Month; var sun = " "; switch (dw) { case DayOfWeek.Sunday: sun = "S"; break; case DayOfWeek.Monday: sun = "M"; break; case DayOfWeek.Tuesday: sun = "T"; break; case DayOfWeek.Wednesday: sun = "W"; break; case DayOfWeek.Thursday: sun = "T"; break; case DayOfWeek.Friday: sun = "F"; break; case DayOfWeek.Saturday: sun = "S"; break; } myString3.Append("<td>" + sun + " " + g + "</td>"); } myString3.Append("</tr>"); myString3.Append("<tr>"); for (DateTime date = start; date <= end; date = date.AddDays(1)) { var f = date.Day; myString3.Append("<td>" + f + "</td>"); } myString3.Append("</tr>"); myString3.Append("</table>"); return myString3.ToString(); } Basically, what I have here is a few loops showing all the days of the week and also all the days in a month. This is all placed inside of a table, so you get MTWTFSSMT W T F S S M M TWTFSSM 12345678910 11 12 13 14 + + to 31 1234567 I'm trying to code a way in which I can split all of these days of the week and days in months so that my code returns each month with all its days in the month and all its days of the week, not just all my months between my timeSpan but splits them so MAY MTWTFSSMTWTFSSMTWTFSSMTWTFSSMTWTF 12345678 JUNE MTWTFSSMTWTFSSMTWTFSSMTWTFSSMTWTF 123456789

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  • upload image during registration in asp.net

    - by Vikrant
    I am developing a student registration form in asp.net. there are two tables viz std_registration and gallery(having pic_id and pic_url). During registration, before the click of submit button i want to retrieve pic_id from gallery table and then pass it to the insert query of registration table. image upload is an optional part. if no image is uploaded i want a default image to get uploaded. pls help me on this. thanx.

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  • Creating items in groups in Rails

    - by LearnRails
    My product table is id type price location 1 chips $3 aisle3 I have a question with adding the products in groups. There is a quantity field(nonmodel) where the user can enter the quantity While adding a new product if the user enters: type: soda quantity: 3 Then there 3 records should be created in product model with type= soda like the following. id type 2 soda 3 soda 4 soda If user enters location: aisle4 quantity: 2 Then id location 5 ailse4 6 ailse4 Can you tell me how to pass the nonmodel field 'quantity' to the rails(model or controller) and how use it to add the products in groups as mentioned above? or should I create a column called quantity in my product table? Will the history be updated too for all these new records with after_create filter which I already have ? Is there any good tutorial or book which shows how to pass such nonmodel html/javascript fields from view to rails and then back to the view? Any help will be greatly appreciated. Thanks

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  • Please for efficient query

    - by user278618
    I want to have efficient query to get some rows from my table. Here is I think the best presentation of my table. -Somedate is not duplicated - it is date of modifiedon -a,b,c are parent ids, let say countryCode -1,2,3,4 are subparent, let say citycode -guids are id of rows -true, false are values of rows - one can name this column - freshAir a 1 GUID somedate true a 1 GUID somedate true a 2 GUID somedate false a 2 GUID somedate false b 3 GUID somedate false b 3 GUID somedate false b 3 GUID somedate false b 4 GUID somedate false c 5 GUID somedate true c 6 GUID somedate true c 6 GUID somedate false c 6 GUID somedate false c 7 GUID somedate false I want the most recent rows MAX(modifiedon) grouped by countrycode and citycode and in this groups I need elements which have another values (true, false). And in result I want: a 1 GUID somedate true a 2 GUID somedate false c 5 GUID somedate true c 6 GUID somedate false c 7 GUID somedate false Look that in result I don't want to have records with "b", because all rows have the same value (false). Best regards

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  • IE8 alignment in div issue

    - by xrx215
    How to align the the button in center of div in IE8. Works fine in IE7 but not in IE8 <div id="dPopupFooter" style="background-color: #d9d9d9; position: absolute; z-index: 5; bottom: 0px; width: 100%; height: 30px; border-top: solid 1px #acacac; text-align: center; padding-top: 3px;"> <table><tr><td><xrx:CustomButton id="btnClose" runat="server" OnClientClick="ClosePopup();" /></td></tr></table> </div>

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  • SQLServer 2008 Pivot

    - by Mitch
    I need to show some information in a graph, the data is held in a SQL Server 2008 table. The graph is expecting 2 columns, one for QuestionNumber and the other for Score. The table containing the data has column names that correspond to the question numbers ie A1, A2, A3, A4, B1, B2, B3, B4, C1, C2. Each question is given a score of 1 to 5. I need to show a graph where the X axis shows A1, A2, A3 etc and the Y axis shows the score. I'm thinking I somehow need to rotate the data to achive this, but I'm not sure how. Maybe a different technique can acheive this rather that a Rotate, so I'm open to any ideas.

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  • CSS centering text between two images

    - by David Lively
    I need to display two images and some text like so: ------------------------------------------ img1--------some centered text-------img2 ------------------------------------------ img1 and img2 are not the same dimensions, but their widths are very close The text is variable depending on the page in which it is displayed, and may include two lines instead of one. The text needs to centered horizontally between the two images, or between the outside of the container (either will be fine) the text AND the images need to be centered vertically within the container. I can do this VERY easily with a table, but I'd rather not retreat to that for layout. The position:inline-block and display:table-cell attributes work great in some browsers, but I need to support IE6+.

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  • liquid CSS issues - rtl, floating and scrollers

    - by Rani
    hi I want to build a site that will have these restrictions: RTL direction vertical scroll on the right side whole page is floating to the right page has 2 columns the right (main) column has min width the right (main) column has table inside it that can expend in its data and get wider making all other data in the column expend to the same width as well the sidebar should be on the left side but still floating to the right of the main div it should fit low resolution so the page will be able to add horizontal scroll if needed should work in all major browsers don't use table for constructing the page Can someone help or direct me? Thanks Rani

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  • How do you make a Custom Data Generator for SQL XML DataType.

    - by Keith Sirmons
    Howdy, I am using Visual Studio 2010 and am playing around with the Database Projects. I am creating a DataGenerationPlan to insert data into a simple table, in which one of the column datatypes is XML. Out of the box, the generation plan uses the Regular Expression generator and generates something like this : HGcSv9wa7yM44T9x5oFT4pmBkEmv62lJ7OyAmCnL6yqXC2X.......... I am looking at creating a custom data Generator for this data type and have followed this site for the basics: http://msdn.microsoft.com/en-us/library/aa833244.aspx This example works if I am creating a string datatype and using it for a nvarchar datatype. What do I need to change to hook this Generator to the XML Datatype? Below are my code files. The string property works for nvarchar. The XElement property does not work for the xml datatype, and the RecordXMLDataGenerator is not listed as an option in the Generator column for the generation plan. CustomDataGenerators: using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Data.Schema.Tools.DataGenerator; using Microsoft.Data.Schema.Extensibility; using Microsoft.Data.Schema; using Microsoft.Data.Schema.Sql; using System.Xml.Linq; namespace CustomDataGenerators { [DatabaseSchemaProviderCompatibility(typeof(SqlDatabaseSchemaProvider))] public class RecordXMLDataGenerator : Generator { private XElement _RecordData; [Output(Description = "Generates string of XML Data for the Record.", Name = "RecordDataString")] public string RecordDataString { get { return _RecordData.ToString(SaveOptions.None); } } [Output(Description = "Generates XML Data for the Record.", Name = "RecordData")] public XElement RecordData { get { return _RecordData; } } protected override void OnGenerateNextValues() { base.OnGenerateNextValues(); XElement element = new XElement("Root", new XElement("Children1", 1), new XElement("Children6", 6) ); _RecordData = element; } } } XML Extensions File: <?xml version="1.0" encoding="utf-8" ?> <extensions assembly="" version="1" xmlns="urn:Microsoft.Data.Schema.Extensions" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:Microsoft.Data.Schema.Extensions Microsoft.Data.Schema.Extensions.xsd"> <extension type="CustomDataGenerators.RecordXMLDataGenerator" assembly="CustomDataGenerators, Version=1.0.0.0, Culture=neutral, PublicKeyToken=xxxxxxxxxxxx" enabled="true"/> </extensions> Table.sql: CREATE TABLE [dbo].[Record] ( id int IDENTITY (1,1) NOT NULL, recordData xml NULL, userId int NULL, test nvarchar(max) NULL, rowver rowversion NULL, CONSTRAINT pk_RecordID PRIMARY KEY (id) )

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  • Restoring multiple database backups in a transaction

    - by Raghu Dodda
    I wrote a stored procedure that restores as set of the database backups. It takes two parameters - a source directory and a restore directory. The procedure looks for all .bak files in the source directory (recursively) and restores all the databases. The stored procedure works as expected, but it has one issue - if I uncomment the try-catch statements, the procedure terminates with the following error: error_number = 3013 error_severity = 16 error_state = 1 error_message = DATABASE is terminating abnormally. The weird part is sometimes (it is not consistent) the restore is done even if the error occurs. The procedure: create proc usp_restore_databases ( @source_directory varchar(1000), @restore_directory varchar(1000) ) as begin declare @number_of_backup_files int -- begin transaction -- begin try -- step 0: Initial validation if(right(@source_directory, 1) <> '\') set @source_directory = @source_directory + '\' if(right(@restore_directory, 1) <> '\') set @restore_directory = @restore_directory + '\' -- step 1: Put all the backup files in the specified directory in a table -- declare @backup_files table ( file_path varchar(1000)) declare @dos_command varchar(1000) set @dos_command = 'dir ' + '"' + @source_directory + '*.bak" /s/b' /* DEBUG */ print @dos_command insert into @backup_files(file_path) exec xp_cmdshell @dos_command delete from @backup_files where file_path IS NULL select @number_of_backup_files = count(1) from @backup_files /* DEBUG */ select * from @backup_files /* DEBUG */ print @number_of_backup_files -- step 2: restore each backup file -- declare backup_file_cursor cursor for select file_path from @backup_files open backup_file_cursor declare @index int; set @index = 0 while(@index < @number_of_backup_files) begin declare @backup_file_path varchar(1000) fetch next from backup_file_cursor into @backup_file_path /* DEBUG */ print @backup_file_path -- step 2a: parse the full backup file name to get the DB file name. declare @db_name varchar(100) set @db_name = right(@backup_file_path, charindex('\', reverse(@backup_file_path)) -1) -- still has the .bak extension /* DEBUG */ print @db_name set @db_name = left(@db_name, charindex('.', @db_name) -1) /* DEBUG */ print @db_name set @db_name = lower(@db_name) /* DEBUG */ print @db_name -- step 2b: find out the logical names of the mdf and ldf files declare @mdf_logical_name varchar(100), @ldf_logical_name varchar(100) declare @backup_file_contents table ( LogicalName nvarchar(128), PhysicalName nvarchar(260), [Type] char(1), FileGroupName nvarchar(128), [Size] numeric(20,0), [MaxSize] numeric(20,0), FileID bigint, CreateLSN numeric(25,0), DropLSN numeric(25,0) NULL, UniqueID uniqueidentifier, ReadOnlyLSN numeric(25,0) NULL, ReadWriteLSN numeric(25,0) NULL, BackupSizeInBytes bigint, SourceBlockSize int, FileGroupID int, LogGroupGUID uniqueidentifier NULL, DifferentialBaseLSN numeric(25,0) NULL, DifferentialBaseGUID uniqueidentifier, IsReadOnly bit, IsPresent bit ) insert into @backup_file_contents exec ('restore filelistonly from disk=' + '''' + @backup_file_path + '''') select @mdf_logical_name = LogicalName from @backup_file_contents where [Type] = 'D' select @ldf_logical_name = LogicalName from @backup_file_contents where [Type] = 'L' /* DEBUG */ print @mdf_logical_name + ', ' + @ldf_logical_name -- step 2c: restore declare @mdf_file_name varchar(1000), @ldf_file_name varchar(1000) set @mdf_file_name = @restore_directory + @db_name + '.mdf' set @ldf_file_name = @restore_directory + @db_name + '.ldf' /* DEBUG */ print 'mdf_logical_name = ' + @mdf_logical_name + '|' + 'ldf_logical_name = ' + @ldf_logical_name + '|' + 'db_name = ' + @db_name + '|' + 'backup_file_path = ' + @backup_file_path + '|' + 'restore_directory = ' + @restore_directory + '|' + 'mdf_file_name = ' + @mdf_file_name + '|' + 'ldf_file_name = ' + @ldf_file_name restore database @db_name from disk = @backup_file_path with move @mdf_logical_name to @mdf_file_name, move @ldf_logical_name to @ldf_file_name -- step 2d: iterate set @index = @index + 1 end close backup_file_cursor deallocate backup_file_cursor -- end try -- begin catch -- print error_message() -- rollback transaction -- return -- end catch -- -- commit transaction end Does anybody have any ideas why this might be happening? Another question: is the transaction code useful ? i.e., if there are 2 databases to be restored, will SQL Server undo the restore of one database if the second restore fails?

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  • Relationship Modelling in Core Data

    - by Stevie
    Hi there, I'm fairly new to Objective C and Core Data and have a problem designing a case where players team up one-on-one and have multiple matches that end up with a specific result. With MySQL, I would have a Player table (player primary key, name) and a match table (player A foreign key, player B foreign key, result). Now how do I do this with Core Data? I can easily tie a player entity to a match entity using a relationship. But how do I model the inverse direction for the second player ref. in the match entity? Player Name: Attribute Match: Relationship Match Match Result: Attribute PlayerA: Relationship to Player (<- Inverse to Player.Match) PlayerB: Relationship to Player (<- Inverse to ????) Would be great if someone could give me an idea on this! Thanks, Stevie.

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  • doctrine2: many-to-one with non default referencedColumnName does not persist entity

    - by timaschew
    I'm using symfony 2.1.2 with FOSUserBundle. I extend the User from FOS and define a many-to-one (bidirectional) association to a Customer entity. I don't want to use primary key for the association (referencedColumnName). I will use another integer uniqe column: customer_no use FOS\UserBundle\Entity\User as BaseUser; /** * @ORM\Entity * @ORM\Table(name="t_myuser") */ class MyUser extends BaseUser { /** * @ORM\ManyToOne(targetEntity="Customer", inversedBy="user") * @ORM\JoinColumn(name="customer_no", referencedColumnName="customer_no", nullable=false) */ $public $customer; } /** * @ORM\Entity * @ORM\Table(name="t_customer") */ class Customer extends BaseEntity // provides an id (pk) { /** * @ORM\Column(type="integer", unique=true, nullable=false) */ public $customer_no; /** * @ORM\OneToMany(targetEntity="MyUser", mappedBy="customer") */ public $user; } When I try to persist (via a form) a new MyUser entity with an (already in db existing and) loaded Customer entity from db, I get this error: Notice: Undefined index: customer_no in ...\vendor\doctrine\orm\lib\Doctrine\ORM\Persisters\BasicEntityPersister.php line 608 The schema on the db is all right. //update: I fix the inversedBy and mappedBy stuff, but this is not the problem.

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  • Efficiency of checking for null varbinary(max) column ?

    - by Moe Sisko
    Using SQL Server 2008. Example table : CREATE table dbo.blobtest (id int primary key not null, name nvarchar(200) not null, data varbinary(max) null) Example query : select id, name, cast((case when data is null then 0 else 1 end) as bit) as DataExists from dbo.blobtest Now, the query needs to return a "DataExists" column, that returns 0 if the blob is null, else 1. This all works fine, but I'm wondering how efficient it is. i.e. does SQL server need to read in the whole blob to its memory, or is there some optimization so that it just does enough reads to figure out if the blob is null or not ? (FWIW, the sp_tableoption "large value types out of row" option is set to OFF for this example).

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  • SSRS: Report label position dynamic

    - by Nauman
    I have a report which displays customer address in multiple labels. My customers use windowed envelopes for mailing. I need the address labels position to be configurable. Something like, I'll have a database table which stores the Top/Left position of each label per customer. Based on this table, I need to position the address labels on my report. I thought, it is doable by expressions, but Location property doesn't provides ability to set an expression and make the label's top and left dynamic. Anybody, any ideas, on how to achieve this?

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  • T-SQL Re-Assigning Order Numbering

    - by Meltdown
    Say I have a table with a field called "ordernum" that denotes the order of a given set of rows. Now imagine that I delete one of these rows. What type of query would work best for re-assigning the order numbers so that they remain sequential? Here's an example: id group_id name ordernum active --------------------------------------------------- 0_____0______'Name1'___5__true 1_____0______'Name2'___4__true 2_____0______'Name3'___3__true 3_____1______'Name4'___2__true 4_____1______'Name5'__1__true 5_____1______'Name6'__NULL___false Now if I deleted the column with id='4' how would I reset the values in the 'ordernum' field for that specific group? Is this even possible? Or if I added a new row. (The first time the rows are created they are sorted by date, but then the user has the option to set the order himself.) In my table design I have a column 'active' boolean. If 'active' is set to false, then 'ordernum' is set to NULL. Otherwise it should be given an order number.

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  • derby + hibernate ConstraintViolationException using manytomany relationships

    - by user364470
    Hi, I'm new to Hibernate+Derby... I've seen this issue mentioned throughout the google, but have not seen a proper resolution. This following code works fine with mysql, but when I try this on derby i get exceptions: ( each Tag has two sets of files and vise-versa - manytomany) Tags.java @Entity @Table(name="TAGS") public class Tags implements Serializable { @Id @GeneratedValue(strategy=GenerationType.AUTO) public long getId() { return id; } @ManyToMany(targetEntity=Files.class ) @ForeignKey(name="USER_TAGS_FILES",inverseName="USER_FILES_TAGS") @JoinTable(name="USERTAGS_FILES", joinColumns=@JoinColumn(name="TAGS_ID"), inverseJoinColumns=@JoinColumn(name="FILES_ID")) public Set<data.Files> getUserFiles() { return userFiles; } @ManyToMany(mappedBy="autoTags", targetEntity=data.Files.class) public Set<data.Files> getAutoFiles() { return autoFiles; } Files.java @Entity @Table(name="FILES") public class Files implements Serializable { @Id @GeneratedValue(strategy=GenerationType.AUTO) public long getId() { return id; } @ManyToMany(mappedBy="userFiles", targetEntity=data.Tags.class) public Set getUserTags() { return userTags; } @ManyToMany(targetEntity=Tags.class ) @ForeignKey(name="AUTO_FILES_TAGS",inverseName="AUTO_TAGS_FILES") @JoinTable(name="AUTOTAGS_FILES", joinColumns=@JoinColumn(name="FILES_ID"), inverseJoinColumns=@JoinColumn(name="TAGS_ID")) public Set getAutoTags() { return autoTags; } I add some data to the DB, but when running over Derby these exception turn up (the don't using mysql) Exceptions SEVERE: DELETE on table 'FILES' caused a violation of foreign key constraint 'USER_FILES_TAGS' for key (3). The statement has been rolled back. Jun 10, 2010 9:49:52 AM org.hibernate.event.def.AbstractFlushingEventListener performExecutions SEVERE: Could not synchronize database state with session org.hibernate.exception.ConstraintViolationException: could not delete: [data.Files#3] at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96) at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66) at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:2712) at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:2895) at org.hibernate.action.EntityDeleteAction.execute(EntityDeleteAction.java:97) at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:268) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:260) at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:184) at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321) at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51) at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1206) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:613) at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:344) at $Proxy13.flush(Unknown Source) at data.HibernateORM.removeFile(HibernateORM.java:285) at data.DataImp.removeFile(DataImp.java:195) at booting.DemoBootForTestUntilTestClassesExist.main(DemoBootForTestUntilTestClassesExist.java:62) I have never used derby before so maybe there is something crutal that i'm missing 1) what am I doing wrong? 2) is there any way of cascading properly when I have 2 many-to-many relationships between two classes? Thanks!

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  • EF problem with entity re-ordering and uniqueness constraint

    - by wpfwannabe
    I am using Entity Framework and I've come to an interesting stumbling block. Let's say there is a db table "Item" with "sequence" column of type int (and others of course). Column "sequence" must be unique and it is used for (re)ordering of items. EF maps this table to "Item" class with "sequence" int property. Now let's say I want to swap position of two items by mutually exchanging each other's sequence number. Upon calling SaveChanges() EF throws an exception complaining about "sequence" uniqueness. It probably generates two UPDATEs and the first one probably fails. I assume that plain SQL solution to this issue is using a third UPDATE to introduce a unique sequence value in the process but I am stuck with EF. Any thoughts?

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  • MySQL - how long to create an index?

    - by user293594
    Can anyone tell me how adding a key scales in MySQL? I have 500,000,000 rows in a database, trans, with columns i (INT UNSIGNED), j (INT UNSIGNED), nu (DOUBLE), A (DOUBLE). I try to index a column, e.g. ALTER TABLE trans ADD KEY idx_A (A); and I wait. For a table of 14,000,000 rows it took about 2 minutes to execute on my MacBook Pro, but for the whole half a billion, it's taking 15hrs and counting. Am I doing something wrong, or am I just being naive about how indexing a database scales with the number of rows?

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  • operating systems - TLBs

    - by stabGreeol
    I'm trying to get my head round this (okay, tbh cramming a night before the exams :) but i can't figure out (nor find a good high level overview on the net) of this: 'page table entries can be mapped to more than one TLB entry.. if for example every page table entry is mappped to two TLB entries, this is know as 2-way set associative TLB' My question is, why would we want to map this more than once? surely we want to have the maximum number of possible entries represented in the TLB, and duplication would waste space right ? What am i missing? Many thanks

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  • Why doesn't this (translated) VB.NET code work?

    - by ropstah
    I had a piece of C# code converted, but the translated code isn't valid... Can somebody help out? C# <table> <% Html.Repeater<Hobby>("Hobbies", "row", "row-alt", (hobby, css) => { %> <tr class="<%= css %>"> <td><%= hobby.Title%></td> </tr> <% }); %> </table> VB <% Html.Repeater(of Jrc3.BLL.Product)(Model.ProductCollectionByPrcAutoKey, "row", "row-alt", Function(product, css) Do %> <tr class="<%= css %>"> <td><%= hobby.Title%></td> </tr> <% End Function)%>

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  • How to define one-to-many connection between a same model through another model

    - by Mekajiki
    I want to define one-to-many relationship as follows; User has one introducer User has many newcomers(who is introduced by the user) Use "Introduction" model instead of adding a column to users table. My table and model definition is as follows; DB Scheme: create_table "introductions", force: true do |t| t.integer "introducer_id" t.integer "newcomer_id" t.datetime "created_at" t.datetime "updated_at" User model: class User < ActiveRecord::Base has_many :introductions, foreign_key: :introducer_id has_many :newcomers, through: :introductions, source: :newcomer belongs_to :introduction, foreign_key: :newcomer_id belongs_to :introducer end Introduction model: class Introduction < ActiveRecord::Base belongs_to :introducer, class_name: 'User' belongs_to :newcomer, class_name: 'User' end This works fine: user1.newcomers.push user2 but, user2.introducer # => nil How can I define belongs_to relationship correctly?

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