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• Adjacency List Tree Using Recursive WITH (Postgres 8.4) instead of Nested Set

  - by Koobz

  I'm looking for a Django tree library and doing my best to avoid Nested Sets (they're a nightmare to maintain). The cons of the adjacency list model have always been an inability to fetch descendants without resorting to multiple queries. The WITH clause in Postgres seems like a solid solution to this problem. Has anyone seen any performance reports regarding WITH vs. Nested Set? I assume the Nested set will still be faster but as long as they're in the same complexity class, I could swallow a 2x performance discrepancy. Django-Treebeard interests me. Does anyone know if they've implemented the WITH clause when running under Postgres? Has anyone here made the switch away from Nested Sets in light of the WITH clause?

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• Lucene search taking TOOO long.

  - by Josh Handel

  I;m using Lucene.net (2.9.2.2) on a (currently) 70Gig index.. I can do a fairly complicated search and get all the document IDs back in 1 ~ 2 seconds.. But to actually load up all the hits (about 700 thousand in my test queries) takes 5+ minutes. We aren't using lucene for UI, this is a datastore between processes where we have hundreds of millions of pre-cached data elements, and the part I am working on exports a few specific fields from each found document. (ergo, pagination doesn't make since as this is an export between processes). My question is what is the best way to get all of the documents in a search result? currently I am using a custom collector that does a get on the document (with a MapFieldSelector) as its collecting.. I've also tried iterating through the list after the collector has finished.. but that was even worse. I'm open to ideas :-). Thanks in advance.

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• Best practices: Sending email on behalf of users

  - by Ben Doom

  The company I work for provides testing services for the healthcare industry. As part of our services, we need to send email to our clients' employees. Typically, these are temp, part-time, or contract employees, and so have private email addresses (eg Hotmail, GMail, Yahoo!, etc). Up to now, we've been sending from an internal address, but this means that replies come back to us when employees aren't paying attention or don't know to send queries to our clients. I'd like to change this, so that the person who requests that the email is sent is the person that is replied to. We've used reply-to: in the past, but it seemed to cause additional mail to be trapped by spam filters. I've been reading about sender: and on-behalf-of: headers, and was wondering what the current best-practice was for sending email in a scenario where we need to send email such that the reply goes to a domain we don't control.

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• .NET application per-machine/per-user licensing

  - by MainMa

  I am about to implement a very basic licensing feature for my application. A serial number may be granted per-machine (or per-operating-system) or per-user (as for CAL in Windows Server: if my application is used by several users on one machine or if it is used by one user on several machines). For per-operating-system licensing, I use SerialNumber of Win32_OperatingSystem. For per-user licensing, I use: WindowsIdentity currentIdentity = WindowsIdentity.GetCurrent(); if (currentIdentity != null) { SecurityIdentifier userSid = currentIdentity.User.AccountDomainSid; Console.WriteLine(userSid); } A hash of an obtained OS serial number or SID is then stored in the database, associated with application serial; each time the program starts, it queries the server, sending hash of OS SN/SID and application serial. Is it a right thing to do it or is it completely wrong? Will it work on every Windows machine? (For example, using motherboard serial is wrong)

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• Overriding SQLMembershipProvider

  - by vikp

  Is there built in methods into .net framework to do the following: Get role GUID from user name/user GUID Get role name from role GUID So far I have been sending queries to the asp_roles and asp_users tables to obtain that information and I'm wondering if there is a nicer way of doing this? I have the following methods that I store in the ASPUtilities class: getRoleGUID(guid userGuid) { LINQ joins } getRoleGuid(string userName) { LINQ joins } getRoleName(guid roleGuid) { LINQ joins } EDIT: I have just looked into extending SQLMembershipProvider examples. Few examples completely override the SQLMembershipProvider, but I think what I'm interested is just adding few extra methods to deal with the roles by using LINQ. Is this feasible?

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• Entity Framework Performance Problem

  - by Steve Horn

  I'm hoping that someone can help me understand how to overcome a performance problem I'm running into with the latest version of the Entity Framework. In my test, I created my model from a database consisting of around 80 tables. The problem that I'm running into is that the cost of the very first query I run on a thread is very expensive. If I run without pre-compiling views the first query takes anywhere from 5800 to 6600 milliseconds. If I pre-compile the views (see this article) I can get the initial query cost down to about 2800 to 3200 milliseconds. 3 seconds for each request is still unacceptable for my needs. Subsequent queries are very fast. Can you please help me understand how to eliminate the poor performance of the initial query? I'm using the version of entity framework that ships with Visual Studio 2010 RC.

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• DAO, Spring and Hibernate

  - by EugeneP

  Correct me if anything is wrong. Now when we use Spring DAO for ORM templates, when we use @Transactional attribute, we do not have control over the transaction and/or session when the method is called externally, not within the method. Lazy loading saves resources - less queries to the db, less memory to keep all the collections fetched in the app memory. So, if lazy=false, then everything is fetched, all associated collections, that is not effectively, if there are 10,000 records in a linked set. Now, I have a method in a DAO class that is supposed to return me a User object. It has collections that represent linked tables of the database. I need to get a object by id and then query its collections. Hibernate "failed to lazily initialize a collection" exception occurs when I try to access the linked collection that this DAO method returns. Explain please, what is a workaround here?

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• Override default operations order in LINQ

  - by Erick

  For one of our applications we do use LINQ to update a few reccords of the database. For business reasons we do require that only one item of a list to be primary. When we designed we decided to fire all of queries at the database at once. The problems occurs when we add one row and update the primary element to be the second item. See, the default behavior for order of operations with LINQ is to Insert, Update, Delete. If I Insert a first element I get a check constraint error with SQL Server. The best in my opinion would be to override and make sure to Update before Insert, this way we make sure that check constraints are kept. Tho there is not a lot of documentation on the mather. Any idea ?

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• SQL Injection with Plain-Vanilla NHibernate

  - by James D

  Hello, Plain-vanilla NHibernate setup, eg, no fluent NHibernate, no HQL, nothing except domain objects and NHibernate mapping files. I load objects via: _lightSabers = session.CreateCriteria(typeof(LightSaber)).List<LightSaber>(); I apply raw user input directly to one property on the "LightSaber" class: myLightSaber.NameTag = "Raw malicious text from user"; I then save the LightSaber: session.SaveOrUpdate(myLightSaber); Everything I've seen says that yes, under this situation you are immune to SQL injection, because of the way NHibernate parameterizes and escapes the queries under the hood. However, I'm also a relative NHibernate beginner so I wanted to double-check. *waves hand* these aren't the droids you're looking for. Thanks!

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• Django : json serialize a queryset which uses defer() or only()

  - by PlanetUnknown

  Now I've been using json serializer and it works great. I had to modify my queries where I started using the only() & defer() filters, like so - retObj = OBJModel.objects.defer("create_dt").filter(loged_in_dt__gte=dtStart) After I've done the above, suddenly the json serializer is returning empty fields - {"pk": 19047, "model": "OBJModel_deferred_create_dt", "fields": {}} If I remove the defer(), the serializer gives all the data correctly. import json from django.utils import simplejson from django.core import serializers json_serializer = serializers.get_serializer("json")() retObj = OBJModel.objects.defer("create_dt").filter(loged_in_dt__gte=dtStart) json_serializer.serialize(retObj, ensure_ascii=False) I've scratched my head on this for a while now. Any insight would be great. NOTE : I am using django 1.1

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• Rails: blank page - no errors or stack trace

  - by Nathan Long

  I've been trying to fix a bug in the Rails app I'm developing, and I keep getting a blank screen with no errors. I haven't found anything helpful in development.log, either (though it does show queries being run and such). Finally, I started to wonder if it's somehow set not to show errors anymore. I tried commenting out a necessary route, and sure enough, I got a blank page instead of the error and stack trace I expected. What might cause this? (I wondered if maybe I'm accidentally running production mode and errors aren't supposed to show then, but development.log is being appended, and if I open script/console and echo ENV['RAILS_ENV'], it says development.)

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• Pros and cons of programmatically enforcing foreign key than in database

  - by Jeffrey

  It is causing so much trouble in terms of development just by letting database enforcing foreign key. Especially during unit test I can’t drop table due to foreign key constrains, I need to create table in such an order that foreign key constrain warning won’t get triggered. In reality I don’t see too much point of letting database enforcing the foreign key constrains. If the application has been properly designed there should not be any manual database manipulation other than select queries. I just want to make sure that I am not digging myself into a hole by not having foreign key constrains in database and leaving it solely to the application’s responsibility. Am I missing anything? P.S. my real unit tests (not those that use mocking) will drop existing tables if the structure of underlying domain object has been modified.

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• Jquery tabs and forms

  - by Lee

  Hi, this may be a weird problem but I’m not sure the best way to go about it.. I am using JQuery ajax tabs. The tab section is dynamic so multiple tabs can be added, as the content is loaded via Ajax the same content can be loaded into different tabs. The other important detail is that i am using the Cache option so the tabs maintain state. Now problems arise when more than one tab has been loaded. It looks like HTML items such as forms and divs now have duplicated id's within the DOM, so Ajax queries can no longer distinguish between the elements.. The result is that any JavaScript/Ajax breaks. Does anyone have any suggestions for way to tackle such a problem? Thanks in advance..

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• Good way to capture/replay sessions from Apache Log?

  - by Mark Harrison

  For performance testing, I would like to capture some traffic from a production server and use that as a basis to replay the request to a test server in order to simulate a realistic load in our development environment. These are all stateless queries, so no issues regarding cookies, sessions, etc. The Apache log timestamps everything down to a 1 second resolution, but that's not fine enough granularity for our peak times. What's the best way to capture more fine-grained timestamps for replay? And is there some ab-like load generating program that can use this data to replicate load?

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• Reverse engineer an ORM

  - by Oren Mazor

  Given a [mysql] database with a given schema, is it possible to generate an ORM interface for it? doesn't matter if its php, python or perl. in other words, I have a database and I have to ask it a few questions. while I could just craft a bunch of SQL queries (okay, several dozen), this is way more interesting to think about. is this a valid question, even? I have no design background with ORMs, but I've used a few (django's, symfony's, etc).

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• What should the SQL keyword "ISABOUT" [deprecated?] be replaced with?

  - by Atomiton

  In MS SQL Full-text search, I'm using ISABOUT in my queries. For example, this should return the top 10 ProductIDs (PK) with a RANK Field in the ProductDetails Table SELECT * FROM CONTAINSTABLE( ProductDetails, *, ISABOUT("Nikon" WEIGHT (1.0), "Cameras" Weight(0.9)), 10 ) However, according to the SQL Documentation ISABOUT is deprecated. So, I have two questions: What is ISABOUT being replaced with? DO I even NEED any extra SQL Command there? ( IOW, would just putting the search phrase 'Nikon Cameras' be better? ) What I was originally trying to accomplish here was to weight the first word the highest, then the second word lower, and keep descending to 0.5 where I would just rank the remaining words at 0.5. My logic ( and perhaps it's flawed ) was that people's most relevant search words usually happen near the beginning of a phrase ( in English ). Am I going about this the wrong way? Is there a better way? Am I asking too many questions? (^_^) Thanks all for your time...

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• MySQL top count({column}) with a limit

  - by Josh K

  I have a table with an ip address column. I would like to find the top five addresses which are listed. Right now I'm planning it out the following: Select all distinct ip addresses Loop through them all saying count(id) where IP='{ip}' and storing the count List the top five counts. Downsides include what if I have 500 ip addresses. That's 500 queries I have to run to figure out what are the top five. I'd like to build a query like so select ip from table where 1 order by count({distinct ip}) asc limit 5

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• Tutorials for C# database app

  - by ChrisC

  My question and comments here http://stackoverflow.com/questions/2471198/what-is-ado-net shows my level of knowledge about c# database apps. Can someone point me to tutorials and/or primers that can help me proceed from where I am (also stated in other question)? I've looked and all I've found are tutorials that talk about general db basics (ie, not helping with VS/C#), or talk about connecting to existing SQL db's. I need help setting one up and configuring it, as well as help on how to create and use queries to test the db schema.

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• C# Linq Entity Conversion Error on Nonexistent Value?

  - by Ryan

  While trying to query some data using the Linq Entity Framework I'm receiving the following exception: {"Conversion failed when converting the varchar value '3208,7' to data type int."} The thing that is confusing is that this value does not even exist in the view I am querying from. It does exist in the table the view is based on, however. The query I'm running is the following: return context.vb_audit_department .Where(x => x.department_id == department_id && x.version_id == version_id) .GroupBy(x => new { x.action_date, x.change_type, x.user_ntid, x.label }) .Select(x => new { action_date = x.Key.action_date, change_type = x.Key.change_type, user_ntid = x.Key.user_ntid, label = x.Key.label, count = x.Count(), items = x }) .OrderByDescending(x => x.action_date) .Skip(startRowIndex) .Take(maximumRows) .ToList(); Can somebody explain why LINQ queries the underlying table instead of the actual view, and if there is any way around this behavior?

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• Http 404: Not Found (WebException)

  - by Rajeev

  Hi, I am using a console app/class library to invoke a asp.net web service. The class library queries the database and sends the data to the web service. What I notice is that when the amount of data is huge (with 20 columns and 18K records), i get a HTTP 404: Not Found exception from the web service. I have tried increasing the maxReqeustLength and executionTimeout properties in the httpRuntime tag in the web.config of the web service. Is there any thing that I can do to overcome this? Thanks, Rajeev

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• HTTP Cache Control max-age, must-revalidate

  - by nyb

  I have a couple of queries related to Cache-Control. If I specify Cache-Control "max-age=3600, must-revalidate" for a static html/js/images/css file, with Last Modified Header defined in HTTP header, a. Does browser/proxy cache(liek Squid/Akamai) go all the way to orgin server to validate before max-age expires? Or will it serve content from cache till max-age expires? b. After max-age expiry(that is expiry from cache), is there a IMS check or is content re-downloaded from origin server w/o IMS check?

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• What's the cause of (and treatment for) this java MySQL exception?

  - by justkevin

  I'm getting the following exception when executing the first preparedstatement after a period of inactivity: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure The last packet successfully received from the server was 2,855,054 milliseconds ago. The last packet sent successfully to the server was 123 milliseconds ago. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) at java.lang.reflect.Constructor.newInstance(Unknown Source) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3052) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2938) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3481) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2109) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2648) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2077) at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2228) This only shows up if my application hasn't communicated with MySQL recently. Subsequent queries execute normally. I suspect it's some kind of timeout issue, but the periods of inactivity are way below the 8 hour timeout for MySQL. Any suggestions?

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• Rails - how can I query the db w/o touching the sessions table

  - by sa125

  Hi - I'm trying to provide a HTTP api to my app that queries a db that's read-only (for replication purposes). I find that my app crashes repeatedly when making a request b/c the call is trying to update the sessions table whenever I query the db. This doesn't happen when I return some text without hitting the database for info. class APIController < AplicationController def view data = Product.find(params[:id]).to_json # will fail data = { :one => 1, :two => 2 }.to_json # will succeed respond_to do |format| format.html { render :json => data } end end end How do I restrict it from touching the sessions table on this request (it's currently issuing an UPDATE on the updated_at field for that session). thanks.

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• SQL - query inside NOT IN takes longer than the complete query ??

  - by Aleksandar Tomic

  Hi every1, I'm using NOT IN inside my SQL query. For example: select columnA from table1 where columnA not in ( select columnB from table2) How is it possible that this part of the query select columnB from table2 takes 30sec to complete, but the whole query above takes 0.1sec to complete?? Shouldn't the complete query take 30sec + ? BTW, both queries return valid results. Thanks! Answers to Comments Is it because the second query hasn't actually completed but has only returned back the first 'x' rows (out of a very large table?) No, the query is completed after 30 seconds, not to many rows returned (eg. 50). But @Aleksandar wondered why the question congaing the performance killer was so fast. my point exactly Also how long does select distinct columnB from table2 take to execute? actually, the original query is "select distinct...

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• custom MSSQL driver

  - by hoodoos

  I had a crazy thought about writing my own MSSQL driver to make it work something like non-blocking http client, so it won't be thread thirsty and could handle lots of db queries within one thread. I tried to look over google for some guidelines about implementing MSSQL client protocol, but found none really, where do those guys get information about it when they write own implementations for PHP or python? I need a really low level to be documented so I can implement all phases of working with a connection through sockets. And would be really nice to have a an example in c# langauge. :)

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