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  • Migrating from hand-written persistence layer to ORM

    - by Sergey Mikhanov
    Hi community, We are currently evaluating options for migrating from hand-written persistence layer to ORM. We have a bunch of legacy persistent objects (~200), that implement simple interface like this: interface JDBC { public long getId(); public void setId(long id); public void retrieve(); public void setDataSource(DataSource ds); } When retrieve() is called, object populates itself by issuing handwritten SQL queries to the connection provided using the ID it received in the setter (this usually is the only parameter to the query). It manages its statements, result sets, etc itself. Some of the objects have special flavors of retrive() method, like retrieveByName(), in this case a different SQL is issued. Queries could be quite complex, we often join several tables to populate the sets representing relations to other objects, sometimes join queries are issued on-demand in the specific getter (lazy loading). So basically, we have implemented most of the ORM's functionality manually. The reason for that was performance. We have very strong requirements for speed, and back in 2005 (when this code was written) performance tests has shown that none of mainstream ORMs were that fast as hand-written SQL. The problems we are facing now that make us think of ORM are: Most of the paths in this code are well-tested and are stable. However, some rarely-used code is prone to result set and connection leaks that are very hard to detect We are currently squeezing some additional performance by adding caching to our persistence layer and it's a huge pain to maintain the cached objects manually in this setup Support of this code when DB schema changes is a big problem. I am looking for an advice on what could be the best alternative for us. As far as I know, ORMs has advanced in last 5 years, so it might be that now there's one that offers an acceptable performance. As I see this issue, we need to address those points: Find some way to reuse at least some of the written SQL to express mappings Have the possibility to issue native SQL queries without the necessity to manually decompose their results (i.e. avoid manual rs.getInt(42) as they are very sensitive to schema changes) Add a non-intrusive caching layer Keep the performance figures. Is there any ORM framework you could recommend with regards to that?

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  • MSSQL 2005: Rename DB Server Instance Name?

    - by Code Sherpa
    Hi, Can somebody tell me how to rename the DB server instance name and a DB name in MSSQL 2005? Right Now I Have SERVER/OLDNAME -- oldnameDB I want to change the server instance and also change the db name. I have tried: EXEC sp_renamedb 'oldName', 'newName' and that has changed the dbname as it appers in the tree directory. But, when I do "select @@servername" it is the old name. Also, the MDF and LDF files are still the old name. How do change instance and db names as a clean sweep across the server? Thanks.

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  • How do you determine an acceptable response time for App Engine DB requests?

    - by qiq
    According to this discussion of Google App Engine on Hacker News, A DB (read) request takes over 100ms on the datastore. That's insane and unusable for about 90% of applications. How do you determine what is an acceptable response time for a DB read request? I have been using App Engine without noticing any issues with DB responsiveness. But, on the other hand, I'm not sure I would even know what to look for in that regard :)

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  • about null values!

    - by user329820
    Hi I have a question that if we declare a variable and then do not set it explicitly to null value then it would be null outomatically ,i mean that the below code will return true or false ? thanks DECLARE @val CHAR(4) If @val = NULL

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  • querying larg text file containing JSON objects.

    - by Maciek Sawicki
    Hi, I have few Gigabytes text file in format: {"user_ip":"x.x.x.x", "action_type":"xxx", "action_data":{"some_key":"some_value"...},...} each entry is one line. First I would like to easily find entries for given ip. This part is easy because I can use grep for example. However even for this I would like to find better solution because I would like to get response as fast as possible. Next part is more complicated because I would like to find entries from selected ip and of selected type and with particular value of some_key in action_data. Probably I would have to convert this file to SQL db (probably SQLite, because it will be desktop APP), but I would ask if there are exists better solutions?

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  • Using NULLs in matchup table

    - by TomWilsonFL
    I am working on the accounting portion of a reservation system (think limo company). In the system there are multiple objects that can either be paid or submit a payment. I am tracking all of these "transactions" in three tables called: tx, tx_cc, and tx_ch. tx generates a new tx_id (for transaction ID) and keeps the information about amount, validity, etc. Tx_cc and tx_ch keep the information about the credit card or check used, respectively, which link to other tables (credit_card and bank_account among others). This seems fairly normalized to me, no? Now here is my problem: The payment transaction can take place for a myriad of reasons. Either a reservation is being paid for, a travel agent that booked a reservation is being paid, a driver is being paid, etc. This results in multiple tables, one for each of the entities: agent_tx, driver_tx, reservation_tx, etc. They look like this: CREATE TABLE IF NOT EXISTS `driver_tx` ( `tx_id` int(10) unsigned zerofill NOT NULL, `driver_id` int(11) NOT NULL, `reservation_id` int(11) default NULL, `reservation_item_id` int(11) default NULL, PRIMARY KEY (`tx_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; Now this transaction is for a driver, but could be applied to an individual item on the reservation or the entire reservation overall. Therefore I demand either reservation_id OR reservation_item_id to be null. In the future there may be other things which a driver is paid for, which I would also add to this table, defaulting to null. What is the rule on this? Opinion? Obviously I could break this out into MANY three column tables, but the amount of OUTER JOINing needed seems outrageous. Your input is appreciated. Peace, Tom

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  • Sqlite and Python -- return a dictionary using fetchone()?

    - by AndrewO
    I'm using sqlite3 in python 2.5. I've created a table that looks like this: create table votes ( bill text, senator_id text, vote text) I'm accessing it with something like this: v_cur.execute("select * from votes") row = v_cur.fetchone() bill = row[0] senator_id = row[1] vote = row[2] What I'd like to be able to do is have fetchone (or some other method) return a dictionary, rather than a list, so that I can refer to the field by name rather than position. For example: bill = row['bill'] senator_id = row['senator_id'] vote = row['vote'] I know you can do this with MySQL, but does anyone know how to do it with SQLite? Thanks!!!

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  • How to efficiently store and update binary data in Mongodb?

    - by Rocketman
    I am storing a large binary array within a document. I wish to continually add bytes to this array and sometimes change the value of existing bytes. I was looking for some $append_bytes and $replace_bytes type of modifiers but it appears that the best I can do is $push for arrays. It seems like this would be doable by performing seek-write type operations if I had access somehow to the underlying bson on disk, but it does not appear to me that there is anyway to do this in mongodb (and probably for good reason). If I were instead to just query this binary array, edit or add to it, and then update the document by rewriting the entire field, how costly will this be? Each binary array will be on the order of 1-2MB, and updates occur once every 5 minutes and across 1000s of documents. Worse, yet there is no easy way to spread these out (in time) and they will usually be happening close to one another on the 5 minute intervals. Does anyone have a good feel for how disastrous this will be? Seems like it would be problematic. An alternative would be to store this binary data as separate files on disk, implement a thread pool to efficiently manipulate the files on disk, and reference the filename from my mongodb document. (I'm using python and pymongo so I was looking at pytables). I'd prefer to avoid this though if possible. Is there any other alternative that I am overlooking here? Thanks in advnace.

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  • Can I do transactions and locks in CouchDB?

    - by damian
    I need to do transactions (begin, commit or rollback), locks (select for update). How can I do it in a document model db? Edit: The case is this: I want to run an auctions site. And I think how to direct purchase as well. In a direct purchase I have to decrement the quantity field in the item record, but only if the quantity is greater than zero. That is why I need locks and transactions. I don't know how to address that without locks and/or transactions. Can I solve this with CouchDB?

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  • What is the best design for these data base tables?

    - by Mohammed Jamal
    I need to find the best solution to make the DB Normalized with large amount of data expected. My site has a Table Tags (contain key word,id) and also 4 types of data related to this tags table like(articles,resources,jobs,...). The big question is:- for the relation with tags what best solution for optimazaion & query speed? make a table for each relation like: table articlesToTags(ArticleID,TagID) table jobsToTags(jobid,tagid) etc. or put it all in one table like table tagsrelation(tagid,itemid,itemtype) I need your help. Please provide me with articles to help me in this design consider that in future the site can conation new section relate to tag Thanks

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  • Cursor returns zero rows from query to table

    - by brockoli
    I've created an SQLiteDatabase in my app and populated it with some data. I can connect to my AVD with a terminal and when I issue select * from articles; I get a list of all the rows in my table and everything looks fine. However, in my code when I query my table, I get a cursor back that has my tables columns, but zero rows of data. Here is my code.. mDbHelper.open(); Cursor articles = mDbHelper.fetchAllArticles(); startManagingCursor(articles); Cursor feeds = mDbHelper.fetchAllFeeds(); startManagingCursor(feeds); mDbHelper.close(); int titleColumn = articles.getColumnIndex("title"); int feedIdColumn = articles.getColumnIndex("feed_id"); int feedTitleColumn = feeds.getColumnIndex("title"); /* Check if our result was valid. */ if (articles != null) { int count = articles.getCount(); /* Check if at least one Result was returned. */ if (articles.moveToFirst()) { In the above code, my Cursor articles returns with my 4 columns, but when I call getCount() it returns zero, even though I can see hundreds of rows of data in that table from command line. Any idea what I might be doing wrong here? Also.. here is my code for fetchAllArticles.. public Cursor fetchAllArticles() { return mDb.query(ARTICLES_TABLE, new String[] {ARTICLE_KEY_ROWID, ARTICLE_KEY_FEED_ID, ARTICLE_KEY_TITLE, ARTICLE_KEY_URL}, null, null, null, null, null); } Rob W.

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  • mysql filtering result using left outer join

    - by user288178
    my query: SELECT content.*, activity_log.content_id FROM content LEFT JOIN activity_log ON content.id = activity_log.content_id AND sess_id = '$sess_id' WHERE activity_log.content_id IS NULL AND visibility = $visibility AND content.reported < ".REPORTED_LIMIT." AND content.file_ready = 1 LIMIT 1 The purpose of that query is to get 1 row from the content table that has not been viewed by the user (identified by session_id), but it still returns contents that have been viewed. What is wrong? ( I have checked the table making sure that the content_ids are there) Note: I think this is more efficient than using subqueries, thoughts?

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  • How Can i Create This Complicated Query ?

    - by mTuran
    Hi, I have 3 tables: projects, skills and project_skills. In projects table i hold project's general data. Second table skills i hold skill id and skill name also i have projects_skills table which is hold project's skill relationships. Here is scheme of tables: CREATE TABLE IF NOT EXISTS `project_skills` ( `project_id` int(11) NOT NULL, `skill_id` int(11) NOT NULL, KEY `project_id` (`project_id`), KEY `skill_id` (`skill_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci; CREATE TABLE IF NOT EXISTS `projects` ( `id` int(11) NOT NULL AUTO_INCREMENT, `employer_id` int(11) NOT NULL, `project_title` varchar(100) COLLATE utf8_turkish_ci NOT NULL, `project_description` text COLLATE utf8_turkish_ci NOT NULL, `project_budget` int(11) NOT NULL, `project_allowedtime` int(11) NOT NULL, `project_deadline` datetime NOT NULL, `total_bids` int(11) NOT NULL, `average_bid` int(11) NOT NULL, `created` datetime NOT NULL, `active` tinyint(1) NOT NULL, PRIMARY KEY (`id`), KEY `created` (`created`), KEY `employer_id` (`employer_id`), KEY `active` (`active`), FULLTEXT KEY `project_title` (`project_title`,`project_description`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci AUTO_INCREMENT=3 ; CREATE TABLE IF NOT EXISTS `skills` ( `id` int(11) NOT NULL AUTO_INCREMENT, `category` int(11) NOT NULL, `name` varchar(100) COLLATE utf8_turkish_ci NOT NULL, `seo_name` varchar(100) COLLATE utf8_turkish_ci NOT NULL, `total_projects` int(11) NOT NULL, PRIMARY KEY (`id`), KEY `seo_name` (`seo_name`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_turkish_ci AUTO_INCREMENT=224 ; I want to select projects with related skill names. I think i have to use JOIN but i don't know how can i do. Thanks

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  • importing csv file into pgsql

    - by running4surival
    ok im trying to upload this csv file onto my table in pgsql but im getting this error ERROR: invalid input syntax for integer: "mlname,mfname,slname,sfname,address,postalcode,membershiptype,hphone,email" CONTEXT: COPY members2, line 1, column id: "mlname,mfname,slname,sfname,address,postalcode,membershiptype,hphone,email" i really understand why im getting this error, both my table and my csv file have the same column names

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  • Datamapper Clone Record w/ New ID

    - by BouncePast
    class Item include DataMapper::Resource property :id, Serial property :title, String end item = Item.new(:title = 'Title 1') # :id = 1 item_clone = Item.first(:id = 1).clone item_clone.save This does "clone" the object as described but how can this be done so it applies a different ID once the record is saved, e.g. #

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  • Two radically different queries against 4 mil records execute in the same time - one uses brute force.

    - by IanC
    I'm using SQL Server 2008. I have a table with over 3 million records, which is related to another table with a million records. I have spent a few days experimenting with different ways of querying these tables. I have it down to two radically different queries, both of which take 6s to execute on my laptop. The first query uses a brute force method of evaluating possibly likely matches, and removes incorrect matches via aggregate summation calculations. The second gets all possibly likely matches, then removes incorrect matches via an EXCEPT query that uses two dedicated indexes to find the low and high mismatches. Logically, one would expect the brute force to be slow and the indexes one to be fast. Not so. And I have experimented heavily with indexes until I got the best speed. Further, the brute force query doesn't require as many indexes, which means that technically it would yield better overall system performance. Below are the two execution plans. If you can't see them, please let me know and I'll re-post then in landscape orientation / mail them to you. Brute-force query: Index-based exception query: My question is, based on the execution plans, which one look more efficient? I realize that thing may change as my data grows.

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  • how to model a follower stream in appengine?

    - by molicule
    I am trying to design tables to buildout a follower relationship. Say I have a stream of 140char records that have user, hashtag and other text. Users follow other users, and can also follow hashtags. I am outlining the way I've designed this below, but there are two limitaions in my design. I was wondering if others had smarter ways to accomplish the same goal. The issues with this are The list of followers is copied in for each record If a new follower is added or one removed, 'all' the records have to be updated. The code class HashtagFollowers(db.Model): """ This table contains the followers for each hashtag """ hashtag = db.StringProperty() followers = db.StringListProperty() class UserFollowers(db.Model): """ This table contains the followers for each user """ username = db.StringProperty() followers = db.StringListProperty() class stream(db.Model): """ This table contains the data stream """ username = db.StringProperty() hashtag = db.StringProperty() text = db.TextProperty() def save(self): """ On each save all the followers for each hashtag and user are added into a another table with this record as the parent """ super(stream, self).save() hfs = HashtagFollowers.all().filter("hashtag =", self.hashtag).fetch(10) for hf in hfs: sh = streamHashtags(parent=self, followers=hf.followers) sh.save() ufs = UserFollowers.all().filter("username =", self.username).fetch(10) for uf in ufs: uh = streamUsers(parent=self, followers=uf.followers) uh.save() class streamHashtags(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() class streamUsers(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() Now, to get the stream of followed hastags indexes = db.GqlQuery("""SELECT __key__ from streamHashtags where followers = 'myusername'""") keys = [k,parent() for k in indexes[offset:numresults]] return db.get(keys) Is there a smarter way to do this?

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  • Self-relation messes up contents in fetching

    - by holographix
    Hi folks, I'm dealing with an annoying problem in core data I've got a table named Character, which is made as follows I'm filling the table in various steps: 1) fill the attributes of the table 2) fill the Character Relation (charRel) FYI charRel is defined as follows I'm feeding the contents by pulling the data from an xml, the feeding code is this curStr = [[NSMutableString stringWithString:[curStr stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]]] retain]; NSLog(@"Parsing relation within these keys %@, in order to get'em associated",curStr); NSArray *chunks = [curStr componentsSeparatedByString: @","]; for( NSString *relId in chunks ) { NSLog(@"Associating %@ with id %@",[currentCharacter valueForKey:@"character_id"], relId); NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"character_id == %@", relId]; [request setEntity:[NSEntityDescription entityForName:@"Character" inManagedObjectContext:[self managedObjectContext] ]]; [request setPredicate:predicate]; NSerror *error = nil; NSArray *results = [[self managedObjectContext] executeFetchRequest:request error:&error]; // error handling code if(error != nil) { NSLog(@"[SYMBOL CORRELATION]: retrieving correlated symbol error: %@", [error localizedDescription]); } else if([results count] > 0) { Character *relatedChar = [results objectAtIndex:0]; // grab the first result in the stack, could be done better! [currentCharacter addCharRelObject:relatedChar]; //VICE VERSA RELATIONS NSArray *charRels = [relatedChar valueForKey:@"charRel"]; BOOL alreadyRelated = NO; for(Character *charRel in charRels) { if([[charRel valueForKey:@"character_id"] isEqual:[currentCharacter valueForKey:@"character_id"]]) { alreadyRelated = YES; break; } } if(!alreadyRelated) { NSLog(@"\n\t\trelating %@ with %@", [relatedChar valueForKey:@"character_id"], [currentCharacter valueForKey:@"character_id"]); [relatedChar addCharRelObject:currentCharacter]; } } else { NSLog(@"[SYMBOL CORRELATION]: related symbol was not found! ##SKIPPING-->"); } [request release]; } NSLog(@"\t\t### TOTAL OF REALTIONS FOR ID %@: %d\n%@", [currentCharacter valueForKey:@"character_id"], [[currentCharacter valueForKey:@"charRel"] count], currentCharacter); error = nil; /* SAVE THE CONTEXT */ if (![managedObjectContext save:&error]) { NSLog(@"Whoops, couldn't save the symbol record: %@", [error localizedDescription]); NSArray* detailedErrors = [[error userInfo] objectForKey:NSDetailedErrorsKey]; if(detailedErrors != nil && [detailedErrors count] > 0) { for(NSError* detailedError in detailedErrors) { NSLog(@"\n################\t\tDetailedError: %@\n################", [detailedError userInfo]); } } else { NSLog(@" %@", [error userInfo]); } } at this point when I print out the values of the currentCharacter, everything looks perfect. every relation is in its place. in example in this log we can clearly see that this element has got 3 items in charRel: <Character: 0x5593af0> (entity: Character; id: 0x55938c0 <x-coredata://67288D50-D349-4B19-B7CB-F7AC4671AD61/Character/p86> ; data: { catRel = "<relationship fault: 0x9a29db0 'catRel'>"; charRel = ( "0x9a1f870 <x-coredata://67288D50-D349-4B19-B7CB-F7AC4671AD61/Character/p74>", "0x9a14bd0 <x-coredata://67288D50-D349-4B19-B7CB-F7AC4671AD61/Character/p109>", "0x558ba00 <x-coredata://67288D50-D349-4B19-B7CB-F7AC4671AD61/Character/p5>" ); "character_id" = 254; examplesRel = "<relationship fault: 0x9a29df0 'examplesRel'>"; meaning = "\n Left"; pinyin = "\n zu\U01d2"; "pronunciation_it" = "\n zu\U01d2"; strokenumber = 5; text = "\n \n <p>The most ancient form of this symbol"; unicodevalue = "\n \U5de6"; }) then when I'm in need of retrieving this item I perform an extraction, like this: // at first I get the single Character record NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSError *error; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"character_id == %@", self.char_id ]; [request setEntity:[NSEntityDescription entityForName:@"Character" inManagedObjectContext:_context ]]; [request setPredicate:predicate]; NSArray *fetchedObjs = [_context executeFetchRequest:request error:&error]; when, for instance, I print out in NSLog the contents of charRel NSArray *correlations = [singleCharacter valueForKey:@"charRel"]; NSLog(@"CHARACTER OBJECT \n%@", correlations); I get this Relationship fault for (<NSRelationshipDescription: 0x5568520>), name charRel, isOptional 1, isTransient 0, entity Character, renamingIdentifier charRel, validation predicates (), warnings (), versionHashModifier (null), destination entity Character, inverseRelationship (null), minCount 1, maxCount 99 on 0x6937f00 hope that I made myself clear. this thing is driving me insane, I've googled all over world, but I couldn't find a solution (and this make me think to as issue related to bad coding somehow :P). thank you in advance guys. k

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  • Can somebody suggest good learning source of IMS?

    - by Raja Reddy
    I would like to learn working with IMS, can somebody suggest me a good source? I'm not sure if it matters to say that I have quite good exposure and experience with INSYNC DB2 and QMF. So anything that can depict and explain the advantages and disadvantages over IMS would be really helpful. Thanks for your help beforehand..

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