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  • Lost Update Anomaly in Sql Server Update Command

    - by Javed
    Hi, I am very much confused. I have a transaction in ReadCommitted Isolation level. Among other things I am also updating a counter value in it, something similar to below: Update tblCount set counter = counter + 1 My application is a desktop application and this transaction happens to occur quite frequently and concurrently. We recently noticed an error that sometimes the counter value doesn't get updated or is missed. We also insert one record on each counter update so we are sure that records have been inserted but somehow counter fails to update. This happens once in 2000 simulaneous transactions. I seriously doubt it is a lost update anomaly I am facing but if you look at the command above, it's just update the counter from its own value: if I have started a transaction and the transaction has reached this statement, it should have locked the row. This should not cause lost update, but it's happening somehow. Is the thing that this update command works in two parts? Like first it reads the counter value (during which it doesn't get the exclusive lock) and then writes the new calculated value (when it does get an exclusive lock)? Please help, I have got really confused.

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  • Cleanest RESTful design for purely "action" calls?

    - by Josh Handel
    Hello all, I am sticking my toe in the RESTful waters and I just can't find a "satisfactory" solution to how to handle truely "action" oriented calls on a RESTful service? My quandry can be broken down into two parts. 1) Transactional calls: I understand the idea of having an ActionTransactor that you get a resource too with a post, update the parameters and then commit with a PUT (as described all over the place and in the Orilly RESTful Web services book).. But I struggle with the idea of keeping URLs with states present for ever.. If we really honestly don't need to keep a transaction for ever can we kill the resource URI? do URIs need to be perminate or can they be transiant URIs that expire 2) Non transactional calls: these might be calls to perform some workflow that spans multiple resources but having a resource just doesn't make since.. An example might be to re-generating some calculated ans cached value like a large aggreget or re-indexing blog or some such "purely" action. Anyways, I'm curious about the communities thoughts on this... Thus far, I've read that Overloading Post is the cleanest way to handle part 2.. But there is an equal amount of argument against that approach as well. And (to me) its not self documenting which I though was one of the key design goals of RESTful APIs.

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  • Indentation (and wrap-indentation) of debug strings output by printf()/fprintf() in C program

    - by mbaitoff
    I'm using a debug output using printf() in my functions, but the output goes to the console starting at the 1st columns. I'd like to distinguish the nesting level of functions by indenting their output strings each time I dive into the function (it's implemented easily having a static int indentlevel; variable, which is incremented at the beginning of a function, used as a space-filler-count and decremented at the end). But the flaw is that once the output line becomes too long to be wrapped at the console edge, lines' wrapped parts start at column 1 of the console. Should I take care about this, since once the output is redirected to a file, lines are, say, one-line-length, and widths of the lines depend only on the text file viewer settings?

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  • Fast block placement algorithm, advice needed?

    - by James Morris
    I need to emulate the window placement strategy of the Fluxbox window manager. As a rough guide, visualize randomly sized windows filling up the screen one at a time, where the rough size of each results in an average of 80 windows on screen without any window overlapping another. It is important to note that windows will close and the space that closed windows previously occupied becomes available once more for the placement of new windows. The window placement strategy has three binary options: Windows build horizontal rows or vertical columns (potentially) Windows are placed from left to right or right to left Windows are placed from top to bottom or bottom to top Why is the algorithm a problem? It needs to operate to the deadlines of a real time thread in an audio application. At this moment I am only concerned with getting a fast algorithm, don't concern yourself over the implications of real time threads and all the hurdles in programming that that brings. So far I have two choices which I have built loose prototypes for: 1) A port of the Fluxbox placement algorithm into my code. The problem with this is, the client (my program) gets kicked out of the audio server (JACK) when I try placing the worst case scenario of 256 blocks using the algorithm. This algorithm performs over 14000 full (linear) scans of the list of blocks already placed when placing the 256th window. 2) My alternative approach. Only partially implemented, this approach uses a data structure for each area of rectangular free unused space (the list of windows can be entirely separate, and is not required for testing of this algorithm). The data structure acts as a node in a doubly linked list (with sorted insertion), as well as containing the coordinates of the top-left corner, and the width and height. Furthermore, each block data structure also contains four links which connect to each immediately adjacent (touching) block on each of the four sides. IMPORTANT RULE: Each block may only touch with one block per side. The problem with this approach is, it's very complex. I have implemented the straightforward cases where 1) space is removed from one corner of a block, 2) splitting neighbouring blocks so that the IMPORTANT RULE is adhered to. The less straightforward case, where the space to be removed can only be found within a column or row of boxes, is only partially implemented - if one of the blocks to be removed is an exact fit for width (ie column) or height (ie row) then problems occur. And don't even mention the fact this only checks columns one box wide, and rows one box tall. I've implemented this algorithm in C - the language I am using for this project (I've not used C++ for a few years and am uncomfortable using it after having focused all my attention to C development, it's a hobby). The implementation is 700+ lines of code (including plenty of blank lines, brace lines, comments etc). The implementation only works for the horizontal-rows + left-right + top-bottom placement strategy. So I've either got to add some way of making this +700 lines of code work for the other 7 placement strategy options, or I'm going to have to duplicate those +700 lines of code for the other seven options. Neither of these is attractive, the first, because the existing code is complex enough, the second, because of bloat. The algorithm is not even at a stage where I can use it in the real time worst case scenario, because of missing functionality, so I still don't know if it actually performs better or worse than the first approach. What else is there? I've skimmed over and discounted: Bin Packing algorithms: their emphasis on optimal fit does not match the requirements of this algorithm. Recursive Bisection Placement algorithms: sounds promising, but these are for circuit design. Their emphasis is optimal wire length. Both of these, especially the latter, all elements to be placed/packs are known before the algorithm begins. I need an algorithm which works accumulatively with what it is given to do when it is told to do it. What are your thoughts on this? How would you approach it? What other algorithms should I look at? Or even what concepts should I research seeing as I've not studied computer science/software engineering? Please ask questions in comments if further information is needed. [edit] If it makes any difference, the units for the coordinates will not be pixels. The units are unimportant, but the grid where windows/blocks/whatever can be placed will be 127 x 127 units.

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  • MDX - Using "iif" function in the "Where" section

    - by Duc Duy Nguyen
    Hi I'd like to know how to make that "iif" work. Basically, I need to filter the engineering "product codes" when originator is "John Smith". currentmember is not working or that iif is not working, SELECT { ( [Time].[Fiscal Hierarchy Time Calculations].[Month to Date], [Measures].[Sell - Bookings] ) } ON COLUMNS, [Originators].[Originator One Letter Name].Children ON ROWS FROM [Sales] WHERE ( [Time].[Fiscal Month].&[2010-02-01T00:00:00], IIF ( [Originators].[Originator One Letter Name].CurrentMember = "John Smith", Except ( [Product Codes].[Product Primary Subcategory].Children, [Product Codes].[Product Primary Subcategory].&[ENGINEERING] ), [Product Codes].[Product Primary Subcategory].Children ) ); Any ideas? Thanks in advance. Duy

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  • Convert a Mysql database from latin to UTF-8

    - by Matthieu
    I am converting a website from ISO to UTF-8, so I need to convert the Mysql database too. On internet, I read various solutions, I don't know wich one to choose. Do I really need to convert my varchar columns to binary, then to utf8 like that : ALTER TABLE t MODIFY col BINARY(150); ALTER TABLE t MODIFY col CHAR(150) CHARACTER SET utf8; This is long to do that for each column, of each table, of each database. I have 10 database, wich 20 tables each, wich around 2 - 3 varchar colums (2 queries each column), this gives me around 1000 queries to write ! How come ? How to do ?

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  • stock management of assemblys and its sub parts

    - by The Disintegrator
    I have to track the stock of individual parts and kits (assembly) and can't find a satisfactory way of doing this. Sample bogus and hyper simplified database: Table prod: prodID 1 prodName Flux capacitor prodCost 900 prodPrice 1350 (900*1.5) prodStock 3 - prodID 2 prodName Mr Fusion prodCost 300 prodPrice 600 (300*2) prodStock 2 - prodID 3 prodName Time travel kit prodCost 1650 (1350+300) prodPrice 2145 (1650*1.3) prodStock 2 Table rels relID 1 relSrc 1 (Flux capacitor) relType 4 (is a subpart of) relDst 3 (Time travel kit) - relID 2 relSrc 2 (Mr Fusion) relType 4 (is a subpart of) relDst 3 (Time travel kit) prodPrice: it's calculated based on the cost but not in a linear way. In this example for costs of 500 or less, the markup is a 200%. For costs of 500-1000 the markup is 150%. For costs of 1000+ the markup is 130% That's why the time travel kit is much cheaper than the individual parts prodStock: here is my problem. I can sell kits or the individual parts, So the stock of the kits is virtual. The problem when I buy: Some providers sell me the Time Travel kit as a whole (with one barcode) and some sells me the individual parts (with a different barcode) So when I load the stock I don't know how to impute it. The problem when I sell: If I only sell kits, calculate the stock would be easy: "I have 3 Flux capacitors and 2 Mr Fusions, so I have 2 Time travel kits and a Flux Capacitor" But I can sell Kits or individual parts. I have to track the stock of the individual parts and the possible kits at the same time (and I have to compensate for the sell price) Probably this is really simple, but I can't see a simple solution. Resuming: I have to find a way of tracking the stock and the database/program is the one who has to do it (I cant ask the clerk to correct the stock) I'm using php+MySql. But this is more a logical problem than a programing one

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  • iPhone - dequeueReusableCellWithIdentifier usage

    - by Jukurrpa
    Hi, I'm working on a iPhone app which has a pretty large UITableView with data taken from the web, so I'm trying to optimize its creation and usage. I found out that dequeueReusableCellWithIdentifier is pretty useful, but after seeing many source codes using this, I'm wondering if the usage I make of this function is the good one. Here is what people usually do: UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"]; if (cell == nil) { cell = [[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:@"Cell"]; // Add elements to the cell return cell; And here is the way I did it: NSString identifier = [NSString stringWithFormat:@"Cell @d", indexPath.row]: // The cell row UITableViewCell* cell = [tableView dequeueReusableCellWithIdentifier:identifier]; if (cell != nil) return cell; cell = [[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:identifier]; // Add elements to the cell return cell; The difference is that people use the same identifier for every cell, so dequeuing one only avoids to alloc a new one. For me, the point of queuing was to give each cell a unique identifier, so when the app asks for a cell it already displayed, neither allocation nor element adding have to be done. In fine I don't know which is best, the "common" method ceils the table's memory usage to the exact number of cells it display, whislt the method I use seems to favor speed as it keeps all calculated cells, but can cause large memory consumption (unless there's an inner limit to the queue). Am I wrong to use it this way? Or is it just up to the developper, depending on his needs?

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  • zf2 \Zend\Db\Sql\Sql using predicate in where condition

    - by RomanKonz
    i really don't get the point how to use predicates in zend framework 2. this is what i got: $sql->select() ->columns(array('GroupedColum' ,'minValue' => new Expression('min(ValueColumn)'))) ->from('ValueTable') ->group('GroupedColum') ->order('minValue') ->order('GroupedColum') ->limit(10); this is working fine now i want to apply somethin like that: $predicate = new Zend\Db\Sql\Predicate\Predicate(); $sql->where($predicate->greaterThan('filterColumn','20); this is what i tried, it throws no error, but it is not working :-( This is what i expect as SQL: select GroupedColum , min(ValueColumn) as minValue from ValueTable where filterColumn > 20 group by GroupedColum order by minValue GroupedColum limit 10;

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  • Changing database structure at runtime with Entity Framework?

    - by Teddy
    Hi. I have to write a solution that uses different databases with different structure from the same code. So, when a user logs to the application I determine to which database he/she is connected to at runtime. The user can create tables and columns at any time and they have to see the change on the fly. The reason that I use one and the same code the information is manipulates the same way for the different databases. How can I accomplish this at runtime? Actually is the Entity Framework a good solution for my problem? Thanks in advance.

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  • LINQ-To-SQL and Many-To-Many Relationship Deletions

    - by Jake
    I have a many-to-many relationship between two tables, let's say Friends and Foods. If a friend likes a food I stick a row into the FriendsFoods table, like this: ID Friend Food 1 'Tom' 'Pizza' FriendsFoods has a Primary Key 'ID', and two non-null foreign keys 'Friend' and 'Food' to the 'Friends' and 'Foods' tables, respectively. Now suppose I have a Friend tom .NET object corresponding to 'Tom', and Tom no longer likes pizza (what is wrong with him?) FriendsFoods ff = tom.FriendsFoods.Where(x => x.Food.Name == 'Pizza').Single(); tom.FriendsFoods.Remove(ff); pizza.FriendsFoods.Remove(ff); If I try to SubmitChanges() on the DataContext, I get an exception because it attempts to insert a null into the Friend and Food columns in the FriendsFoods table. I'm sure I can put together some kind of convoluted logic to track changes to the FriendsFoods table, intercept SubmitChanges() calls, etc to try and get this to work the way I want, but is there a nice, clean way to remove a Many-To-Many relationship with LINQ-To-SQL?

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  • Authentication on odata service

    - by Toad
    I want to add some authentication to my odata service. Depending on the user calling i want to: filter rows and/or remove columns. I read in scott hanselmans fine blogpost on odata ( http://www.hanselman.com/blog/CreatingAnODataAPIForStackOverflowIncludingXMLAndJSONIn30Minutes.aspx )that it is possible to intercept the incoming queries. If this works i could add some extra filtering. How would this intercepting and altering queries work exactly? I can not find any examples of where and how to do this. (i'm using entitie framework and wcf dataservices (just like scotts example blog)

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  • Subsonic 3 - Sequence contains no matching element

    - by bastos.sergio
    I need help creating a LINQ SQL with subsonic. First the basics, this works fine: var query = (from o in bd.concelhos orderby o.descricao select o); var results = query.ToList<concelhos>(); However, I want to filter out some columns and I have created the following code: var query = (from o in bd.concelhos orderby o.descricao select new FilteredConcelhos { id = o.idDistrito + "/" + o.idConcelho, descricao = o.descricao }); var results = query.ToList<FilteredConcelhos>(); which errors out in the ToList method with the description "Sequence contains no matching element" Any help would be great with this...

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  • MySQL index cardinality - performance vs storage efficiency

    - by Sean
    Say you have a MySQL 5.0 MyISAM table with 100 million rows, with one index (other than primary key) on two integer columns. From my admittedly poor understanding of B-tree structure, I believe that a lower cardinality means the storage efficiency of the index is better, because there are less parent nodes. Whereas a higher cardinality means less efficient storage, but faster read performance, because it has to navigate through less branches to get to whatever data it is looking for to narrow down the rows for the query. (Note - by "low" vs "high", I don't mean e.g. 1 million vs 99 million for a 100 million row table. I mean more like 90 million vs 95 million) Is my understanding correct? Related question - How does cardinality affect write performance?

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  • PHP mssql_query double quotes cannot be used

    - by Nilesh
    Hi all, In java-jdbc, I can easily run the following SQL (NOTE the double quotes around columns and table names) Select cus."customer_id" , cus."organisation_or_person" , cus."organisation_name" , cus."first_name" , cus."last_name" , cus."date_became_customer" , cus."other_customer_details" From "Contact_Management"."dbo"."Customers" cus But the same query in PHP errors out saying invalid syntax "Warning: mssql_query() [function.mssql-query]: message: Incorrect syntax near 'customer_id'. (severity 15) " But If remove all the double quotes, the query works fine and no errors. The query is ported from a java application so I would like to keep the double quotes and the SQL as it is. Any alternative solutions? Thank you Nilesh

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  • How to configure SQLite db in Visual Studio

    - by ChrisC
    I've messed with Access a little bit in the past, had one class on OO theory, and one class on console c++ apps. Now, as a hobby project, I'm undertaking to write an actual app, which will be a database app using System.Data.SQLite and C#. I have the db's table structure planned. I have System.Data.SQLite installed and connected to VS Pro. I entered my tables and columns in VS, but that's where I'm stuck. I really don't know how to finish the db set up so I can start creating queries and testing the db structure. Can someone give me guidance to online resources that will help me learn how to get the db properly set up so I can proceed with testing it? I'm hoping for online resources specific to beginners using C# and System.Data.SQLite, but I'll use the closest I can get. Thanks.

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  • Selecting arbitrary strings with Zend DB Select?

    - by wizzard
    I am using the fluent interface to create a Zend DB Select object/query. As part of the query, I would like to select an arbitrary string, like "SELECT 'foo' AS 'type' FROM ...". foo is not a column, it's just a string literal. When I select an arbitrary number, the query works as expected. When I change it to a string, Zend tries to treat foo as a column, and throws an error: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'l.foo' in 'field list' I have tried wrapping the string in Zend_Db_Expr in various ways such as: $select->columns(array('type' => new Zend_Db_Expr('foo'))); That stops Zend from adding the correlation name, but it still treats it as a column: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'foo' in 'field list' I feel like I must be missing something obvious here. How do I tell Zend to stop treating this as a column?

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  • NHibernate - mappping composite-id to table with non-composite primary key

    - by Dmitry
    I have table like this: ID - PK; KEY1 - UNIQUE1; KEY2 - UNIQUE1; If I don't want to use ID in my mappings, can I tell NHibernate to use KEY1 & KEY2 as a composite id? When I declare composite id like this: <composite-id> <key-property name="KEY1"/> <key-property name="KEY2"/> </composite-id> I get FKUnmatchingColumnsException (Foreign key ... must have same number of columns as the referenced primary key ...)

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  • PLT Scheme Extracting field ids from structures

    - by Steve Knight
    I want to see if I can map PLT Scheme structure fields to columns in a DB. I've figured out how to extract accessor functions from structures in PLT scheme using the fourth return value of: (struct-type-info) However the returned procedure indexes into the struct using an integer. Is there some way that I can find out what the field names were at point of definition? Looking at the documentation it seems like this information is "forgotten" after the structure is defined and exists only via the generated-accessor functions: (<id>-<field-id> s). So I can think of two possible solutions: Search the namespace symbols for ones that start with my struct name (yuk); Define a custom define-struct macro that captures the ordered sequence of field-names inside some hash that is keyed by struct name (eek).

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  • Ordered many-to-many relationship in NHibernate

    - by Kristoffer
    Let's say I have two classes: Item and ItemCollection, where ItemCollection contains an ordered list of Item objects with an index, i.e. the list is ordered in a way specified by the user. Let's also say that they have a many-to-many relationship, an ItemCollection can contain many items and an Item can belong to several ItemCollections. That would, in my head, require three tables in the database. One for Item, one for ItemCollection and one for the ordered mapping. The mapping table would contain three columns: int ItemID int ItemCollectionID int ListIndex QUESTION: How would you design the ItemCollection class? Should the list of Item objects be a list, dictionary or other? What would the NHibernate mapping look like to get the ListIndex into the picture?

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  • how can I add a custom non-DataTable column to my DataView, in a winforms ADO.net application?

    - by Greg
    Hi, How could I (/is it possible) to add a custom column to my DataView, and in this column display the result of a specific calculation. That is, I currently have a dataGridView which has a binding to a DataView, based on the DataTable from my database. I'd like to add an additional column to the dataGridView to display a number which is calculated by looking at this current row plus it's children row. In other words the info for the column isn't just derivable from the row data itself. Specific questions might be: a) where to add the column itself? to the DataView I assume? b) which method / event to trigger the re-calculation of the value of this custom column from ( / how do I control this) Thanks PS. I've also noted if I use the following code/approach I get a infinite loop... // Custom Items DataColumn dc = new DataColumn("OverallSize", typeof(long)); DT_Webfiles.Columns.Add(dc); DT_Webfiles.RowChanged += new DataRowChangeEventHandler(DT_Row_Changed); private static void DT_Row_Changed(object sender, DataRowChangeEventArgs e) { e.Row["OverallSize"] = e.Row["OverallSize"] ?? 0; e.Row["OverallSize"] = (long)e.Row["OverallSize"] + 1; } What other approach could avoid this looping. i.e. currently I'm saying update the value of the custom column when the row changes, however after then changing the row it triggers antoher 'row has changed' event...

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  • Combobox in bound DataGridView

    - by Dan
    Hi. I've got a DataGridView control which is bound to a database table. I want one of the columns in the gridview to be of combobox type. The combobox should contain a list of hardcoded strings, which is the same for all rows in the datagridview. One of the fields in my database table is an index for this list of hardcoded strings. I've programatically added a new column to the gridview of type "DataGridViewComboBoxColumn", which successfully creates the column with comboboxes in it. However, that's then not bound to the index field in my DB table. The index field in my DB table is actually automatically bound to a column via the DataAdapter::Fill method. I've set this column to hidden, so it's hidden to the user. Obviously just before updating the dataadapter, I can programatically fixup the hidden column in my datatable with the SelectedIndex of my combobox. Just wondering if there's a better way of doing this? Thankyou for any help with this, Dan.

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  • How to simply a foreach iteration using reflection

    - by Priya
    Consider that I have to get the overall performance of X. X has Y elements and Y in turn has Z elements which inturn has some N elements. To get the performance of X I do this: List<double> XQ = new List<double>(); foreach (Elem Y in X.Y){ List<double> YQ = new List<double>(); foreach (Elem Z in Y.Z){ List<double> ZQ = new List<double>(); foreach (Elem N in Z.N){ ZQ.Add(GetPerformance(N)); } YQ.Add(AVG(ZQ)); } XQ.Add(AVG(YQ)); } AVG of XQ list gives the performance of X. The performance can be calculated for either X or Y or for Z. X, Y and Z share the same base class. So depending on the item given the foreach loop has to be executed. Currently I have a switch case to determine each item (X or Y or Z) and the foreach loop is repeated in the code pertaining to the item (eg. If Y foreach starts from Y.Z). Is is possible to convert this whole code generic using reflection instead of having to repeat it in each switch case? Thanks

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  • ORM in the realworld

    - by josh
    I am begining a new project that i think will last for some years. Am in the point of deciding the ORM framework to use (or whether to use one at all). Can anyone with experience tell me whether orm frameworks are used in realworld applications. The problem i have in mind is this: The orm tool will generate for me tables and columns etc as i create and modify my entities. However, after the project has gone live and is in production, certain database changes will not be possible. Can this hinder the advancement of the project. If i had used a framework like ibatis for example, i know i would only need to adjust the sql statements based on the database changes. Can someone tell me whether ORM tools have survived the live environment. At my office, we use java based ERP that was done long ago and it was never done using any ORM framework. Regards. Josh

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  • Rails: creating a custom data type / creating a shorthand

    - by Shyam
    Hi, I am wondering how I could create a custom data type to use within the rake migration file. Example: if you would be creating a model, inside the migration file you can add columns. It could look like this: def self.up create_table :products do |t| t.column :name, :string t.timestamps end end I would like to know how to create something like this: t.column :name, :my_custom_data_type The reason for this to create for example a "currency" type, which is nothing more than a decimal with a precision of 8 and a scale of 2. Since I use only MySQL, the solution for this database is sufficient enough. Thank you for your feedback and comments!

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