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  • How to represent a 3-way relation with JPA?

    - by simpatico
    A user may have several labels, and links. Then, a user associates a label (or more) to a link. How does one represent the later relationship? A solution could be a many-to-many relationship btw user and link with the optional attribute label. http://en.wikibooks.org/wiki/Java_Persistence/ManyToMany#Mapping_a_Join_Table_with_Additional_Columns In this case the relationship btw user and label may better be 'virtual'. Any alternative I'm not seeing? PS: I've used google bookmarks terminology, as it matches my case quite well.

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  • dymanic columns in mysql tables?

    - by fayer
    i want to add dynamic columns in a mysql table. but i dont know exactly how. i want to let the user add some columns (fields) in a thread. eg. let him add a integer field and a value (eg. price: 199) or a string field and a value (eg. name: teddybear). the user can add as many field/value-pairs as he wants. i thought i could create a many-to-many table: thread <- thread_field <- field thread: id, title thread_field: field_id, thread_id, value field: id, name is this a good structure? but in this way i have to set a specific column type of thread_field.value. either its an integer or a string. i want to have the possibility to have it dymanic, let the user choose. how can i do this? thanks!

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  • How do I delete in Django? (mysql transactions)

    - by alex
    If you are familiar with Django, you know that they have a Authentication system with User model. Of course, I have many other tables that have a Foreign Key to this User model. If I want to delete this user, how do I architect a script (or through mysql itself) to delete every table that is related to this user? My only worry is that I can do this manually...but if I add a table , but I forget to add that table to my DELETE operation...then I have a row that links to a deleted, non-existing User.

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  • Why should I abstract my data layer?

    - by Gazillion
    OOP principles were difficult for me to grasp because for some reason I could never apply them to web development. As I developed more and more projects I started understanding how some parts of my code could use certain design patterns to make them easier to read, reuse, and maintain so I started to use it more and more. The one thing I still can't quite comprehend is why I should abstract my data layer. Basically if I need to print a list of items stored in my DB to the browser I do something along the lines of: $sql = 'SELECT * FROM table WHERE type = "type1"';' $result = mysql_query($sql); while($row = mysql_fetch_assoc($result)) { echo '<li>'.$row['name'].'</li>'; } I'm reading all these How-Tos or articles preaching about the greatness of PDO but I don't understand why. I don't seem to be saving any LoCs and I don't see how it would be more reusable because all the functions that I call above just seem to be encapsulated in a class but do the exact same thing. The only advantage I'm seeing to PDO are prepared statements. I'm not saying data abstraction is a bad thing, I'm asking these questions because I'm trying to design my current classes correctly and they need to connect to a DB so I figured I'd do this the right way. Maybe I'm just reading bad articles on the subject :) I would really appreciate any advice, links, or concrete real-life examples on the subject!

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  • select a database and in that select tables. using c# . use web config

    - by syedsaleemss
    Im using c# .net windows form application. I have many databases created using sql server Management studio 2005. Each database has several tables. i have a button, when clicked should allow me to select a database among several databases and in that database i want to select a single table. Later i need to display the contents of the selected table into a datagrid view.I came to know that it can be done using Webconfig. How can i acheive this? It goes like this a) select a database b) In that database select a table c) display the contents into a datagridview.

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  • Trying to create fields based on a case statement

    - by dido
    I'm having some trouble with the query below. I am trying to determine if the "category" field is A, B or C and then creating a field based on the category. That field would sum up payments field. But I'm running into error saying "incorrect syntax near keyword As". I am creating this in a SQL View. Using SQL Server 2008 SELECT r.id, r.category CASE WHEN r.category = 'A' then SUM(r.payment) As A_payments WHEN r.category = 'B' then SUM(r.payment) As B_payments WHEN r.category = 'C' then SUM(r.payment) As C_payments END FROM r_invoiceTable As r GROUP BY r.id, r.category I have data where all of the above cases should be executed because the data that I have has A,B and C Sample Data- r_invoiceTable Id --- Category ---- Payment 222 A ---- 50 444 A ---- 30 111 B ---- 90 777 C ---- 20 555 C ---- 40 Desired Output A_payments = 80, B_payments = 90, C_payments = 60

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  • Hibernate not Loading a class

    - by Noor
    Hi, I have a class Auction that contains a Class Item and Users but when I am getting the class, the class item and Users are not being loaded. Auction Class Mapping File: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <!-- Generated Dec 28, 2010 9:14:12 PM by Hibernate Tools 3.4.0.Beta1 --> <hibernate-mapping> <class name="com.BiddingSystem.Models.Auction" table="AUCTION"> <id name="AuctionId" type="long"> <column name="AUCTIONID" /> <generator class="native" /> </id> <property name="StartTime" type="java.util.Date"> <column name="STARTTIME" /> </property> <property name="EndTime" type="java.util.Date"> <column name="ENDTIME" /> </property> <property name="StartingBid" type="long"> <column name="STARTINGBID" /> </property> <property name="MinIncrement" type="long"> <column name="MININCREMENT" /> </property> <many-to-one name="CurrentItem" class="com.BiddingSystem.Models.Item" fetch="join" cascade="all"> <column name="ItemId" /> </many-to-one> <property name="AuctionStatus" type="java.lang.String"> <column name="AUCTIONSTATUS" /> </property> <property name="BestBid" type="long"> <column name="BESTBID" /> </property> <many-to-one name="User" class="com.BiddingSystem.Models.Users" fetch="join"> <column name="UserId" /> </many-to-one> </class> </hibernate-mapping> When I am doing this: Query query=session.createQuery("from Auction where UserId="+UserId); List <Auction> AllAuctions= new LinkedList<Auction>(query.list()); The Users and Item are null

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  • Mysql query question

    - by brux
    I have 2 tables: Customer: customerid - int, pri-key,auto fname - varchar sname -varchar housenum - varchar street -varchar Items: itemid - int,pri-key,auto type - varchar collectiondate - date releasedate - date customerid - int I need a query which will get me all items that have a releasedate 3 days prior to (and including) the current date. i.e The query should return customerid,fname,sname,street,housenum,type,releasedate for all items which have releasedate within (and including)3 days prior today thanks in advance

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  • Many-to-one relationship in SQLAlchemy

    - by Arrieta
    This is a beginner-level question. I have a catalog of mtypes: mtype_id name 1 'mtype1' 2 'mtype2' [etc] and a catalog of Objects, which must have an associated mtype: obj_id mtype_id name 1 1 'obj1' 2 1 'obj2' 3 2 'obj3' [etc] I am trying to do this in SQLAlchemy by creating the following schemas: mtypes_table = Table('mtypes', metadata, Column('mtype_id', Integer, primary_key=True), Column('name', String(50), nullable=False, unique=True), ) objs_table = Table('objects', metadata, Column('obj_id', Integer, primary_key=True), Column('mtype_id', None, ForeignKey('mtypes.mtype_id')), Column('name', String(50), nullable=False, unique=True), ) mapper(MType, mtypes_table) mapper(MyObject, objs_table, properties={'mtype':Relationship(MType, backref='objs', cascade="all, delete-orphan")} ) When I try to add a simple element like: mtype1 = MType('mtype1') obj1 = MyObject('obj1') obj1.mtype=mtype1 session.add(obj1) I get the error: AttributeError: 'NoneType' object has no attribute 'cascade_iterator' Any ideas?

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  • Use DataContext to create schema in an existing blank database file?

    - by jdk
    With a DataContext and a blank file-based database that already exists, is it possible to write the Data Context classes (i.e. the ones I added to the designer) to create the db schema? With a data context I only see the abilities to either: create a new database file and have its structure created at the same time, or to populate data into an existing database having preexisting schema. I'm looking for a hybrid solution between those two worlds. Update 1: My proof that a preexisting db is not compatible with the Data Context CreateDatabase() operation is this error Database 'C:...\App_Data\IntermediateData.mdf' already exists. Choose a different database name. based on this code using (IntermediateClassesDataContext intermediateContext = new IntermediateClassesDataContext(_getIntermediateConn())) { intermediateContext.CreateDatabase(); }

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  • DB management for Heroku apps

    - by zetarun
    Hi all, I'm fairly new to both Rails and Heroku but I'm seriously thinking of using it as a platform to deploy my Ruby/Rails applications. I want to use all the power of Heroku, so I prefer the "embedded" PostgreSQL managed by Heroku instead of the addon for Amazon RDS for MySQL, but I'm not so confident without the possibility to access my data in a SQL client... I know that in a well made app you have no need to access DB, but there are some situations (add rows to a config table, see data not mapped in a view, update some columns for debugging issues, performance monitoring, running queries for reporting, etc.) when this can be good... How do you solve this problem? What's you experience in a real life app powered by Heroku? Thanks!

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  • What tool for managing Oracle DB do you suggest?

    - by Artic
    What tool for managing Oracle DB do you suggest? I need to execute scripts and manage data in tables and develop some scripts and packages. I'v tried SQL developer and actually don't like it. Want some more features for developing (debug, code assist, integrated help and so on.)

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  • iPhone - Create not persistant entities in core data

    - by ncohen
    Hi everyone, I would like to use entity objects but not store them... I read that I could create them like this: myElement = (Element *)[NSEntityDescription insertNewObjectForEntityForName:@"Element" inManagedObjectContext:managedObjectContext]; And right after that remove them: [managedObjectContext deleteObject:myElement]; then I can use my elements: myElement.property1 = @"Hello"; This works pretty well even though I think this is probably not the most optimal way to do it... Then I try to use it in my UITableView... the problem is that the object get released after the initialization. My table becomes empty when I move it! Thanks

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  • Three-way full outer join in SQLite

    - by Vince
    I have three tables with a common key field, and I need to join them on this key. Given SQLite doesn't have full outer or right joins, I've used the full outer join without right join technique on Wikipedia with much success. But I'm curious, how would one use this technique to join three tables by a common key? What are the efficiency impacts of this (the current query takes about ten minutes)? Thanks!

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  • MySQL Query to get count of unique values?

    - by RD
    Hits Table: hid | lid | IP 1 | 1 | 123.123.123.123 2 | 1 | 123.123.123.123 3 | 2 | 123.123.123.123 4 | 2 | 123.123.123.123 5 | 2 | 123.123.123.124 6 | 2 | 123.123.123.124 7 | 3 | 123.123.123.124 8 | 3 | 123.123.123.124 9 | 3 | 123.123.123.124 As you can see, there following are the unique hits for the various lid: lid 1: 1 unique hit lid 2: 2 unique hits lid 3: 1 unique hit So basically, I need a query that will return the following: lid | uhits | 1 | 1 | 2 | 2 | 3 | 1 | Anybody know how to get that?

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  • Which MySql line is faster:

    - by Camran
    I have a classified_id variable which matches one document in a MySql table. I am currently fetching the information about that one record like this: SELECT * FROM table WHERE table.classified_id = $classified_id I wonder if there is a faster approach, for example like this: SELECT 1 FROM table WHERE table.classified_id = $classified_id Wont the last one only select 1 record, which is exactly what I need, so that it doesn't have to scan the entire table but instead stops searching for records after 1 is found? Or am I dreaming this? Thanks

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  • PHP - How to retrieve session in php

    - by Klaus Jasper
    I created a table that contains id - names - jobs and page that shows the names only and beside each name there is button Job and session that contains the id. this is my code $query = mysql_query("SELECT * FROM table"); while($fetch = mysql_fetch_array("$query")){ $name = $fetch['names']; $id = $fetch['id']; echo '</br>'; echo $name; $_SESSION['name'] = $id; echo "<button>Job</button>"; } I want when the user click on button Job redirect to a page that contains the job of that session. so how can I do it?

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  • Relation to multiple tables of different types for rating?

    - by Tronic
    i have a table structure like this Products Team Images and want to implement a rating/commenting-feature, where users can rate each entry of all tables. what's the best way to make a single rating table? e.g. a user votes a a product and a team entry, and it should be possible to get alle these entries from a single table. what kind of table-structure is best for this purpose? i hope, my questions is clear enough :/ thanks in advance!

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  • get n records at a time from a temporary table

    - by Claudiu
    I have a temporary table with about 1 million entries. The temporary table stores the result of a larger query. I want to process these records 1000 at a time, for example. What's the best way to set up queries such that I get the first 1000 rows, then the next 1000, etc.? They are not inherently ordered, but the temporary table just has one column with an ID, so I can order it if necessary. I was thinking of creating an extra column with the temporary table to number all the rows, something like: CREATE TEMP TABLE tmptmp AS SELECT ##autonumber somehow##, id FROM .... --complicated query then I can do: SELECT * FROM tmptmp WHERE autonumber>=0 AND autonumber < 1000 etc... how would I actually accomplish this? Or is there a better way? I'm using Python and PostgreSQL.

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