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  • JPA - Real primary key generated ID for references

    - by Val
    I have ~10 classes, each of them, have composite key, consist of 2-4 values. 1 of the classes is a main one (let's call it "Center") and related to other as one-to-one or one-to-many. Thinking about correct way of describing this in JPA I think I need to describe all the primary keys using @Embedded / @PrimaryKey annotations. Question #1: My concern is - does it mean that on the database level I will have # of additional columns in each table referring to the "Center" equal to number of column in "Center" PK? If yes, is it possible to avoid it by using some artificial unique key for references? Could you please give an idea how real PK and the artificial one needs to be described in this case? Note: The reason why I would like to keep the real PK and not just use the unique id as PK is - my application have some data loading functionality from external data sources and sometimes they may return records which I already have in local database. If unique ID will be used as PK - for new records I won't be able to do data update, since the unique ID will not be available for just downloaded ones. At the same time it is normal case scenario for application and it just need to update of insert new records depends on if the real composite primary key matches. Question #2: All of the 10 classes have common field "date" which I described in an abstract class which each of them extends. The "date" itself is never a key, but it always a part of composite key for each class. Composite key is different for each class. To be able to use this field as a part of PK should I describe it in each class or is there any way to use it as is? I experimented with @Embedded and @PrimaryKey annotations and always got an error that eclipselink can't find field described in an abstract class. Thank you in advance! PS. I'm using latest version of eclipselink & H2 database.

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  • MySQL: optimization of table (indexing, foreign key) with no primary keys

    - by Haradzieniec
    Each member has 0 or more orders. Each order contains at least 1 item. memberid - varchar, not integer - that's OK (please do not mention that's not very good, I can't change it). So, thera 3 tables: members, orders and order_items. Orders and order_items are below: CREATE TABLE `orders` ( `orderid` INT(11) UNSIGNED NOT NULL AUTO_INCREMENT, `memberid` VARCHAR( 20 ), `Time` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP , `info` VARCHAR( 3200 ) NULL , PRIMARY KEY (orderid) , FOREIGN KEY (memberid) REFERENCES members(memberid) ) ENGINE = InnoDB; CREATE TABLE `order_items` ( `orderid` INT(11) UNSIGNED NOT NULL, `item_number_in_cart` tinyint(1) NOT NULL , --- 5 items in cart= 5 rows `price` DECIMAL (6,2) NOT NULL, FOREIGN KEY (orderid) REFERENCES orders(orderid) ) ENGINE = InnoDB; So, order_items table looks like: orderid - item_number_in_cart - price: ... 1000456 - 1 - 24.99 1000456 - 2 - 39.99 1000456 - 3 - 4.99 1000456 - 4 - 17.97 1000457 - 1 - 20.00 1000458 - 1 - 99.99 1000459 - 1 - 2.99 1000459 - 2 - 69.99 1000460 - 1 - 4.99 ... As you see, order_items table has no primary keys (and I think there is no sense to create an auto_increment id for this table, because once we want to extract data, we always extract it as WHERE orderid='1000456' order by item_number_in_card asc - the whole block, id woudn't be helpful in queries). Once data is inserted into order_items, it's not UPDATEd, just SELECTed. The questions are: I think it's a good idea to put index on item_number_in_cart. Could anybody please confirm that? Is there anything else I have to do with order_items to increase the performance, or that looks pretty good? I could miss something because I'm a newbie. Thank you in advance.

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  • Checking for alternate keys with XNA IsKeyDown

    - by jocull
    I'm working on picking up XNA and this was a confusing point for me. KeyboardState keyState = Keyboard.GetState(); if (keyState.IsKeyDown(Keys.Left) || keyState.IsKeyDown(Keys.A)) { //Do stuff... } The book I'm using (Learning XNA 4.0, O'Rielly) says that this method accepts a bitwise OR series of keys, which I think should look like this... KeyboardState keyState = Keyboard.GetState(); if (keyState.IsKeyDown(Keys.Left | Keys.A)) { //Do stuff... } But I can't get it work. I also tried using !IsKeyUp(... | ...) as it said that all keys had to be down for it to be true, but had no luck with that either. Ideas? Thanks.

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  • Is it OK to create all primary partitions.?

    - by james
    I have a 320GB hard disk. I only use either ubuntu or kubuntu (12.04 for now). I don't want to use windows or any other dual boot os. And i need only 3 partitions on my hard disk. One for the OS and remaining two for data storage. I don't want to create swap also. Now can i create all primary partitions on the hard disk. Are there any disadvantages in doing so. If all the partitions are primary i think i can easily resize partitions in future. On second thought i have the idea of using seperate partition for /home. Is it good practice . If i have to do this, i will create 4 partitions all primary. In any case i don't want to create more than 4 partitions . And i know the limit will be 4. So is it safe to create all 3 or 4 primary partitions. Pls suggest me, What are the good practices . (previously i used win-xp and win-7 on dual boot with 2 primary partitions and that bugged me somehow i don't remember. Since then i felt there should be only one primary partition in a hard disk.) EDIT 1 : Now i will use four partitions in the sequence - / , /home , /for-data , /swap . I have another question. Does a partition need continuous blocks on the disk. I mean if i want to resize partitions later, can i add space from sda3 to sda1. Is it possible and is it safe to do ?

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  • Is is OK to use a non-primary key as the id in a rails resource?

    - by nPn
    I am getting ready to set up a resource for some new api calls to my rails application. I am planning on calling the resource devices ie resources :devices This is going to represent a android mobile devices I know this will get me routes such as GET devices/:id In most cases :id would be an integer representing the primary key, and in the controller we would use :id as such: GET devices/1 @device = Device.find(params[:id]) In this case I would like to use :id as the google_cloud_messaging_reg_id So I would like to have requests like this: GET devices/some_long_gcm_id and then in the controller , just us params[:id] to look up the device by the gcm registration id. This seem more natural, since the device will know it's gcm id rather than it's rails integer id. Are there any reasons I should avoid doing this?

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  • Should foreign keys become table primary key?

    - by Carvell Fenton
    Hello again, I have a table (session_comments) with the following fields structure: student_id (foreign key to students table) session_id (foreign key to sessions table) session_subject_ID (foreign key to session_subjects table) user_id (foreign key to users table) comment_date_time comment Now, the combination of student_id, session_id, and session_subject_id will uniquely identify a comment about that student for that session subject. Given that combined they are unique, even though they are foreign keys, is there an advantage to me making them the combined primary key for that table? Thanks again.

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  • How To Disable Subsonic's Primary Key Autoincrement?

    - by mamoo
    Hi everybody, I'm using Subsonic (simplerepository) and SQLite, and I have a class with an Int64 property marked as [SubSonicPrimaryKey]: [SubSonicPrimaryKey] public Int64 MyID; which is transformed into: [MyID] integer NOT NULL PRIMARY KEY AUTOINCREMENT Is it possible to disable the AUTOINCREMENT feature?

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  • Negative Primary Keys

    - by bjax
    Are there any repercussions using Negative Primary Keys for tables (Identity Increment -1, Identity Seed -1 in SQL Server 2005)? The reason for this is we're creating a new database to replace an existing one. There are similar tables between the two databases and we'd like the "source" of the information to be transparent to our applications. The approach is to create views that unions tables from both databases. Negative PKs ensures the identities don't overlap.

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  • Android: Text primary key with different name

    - by Echilon
    I have an existing Windows app for which I'm writing an Android port. The app uses a unique string as the primary key, but the SQLite methods in Android all seem to work with integers and a column names _id, whereas my ID column isn't called this. Is there a way to let Android know I have a key with a different column name?

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  • Mysql Removal of primary key

    - by marionmaiden
    Hello, I've removed the primary key of one table of my MySQL database, but now, when I use the MySQL Administrator and try to edit the data of this table, it doesn't allow me to do this. The button edit that appears in the bottom of the table keeps visible, but unable to click.

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  • Removal of table primary key in MySQL

    - by marionmaiden
    Hello, I've removed the primary key of one table of my MySQL database, but now, when I use the MySQL Administrator and try to edit some data of this table, it doesn't allow me to do this. The button edit that appears in the bottom of the table keeps visible, but disabled to click.

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  • primary key datatype in sql server database

    - by ooo
    i see after installing the asp.net membership tables, they use the data type "uniqueidentifier" for all of the primary key fields. I have been using "int" data type and doing increment by one on inserts. Is there any particular benefits to using the uniqueIdentifier data type compared to my current model of using int and auto increments on new inserts ?

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  • Update multiple rows with known keys without inserting new rows if nonexistent keys are found

    - by Kirzilla
    Hello, Let's imagine that we have table items... table: items item_id INT PRIMARY AUTO_INCREMENT title VARCHAR(255) views INT Let's imagine that it is filled with something like (1, item-1, 10), (2, item-2, 10), (3, item-3, 15) I want to make multi update view for this items from data taken from this array [item_id] = [views] '1' => '50', '2' => '60', '3' => '70', '5' => '10' IMPORTANT! Please note that we have item_id=5 in array, but we don't have item_id=5 in database. I can use INSERT ... ON DUPLICATE KEY UPDATE, but this way image_id=5 will be inserted into talbe items. How to avoid inserting new key? I just want item_id=5 be skipped because it is not in table. Of course, before execution I can select existing keys from items table; then compare with keys in array; delete nonexistent keys and perform INSERT ... ON DUPLICATE KEY UPDATE. But maybe there is some more elegant solutions? Thank you.

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  • Entity Framework and associations between string keys

    - by fredrik
    Hi, I am new to Entity Framework, and ORM's for that mather. In the project that I'm involed in we have a legacy database, with all its keys as strings, case-insensitive. We are converting to MSSQL and want to use EF as ORM, but have run in to a problem. Here is an example that illustrates our problem: TableA has a primary string key, TableB has a reference to this primary key. In LINQ we write something like: var result = from t in context.TableB select t.TableA; foreach( var r in result ) Console.WriteLine( r.someFieldInTableA ); if TableA contains a primary key that reads "A", and TableB contains two rows that references TableA but with different cases in the referenceing field, "a" and "A". In our project we want both of the rows to endup in the result, but only the one with the matching case will end up there. Using the SQL Profiler, I have noticed that both of the rows are selected. Is there a way to tell Entity Framework that the keys are case insensitive? Edit:We have now tested this with NHibernate and come to the conclution that NHibernate works with case-insensitive keys. So NHibernate might be a better choice for us.I am however still interested in finding out if there is any way to change the behaviour of Entity Framework.

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  • PostgreSQL, Foreign Keys, Insert speed & Django

    - by Miles
    A few days ago, I ran into an unexpected performance problem with a pretty standard Django setup. For an upcoming feature, we have to regenerate a table hourly, containing about 100k rows of data, 9M on the disk, 10M indexes according to pgAdmin. The problem is that inserting them by whatever method literally takes ages, up to 3 minutes of 100% disk busy time. That's not something you want on a production site. It doesn't matter if the inserts were in a transaction, issued via plain insert, multi-row insert, COPY FROM or even INSERT INTO t1 SELECT * FROM t2. After noticing this isn't Django's fault, I followed a trial and error route, and hey, the problem disappeared after dropping all foreign keys! Instead of 3 minutes, the INSERT INTO SELECT FROM took less than a second to execute, which isn't too surprising for a table <= 20M on the disk. What is weird is that PostgreSQL manages to slow down inserts by 180x just by using 3 foreign keys. Oh, disk activity was pure writing, as everything is cached in RAM; only writes go to the disks. It looks like PostgreSQL is working very hard to touch every row in the referred tables, as 3MB/sec * 180s is way more data than the 20MB this new table takes on disk. No WAL for the 180s case, I was testing in psql directly, in Django, add ~50% overhead for WAL logging. Tried @commit_on_success, same slowness, I had even implemented multi row insert and COPY FROM with psycopg2. That's another weird thing, how can 10M worth of inserts generate 10x 16M log segments? Table layout: id serial primary, a bunch of int32, 3 foreign keys to small table, 198 rows, 16k on disk large table, 1.2M rows, 59 data + 89 index MB on disk large table, 2.2M rows, 198 + 210MB So, am I doomed to either drop the foreign keys manually or use the table in a very un-Django way by defining saving bla_id x3 and skip using models.ForeignKey? I'd love to hear about some magical antidote / pg setting to fix this.

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  • Joining Tables Based on Foreign Keys

    - by maestrojed
    I have a table that has a lot of fields that are foreign keys referencing a related table. I am writing a script in PHP that will do the db queries. When I query this table for its data I need to know the values associated with these keys not the key. How do most people go about this? A 101 way to do this would be to query this table for its data including the foreign keys and then query the related tables to get each key's value. This could be a lot of queries (~10). Question 1: I think I could write 1 query with a bunch of joins. Would that be better? This approach also requires the querying script to know which table fields are foreign keys. Since I have many tables like this but all with different fields, this means writing nice generic functions is hard. MySQL InnoDB tables allow for foreign constraints. I know the database has these set up correctly. Question 2: What about the idea of querying the table and identifying what the constraints are and then matching them up using whatever process I decide on from Question 1. I like this idea but never see it being used in code. Makes me think its not a good idea for some reason. I would use something like SHOW CREATE TABLE tbl_name; to find what constraints/relationships exist for that table. Thank you for any suggestions or advice.

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  • Is the location of SSH keys on Windows fixed?

    - by user16654
    I read an article: Determine whether you've already generated SSH keys which says that ssh in Windows, keys are in C:\Documents and Settings\userName\Application Data\SSH\UserKeys\ but I have found the keys to be in C:\Documents and Settings\userName\Application Data.SSH . Is there a setting to determine where to put these keys or am I reading the wrong documentation or what?

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  • ROO: how to create composit primary key in Entity

    - by Paul
    Hi, What can I do if I need to create entity for a table in production DB (Oracle 10g) with composite primary key. For example: [CODE] CREATE TABLE TACCOUNT ( BRANCHID NUMBER(3) NOT NULL, ACC VARCHAR2(18 BYTE) NOT NULL, DATE_OPEN DATE NOT NULL, DATE_CLOSE DATE, NOTE VARCHAR2(38 BYTE) ); CREATE UNIQUE INDEX PK_TACCOUNT ON TACCOUNT (BRANCHID, ACC); I don't want to change the structure of this table. Is it possible to create an "id" field using roo commands? I use Spring Roo 1.0.2.RELEASE [rev 638] Paul

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  • Django BigInteger auto-increment field as primary key?

    - by Alex Letoosh
    Hi all, I'm currently building a project which involves a lot of collective intelligence. Every user visiting the web site gets created a unique profile and their data is later used to calculate best matches for themselves and other users. By default, Django creates an INT(11) id field to handle models primary keys. I'm concerned with this being overflown very quickly (i.e. ~2.4b devices visiting the page without prior cookie set up). How can I change it to be represented as BIGINT in MySQL and long() inside Django itself? I've found I could do the following (http://docs.djangoproject.com/en/dev/ref/models/fields/#bigintegerfield): class MyProfile(models.Model): id = BigIntegerField(primary_key=True) But is there a way to make it autoincrement, like usual id fields? Additionally, can I make it unsigned so that I get more space to fill in? Thanks!

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  • Using Spring's KeyHolder with programmatically-generated primary keys

    - by smayers81
    Hello, I am using Spring's NamedParameterJdbcTemplate to perform an insert into a table. The table uses a NEXTVAL on a sequence to obtain the primary key. I then want this generated ID to be passed back to me. I am using Spring's KeyHolder implementation like this: KeyHolder key = new GeneratedKeyHolder(); jdbcTemplate.update(Constants.INSERT_ORDER_STATEMENT, params, key); However, when I run this statement, I am getting: org.springframework.dao.DataRetrievalFailureException: The generated key is not of a supported numeric type. Unable to cast [oracle.sql.ROWID] to [java.lang.Number] at org.springframework.jdbc.support.GeneratedKeyHolder.getKey(GeneratedKeyHolder.java:73) Any ideas what I am missing?

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