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• hibernate order by association

  - by Gary Kephart

  I'm using Hibernate 3.2, and using criteria to build a query. I'd like to add and "order by" for a many-to-one association, but I don't see how that can be done. The Hibernate query would end up looking like this, I guess: select t1.a, t1.b, t1.c, t2.dd, t2.ee from t1 inner join t2 on t1.a = t2.aa order by t2.dd <-- need to add this I've tried criteria.addOrder("assnName.propertyName") but it doesn't work. I know it can be done for normal properties. Am I missing something?

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• Is it worth caching a Dictionary for foreign key values in ASP.net?

  - by user169867

  I have a Dictionary<int, string> cached (for 20 minutes) that has ~120 ID/Name pairs for a reference table. I iterate over this collection when populating dropdown lists and I'm pretty sure this is faster than querying the DB for the full list each time. My question is more about if it makes sense to use this cached dictionary when displaying records that have a foreign key into this reference table. Say this cached reference table is a EmployeeType table. If I were to query and display a list of employee names and types should I query for EmployeeName and EmployeeTypeID and use my cached dictionary to grab the EmployeeTypeIDs name as each record is displayed or is it faster to just have the DB grab the EmployeeName and JOIN to get the EmployeeType string bypassing the cached Dictionary all together. I know both will work but I'm interested in what will perform the fastest. Thanks for any help.

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• Error : while creating a file.

  - by Harikrishna

  I am storing records of datatable to csv file with the help of the following code : // we'll use these to check for rows with nulls var columns = yourTable.Columns .Cast<DataColumn>(); using (var writer = new StreamWriter(yourPath)) { for (int i = 0; i < yourTable.Rows.Count; i++) { DataRow row = yourTable.Rows[i]; // check for any null cells if (columns.Any(column => row.IsNull(column))) continue; string[] textCells = row.ItemArray .Select(cell => cell.ToString()) // may need to pick a text qualifier here .ToArray(); // check for non-null but EMPTY cells if (textCells.Any(text => string.IsNullOrEmpty(text))) continue; writer.WriteLine(string.Join(",", textCells)); } } But I get the error like System.UnauthorizedAccessException was unhandled Message="Access to the path 'D:\\Harikrishna\\Monthly Reports' is denied." What can be the problem and solution ?

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• Dynamic openrowset in T-Sql Function or viable alternative?

  - by IronicMuffin

  I'm not quite sure how to phrase this. Here is the problem: I have 1-n items that I need to join to a different system (AS400) to get some data. The openrowset takes forever if I specify the where criteria outside of the openrowset, e.g.: select * from openrowset('my connection string', 'select code, myfield from myTable') where code = @code My idea was to create a function that takes in the item number and uses dynamic sql to inject it into the openrowset string, a la: declare @cmd varchar(1000) set @cmd = 'select * from openrowset('my connection string', ''select code, myfield from myTable where code = ' + @code + ''')' Apparently I can't use the insert.. exec.. strategy inside of a function. Is there any better way to achieve this? I was going to use this in joins where I needed the external data using cross apply. I'm not married to tvf and cross apply, but I do need a method of getting this data quickly. Thanks for any help.

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• Insert rownumber repeatedly in records in t-sql.

  - by jeff

  Hi, I want to insert a row number in a records like counting rows in a specific number of range. example output: RowNumber ID Name 1 20 a 2 21 b 3 22 c 1 23 d 2 24 e 3 25 f 1 26 g 2 27 h 3 28 i 1 29 j 2 30 k I rather to try using the rownumber() over (partition by order by column name) but my real records are not containing columns that will count into 1-3 rownumber. I already try to loop each of record to insert a row count 1-3 but this loop affects the performance of the query. The query will use for the RDL report, that is why as much as possible the performance of the query must be good. any suggestions are welcome. Thanks

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• Why does Spring Security's BindAuthenticator require read permissions for users?

  - by Thomas

  Hi all, I'm currently implementing/configuring the LDAP authentication of a Java web application using Spring Security 3.0. I'm using Microsoft AD LDS as LDAP server and chose the Spring's BindAuthenticator. I found out that the authentication only works if the authenticated user is a member of the partition's Readers role. The BindAuthenticator tries to read the user's attributes after the authentication, which seems reasonable in scenarios where authorities are retrieved from the directory service. Being new to LDAP and AD, is this an acceptable practise when the application is integrated in an existing AD structure? Can fine-tune an give the user dns only read permissions for their own attributes rather than adding them to the Reader group? Thanks Thomas

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• How to program critical section for reader-writer systems?

  - by Srinivas Nayak

  Hi, Lets say, I have a reader-writer system where reader and writer are concurrently running. 'a' and 'b' are two shared variables, which are related to each other, so modification to them needs to be an atomic operation. A reader-writer system can be of the following types: rr ww r-w r-ww rr-w rr-ww where [ r : single reader rr: multiple reader w : single writer ww: multiple writer ] Now, We can have a read method for a reader and a write method for a writer as follows. I have written them system type wise. rr read_method { read a; read b; } ww write_method { lock(m); write a; write b; unlock(m); } r-w r-ww rr-w rr-ww read_method { lock(m); read a; read b; unlock(m); } write_method { lock(m); write a; write b; unlock(m); } For multiple reader system, shared variable access doesn't need to be atomic. For multiple writer system, shared variable access need to be atomic, so locked with 'm'. But, for system types 3 to 6, is my read_method and write_method correct? How can I improve? Sincerely, Srinivas Nayak

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• Recommendations for 'C' Project architecture guidelines?

  - by SiegeX

  Now that I got my head wrapped around the 'C' language to a point where I feel proficient enough to write clean code, I'd like to focus my attention on project architecture guidelines. I'm looking for a good resource that coves the following topics: How to create an interface that promotes code maintainability and is extensible for future upgrades. Library creation guidelines. Example, when should I consider using static vs dynamic libraries. How to properly design an ABI to cope with either one. Header files: what to partition out and when. Examples on when to use 1:1 vs 1:many .h to .c Anything you feel I missed but is important when attempting to architect a new C project. Ideally, I'd like to see some example projects ranging from small to large and see how the architecture changes depending on project size, function or customer. What resource(s) would you recommend for such topics?

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• accessing files after setup.py install

  - by Matthew

  I'm developing a python application and have a question regarding coding it so that it still works after an user has installed it on his or her machine via setup.py install or similar. In one of my files, I use the following: file = "TestParser/View/MainWindow.ui" cwd = os.getcwd() argv_path = os.path.dirname(sys.argv[0]) file_path = os.path.join(cwd, argv_path, file) in order to get the path to MainWindow.ui, when I only know the path relative to the main script's location. This works regardless of from where I call the main script. The issue is that after an user installs the application on his or her machine, the relative path is different, so this doesn't work. I could use __file__, but according to this, py2exe doesn't have __file__. Is there a standard way of achieving this? Or a better way?

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• LLBL Gen Predicate Filter

  - by Neil

  I am new to LLBLGen Pro and am checking for duplicate, I have the following SQL: SQL: select a.TopicId,atc.TopicCategoryId,a.Headline from article a inner join ArticleTopicCategory atc on atc.ArticleId = a.Id where a.TopicId = 'C0064FAE-093B-466E-8745-230534867D2F' and a.Headline = 'Test' and atc.TopicCategoryId in ('004D64F7-474C-48F9-9887-17B1E7532A84') Whenever I step though my function, it always returns 0: LLBLGen Code: public bool CheckDuplicateArticle(Guid topicId, List<Guid> categories, string headline) { ArticleCollection articles = new ArticleCollection(); PredicateExpression filter = new PredicateExpression(); RelationCollection relation = new RelationCollection(); relation.Add(ArticleEntity.Relations.ArticleTopicCategoryEntityUsingArticleId); filter.AddWithAnd(ArticleFields.TopicId == topicId); filter.AddWithAnd(ArticleTopicCategoryFields.Id == categories); filter.AddWithAnd(ArticleFields.Headline == headline); articles.GetMulti(filter, 0, null, relation); return articles.Count > 0; } Any help would be appreciated!

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• SQL Server (2005) Linked Server Issue

  - by David.Chu.ca

  I have SQL Server 2005 with several linked server defined. One of them is a connection to an Oracle server and another one is an ODBC bridge to another server on a remote machine (ODBC server). Recently I tried to use the linked server to Oracle to update data with two large size tables by using several joints. The update query took too long time and finally there was exception thrown: Update O set value = l.value FROM OracleServer..schema.largesizeTable O Join localLargeSizeTable l on .... The problem is that after the exception, I realized that another linked server to ODBC was not working any more. I had to restart SQL server to get the ODBC linked server back. It looks that the linked server pool could be crashed if any of them failed(not like sandbox in Chrome for each tab and no impact on other tabs or Chrome application at all). I am not sure if my assumption is correct or not. Is this a known issue of SQL server 2005?

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• Is possible to auto-import a module from a diferent subfolder in other subfolder?

  - by mamcx

  I have a kind of plugin system, with this layout: - Python -- SDK -- Plugins ---- Plugin1 ---- Plugin2 All 3 have a __init__.py file. I wonder if is possible to be able to do import SDK from any plugin (as if SDK was in the site-packages folder). I'm in a situation where need to deploy, update, delete, add or change SDK files or any of the plugins under non-admin accounts, and wonder if I can get SDK in a clean way (I could sys.path.append in all plugins but I wonder if exist a better option). I imagine that using this in the Plugins init coulkd work: import sys import os ROOT_DIR = os.path.abspath(os.path.join(os.path.dirname(__file__),'..')) print ROOT_DIR sys.path.append( ROOT_DIR ) But clearly is not executed this code (I imagine init was auto-magicalled executed in the load of the module :( )

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• finding numbers of days between two date to make a dynamic columns

  - by Chandradyani

  Dear all, I have a select query that currently produces the following results: DoctorName Team 1 2 3 4 5 6 7 ... 31 Visited dr. As   A                             x    x ...      2 times dr. Sc   A                          x          ...      1 times dr. Gh   B                                  x ...      1 times dr. Nd   C                                     ... x    1 times Using the following query: DECLARE @startDate = '1/1/2010', @enddate = '1/31/2010' SELECT d.doctorname, t.teamname, MAX(CASE WHEN ca.visitdate = 1 THEN 'x' ELSE NULL END) AS 1, MAX(CASE WHEN ca.visitdate = 2 THEN 'x' ELSE NULL END) AS 2, MAX(CASE WHEN ca.visitdate = 3 THEN 'x' ELSE NULL END) AS 3, ... MAX(CASE WHEN ca.visitdate = 31 THEN 'x' ELSE NULL END) AS 31, COUNT(*) AS visited FROM CACTIVITY ca JOIN DOCTOR d ON d.id = ca.doctorid JOIN TEAM t ON t.id = ca.teamid WHERE ca.visitdate BETWEEN @startdate AND @enddate GROUP BY d.doctorname, t.teamname the problem is I want to make the column of date are dynamic for example if ca.visitdate BETWEEN '2/1/2012' AND '2/29/2012' so the result will be : DoctorName Team 1 2 3 4 5 6 7 ... 29 Visited dr. As   A                             x    x ...      2 times dr. Sc   A                          x          ...      1 times dr. Gh   B                                  x ...      1 times dr. Nd   C                                     ... x    1 times Can somebody help me how to get numbers of days between two date and help me revised the query so it can looping MAX(CASE WHEN ca.visitdate = 1 THEN 'x' ELSE NULL END) AS 1 as many as numbers of days? Please please

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• Databases design - one link table or multiple link tables?

  - by David

  Hi there, I'm working on a front end for a database where each table essentially has a many to many relationship with all other tables. I'm not a DB admin, just a few basic DB courses. The typical solution in this case, as I understand it, would be multiple link tables to join each 'real' table. Here's what I'm proposing instead: one link table that has foreign key dependencies to all other PKs of the other tables. Is there any reason this could turn out badly in terms of scalability, flexibility, etc down the road?

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• SQL GROUP BY - also SELECT not-constant columns

  - by Michal Kosek

  can someone please help me with this query? I have 2 tables in my database: log_visitors: -------------------- id | host_id log_access: -------------------- visitor | document | timestamp "log_access.visitor" links to "log_visitors.id" Currently, I'm using this query: SELECT log_visitors.host_id , MIM(log_access.timestamp) AS min_timestamp FROM log_access INNER JOIN log_visitors ON (log_access.visitor = log_visitors.id) GROUP BY log_visitors.host_id; to get "MIN(timestamp)" for each "host_id" in the database. HERE'S MY QUESTION: I also need to get "document" for that access with that timestamp... I can't simply add "log_access.document" into SELECT list, since it's not constant and I am not grouping by document... Any ideas?

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• Can't figure out how to list all the people that don't live in same City as...

  - by AspOnMyNet

  I’d like to list all the people ( Person table ) that don’t live in same city as those cities listed in Location table. Thus, if Location table holds a record with City=’New York’ and State=’Moon’, but Person table holds a record with FirstName=’Someone’, City=’New York’ and Location=’Mars’, then Someone is listed in the resulting set, since she lives in New York located on Mars and not New York located on Moon, thus we’re talking about different cities with the same name. I tried solving it with the following query, but results are wrong: SELECT Person.FirstName, Person.LastName, Person.City, Person.State FROM Person INNER JOIN Location ON (Person.City <> Location.City AND Person.State = Location.State) OR (Person.City = Location.City AND Person.State <> Location.State) OR (Person.City <> Location.City AND Person.State <> Location.State) ORDER BY Person.LastName; Any ideas?

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• Trying to execute netdom.exe from a ruby script or IRB does nothing

  - by Joraff

  I'm trying to write a script that will rename a computer and join it to a domain, and was planning to call on netdom.exe to do the dirty work. However, trying to run this utility in the script (same results in irb) does absolutely nothing. No output, no execution. I tried with backticks and with the system() method. System() returns false for everything but system("netdom") (which returns true). Backticks never return anything but an empty string. I have verified that netdom runs and works in the environment the script will be running in, and I'm calling other command-line utilities earlier in the script that work (w32tm, getmac, ping). Here's the exact line that gets executed: `netdom renamecomputer %COMPUTERNAME% /NewName:#{newname} /force` FYI, This is windows 7 x64

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• Build dynamic LINQ?

  - by d daly

  Hi Im using #LINQ# to query data, but can anyone tell me how to build the query dynamically, if the user only wants to report on say 1 of the 3 fields? (see below) Thanks DD var query = from cl in db.tblClaims join cs in db.tblCases on cl.ref_no equals cs.ref_no where cl.claim_status == "Appeal" && cl.appeal_date >= Convert.ToDateTime(txtReferedFromDate.Text) && cl.appeal_date <= Convert.ToDateTime(txtReferedToDate.Text) && cs.referred_from_lho == dlLHO.Text && cs.adviser == dlAdviser.Text select new { Ref = cs.ref_no, ClaimType = cl.claim_type, ClaimStatus = cl.claim_status, AppealDate = cl.appeal_date }; gvReport.DataSource = query;

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• Custom validation works in development but not in unit test

  - by Geolev

  I want to validate that at least one of two columns have a value in my model. I found somewhere on the web that I could create a custom validator as follows: # Check for the presence of one or another field: # :validates_presence_of_at_least_one_field :last_name, :company_name - would require either last_name or company_name to be filled in # also works with arrays # :validates_presence_of_at_least_one_field :email, [:name, :address, :city, :state] - would require email or a mailing type address module ActiveRecord module Validations module ClassMethods def validates_presence_of_at_least_one_field(*attr_names) msg = attr_names.collect {|a| a.is_a?(Array) ? " ( #{a.join(", ")} ) " : a.to_s}.join(", ") + "can't all be blank. At least one field must be filled in." configuration = { :on => :save, :message => msg } configuration.update(attr_names.extract_options!) send(validation_method(configuration[:on]), configuration) do |record| found = false attr_names.each do |a| a = [a] unless a.is_a?(Array) found = true a.each do |attr| value = record.respond_to?(attr.to_s) ? record.send(attr.to_s) : record[attr.to_s] found = !value.blank? end break if found end record.errors.add_to_base(configuration[:message]) unless found end end end end end I put this in a file called lib/acs_validator.rb in my project and added "require 'acs_validator'" to my environment.rb. This does exactly what I want. It works perfectly when I manually test it in the development environment but when I write a unit test it breaks my test environment. This is my unit test: require 'test_helper' class CustomerTest < ActiveSupport::TestCase # Replace this with your real tests. test "the truth" do assert true end test "customer not valid" do puts "customer not valid" customer = Customer.new assert !customer.valid? assert customer.errors.invalid?(:subdomain) assert_equal "Company Name and Last Name can't both be blank.", customer.errors.on(:contact_lname) end end This is my model: class Customer < ActiveRecord::Base validates_presence_of :subdomain validates_presence_of_at_least_one_field :customer_company_name, :contact_lname, :message => "Company Name and Last Name can't both be blank." has_one :service_plan end When I run the unit test, I get the following error: DEPRECATION WARNING: Rake tasks in vendor/plugins/admin_data/tasks, vendor/plugins/admin_data/tasks, and vendor/plugins/admin_data/tasks are deprecated. Use lib/tasks instead. (called from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/tasks/rails.rb:10) Couldn't drop acs_test : #<ActiveRecord::StatementInvalid: PGError: ERROR: database "acs_test" is being accessed by other users DETAIL: There are 1 other session(s) using the database. : DROP DATABASE IF EXISTS "acs_test"> acs_test already exists NOTICE: CREATE TABLE will create implicit sequence "customers_id_seq" for serial column "customers.id" NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "customers_pkey" for table "customers" NOTICE: CREATE TABLE will create implicit sequence "service_plans_id_seq" for serial column "service_plans.id" NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "service_plans_pkey" for table "service_plans" /usr/bin/ruby1.8 -I"lib:test" "/usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb" "test/unit/customer_test.rb" "test/unit/service_plan_test.rb" "test/unit/helpers/dashboard_helper_test.rb" "test/unit/helpers/customers_helper_test.rb" "test/unit/helpers/service_plans_helper_test.rb" /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:1994:in `method_missing_without_paginate': undefined method `validates_presence_of_at_least_one_field' for #<Class:0xb7076bd0> (NoMethodError) from /usr/lib/ruby/gems/1.8/gems/will_paginate-2.3.12/lib/will_paginate/finder.rb:170:in `method_missing' from /home/george/projects/advancedcomfortcs/app/models/customer.rb:3 from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:158:in `require' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:265:in `require_or_load' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:224:in `depend_on' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:136:in `require_dependency' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:414:in `load_application_classes' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:413:in `each' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:413:in `load_application_classes' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:411:in `each' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:411:in `load_application_classes' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:197:in `process' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:113:in `send' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:113:in `run' from /home/george/projects/advancedcomfortcs/config/environment.rb:9 from ./test/test_helper.rb:2:in `require' from ./test/test_helper.rb:2 from ./test/unit/customer_test.rb:1:in `require' from ./test/unit/customer_test.rb:1 from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5:in `load' from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5 from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5:in `each' from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5 rake aborted! Command failed with status (1): [/usr/bin/ruby1.8 -I"lib:test" "/usr/lib/ru...] (See full trace by running task with --trace) It seems to have stepped on will_paginate somehow. Does anyone have any suggestions? Is there another way to do the validation I'm attempting to do? Thanks, George

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• complex mysql query problem

  - by Scarface

  Hey guys I have a query that selects data and organizes but not in the correct order. What I want to do is select all the comments for a user in that week and sort it by each topic, then sort the cluster by the latest timestamp of each comment in their respective cluster. My current query selects the right data, but in seemingly random order. Does anyone have any ideas? select * from ( SELECT topic.topic_title, topic.topic_id FROM comments JOIN topic ON topic.topic_id=comments.topic_id WHERE comments.user='$user' AND comments.timestamp>$week order by comments.timestamp desc) derived_table group by topic_id

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• Fragment caching

  - by red5

  I would like to fragment cache part of a page. On the view I have <% cache("saved_area") do %> . <% end -%> In the controller: def index read_fragment("saved_area") end In config/production: config.cache_store = :file_store, File.join(RAILS_ROOT, 'tmp', 'cache') The file was created in the tmp/cache directory. But I am not sure if the cache is being used in the request, since I presume there should be a line in the log stating that the cache is being used (and there is not).

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• Visual Studio error on valid SQL

  - by Sam

  I'm getting an annoying error in visual studio for SQL that executes fine. SELECT InvoiceLines.LineID, InvoiceLines.InvoiceID, InvoiceLines.Text, InvoiceLines.Rate, InvoiceLines.Count, InvoiceLines.Rate * InvoiceLines.Count AS LineTotal, ((InvoiceLines.Rate * InvoiceLines.Count) * (1 + Invoices.VatRate / 100)) * (1 - CAST(Invoices.Discount AS money) * InvoiceLines.ApplyDiscount / 100) AS LineTotalIncVat, InvoiceLines.ApplyDiscount FROM InvoiceLines LEFT JOIN Invoices ON Invoices.InvoiceID = InvoiceLines.InvoiceID What LineTotalIncVat is trying to do is compute the total for the invoice item while adding the vat and subtracting the discount, and yes, probably better to do this in code (would if I could) The error visual studio gives is: There was an error parsing the query [token line number =1, token line offset =14, token in error = InvoiceLines] Even though it will validate and execute without a problem in the query builder...

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• archiving strategies and limitations of data in a table

  - by Samuel

  Environment: Jboss, Mysql, JPA, Hibernate Our web application will be catering to a large amount of users (~ 1,000,000) and there are a lots of child table where user specific data are stored (e.g. personal, health, forum contributions ...). What would be the best practice to archive user & user specific information. [a] Would it be wise to move the archived user & user specific information to their respective tables within the same database (e.g. user_archive, user_forum_comments_archive ...) OR [b] Would you just mark the database entries with a flag in the original table(s) and just query only non archived entries. We have a unique constraint on User.loginid, how do you handle this requirement if the users are archived via 1-[a] (i.e if a user with loginid 'samuel' gets moved into the archive table and if a new user gets added with the same name in the original table, how would you prevent this. What would be the best strategy to address the unique key constraints. We have a requirement to selectively archive records and bring it back if necessary, will you rely on database tools are would you handle this via your persistence APIs exposed by the JPA entity model.

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• mySQL one-to-many query

  - by Stomped

  I've got 3 tables that are something like this (simplified here ofc): users user_id user_name info info_id user_id rate contacts contact_id user_id contact_data users has a one-to-one relationship with info, although info doesn't always have a related entry. users has a one-to-many relationship with contacts, although contacts doesn't always have related entries. I know I can grab the proper 'users' + 'info' with a left join, is there a way to get all the data I want at once? For example, one returned record might be: user_id: 5 user_name: tom info_id: 1 rate: 25.00 contact_id: 7 contact_data: 555-1212 contact_id: 8 contact_data: 555-1315 contact_id: 9 contact_data: 555-5511 Is this possible with a single query? Or must I use multiple?

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• Building a subquery with ARel in Rails3

  - by Christopher

  I am trying to build this query in ARel: SELECT FLOOR(AVG(num)) FROM ( SELECT COUNT(attendees.id) AS num, meetings.club_id FROM `meetings` INNER JOIN `attendees` ON `attendees`.`meeting_id` = `meetings`.`id` WHERE (`meetings`.club_id = 1) GROUP BY meetings.id) tmp GROUP BY tmp.club_id It returns the average number of attendees per meeting, per club. (a club has many meetings and a meeting has many attendees) So far I have (declared in class Club < ActiveRecord::Base): num_attendees = meetings.select("COUNT(attendees.id) AS num").joins(:attendees).group('meetings.id') Arel::Table.new('tmp', self.class.arel_engine).from(num_attendees).project('FLOOR(AVG(num))').group('tmp.club_id').to_sql but, I am getting the error: undefined method `visit_ActiveRecord_Relation' for #<Arel::Visitors::MySQL:0x9b42180> The documentation for generating non trivial ARel queries is a bit hard to come by. I have been using http://rdoc.info/github/rails/arel/master/frames Am I approaching this incorrectly? Or am I a few methods away from a solution?

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