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• MongoDB Schema Design - Real-time Chat

  - by Nick

  I'm starting a project which I think will be particularly suited to MongoDB due to the speed and scalability it affords. The module I'm currently interested in is to do with real-time chat. If I was to do this in a traditional RDBMS I'd split it out into: Channel (A channel has many users) User (A user has one channel but many messages) Message (A message has a user) The the purpose of this use case, I'd like to assume that there will be typically 5 channels active at one time, each handling at most 5 messages per second. Specific queries that need to be fast: Fetch new messages (based on an bookmark, time stamp maybe, or an incrementing counter?) Post a message to a channel Verify that a user can post in a channel Bearing in mind that the document limit with MongoDB is 4mb, how would you go about designing the schema? What would yours look like? Are there any gotchas I should watch out for?

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• How to delete data in DB efficiently using LinQ to NHibernate (one-shot-delete)

  - by kastanf

  Hello, producing software for customers, mostly using MS SQL but some Oracle, a decision was made to plunge into Nhibernate (and C#). The task is to delete efficiently e.g. 10 000 rows from 100 000 and still stay sticked to ORM. I've tried named queries - link already, IQuery sql = s.GetNamedQuery("native-delete-car").SetString(0, "Kirsten"); sql.ExecuteUpdate(); but the best I have ever found seems to be: using (ITransaction tx = _session.BeginTransaction()) { try { string cmd = "delete from Customer where Id < GetSomeId()"; var count = _session.CreateSQLQuery(cmd).ExecuteUpdate(); ... Since it may not get into dB to get all complete rows before deleting them. My questions are: If there is a better way for this kind of delete. If there is a possibility to get the Where condition for Delete like this: Having a select statement (using LinQ to NHibernate) = which will generate appropriate SQL for DB = we get that Where condition and use it for Delete. Thanks :-)

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• How to calculate change in ANSI SQL

  - by morpheous

  I have a table that contains sales data. The data is stored in a table that looks like this: CREATE table sales_data ( sales_time timestamp , sales_amt double ) I need to write parameterized queries that will allow me to do the following: Return the change in sales_amt between times t2 and t1, where t2 and t1 are separated by a time interval (integer) of N. This query will allow for querying for weekly changes in sales (for example). Return the change in change of sales_amt between times t2 and t1, and time t3 and t4. Thats is to calculate the value (val(t2)-val(t1)) - (val(t4)-val(t3)). where t2 and t1 are separated by the same time interval (interval N) as the interval between t4 and t3. This query will allow for querying for changes in weekly changes in sales (for example).

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• Creating a proper CMS thoughts

  - by dallasclark

  I'm just about to expand the functionality of our own CMS but was thinking of restructuring the database to make it simpler to add/edit data types and values. Currently, the CMS is quite flat - the CMS requires a field in the database for every type of stored value. The first option that comes to mind is simply a table which keeps the data types (ie: Address 1, Suburb, Email Address etc) and another table which holds values for each of these data types. Just like how Wordpress keeps values in the 'options' table, serialize would be used to store an array of values. The second option is how Drupal works, the CMS creates tables for every data type. Unlike Wordpress, this can be a bit of an overkill but really useful for SQL queries when ordering and grouping by a particular value. What's everyone's thoughts?

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• Group by/count in LINQ against SQL Compact 3.5 SP2

  - by bash74

  Hello, I am using LINQ-To-Entities in C# and run queries against a SQL Compact Server 3.5 SP2. What I try to achieve is a simple group by with an additional where clause which includes a Count(). var baseIdent="expression"; var found=from o in ObservedElements where o.ObservedRoots.BaseIdent==baseIdent group o by o.ID into grouped where grouped.Count()==1 select new {key=grouped.Key, val=grouped}; foreach(var res in found){ //do something here } This query throws the famous exception "A parameter is not allowed in this location. Ensure that the '@' sign and all other parameters are in a valid location in the SQL statement." When I either omit the where clause OR directly enter the expression "expression" in the query (where o.ObservedRoots.BaseIdent=="expression") everything just works fine. Does anybody know how to solve this? Workaround would also be fine? Thanks in advance, Sebastian

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• Rails flash hash violation of MVC?

  - by user94154

  I know Rails' flash hash is nothing new, but I keep running into the same problem with it. Controllers should be for business logic and db queries, not formatting strings for display to the user. But the flash hash is always set in the controller. This means that I need to hack and work around Rails to use Helpers that I made to format strings for the flash hash. Is this just a pragmatic compromise to MVC or am I missing something here? How do you deal with this problem? Or do you not even see it as one?

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• .NET Database Apps: Your Preferred Setup

  - by mdvaldosta

  I'm struggling to settle into a pattern for developing typical database driven apps in C# and Visual Studio. There are so many ways to set them up, using drag/drop datasets and adapters or writing the queries manually in ADO.NET or Linq to SQL, Linq to Entities, to bind or not to data bind etc etc. Where to store the connection string, in app.config or in a method or both etc etc. So many tutorials and all of them are different. Everytime I write something I start hating the way it looks and works, so I scrap it and start over. It's getting a bit tedious. Maybe it's alittle of the OCD in me. Would any of you professional developers out there share your method of setting up and structuring your database logic and maybe some sample code? It's really how to go about organizing the code and the method(s) of interacting with SQL that I'm trying to get into a routine with, one that works and won't get me laughed at by someone reviewing it.

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• Lexing partial SQL in C#

  - by Chris T

  I'd need to parse partial SQL queries (it's for a SQL injection auditing tool). For example '1' AND 1=1-- Should break down into tokens like [0] => [SQL_STRING, '1'] [1] => [SQL_AND] [2] => [SQL_INT, 1] [3] => [SQL_AND] [4] => [SQL_INT, 1] [5] => [SQL_COMMENT] [6] => [SQL_QUERY_END] Are their any at least lexers for SQL that I base mine off of or any good tools like bison for C# (though I'd rather not write my own grammar as I need to support most if not all the grammar of MySQL 5)

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• subscript for a join (\bowtie) operation in LyX/LaTeX

  - by Amir Rachum

  I'm using LyX to write some Relational Algebra queries. I'm using the \bowtie symbol for the join operation but when I try to put a text in subscript directly under the symbol, I get the following error: ...a_{\t{pId}}\t{person}\right)\bowtie\limits {\t{pId}{1}=\t{pId}_{2}... I'm ignoring this misplaced \limits or \nolimits command. Anyone knows how to do what I want? Preferably in LyX, but ERT code snippets will also be appreciated. Thanks! Edit: \t is a macro for \text.

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• Using LINQ-To-Entities to Generate Information

  - by parminder

  I am working on a website where a user can add tags to their posted books, much like is currently done for questions on Stack Overflow. Classes: Books { bookId, Title } Tags { Id Tag } BooksTags { Id BookId TagId } Here are few sample records. Books BookId Title 113421 A 113422 B Tags Id Tag 1 ASP 2 C# 3 CSS 4 VB 5 VB.NET 6 PHP 7 java 8 pascal BooksTags Id BookId TagId 1 113421 1 2 113421 2 3 113421 3 4 113421 4 5 113422 1 6 113422 4 7 113422 8 Questions I need to write something in LINQ to entity queries which gives me data according to the tags: Query: bookIds where tagid = 1 Returns: bookid: 113421, 113422 Query 2: tags 1 and 2 Returns: 113421 I need tags and their count to to show in related tags, so in first case my related tags class should have following result. RelatedTags Tag Count 2 1 3 1 4 2 8 1 Second Case: RelatedTags Tag Count 3 1 4 1 How do I do this in LINQ?

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• Will SQL Server Partitioning increase performance without changing filegroups

  - by Tom

  Scenario I have a 10 million row table. I partition it into 10 partitions, which results in 1 million rows per partition but I do not do anything else (like move the partitions to different file groups or spindles) Will I see a performance increase? Is this in effect like creating 10 smaller tables? If I have queries that perform key lookups or scans, will the performance increase as if they were operating against a much smaller table? I'm trying to understand how partitioning is different from just having a well indexed table, and where it can be used to improve performance. Would a better scenario be to move the old data (using partition switching) out of the primary table to a read only archive table? Is having a table with a 1 million row partition and a 9 million row partition analagous (performance wise) to moving the 9 million rows to another table and leaving only 1 million rows in the original table?

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• In-memory Database in Excel

  - by user329174

  Hello, I am looking for a way to import a datatable from Access into an Excel variable and then run queries through this variable to speed up the process. I am trying to migrate from C# .NET where I read a data table from an access database into memory and then used LINQ to query this dataset. It is MUCH faster than how I have it currently coded in VBA where I must make lots of calls to the actual database, which is slow. I have seen the QueryTable mentioned, but it appears that this requires pasting the data into the excel sheet. I would like to keep everything in memory and minimize the interaction between the Excel Sheet and the VBA code as much as possible. I wish we didn't need to use Excel+VBA to do this, but we're kind of stuck with that for now. Thanks for the help!

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• Most optimal order (of joins) for left join

  - by Ram

  I have 3 tables Table1 (with 1020690 records), Table2(with 289425 records), Table 3(with 83692 records).I have something like this SELECT * FROM Table1 T1 /* OK fine select * is bad when not all columns are needed, this is just an example*/ LEFT JOIN Table2 T2 ON T1.id=T2.id LEFT JOIN Table3 T3 ON T1.id=T3.id and a query like this SELECT * FROM Table1 T1 LEFT JOIN Table3 T3 ON T1.id=T3.id LEFT JOIN Table2 T2 ON T1.id=T2.id The query plan shows me that it uses 2 Merge Join for both the joins. For the first query, the first merge is with T1 and T2 and then with T3. For the second query, the first merge is with T1 and T3 and then with T2. Both these queries take about the same time(40 seconds approx.) or sometimes Query1 takes couple of seconds longer. So my question is, does the join order matter ?

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• MSSQL Search Proper Names Full Text Index vs LIKE + SOUNDEX

  - by Matthew Talbert

  I have a database of names of people that has (currently) 35 million rows. I need to know what is the best method for quickly searching these names. The current system (not designed by me), simply has the first and last name columns indexed and uses "LIKE" queries with the additional option of using SOUNDEX (though I'm not sure this is actually used much). Performance has always been a problem with this system, and so currently the searches are limited to 200 results (which still takes too long to run). So, I have a few questions: Does full text index work well for proper names? If so, what is the best way to query proper names? (CONTAINS, FREETEXT, etc) Is there some other system (like Lucene.net) that would be better? Just for reference, I'm using Fluent NHibernate for data access, so methods that work will with that will be preferred. I'm using MS SQL 2008 currently.

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• Complicated idea - how to create car racing for my RPG game's players

  - by Donator

  So, I want to create car racing for my RPG game's players. Player can create race and choose how many participants can participate in race. After race is being created, other people can join it. When the maximum participants are collected, race begins. My idea, when the last participant joins, then instantly choose the winner (who's car is the best, that person wins), but how can I do it? If I choose to pick the winner after the last participant joins, then I have to put many queries in one page (select data from table, then delete the race, then select players' cars' statistics and pick the winner and then again, using mysql, send message to everyone). But this idea is really not optimal and it will lag cruelly for that last person. Maybe you have any ideas how I can avoid lag and make it more optimal. Thank you very much.

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• Programmatically allow write access for a Registry key

  - by Kerido

  Hi everybody, I need to programmatically modify the Access Descriptors on a known Registry key during product installation. The way I want it to work is: The installer is run in Administrative mode. A Registry key is created. A function (the one I need) queries the ACL from the key. If this function finds that the group 'Users' already has write access, nothing should be done. If not, it should add a new permission allowing write access to the 'Users' group. The permissions are saved for the Registry key. This question is similar to Setting Registry key write permissions using .NET, however, I need a C++/Win32 implementation. Thanks in advance

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• LINQ to SQL Translation

  - by Ben

  Hi, Depending on how I map my linq queries to my domain objects, I get the following error The member 'member' has no supported translation to SQL. This code causes the error: public IQueryable<ShippingMethod> ShippingMethods { get { return from sm in _db.ShippingMethods select new ShippingMethod( sm.ShippingMethodID, sm.Carrier, sm.ServiceName, sm.RatePerUnit, sm.EstimatedDelivery, sm.DaysToDeliver, sm.BaseRate, sm.Enabled ); } } This code works fine: public IQueryable<ShippingMethod> ShippingMethods { get { return from sm in _db.ShippingMethods select new ShippingMethod { Id = sm.ShippingMethodID, Carrier = sm.Carrier, ServiceName = sm.ServiceName, EstimatedDelivery = sm.EstimatedDelivery, DaysToDeliver = sm.DaysToDeliver, RatePerUnit = sm.RatePerUnit, IsEnabled = sm.Enabled, BaseRate = sm.BaseRate }; } } This is my testmethod I am testing with: [TestMethod] public void Test_Shipping_Methods() { IOrderRepository orderRepo = new SqlOrderRepository(); var items = orderRepo.ShippingMethods.Where(x => x.IsEnabled); Assert.IsTrue(items.Count() > 0); } How does the way in which I instantiate my object affect the linq to sql translation? Thanks Ben

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• Freebase Query with "JOINS"

  - by codemonkey

  ... Yeah, yeah, I know traditional joins don't exist. I actually like the freebase query methodology in theory, just having a little trouble getting it to actually work for me : ) Anyone have a dumb-simple example of getting Freebase data via MQL that pulls from two different "tables"? In particular, I'm trying to get automotive data... so for example, pulling fields from both /automotive/model_year and /automotive/trim_year. I've read the documentation (for hours actually). There's a distinct possibility that I'm looking right at such an example somewhere and just not seeing it because my OLTP brain just doesn't comprehend what it's seeing. * Note * ... that the two "types" I'm working with above are siblings, not parent/child. Does freebase even allow joining data between sibling nodes... I see examples of queries pulling from parent/child, but not from siblings I don't think (or I've overlooked them).

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• SPARQL UNION - Result set incomplete

  - by jplevac

  I have two queries: query 1: SELECT DISTINCT ?o COUNT(?o) WHERE { ?s1 ?somep1 <predicate_one-uri>. ?s1 ?p ?o} query 2: SELECT DISTINCT ?o COUNT(?o) WHERE {?s2 ?somep2 <predicate_two-uri>.?s2 ?p ?o.} Each query gives me a different result set (as expected). I need to make a union of these two sets, from what I understand the query below should give me the set I want: SELECT DISTINCT ?o COUNT(?o) WHERE { { ?s1 ?somep1 <predicate_one-uri>.?s1 ?p1 ?o} UNION {?s2 ?somep2 <predicate_two-uri>.?s2 ?p2 ?o.} } The problem is that some results from query 1 are not in the union set and vice-versa for query 2. The union is not working properly as it does not incorporate all results of query 1 and query 2. Please advise on the proper structure of the sparql query for achieving the desired result set. Thanks in advance! JP Levac

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• Open source political campaign management software?

  - by carolclarinet

  Does anyone know of any active open source projects working on political campaign management software? I looked on sourceforge but didn't see anything relevant from the queries "political", "politics", "donations", "campaign", or in the categories "accounting", "politics" or "voting". I'm involved with a political campaign that is currently paying out the nose for some horribly designed SaaS (whose Name i Guess i should Protect, ahem) to basically just keep track of donations people have made now, donations people have made in the past, donations people have pledged to make, contact information, the way they will likely vote, etc. It's a bit much to manage in spreadsheets, but doesn't seem like it's something complex enough that political campaigns should have to pay for (especially low-budget local ones). I'd love to help out if such a project exists, or start/revive one if it doesn't. Any hints, places to look, etc are much appreciated.

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• Design from scratch - building classes

  - by Tony

  Hi All, I've started a new project where I'm writing a WPF business application, but I'm having trouble with the design. The database was easy to put together, but I'm not sure how I have to go about the designing the application itself. The main thing that I find hard is the code design. I've decided that the MVVM pattern is very applicable for this application, but how do I go about deciding what classes to build and how things go from there? Does anyone have some guidelines I could use? This is a standard business application that just stores and retrieves data. Some data queries will also need to be performed.

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• I am not able to drop foreign key in mysql Error 150. Please help

  - by Shantanu Gupta

  i am trying to create a foreign key in my table. But when i executes my query it shows me error 150 Error Code : 1005 Can't create table '.\vts#sql-6ec_1.frm' (errno: 150) (0 ms taken) My Queries are Query to create a foreign Key alter table `vts`.`tblguardian` add constraint `FK_tblguardian` FOREIGN KEY (`GuardianPickPointId`) REFERENCES `tblpickpoint` (`PickPointId`) EDIT: Now I am trying to drop this constraint But it fails again and shows me same error as it was giving when i was trying to create foreign key. alter table `vts`.`tblguardian` drop index `FK_tblguardian` Primary Key table CREATE TABLE `tblpickpoint` ( `PickPointId` int(4) NOT NULL auto_increment, `PickPointName` varchar(500) default NULL, `PickPointLabel` varchar(500) default NULL, `PickPointLatLong` varchar(100) NOT NULL, PRIMARY KEY (`PickPointId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 CHECKSUM=1 DELAY_KEY_WRITE=1 ROW_FORMAT=DYNAMIC Foreign Key Table CREATE TABLE `tblguardian` ( `GuardianId` int(4) NOT NULL auto_increment, `GuardianName` varchar(500) default NULL, `GuardianAddress` varchar(500) default NULL, `GuardianMobilePrimary` varchar(15) NOT NULL, `GuardianMobileSecondary` varchar(15) default NULL, `GuardianPickPointId` int(4) default NULL, PRIMARY KEY (`GuardianId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1

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• Custom Classes Passed from Service to a UI threads via AIDL

  - by Honza Pokorny

  I have a service that regularly queries a web server for new messages. The service stores the new messages in an arrayList. These messages are implemented using a custom class, storing all kinds of metadata (strings and longs). An activity then connects to this service to retrieve those messages and display them to the user. I have an .aidl file that describes the interface that the service exposes. package com.example.package; interface MyInterface { List<Message> getMessages(); } The Message class extends the Parcelable class which should allow for the IPC transfer. The problem is this: Eclipse gives me an error saying that the type of List<Message> is unknown. Any imports are marked as invalid. Ideas? Thanks

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• NHibernate Lazy="Extra"

  - by Adam Rackis

  Is there a good explanation out there on what exactly lazy="extra" is capable of? All the posts I've seen all just repeat the fact that it turns references to MyObject.ItsCollection.Count into select count(*) queries (assuming they're not loaded already). I'd like to know if it's capable of more robust things, like turning MyObject.ItsCollection.Any(o => o.Whatever == 5) into a SELECT ...EXISTS query. Section 18.1 of the docs only touches on it. I'm not an NH developer, so I can't really experiment with it and watch SQL Profiler without doing a bit of work getting everything set up; I'm just looking for some sort of reference describing what this feature is capable of. Thank you!

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• MySQL UNION query from one table + ORDER BY

  - by ilnur777

  I have one table with two queries and I need to sort it with descending type using ORDER BY. Here is my MySQL query that does not work properly: (SELECT `text` FROM `comments` WHERE user_fr='".$user."' && archive='1' ORDER BY `is_new_fr` DESC) UNION (SELECT `text` FROM `message` WHERE user_to='".$user."' && archive='1' ORDER BY `is_new_to` DESC) Description! is_new_fr and is_new_to counts total new messages. Here is my table contant: user_fr | user_to | archive | is_new_fr | is_new_to| text name1 | name2 | 1 | 2 | 0 | testing... name2 | name1 | 1 | 0 | 5 | testing ... I want to make an order that 1st will display note that has more messages to few, or by another words using DESCending type. This is the display on the page I want to do: Open dialog with name2. Messages (5) Open dialog with name1. Messages (2) Thank you!

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