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• Ordering by number of rows?

  - by Rob

  Alright, so I have a table outputting data from a MySQL table in a while loop. Well one of the columns it outputs isn't stored statically in the table, instead it's the sum of how many times it appears in a different MySQL table. Sorry I'm not sure this is easy to understand. Here's my code: $query="SELECT * FROM list WHERE added='$addedby' ORDER BY time DESC"; $result=mysql_query($query); while($row=mysql_fetch_array($result, MYSQL_ASSOC)){ $loghwid = $row['hwid']; $sql="SELECT * FROM logs WHERE hwid='$loghwid' AND time < now() + interval 1 hour"; $query = mysql_query($sql) OR DIE(mysql_error()); $boots = mysql_num_rows($query); //Display the table } The above is the code displaying the table. As you can see it's grabbing data from two different MySQL tables. However I want to be able to ORDER BY $boots DESC. But as its a counting of a completely different table, I have no idea of how to go about doing that. I would appreciate any help, thank you.

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• Mapping many-to-many association table with extra column(s)

  - by user635524

  My database contains 3 tables: User and Service entities have many-to-many relationship and are joined with the SERVICE_USER table as follows: USERS - SERVICE_USER - SERVICES SERVICE_USER table contains additional BLOCKED column. What is the best way to perform such a mapping? These are my Entity classes @Entity @Table(name = "USERS") public class User implements java.io.Serializable { private String userid; private String email; @Id @Column(name = "USERID", unique = true, nullable = false,) public String getUserid() { return this.userid; } .... some get/set methods } @Entity @Table(name = "SERVICES") public class CmsService implements java.io.Serializable { private String serviceCode; @Id @Column(name = "SERVICE_CODE", unique = true, nullable = false, length = 100) public String getServiceCode() { return this.serviceCode; } .... some additional fields and get/set methods } I followed this example http://giannigar.wordpress.com/2009/09/04/m ... using-jpa/ Here is some test code: User user = new User(); user.setEmail("e2"); user.setUserid("ui2"); user.setPassword("p2"); CmsService service= new CmsService("cd2","name2"); List<UserService> userServiceList = new ArrayList<UserService>(); UserService userService = new UserService(); userService.setService(service); userService.setUser(user); userService.setBlocked(true); service.getUserServices().add(userService); userDAO.save(user); The problem is that hibernate persists User object and UserService one. No success with the CmsService object I tried to use EAGER fetch - no progress Is it possible to achieve the behaviour I'm expecting with the mapping provided above? Maybe there is some more elegant way of mapping many to many join table with additional column?

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• Why would this query cause a Merge Cartesian Join in Oracle

  - by decompiled

  I have a query that was recently required to be modified. Here's the original SELECT RTRIM (position) AS "POSITION", . // Other fields . . FROM schema.table x WHERE hours > 0 AND pay = 'RGW' AND NOT EXISTS( SELECT position FROM schema.table2 y where y.position = x.position ) Here's the new version SELECT RTRIM (position) AS "POSITION", . // Other fields . . FROM schema.table x WHERE hours > 0 AND pay = 'RGW' AND NOT EXISTS( SELECT position FROM schema.table2 y where y.date = get_fiscal_year_start_date (SYSDATE) AND y.position = x.position ) The UDF get_fiscal_year_start_date() returns the fiscal year start date of the date parameter. The first query runs fine, but the second creates a merge Cartesian join. I looked at the indexes on the tables and found that position and date were both indexed. My question for you stackoverflow is why would the addition of 'y.date = get_fiscal_year_start_date (SYSDATE)' cause a merge cartesian join in Oracle 10g.

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• Saving Data to Relational Database (Entity Framework)

  - by sheefy

  I'm having a little bit of trouble saving data to a database. Basically, I have a main table that has associations to other tables (Example Below). Tbl_Listing ID UserID - Associated to ID in User Table CategoryID - Associated to ID in Category Table LevelID - Associated to ID in Level Table. Name Address Normally, it's easy for me to add data to the DB (using Entity Framework). However, I'm not sure how to add data to the fields with associations. The numerous ID fields just need to hold an int value that corresponds with the ID in the associated table. For example; when I try to access the column in the following manner I get a "Object reference not set to an instance of an object." error. Listing NewListing = new Listing(); NewListing.Tbl_User.ID = 1; NewListing.Tbl_Category.ID = 2; ... DBEntities.AddToListingSet(NewListing); DBEntities.SaveChanges(); I am using NewListing.Tbl_User.ID instead of NewListing.UserID because the UserID field is not available through intellisense. If I try and create an object for each related field I get a "The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects." error. With this method, I am trying to add the object without the .ID shown above - example NewListing.User = UserObject. I know this should be simple as I just want to reference the ID from the associated table in the main Listing's table. Any help would be greatly appreciated. Thanks in advance, -S

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• How to efficiently use LOCK_ESCALATION mssql 2008

  - by Avias

  I'm currently having troubles with frequent deadlocks with a specific user table in MS SQL 2008. Here are some facts about this particular table: Has a large amount of rows (1 to 2 million) All the indexes used on this table only has "use row lock" ticked on its option rows are frequently updated by multiple transactions but are unique (e.g. probably a thousand or more update statements are executed to different unique rows every hour) the table does not use partitions. Upon checking the table on sys.tables, I found that the lock_escalation is set to TABLE I'm very tempted to turn the lock_escalation for this table to DISABLE but I'm not really sure what side effect this would incur. From What I understand, using DISABLE will minimize escalating locks to TABLE level which if combined with the row lock settings of the indexes should theoretically minimize the deadlocks I am encountering.. From what I have read in Determining threshold for lock escalation it seems that locking automatically escalates when a single transaction fetches 5000 rows.. What does a single transaction mean in this sense? A single session/connection getting 5000 rows thru individual update/select statements? Or is it a single sql update/select statement that fetches 5000 or more rows? Any insight is appreciated, btw, n00b DBA here Thanks

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• Mysql dropping inserts with triggers

  - by user2891127

  Using mysql 5.5. I have two tables. One has a whitelist of hashes. When I insert a new row into the other table, I want to first compare the hash in the insert statement to the whitelist. If it's in the whitelist, I don't want to do the insert (less data to plow through later). The inserts are generated from another program and are text files with sql statements. I've been playing with triggers, and almost have it working: BEGIN IF (select count(md5hash) from whitelist where md5hash=new.md5hash) 0 THEN SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Already Whitelisted'; END IF; END But there's a problem. The Signal throwing up the error stops the import. I want to skip that line, not stop the whole import. Some searching didn't find any way to silently skip the import. My next idea was to create a duplicate table definition, and redirect the insert to that dup table. But the old and new don't seem to apply to table names. Other then adding an ignore column to my table then doing a mass drop based on that column after the import, is there any way to achieve my goal?

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• Database PK-FK design for future-effective-date entries?

  - by Scott Balmos

  Ultimately I'm going to convert this into a Hibernate/JPA design. But I wanted to start out from purely a database perspective. We have various tables containing data that is future-effective-dated. Take an employee table with the following pseudo-definition: employee id INT AUTO_INCREMENT ... data fields ... effectiveFrom DATE effectiveTo DATE employee_reviews id INT AUTO_INCREMENT employee_id INT FK employee.id Very simplistic. But let's say Employee A has id = 1, effectiveFrom = 1/1/2011, effectiveTo = 1/1/2099. That employee is going to be changing jobs in the future, which would in theory create a new row, id = 2 with effectiveFrom = 7/1/2011, effectiveTo = 1/1/2099, and id = 1's effectiveTo updated to 6/30/2011. But now, my program would have to go through any table that has a FK relationship to employee every night, and update those FK to reference the newly-effective employee entry. I have seen various postings in both pure SQL and Hibernate forums that I should have a separate employee_versions table, which is where I would have all effective-dated data stored, resulting in the updated pseudo-definition below: employee id INT AUTO_INCREMENT employee_versions id INT AUTO_INCREMENT employee_id INT FK employee.id ... data fields ... effectiveFrom DATE effectiveTo DATE employee_reviews id INT AUTO_INCREMENT employee_id INT FK employee.id Then to get any actual data, one would have to actually select from employee_versions with the proper employee_id and date range. This feels rather unnatural to have this secondary "versions" table for each versioned entity. Anyone have any opinions, suggestions from your own prior work, etc? Like I said, I'm taking this purely from a general SQL design standpoint first before layering in Hibernate on top. Thanks!

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• Looping Through Database Query

  - by DrakeNET

  I am creating a very simple script. The purpose of the script is to pull a question from the database and display all answers associated with that particular question. We are dealing with two tables here and there is a foreign key from the question database to the answer database so answers are associated with questions. Hope that is enough explanation. Here is my code. I was wondering if this is the most efficient way to complete this or is there an easier way? <html> <head> <title>Advise Me</title> <head> <body> <h1>Today's Question</h1> <?php //Establish connection to database require_once('config.php'); require_once('open_connection.php'); //Pull the "active" question from the database $todays_question = mysql_query("SELECT name, question FROM approvedQuestions WHERE status = active") or die(mysql_error()); //Variable to hold $todays_question aQID $questionID = mysql_query("SELECT commentID FROM approvedQuestions WHERE status = active") or die(mysql_error()); //Print today's question echo $todays_question; //Print comments associated with today's question $sql = "SELECT commentID FROM approvedQuestions WHERE status = active"; $result_set = mysql_query($sql); $result_num = mysql_numrows($result_set); for ($a = 0; $a < $result_num; $a++) { echo $sql; } ?> </body> </html>

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• localhost yes but phpmyadmin blank

  - by Giskin Leow

  WAMP people having problem with both localhost and phpmyadmin loads blank which usually the port problem. Mine is only phpmyadmin blank. sqlbuddy and phpinfo no problem. tried uninstall reinstalled wamp. tried xampp, same problem, all works well, not phpmyadmin. mysql log: 120905 8:03:08 [Note] Plugin 'FEDERATED' is disabled. 120905 8:03:08 InnoDB: The InnoDB memory heap is disabled 120905 8:03:08 InnoDB: Mutexes and rw_locks use Windows interlocked functions 120905 8:03:08 InnoDB: Compressed tables use zlib 1.2.3 120905 8:03:09 InnoDB: Initializing buffer pool, size = 128.0M 120905 8:03:09 InnoDB: Completed initialization of buffer pool 120905 8:03:09 InnoDB: highest supported file format is Barracuda. 120905 8:03:09 InnoDB: Waiting for the background threads to start 120905 8:03:10 InnoDB: 1.1.8 started; log sequence number 1595675 120905 8:03:11 [Note] Server hostname (bind-address): '(null)'; port: 3306 120905 8:03:11 [Note] - '(null)' resolves to '::'; 120905 8:03:11 [Note] - '(null)' resolves to '0.0.0.0'; 120905 8:03:11 [Note] Server socket created on IP: '0.0.0.0'. 120905 8:03:13 [Note] Event Scheduler: Loaded 0 events 120905 8:03:13 [Note] wampmysqld: ready for connections. apache log [Wed Sep 05 08:03:09 2012] [notice] Apache/2.2.22 (Win32) PHP/5.4.3 configured -- resuming normal operations [Wed Sep 05 08:03:09 2012] [notice] Server built: May 13 2012 13:32:42 [Wed Sep 05 08:03:09 2012] [notice] Parent: Created child process 3812 [Wed Sep 05 08:03:09 2012] [notice] Child 3812: Child process is running [Wed Sep 05 08:03:09 2012] [notice] Child 3812: Acquired the start mutex. [Wed Sep 05 08:03:09 2012] [notice] Child 3812: Starting 64 worker threads. [Wed Sep 05 08:03:09 2012] [notice] Child 3812: Starting thread to listen on port 80. [Wed Sep 05 08:03:09 2012] [notice] Child 3812: Starting thread to listen on port 80. [Wed Sep 05 08:04:14 2012] [error] [client 127.0.0.1] File does not exist: C:/wamp/www/favicon.ico [Wed Sep 05 08:09:50 2012] [error] [client 127.0.0.1] File does not exist: C:/wamp/www/favicon.ico [Wed Sep 05 08:41:03 2012] [error] [client 127.0.0.1] File does not exist: C:/wamp/www/phpMyAdmin

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• Separating code logic from the actual data structures. Best practices?

  - by Patrick

  I have an application that loads lots of data into memory (this is because it needs to perform some mathematical simulation on big data sets). This data comes from several database tables, that all refer to each other. The consistency rules on the data are rather complex, and looking up all the relevant data requires quite some hashes and other additional data structures on the data. Problem is that this data may also be changed interactively by the user in a dialog. When the user presses the OK button, I want to perform all the checks to see that he didn't introduce inconsistencies in the data. In practice all the data needs to be checked at once, so I cannot update my data set incrementally and perform the checks one by one. However, all the checking code work on the actual data set loaded in memory, and use the hashing and other data structures. This means I have to do the following: Take the user's changes from the dialog Apply them to the big data set Perform the checks on the big data set Undo all the changes if the checks fail I don't like this solution since other threads are also continuously using the data set, and I don't want to halt them while performing the checks. Also, the undo means that the old situation needs to be put aside, which is also not possible. An alternative is to separate the checking code from the data set (and let it work on explicitly given data, e.g. coming from the dialog) but this means that the checking code cannot use hashing and other additional data structures, because they only work on the big data set, making the checks much slower. What is a good practice to check user's changes on complex data before applying them to the 'application's' data set?

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• MySQL Multiple Table Join

  - by hitman001

  I have a 3 tables that I'm trying to join and get distinct results. CREATE TABLE `car` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL DEFAULT '', PRIMARY KEY (`id`) ) ENGINE=InnoDB mysql> select * from car; +----+-------+ | id | name | +----+-------+ | 1 | acura | +----+-------+ CREATE TABLE `tires` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `tire_desc` varchar(255) DEFAULT NULL, `car_id` int(10) unsigned NOT NULL, PRIMARY KEY (`id`), KEY `new_fk_constraint` (`car_id`), CONSTRAINT `new_fk_constraint` FOREIGN KEY (`car_id`) REFERENCES `car` (`id`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB mysql> select * from tires; +----+-------------+--------+ | id | tire_desc | car_id | +----+-------------+--------+ | 1 | front_right | 1 | | 2 | front_left | 1 | +----+-------------+--------+ CREATE TABLE `lights` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `lights_desc` varchar(255) NOT NULL, `car_id` int(10) unsigned NOT NULL, PRIMARY KEY (`id`), KEY `new1_fk_constraint` (`car_id`), CONSTRAINT `new1_fk_constraint` FOREIGN KEY (`car_id`) REFERENCES `car` (`id`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=InnoDB mysql> select * from lights; +----+-------------+--------+ | id | lights_desc | car_id | +----+-------------+--------+ | 1 | right_light | 1 | | 2 | left_light | 1 | +----+-------------+--------+ Here is my query. mysql> SELECT name, group_concat(tire_desc), group_concat(lights_desc) FROM car left join tires on car.id = tires.car_id left join lights on car.id = car_id group by car.id; +-------+-----------------------------------------------+-----------------------------------------------+ | name | group_concat(tire_desc) | group_concat(lights_desc) | +-------+-----------------------------------------------+-----------------------------------------------+ | acura | front_right,front_right,front_left,front_left | right_light,left_light,right_light,left_light | +-------+-----------------------------------------------+-----------------------------------------------+ I get duplicate entires and this is what I would like to get. +-------+-----------------------------------------------+--------------------------------+ | name | group_concat(tire_desc) | group_concat(lights_desc) | +-------+-----------------------------------------------+--------------------------------+ | acura | front_right,front_left | right_light,left_light | +-------+-----------------------------------------------+--------------------------------+ I cannot use distinct in group_concat because I might have legitimate duplicates which I would like to keep. Is there any way to do this query using joins and not using inner selects like the statement below? SELECT name, (select group_concat(tire_desc) from tires where car.id = tires.car_id), (select group_concat(lights_desc) from lights where car.id = lights.car_id) FROM car Also, if I will use inner selects, will there be any performance issues over joins?

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• Data base design with Blob

  - by mmuthu

  Hi, I have a situation where i need to store the binary data into database as blob column. There are three different table exists in my database where in i need to store a blob data for each record. Not every record will have the blob data all the time. It is time and user based. The table one will have to store the *.doc files almost for all the record The table two will have to store the *.xml optionally. The table three will have to store images (not sure what is frequency, etc) Now my questions is whether it is a good idea to maintain a separate table to store the blob data pointing it to the respective table PK's (Yes, there will be no FK's and assuming program will maintain it). It will be some thing like below, BLOB|PK_ID|TABLE_NAME Alternatively, is it a good idea to keep the blob column in respective tables. As for as my application runtime is concerned, The table 2 will be read very frequently. Though the blob column will not be required. The table 2 record will gets deleted frequently. Similarly other blob data in respective table will not be accessed frequently. All of the blob content will be read on-demand basis. I'm thinking first approach will work better for me. What do you guys think? Btw, I'm using Oracle.

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• While in a transaction, how can reads to an affected row be prevented until the transaction is done?

  - by Mahn

  I'm fairly sure this has a simple solution, but I haven't been able to find it so far. Provided an InnoDB MySQL database with the isolation level set to SERIALIZABLE, and given the following operation: BEGIN WORK; SELECT * FROM users WHERE userID=1; UPDATE users SET credits=100 WHERE userID=1; COMMIT; I would like to make sure that as soon as the select inside the transaction is issued, the row corresponding to userID=1 is locked for reads until the transaction is done. As it stands now, UPDATEs to this row will wait for the transaction to be finished if it is in process, but SELECTs simply will read the previous value. I understand this is the expected behaviour in this case, but I wonder if there is a way to lock the row in such a way that SELECTs will also wait until the transaction is finished to return the values? The reason I'm looking for that is that at some point, and with enough concurrent users, it could happen that while the previous transaction is in process someone else reads the "credits" to calculate something else. Ideally the code run by that someone else should wait for the transaction to finish to use the new value, because otherwise it could lead to irreversible desync issues. Note that I don't want to lock the entire table for reads, just the specific row. Also, I could add a boolean "locked" field to the tables and set it to 1 every time I'm starting a transaction but I don't really feel this is the most elegant solution here, unless there is absolutely no other way to handle this through mysql directly.

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• [Ruby on Rails] how to add a new entry with a multiple has_many association?

  - by siulamvictor

  I am not sure am I doing these correct. I have 3 models, Account, User, and Event. Account contains a group of Users. Each User have its own username and password for login, but they can access the same Account data under the same Account. Events is create by a User, which other Users in the same Account can also read or edit it. I created the following migrations and models. User migration class CreateUsers < ActiveRecord::Migration def self.up create_table :users do |t| t.integer :account_id t.string :username t.string :password t.timestamps end end def self.down drop_table :users end end Account migration class CreateAccounts < ActiveRecord::Migration def self.up create_table :accounts do |t| t.string :name t.timestamps end end def self.down drop_table :accounts end end Event migration class CreateEvents < ActiveRecord::Migration def self.up create_table :events do |t| t.integer :account_id t.integer :user_id t.string :name t.string :location t.timestamps end end def self.down drop_table :events end end Account model class Account < ActiveRecord::Base has_many :users has_many :events end User model class User < ActiveRecord::Base belongs_to :account end Event model class Event < ActiveRecord::Base belongs_to :account belongs_to :user end so.... Is this setting correct? Every time when a user create a new account, the system will ask for the user information, e.g. username and password. How can I add them into correct tables? How can I add a new event? I am sorry for such a long question. I am not very understand the rails way in handling such data structure. Thank you guys for answering me. :)

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• How to emulate a BEFORE DELETE trigger in SQL Server 2005

  - by Mark

  Let's say I have three tables, [ONE], [ONE_TWO], and [TWO]. [ONE_TWO] is a many-to-many join table with only [ONE_ID and [TWO_ID] columns. There are foreign keys set up to link [ONE] to [ONE_TWO] and [TWO] to [ONE_TWO]. The FKs use the ON DELETE CASCADE option so that if either a [ONE] or [TWO] record is deleted, the associated [ONE_TWO] records will be automatically deleted as well. I want to have a trigger on the [TWO] table such that when a [TWO] record is deleted, it executes a stored procedure that takes a [ONE_ID] as a parameter, passing the [ONE_ID] values that were linked to the [TWO_ID] before the delete occurred: DECLARE @Statement NVARCHAR(max) SET @Statement = '' SELECT @Statement = @Statement + N'EXEC [MyProc] ''' + CAST([one_two].[one_id] AS VARCHAR(36)) + '''; ' FROM deleted JOIN [one_two] ON deleted.[two_id] = [one_two].[two_id] EXEC (@Statement) Clearly, I need a BEFORE DELETE trigger, but there is no such thing in SQL Server 2005. I can't use an INSTEAD OF trigger because of the cascading FK. I get the impression that if I use a FOR DELETE trigger, when I join [deleted] to [ONE_TWO] to find the list of [ONE_ID] values, the FK cascade will have already deleted the associated [ONE_TWO] records so I will never find any [ONE_ID] values. Is this true? If so, how can I achieve my objective? I'm thinking that I'd need to change the FK joining [TWO] to [ONE_TWO] to not use cascades and to do the delete from [ONE_TWO] manually in the trigger just before I manually delete the [TWO] records. But I'd rather not go through all that if there is a simpler way.

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• c# - sqllite dosnt save data i inserted

  - by samy

  I'm messing around with SQL lite and learning it. I got a table called People, I got some method that connect to the database and do some stuff, like show all the info. Now I'm trying to insert some data and here it get wierd for me. I have this method: private void ExecuteQuery(string txtQuery) { SetConnection(); sql_con.Open(); sql_cmd = sql_con.CreateCommand(); sql_cmd.CommandText = txtQuery; sql_cmd.ExecuteNonQuery(); sql_con.Close(); } and to see all the data I've got this method: private void LoadData() { SetConnection(); sql_con.Open(); sql_cmd = sql_con.CreateCommand(); string CommandText = "SELECT * FROM People"; DB = new SQLiteDataAdapter(CommandText, sql_con); DS.Reset(); DB.Fill(DS); DT = DS.Tables[0]; dataGridView1.DataSource = DT; sql_con.Close(); } When I inset some data and right afther it I call the LoadData(), I can see all the changes I made. After I close the program, and then open it agian and call LoadData(), I don't see the new info that I inserted before. I got some data that I used SQL lite GUI app to insert, and I can see that data every time I call the LoadData() method, but not mine. Do I need to do somthing else to make sure SQL lite saves all the data?

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• How to map this class in NHibernate (not FluentNHibernate)?

  - by JMSA

  Suppose I have a database like this: This is set up to give role-wise menu permissions. Please note that, User-table has no direct relationship with Permission-table. Then how should I map this class against the database-tables? class User { public int ID { get; set; } public string Name { get; set; } public string Username { get; set; } public string Password { get; set; } public bool? IsActive { get; set; } public IList<Role> RoleItems { get; set; } public IList<Permission> PermissionItems { get; set; } public IList<string> MenuItemKeys { get; set; } } This means, (1) Every user has some Roles. (2) Every user has some Permissions (depending on to Roles). (3) Every user has some permitted MenuItemKeys (according to Permissions). How should my User.hbm.xml look like?

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• Hibernate OneToMany and ManyToOne confusion! Null List!

  - by squizz

  I have two tables... For example - Company and Employee (let's keep this real simple) Company( id, name ); Employee( id, company_id ); Employee.company_id is a foreign key. My entity model looks like this... Employee @ManyToOne(cascade = CascadeType.PERSIST) @JoinColumn(name = "company_id") Company company; Company @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER) @JoinColumn(name = "company_id") List<Employee> employeeList = new ArrayList<Employee>(); So, yeah I want a list of employees for a company. When I do the following... Employee e = new Employee(); e.setCompany(c); //c is an Company that is already in the database. DAO.insertEmployee(e); //this works fine! If I then get my Company object it's list is empty! Ive tried endless different ways from the Hibernate documentation! Obviously not tried the correct one yet! I just want the list to be populated for me or find out a sensible alternative. Help would be greatly appreciated, thanks!

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• Automatically Persisting a Complex Java Object

  - by VeeArr

  For a project I am working on, I need to persist a number of POJOs to a database. The POJOs class definitions are sometimes highly nested, but they should flatten okay, as the nesting is tree-like and contains no cycles (and the base elements are eventually primitives/Strings). It is preferred that the solution used create one table per data type and that the tables will have one field per primitive member in the POJO. Subclassing and similar problems are not issues for this particular project. Does anybody know of any existing solutions that can: Automatically generate a CREATE TABLE definition from the class definition Automatically generate a query to persist an object to the database, given an instance of the object Automatically generate a query to retrieve an object from the database and return it as a POJO, given a key. Solutions that can do this with minimum modifications/annotions to the class files and minimum external configuration are preferred. Example: Java classes //Class to be persisted class TypeA { String guid; long timestamp; TypeB data1; TypeC data2; } class TypeB { int id; int someData; } class TypeC { int id; int otherData; } Could map to CREATE TABLE TypeA ( guid CHAR(255), timestamp BIGINT, data1_id INT, data1_someData INT, data2_id INt, data2_otherData INT ); Or something similar.

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• EF Query with conditional include that uses Joins

  - by makerofthings7

  This is a follow up to another user's question. I have 5 tables CompanyDetail CompanyContacts FK to CompanyDetail CompanyContactsSecurity FK to CompanyContact UserDetail UserGroupMembership FK to UserDetail How do I return all companies and include the contacts in the same query? I would like to include companies that contain zero contacts. Companies have a 1 to many association to Contacts, however not every user is permitted to see every Contact. My goal is to get a list of every Company regardless of the count of Contacts, but include contact data. Right now I have this working query: var userGroupsQueryable = _entities.UserGroupMembership .Where(ug => ug.UserID == UserID) .Select(a => a.GroupMembership); var contactsGroupsQueryable = _entities.CompanyContactsSecurity;//.Where(c => c.CompanyID == companyID); /// OLD Query that shows permitted contacts /// ... I want to "use this query inside "listOfCompany" /// //var permittedContacts= from c in userGroupsQueryable //join p in contactsGroupsQueryable on c equals p.GroupID //select p; However this is inefficient when I need to get all contacts for all companies, since I use a For..Each loop and query each company individually and update my viewmodel. Question: How do I shoehorn the permittedContacts variable above and insert that into this query: var listOfCompany = from company in _entities.CompanyDetail.Include("CompanyContacts").Include("CompanyContactsSecurity") where company.CompanyContacts.Any( // Insert Query here.... // b => b.CompanyContactsSecurity.Join(/*inner*/,/*OuterKey*/,/*innerKey*/,/*ResultSelector*/) ) select company; My attempt at doing this resulted in: var listOfCompany = from company in _entities.CompanyDetail.Include("CompanyContacts").Include("CompanyContactsSecurity") where company.CompanyContacts.Any( // This is concept only... doesn't work... from grps in userGroupsQueryable join p in company.CompanyContactsSecurity on grps equals p.GroupID select p ) select company;

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• Rails active record association problem

  - by Harm de Wit

  Hello, I'm new at active record association in rails so i don't know how to solve the following problem: I have a tables called 'meetings' and 'users'. I have correctly associated these two together by making a table 'participants' and set the following association statements: class Meeting < ActiveRecord::Base has_many :participants, :dependent => :destroy has_many :users, :through => :participants and class Participant < ActiveRecord::Base belongs_to :meeting belongs_to :user and the last model class User < ActiveRecord::Base has_many :participants, :dependent => :destroy At this point all is going well and i can access the user values of attending participants of a specific meeting by calling @meeting.users in the normal meetingshow.html.erb view. Now i want to make connections between these participants. Therefore i made a model called 'connections' and created the columns of 'meeting_id', 'user_id' and 'connected_user_id'. So these connections are kinda like friendships within a certain meeting. My question is: How can i set the model associations so i can easily control these connections? I would like to see a solution where i could use @meeting.users.each do |user| user.connections.each do |c| <do something> end end I tried this by changing the model of meetings to this: class Meeting < ActiveRecord::Base has_many :participants, :dependent => :destroy has_many :users, :through => :participants has_many :connections, :dependent => :destroy has_many :participating_user_connections, :through => :connections, :source => :user Please, does anyone have a solution/tip how to solve this the rails way?

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• Best way to get distinct values from large table

  - by derivation

  I have a db table with about 10 or so columns, two of which are month and year. The table has about 250k rows now, and we expect it to grow by about 100-150k records a month. A lot of queries involve the month and year column (ex, all records from march 2010), and so we frequently need to get the available month and year combinations (ie do we have records for april 2010?). A coworker thinks that we should have a separate table from our main one that only contains the months and years we have data for. We only add records to our main table once a month, so it would just be a small update on the end of our scripts to add the new entry to this second table. This second table would be queried whenever we need to find the available month/year entries on the first table. This solution feels kludgy to me and a violation of DRY. What do you think is the correct way of solving this problem? Is there a better way than having two tables?

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• Hive performance increase

  - by Sagar Nikam

  I am dealing with a database (2.5 GB) having some tables only 40 row to some having 9 million rows data. when I am doing any query for large table it takes more time. I want results in less time small query on table which have 90 rows only-- hive> select count(*) from cidade; Time taken: 50.172 seconds hdfs-site.xml <configuration> <property> <name>dfs.replication</name> <value>3</value> <description>Default block replication. The actual number of replications can be specified when the file is created. The default is used if replication is not specified in create time. </description> </property> <property> <name>dfs.block.size</name> <value>131072</value> <description>Default block replication. The actual number of replications can be specified when the file is created. The default is used if replication is not specified in create time. </description> </property> </configuration> does these setting affects performance of hive? dfs.replication=3 dfs.block.size=131072 can i set it from hive prompt as hive>set dfs.replication=5 Is this value remains for a perticular session only ? or Is it better to change it in .xml file ?

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• Strangest LINQ to SQL case I have ever seen

  - by kubaw

  OK, so this is the strangest issue in .net programming I have ever seen. It seems that object fields are serialized in .net web services in order of field initialization. It all started with Flex not accepting SOAP response from .net web service. I have found out that it was due to the order of serialized fields was statisfying the order of fields in declared serializable class. It had something to do with generic lists and LINQ to SQL but I can't find out what. This one is really hard to reproduce. Example to get the idea: [Serializable] public class SomeSample { public int A; public int B; public int C; } I was querying some data tables within asmx web service using linq and returning list of SomeSample objects: var r = (from ...... select new SomeSample { A = 1, C = 3 }).ToList(); Now the list was once more iterated and B field was applied some value (ex. 2). However the returned soap envelope contained following excerpt: <A>1</A><C>3</C><B>2</B> Please notice the order of serialization. If I initially initialized all fields: var r = (from ...... select new SomeSample { A = 1, B = 2, C = 3 }).ToList(); object was serialized in correct order. I must add, that in both cases the debugger shows exactly the same content of "r" variable. Am I losing my mind or is this normal behavior? Thanks in advance.

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• Transfering data from Excel to dataGridView

  - by Panecillo

  I have a problem when I want to transfer data from Excel to dataGridView in C#. My Excel's column has numeric and alphanumeric values. But for example, if the column has 3 numbers and 2 alphanumeric values then only the numbers are shown in the dataGridView, and vice versa. Why aren't all the values shown? The next is what happen: Excel's Column: DataGridView's Column: 45654 45654 P745K 31233 31233 23111 23111 45X2Y Here is my code to load the dataGridView: string connectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\test.xls;Extended Properties=""Excel 8.0;HDR=YES;"""; DbProviderFactory factory = DbProviderFactories.GetFactory("System.Data.OleDb"); DbDataAdapter adapter = factory.CreateDataAdapter(); DbCommand selectCommand = factory.CreateCommand(); selectCommand.CommandText = "SELECT * FROM [sheet1$]"; DbConnection connection = factory.CreateConnection(); connection.ConnectionString = connectionString; selectCommand.Connection = connection; adapter.SelectCommand = selectCommand; data = new DataSet(); adapter.Fill(data); dataGridView1.DataSource = data.Tables[0].DefaultView; I hope I explained it well. Sorry my bad english. Thanks.

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