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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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  • How to find the entity with the greatest primary key?

    - by simpatico
    I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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  • Linq to Entities Joins

    - by Bob Avallone
    I have a question about joins when using Linq to Entities. According to the documentation the use on the join without a qualifier performs like a left outer join. However when I execute the code below, I get a count returned of zero. But if I comment out the three join lines I get a count of 1. That would indicate that the join are acting as inner join. I have two questions. One which is right inner or outer as the default? Second how do I do the other one i.e. inner or outer? The key words on inner and outer do not work. var nprs = (from n in db.FMCSA_NPR join u in db.FMCSA_USER on n.CREATED_BY equals u.ID join t in db.LKUP_NPR_TYPE on n.NPR_TYPE_ID equals t.ID join s in db.LKUP_AUDIT_STATUS on n.NPR_STATUS_ID equals s.ID where n.ROLE_ID == pRoleId && n.OWNER_ID == pOwnerId && n.NPR_STATUS_ID == pNPRStatusId && n.ACTIVE == pActive select n).ToList(); if (nprs.Count() == 0) return null;

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  • drawbacks of storing all ''things' in a central table

    - by naiquevin
    Hi, I am not sure if there is a term to describe this, but I have observed that content management systems store all kinds of data in a single table with their bare minimum properties while the meta data is stored in another table in form of key value pairs. for eg. everything (blog posts, pages, images, events etc) is stored in one table and considered as a post. I understand that this allows for abstraction and easy extensibility we are considering designing our new project this way. It is not exactly a CMS but we plan to keep adding modules to it in stages. Lets say initially there will be only posts and images on which comments can be posted. Later on we might add videos which will also have the commenting feature. what are the drawbacks of this approach ? and will it work for a requirement like ours ? Thanks

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  • Many tables for many users?

    - by Seagull
    I am new to web programming, so excuse the ignorance... ;-) I have a web application that in many ways can be considered to be a multi-tenant environment. By this I mean that each user of the application gets their own 'custom' environment, with absolutely no interaction between those users. So far I have built the web application as a 'single user' environment. In other words, I haven't actually done anything to support multi-users, but only worked on the functionality I want from the app. Here is my problem... What's the best way to build a multi-user environment: All users point to the same 'core' backend. In other words, I build the logic to separate users via appropriate SQL queries (eg. select * from table where user='123' and attribute='456'). Each user points to a unique tablespace, which is built separately as they join the system. In this case I would simply generate ALL the relevant SQL tables per user, with some sort of suffix for the user. (eg. now a query would look like 'select * from table_ where attribute ='456'). In short, it's a difference between "select * from table where USER=" and "select * from table_USER".

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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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  • mysql query not running correctly from inside the application

    - by Mala
    I am completely stumped. Here is my php (CodeIgniter) code: function mod() { $uid = $this->session->userdata('uid'); $pid = $this->input->post('pid'); if ($this->_verify($uid,$pid)) { $name = $this->input->post('name'); $price = $this->input->post('price'); $curr = $this->input->post('curr'); $url = $this->input->post('url'); $query = $this->db->query("UPDATE items SET name=".$this->db->escape($name).", price=".$this->db->escape($price).", currency=".$this->db->escape($curr),", url=".$this->db->escape($url)." WHERE pid=".$this->db->escape($pid)." LIMIT 1"); } header('location: '.$this->session->userdata('current')); } The purpose of this code is to modify the properties (name, price, currency, url) of a row in the 'items' table (priary key is pid). However, for some reason, allowing this function to run once modifies the name, price, currency and url of ALL entries in the table, regardless of their pid and of the LIMIT 1 thing I tacked on the end of the query. It's as if the last line of the query is being completely ignored. As if this wasn't strance enough, I replaced "$query = $this->db->query(" with an "echo" to see the SQL query being run, and it outputs a query much like I would expect: UPDATE items SET name='newname', price='newprice', currency='newcurrency', url='newurl' WHERE pid='10' LIMIT 1 Copy-pasting this into a MySQL window acts exactly as I want: it modifies the row with the selected pid. What is going on here???

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  • Can I set ignore_dup_key on for a primary key?

    - by Mr. Flibble
    I have a two-column primary key on a table. I have attempted to alter it to set the ignore_dup_key to on with this command: ALTER INDEX PK_mypk on MyTable SET (IGNORE_DUP_KEY = ON); But I get this error: Cannot use index option ignore_dup_key to alter index 'PK_mypk' as it enforces a primary or unique constraint. How else should I set IGNORE_DUP_KEY to on?

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  • Alter multiple tables' columns length

    - by gdoron
    So, we just found out that 254 tables in our Oracle DBMS have one column named "Foo" with the wrong length- Number(10) instead of Number(3). That foo column is a part from the PK of the tables. Those tables have other tables with forigen keys to it. What I did is: backed-up the table with a temp table. Disabled the forigen keys to the table. Disabled the PK with the foo column. Nulled the foo column for all the rows. Restored all the above But now we found out it's not just couple of tables but 254 tables. Is there an easy way, (or at least easier than this) to alter the columns length? P.S. I have DBA permissions.

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  • Logic: Best way to sample & count bytes of a 100MB+ file

    - by Jami
    Let's say I have this 170mb file (roughly 180 million bytes). What I need to do is to create a table that lists: all 4096 byte combinations found [column 'bytes'], and the number of times each byte combination appeared in it [column 'occurrences'] Assume two things: I can save data very fast, but I can update my saved data very slow. How should I sample the file and save the needed information? Here're some suggestions that are (extremely) slow: Go through each 4096 byte combinations in the file, save each data, but search the table first for existing combinations and update it's values. this is unbelievably slow Go through each 4096 byte combinations in the file, save until 1 million rows of data in a temporary table. Go through that table and fix the entries (combine repeating byte combinations), then copy to the big table. Repeat going through another 1 million rows of data and repeat the process. this is faster by a bit, but still unbelievably slow This is kind of like taking the statistics of the file. NOTE: I know that sampling the file can generate tons of data (around 22Gb from experience), and I know that any solution posted would take a bit of time to finish. I need the most efficient saving process

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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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  • 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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  • How to load the SQL data into several ComboBox easily, am i doing the correctly or is there another way

    - by Dominic Deepan.d
    I have a Combobox to fill the data for City, State and PinCode these combobox is dopdown list and the user will pick it. and it loads once the form opens. Here is the CODE: /// CODE TO BRING A DATA FROM SQL INTO THE FORM DROP LIST /// To fill the sates from States Table cn = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True"); cmd= new SqlCommand("select * from TblState",cn); cn.Open(); SqlDataReader dr; try { dr = cmd.ExecuteReader(); while (dr.Read()) { SelectState.Items.Add(dr["State"].ToString()); } } catch (Exception ex) { MessageBox.Show(ex.Message); } finally { cn.Close(); } //To fill the Cities from City Table cn1 = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True"); cmd1 = new SqlCommand("SELECT * FROM TblCity", cn); cn.Open(); SqlDataReader ds; try { ds = cmd1.ExecuteReader(); while (ds.Read()) { SelectCity.Items.Add(ds["City"].ToString()); } } catch (Exception ex) { MessageBox.Show(ex.Message); } finally { cn1.Close(); } // To fill the Data in the Pincode from the City Table cn2 = new SqlConnection(@"Data Source=Nick-PC\SQLEXPRESS;Initial Catalog=AutoDB;Integrated Security=True"); cmd2 = new SqlCommand("SELECT (Pincode) FROM TblCity ", cn2); cn2.Open(); SqlDataReader dm; try { dm = cmd2.ExecuteReader(); while (dm.Read()) { SelectPinCode.Items.Add(dm["Pincode"].ToString()); } } catch (Exception ex) { MessageBox.Show(ex.Message); } finally { cn2.Close(); } its kinda Big, i am doing the same steps for all the combo-box, but is there a way i can merge it in a simple way.

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  • With SQL can you use a sub-query in a WHERE LIKE clause?

    - by Jason
    I'm not even sure how to even phrase this as it sounds weird conceptually, but I'll give it a try. Basically I'm looking for a way to create a query that is essentially a WHERE IN LIKE SELECT statement. As an example, if I wanted to find all user records with a hotmail.com email address, I could do something like: SELECT UserEmail FROM Users WHERE (UserEmail LIKE '%hotmail.com') But what if I wanted to use a subquery as the matching criteria? Something like this: SELECT UserEmail FROM Users WHERE (UserEmail LIKE (SELECT '%'+ Domain FROM Domains)) Is that even possible? If so, what's the right syntax?

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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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  • In django, how can I include some default records in my models.py?

    - by kdt
    If I have a models.py like class WidgetType(models.Model): name = models.CharField(max_length=200) class Widget(models.Model): typeid = models.ForeignKey(WidgetType) data = models.CharField(max_length=200) How can I build in a set of built in constant values for WidgetType when I know I'm only going to have a certain few types of widget? Clearly I could fire up my admin interface and add them by hand, but I'd like to simplify configuration by having it built into the python.

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  • Solr autocommit and autooptimize?

    - by Camran
    I will be uploading my website to a VPS soon. It is a classifieds website which uses Solr integrated with MySql. Solr is updated whenever a new classified is put or deleted. I need a way to make the commit() and optimize() be automated, for example once every 3 hours or so. How can I do this? (Details Please) When is it ideal to optimize? Thanks

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  • Set to null a parent record so that children are removed: howto?

    - by EugeneP
    How to delete a child row (on delete cascade ?) when setting a null value on a parent? Here's the db design. table A [id, b_id_1, b_id_2] table B [id, other fields...] b_id_1 and b_id_2 can be NULL if any of them is null, it means NO B records for corresponding FK (there are 2 of them) so (b_id_1,b_id_2) can be (null,null), (100, null), (null, 100_or_any_other_number) etc How in one SQL query both set b_id_1 or b_id_2 to null and delete all rows from B that have this id? What FK design should be applied to the 2 tables? what foreign keys should be added? A - B (FK_1: A.b_id_1 references B.id, FK_2: A.b_id_2 references B.id) and also B-A (FK_3: B.id references A.b_id_1, FK_4: B.id references A.b_id_2) ? But again, setting an A's b_id_1 or A's b_id_2 to null - will it remove any of B's records? I don't think so. So how to do that?

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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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  • Should I Use GUID or IDENTITY as Thread Number?

    - by user311509
    offerID is the thread # which represents the thread posted. I see in forums posts are represented by random numbers. Is this achieved by IDENTITY? If not, please advice. nvarchar(max) will carry all kind of texts along with HTML tags. CREATE TABLE Offer ( offerID int IDENTITY (4382,15) PRIMARY KEY, memberID int NOT NULL REFERENCES Member(memberID), title nvarchar(200) NOT NULL, thread nvarchar(max) NOT NULL, . . . );

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  • what does "out of range" mean?

    - by user329820
    Hi I have checked these statements with mysql and no error will happen and also the out put will be 0 rows BUT my friend checked it and he found an error for SELECT becaouse it is out of range !! IS he correct? thanks CREATE TABLE T1(A INTEGER NULL); SELECT * FROM T1;

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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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