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• Specify sorting order for a GROUP BY query to retrieve oldest or newest record for each group

  - by Beau Simensen

  I need to get the most recent record for each device from an upgrade request log table. A device is unique based on a combination of its hardware ID and its MAC address. I have been attempting to do this with GROUP BY but I am not convinced this is safe since it looks like it may be simply returning the "top record" (whatever SQLite or MySQL thinks that is). I had hoped that this "top record" could be hinted at by way of ORDER BY but that does not seem to be having any impact as both of the following queries returns the same records for each device, just in opposite order: SELECT extHwId, mac, created FROM upgradeRequest GROUP BY extHwId, mac ORDER BY created DESC SELECT extHwId, mac, created FROM upgradeRequest GROUP BY extHwId, mac ORDER BY created ASC Is there another way to accomplish this? I've seen several somewhat related posts that have all involved sub selects. If possible, I would like to do this without subselects as I would like to learn how to do this without that.

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• Random select is not always returning a single row.

  - by Lieven

  The intention of following (simplified) code fragment is to return one random row. Unfortunatly, when we run this fragment in the query analyzer, it returns between zero and three results. As our input table consists of exactly 5 rows with unique ID's and as we perform a select on this table where ID equals a random number, we are stumped that there would ever be more than one row returned. Note: among other things, we already tried casting the checksum result to an integer with no avail. DECLARE @Table TABLE ( ID INTEGER IDENTITY (1, 1) , FK1 INTEGER ) INSERT INTO @Table SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 SELECT * FROM @Table WHERE ID = ABS(CHECKSUM(NEWID())) % 5 + 1

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• Hibernate - why use many-to-one to represent a one-to-one?

  - by aberrant80

  I've seen people use many-to-one mappings to represent one-to-one relationships. I've also read this in a book by Gavin King and on articles. For example, if a customer can have exactly one shipping address, and a shipping address can belong to only one customer, the mapping is given as: <class name="Customer" table="CUSTOMERS"> ... <many-to-one name="shippingAddress" class="Address" column="SHIPPING_ADDRESS_ID" cascade="save-update" unique="true"/> ... </class> The book reasons as (quoting it): "You don't care what's on the target side of the association, so you can treat it like a to-one association without the many part." My question is, why use many-to-one and not one-to-one? What is it about a one-to-one that makes it a less desirable option to many-to-one? Thanks.

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• Hibernate many-to-one - bad usage?

  - by DaveA

  Just trying out Hibernate (with Annotations) and I'm having problems with my mappings. I have two entity classes, AudioCD and Artist. @Entity public class AudioCD implements CatalogItem { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; private String title; @ManyToOne(cascade = { CascadeType.ALL }, optional = false) private Artist artist; .... } @Entity @Table(uniqueConstraints = { @UniqueConstraint(columnNames = { "name" }) }) public class Artist { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; @Column(nullable = false) private String name; ..... } I get AudioCD objects from an external source. When I try to persist the AudioCD the Artist gets persisted as well, just like I want to happen. If I try persisting another different CD, but Artist already exists I get errors due to constraint violations. I want Hibernate to recognise that the Artist already exists and shouldn't be inserted again. Can this be done via annotations? Or do I have to manage the persistence of the AudioCD and Artist seperately?

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• Using a JSON web service from a Java client application

  - by user383341

  I am developing a client-side Java application that has a bit of functionality that requires getting data from some web services that transmit in JSON (some RESTful, some not). No JavaScript, no web browser, just a plain JAR file that will run locally with Swing for the GUI. This is not a new or unique problem; surely there must be some open source libraries out there that will handle the JSON data transmission over HTTP. I've already found some that will parse JSON, but I'm having trouble finding any that will handle the HTTP communication to consume the JSON web service. So far I've found Apache Axis2 apparently which might have at least part of the solution, but I don't see enough documentation for it to know if it will do what I need, or how to use it. Maybe part of the problem is that I don't have experience with web services so I'm not able to know a solution when I see it. I hope some of you can point me in the right direction. Examples would be helpful.

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• how to create a auto-incremented attribute in xcode managed object model

  - by Mausimo

  Hey, what i want to do is to make a int that will be the ID of the entity and auto increment itself whenever a new entity is added (just like a SQL identity property). Is this possible? i tried using indexed (checked on attribute) however there is no description to what indexed even does. EDIT: I am adding annotations to a map, when you click the pin the annotationview with a chevron shows up. Now when you click this button i would like to load an associated picture. However the only way i know how to link the picture to this button is to give the picture a unique id, and then set the button.tag to this id and then load based on the button.tag.

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• SQL: Is it quicker to insert sorted data into a table?

  - by AngryWhenHungry

  A table in Sybase has a unique varchar(32) column, and a few other columns. It is indexed on this column too. At regular intervals, I need to truncate it, and repopulate it with fresh data from other tables. insert into MyTable select list_of_columns from OtherTable where some_simple_conditions order by MyUniqueId If we are dealing with a few thousand rows, would it help speed up the insert if we have the order by clause for the select? If so, would this gain in time compensate for the extra time needed to order the select query? I could try this out, but currently my data set is small and the results don't say much.

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• Scraping html WITHOUT uniquie identifiers using python

  - by Nicholas Law

  I would like to design an algorithm using python that scrapes thousands of pages like this one and this one, gathers all the data and inserts it into a MySQL database. The script will be run on a weekly or bi-weekly basis to update the database of any new information added to each individual page. Ideally I would like a scraper that is easy to work with for table structured data but also data that does not have unique identifiers (ie. id and classes attributes). Which scraper add-on should I use? BeautifulSoup, Scrapy or Mechanize? Are there any particular tutorials/books I should be looking at for this desired result? In the long-run I will be implementing a mobile app that works with all this data through querying the database.

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• JPA hibernate OneToOne mapping

  - by Stupidfrog

  enviroment: hibernate 4.1.6.final spring 3.1.2.release spring jpa 1.1.0.release postgresql 9.1-901-1.jdbc4 there is 2 table public A { private Long id; private Long name; } public B { private Long id; private Long table_a_id; } the A.id and B.id is sequential, unique , but no related.(means they are separately id for their own table). how to do mapping? i have tried some method, however the result is not i wanted, because it bind wrong. for example: public A { .... @OneToOne @JoinColumn(name = "id") private B table_b } public B { ... @JsonIgnore @OneToOne(mappedBy = "table_b") private A table_a; } when i query A the result is { "id":5, "table_b":{ "id":5, "table_a_id":4 } } obviously the data join by using their id but not joining using table_a_id. what i expect is { "id":4, "table_b":{ "id":5, "table_a_id":4 } } so can somebody teach me that, how to map this 2 table by using table b table_a_id(foregin key)

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• Why does this javascript code have an infinite loop?

  - by asdas

  optionElements is a 2d array. Each element has an array of length 2. These are an integer number and an element. I have a select list called linkbox, and i want to add all of the elements to the select list. The order I want them to go in is important, and is determined by the number each element has. It should be smallest to highest. So think of it like this: optionElements is: [ [5, <option>], [3, <option], [4, <option], [1, <option], [2, <option]] and it would add them to link box in order of those numbers. BUT that is not what happens. It is an infinite loop after the first time. I added the x constraint just to stop it from freezing my browser but you can ignore it. var b; var smallest; var samllestIndex; var x = 0; while(optionElements.length > 0 && ++x < 100) { smallestIndex = 0; smallest = optionElements[0][0]; b = 0; while( ++b < optionElements.length) { if(optionElements[b][0] > smallest) { smallestIndex = b; smallest = optionElements[b][0]; } } linkbox.appendChild(optionElements[smallestIndex][1]); optionElements.unshift(optionElements[smallestIndex]); } can someone point out to me where my problem is?

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• Where does the data model go in a Prism app?

  - by HawkeyeJoeS

  I'm having trouble where to put our data model in our Prism app. Most, if not all or our data will be coming from web services and the web services are unique for each module. Unfortunately, there will be objects that need to be shared (such as a person/user object). I'm really torn about whether to add these services directly to the module, so that each is truly independent, or create a separate project to house the web service proxies and business entities. The modules are being built by different teams, but will all live in the same solution (and source control, of course).

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• .Net Round-trip Types

  - by Fujiy

  I making a method that generate a unique string key for some parameters. But the same key if call with same values. I just accept primitive types, string, DateTime, Guid, and Nullable(since I append types together, I can distinguish who is int and who is int?), because I can convert all to string without lost values or precision.(for float and double a use ToString("R"), to DateTime ToString("O")). Exists a easy way to know which types I can transform in strings without conflict? And how do this transform(how I said before, float, double and datetime have specific ways) Thanks

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• batch - append either date/time of creation or random to end of filename

  - by Maclovin

  Hi Damsel in distress needing help with a batch-script. I have a bunch of files that one system creates. Either in one of 2 directories, or in the directory above that. The naming is apparently not very important, so It's a bit random. 2 questions for you batch-geniuses out there. a) How can I append date/time of creation to the end of the filename with a batch-script? b) How can I append a random filename (so I make the files unique) with a batch-script? Thanks in advance, dudes and dudettes. Yours sincerely, the Maclovin!

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• using exchange server account

  - by Jack

  I m developing ASP.Net project in company. Every user has an unique exchange account. Im trying to authenticate the user based on teh user's Exchange credentials for web project. I want to use exchange server account for each user. I just dont want to add users to database, because they already have userid and password in exchange server. For example; User id: user_email pass: users email password How can I use this data in my c#.net project? Thanks.

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• Secure to store an ID in an ASP.NET control ID?

  - by Curtis White

  I'm auto-generating a form in my ASP.NET page. This is already tested and working. I want to know if: If there are any security problems with storing the database ID as part of my controls ID? I can see think of 2 issues: the id will be visible in page source (not really important in this case), and the possibility someone could change the name of the control somehow? This second possibility is more serious. Is this a potential problem and how to void it? If there would be a better preferred way to associate a unique data with any type of control? Is it possible to store a custom item in the viewstate for the control?

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• How can one change the primary key using NHibernate.

  - by mark

  Dear ladies and sirs. I want to change the primary key of an entity in database, so that all the relevant foreign key constraints are updated as well./We are using NHibenate as our ORM. Is it possible to do it? Thanks. P.S. I know the practice of changing the primary key is highly discouraged. My problem is that my primary key is backed by a natural Id of the entity, which may sometimes change. We could, theoretically, utilize a unique primary key, unrelated to the natural key of the entity, but this complicates things too much in other places, so this is not an option.

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• How to map it? HasOne x References

  - by Felipe

  Hi everyones, I need to make a mapping One by One, and I have some doubts. I have this classes: public class DocumentType { public virtual int Id { get; set; } /* othes properties for documenttype */ public virtual DocumentConfiguration Configuration { get; set; } public DocumentType () { } } public class DocumentConfiguration { public virtual int Id { get; set; } /* some other properties for configuration */ public virtual DocumentType Type { get; set; } public DocumentConfiguration () { } } A DocumentType object has only one DocumentConfiguration, but it is not a inherits, it's only one by one and unique, to separate properties. How should be my mappings in this case ? Should I use References or HasOne ? Someone could give an example ? When I load a DocumentType object I'd like to auto load the property Configuration (in documentType). Thanks a lot guys! Cheers

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• Is this method of static file serving safe in node.js? (potential security hole?)

  - by MikeC8

  I want to create the simplest node.js server to serve static files. Here's what I came up with: fs = require('fs'); server = require('http').createServer(function(req, res) { res.end(fs.readFileSync(__dirname + '/public/' + req.url)); }); server.listen(8080); Clearly this would map http://localhost:8080/index.html to project_dir/public/index.html, and similarly so for all other files. My one concern is that someone could abuse this to access files outside of project_dir/public. Something like this, for example: http://localhost:8080/../../sensitive_file.txt I tried this a little bit, and it wasn't working. But, it seems like my browser was removing the ".." itself. Which leads me to believe that someone could abuse my poor little node.js server. I know there are npm packages that do static file serving. But I'm actually curious to write my own here. So my questions are: Is this safe? If so, why? If not, why not? And, if further, if not, what is the "right" way to do this? My one constraint is I don't want to have to have an if clause for each possible file, I want the server to serve whatever files I throw in a directory.

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• How to remove options from select element using jquery?

  - by Lapa

  I have n drop-downs like this: <select id="select1"> <option>1</option> <option>2</option> <option>3</option> </select> <select id="select2"> <option>1</option> <option>2</option> <option>3</option> </select> with identical options. All the choices should be unique, so once the option is selected in one combobox, it should be removed from others. Now, http://stackoverflow.com/questions/877328/jquery-disable-select-options-based-on-radio-selected-need-support-for-all-brows offers a nice solution, but how can I modify this to work with selects instead of radio buttons?

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• Should i really use integer primary IDs [sql]

  - by arthurprs

  For example, i always generate an auto-increment field for the users table, but i also specifies an UNIQUE index on their usernames. There is situations that i first need to get the userId for a given username and then execute the desired query. Or use a JOIN in the desired query. It's 2 trips to the database or a JOIN vs. a varchar index The above is just an example There is a real performance benefit on INT over small VARCHAR indexes? Thanks in advance!

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• importing data using get or create - identity error 1062

  - by hamackey

  I am importing data from a mssql database into mysql. Works except when it encounters the id of a previous entry. id is unique. I need to get entries that already exist so that they can be placed in the work of the day. Error is IntegrityError: (1062, "Duplicate entry '001355338' for key 2") This entry is already in the database. I need it entered for that day, but can not have it added to the table. It is already there. def handle(self, *args, **options): 59 #patients_local = Patient.objects.all() 60 #attendings_local = Attending.objects.all() 61 connection = pyodbc.connect("XXXXXXXXXXX") 62 cursor = connection.cursor() 63 cursor.execute(COMMAND) 64 rows = cursor.fetchall() 65 for row in rows: 66 # get_or_create returns (object, boolean) 67 p, created = Patient.objects.get_or_create( 68 first_name = row.Firstname, 69 middle_name = '', 70 last_name = row.Lastname, 71 id = row.id, 72 )

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• Codeigniter: how should I restructure db schema?

  - by Kevin Brown

  I don't even know if that's the right term. May it be known that I'm a major novice! I have three tables: users, profiles, and survey. Each one has user_id as it's first field, (auto-increment for users), and they're all tied by a foreign key constraint, CASCADE on DELETE. Currently, for each user, let's say user_id 1, they have a corresponding db entry in the other tables. For profiles it lists all their information, and the survey table holds all their survey information. Now I must change things...darn scope creep. Users need the ability to have multiple survey results. I imagine that this would be similar to a comment table for a blog... My entire app runs around the idea that a single user is linked to a constraining profile and survey. How should I structure my db? How should I design my app's db so that a user can have multiple tests/profiles for the test? Please assist! Any advice, information and personal-knowledge is appreciated! Right now the only way I know how to accompany my client is to create a pseudo-user for each test (so unnecessary) and list them in a view table (called "your tests")-- these are obtained from the db by saying: where user_id=manager_id

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• Batch processing JDBC

  - by Wai Hein

  I am practicing JDBC batch processing and having errors: error 1: Unsupported feature error 2: Execute cannot be empty or null Property files include: itemsdao.updateBookName = Update Books set bookname = ? where books.id = ? itemsdao.updateAuthorName = Update books set authorname = ? where books.id = ? I know I can execute about DML statements in one update, but I am practicing batch processing in JDBC. Below is my method public void update(Item item) { String query = null; try { connection = DbConnector.getConnection(); property = SqlPropertiesLoader.getProperties("dml.properties"); connection.setAutoCommit(false); if ( property == null ) { Logging.log.debug("dml.properties does not exist. Check property loader or file name is spelled right"); return; } query = property.getProperty("itemsdao.updateBookName"); statement = connection.prepareStatement(query); statement.setString(1, item.getBookName()); statement.setInt(2, item.getId()); statement.addBatch(query); query = property.getProperty("itemsdao.updateAuthorName"); statement = connection.prepareStatement(query); statement.setString(1, item.getAuthorName()); statement.setInt(2, item.getId()); statement.addBatch(query); statement.executeBatch(); connection.commit(); }catch (ClassNotFoundException e) { Logging.log.error("Connection class does not exist", e); } catch (SQLException e) { Logging.log.error("Violating PK constraint",e); } //helper class th finally { DbUtil.close(connection); DbUtil.closePreparedStatement(statement); }

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• jquery dynamically genearate element id in a loop

  - by phil

  This is a loop in a function intending to create elements <li> and give each <li> an unique id. But it's not working. I suspect it's a simple syntax error with the use of quote in .attr(). But I can't get a straight answer from Google. for (i=0;i<array.length;i++) { //create HTML element of tag li $('#suggest').append("<li></li>"); $("li").attr("id",'li'+i); $('#li'+i).html(array[i]); }

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• hibernate: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException

  - by user121196

  when saving an object to database using hibernate, sometimes it fails because certain fields of the object exceed the maximum varchar length defined in the database. There force I am using the following approach: 1. attempt to save 2. if getting an DataException, then I truncate the fields in the object to the max length specified in the db definition, then try to save again. However, in the second save after truncation. I'm getting the following exception: hibernate: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails here's the relevant code, what's wrong? public static void saveLenientObject(Object obj){ try { save2(rec); } catch (org.hibernate.exception.DataException e) { // TODO Auto-generated catch block e.printStackTrace(); saveLenientObject(rec, e); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } } private static void saveLenientObject(Object rec, DataException e) { Util.truncateObject(rec); System.out.println("after truncation "); save2(rec); } public static void save2(Object obj) throws Exception{ try{ beginTransaction(); getSession().save(obj); commitTransaction(); }catch(Exception e){ e.printStackTrace(); rollbackTransaction(); //closeSession(); throw e; }finally{ closeSession(); } }

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