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  • What is the difference between these two linq implementations?

    - by Mahesh Velaga
    I was going through Jon Skeet's Reimplemnting Linq to Objects series. In the implementation of where article, I found the following snippets, but I don't get what is the advantage that we are gettting by splitting the original method into two. Original Method: // Naive validation - broken! public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) { throw new ArgumentNullException("source"); } if (predicate == null) { throw new ArgumentNullException("predicate"); } foreach (TSource item in source) { if (predicate(item)) { yield return item; } } } Refactored Method: public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) { throw new ArgumentNullException("source"); } if (predicate == null) { throw new ArgumentNullException("predicate"); } return WhereImpl(source, predicate); } private static IEnumerable<TSource> WhereImpl<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { foreach (TSource item in source) { if (predicate(item)) { yield return item; } } } Jon says - Its for eager validation and then defferring for the rest of the part. But, I don't get it. Could some one please explain it in a little more detail, whats the difference between these 2 functions and why will the validations be performed in one and not in the other eagerly? Conclusion/Solution: I got confused due to my lack of understanding on which functions are determined to be iterator-generators. I assumed that, it is based on signature of a method like IEnumerable<T>. But, based on the answers, now I get it, a method is an iterator-generator if it uses yield statements.

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  • introduce a join to this query, possible?

    - by Iain Urquhart
    I'm trying to introduce a join to this query: SELECT `n`.*, round((`n`.`rgt` - `n`.`lft` - 1) / 2, 0) AS childs, count(*) - 1 + (`n`.`lft` > 1) + 1 AS level, ((min(`p`.`rgt`) - `n`.`rgt` - (`n`.`lft` > 1)) / 2) > 0 AS lower, (((`n`.`lft` - max(`p`.`lft`) > 1))) AS upper FROM `exp_node_tree_6` `n`, `exp_node_tree_6` `p`, `exp_node_tree_6` WHERE `n`.`lft` BETWEEN `p`.`lft` AND `p`.`rgt` AND ( `p`.`node_id` != `n`.`node_id` OR `n`.`lft` = 1 ) GROUP BY `n`.`node_id` ORDER BY `n`.`lft` by adding LEFT JOIN `exp_channel_titles` ON (`n`.`entry_id`=`exp_channel_titles`.`entry_id`) after the FROM statement... But when I introduce it, it fails with "Unknown column 'n.entry_id' in 'on clause'" Is it even possible to add a join to this query? Can anybody help, thanks!

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  • oracle sql query to list all the dates of previous month

    - by Suresh S
    Guys i have a requirement to list all the dates of the previous month like below 20101201 20101202 20101203 20101204 20101205 .. .. .. .. .. .. .. .. 20101231 kindly let me know if any better way to do than this query. select TO_CHAR(TRUNC(SYSDATE,'MM')-1,'YYYYMMDD')-(level-1) as EACH_DATE from dual A connect by level < (TO_NUMBER(TO_CHAR(TRUNC(SYSDATE,'MM')-1,'DD'))+1) Also please let me know the problem with this query it says "missing right parenthesis" SELECT /*+ PARALLEL (A,8) */ /*+ DRIVING_STATE */ TO_CHAR(TRUNC(TRUNC(SYSDATE,'MM')-1,'MM'),'MONYYYY') "MONTH", TYPE AS "TRAFF", COLUMN, A_COUN AS "A_COUNT",COST FROM DATA_P B WHERE EXISTS ( select TO_NUMBER(TO_CHAR(TRUNC(SYSDATE,'MM')-1,'YYYYMMDD')-(level-1)) EACH_DATE from dual A connect by level < TO_NUMBER(TO_CHAR(TRUNC(SYSDATE,'MM')-1,'DD')+1) WHERE A.EACH_DATE = B.DATE order by EACH_DATE ASC )

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  • Problem with sqlite query when using the wrapper

    - by user285096
    - (IBAction)EnterButtonPressed:(id)sender { Sqlite *sqlite = [[Sqlite alloc] init]; NSArray *paths =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES); NSString *documentsDirectory = [paths objectAtIndex:0]; NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"test.sqlite"]; if (![sqlite open:writableDBPath]) return; NSArray *query = [sqlite executeQuery:@"SELECT AccessCode FROM UserAccess"]; NSLog(@"%@",query); I am getting the output as : { ( AccessCode=abcd; ) } Where as in I want it as : abcd I am using the wrapper from : http://th30z.netsons.org/2008/11/objective-c-sqlite-wrapper/ Please help .

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  • what practical proofs are there about the Turing completeness of neural nets? what nns can execute c

    - by Albert
    I'm interested in the computational power of neural nets. It is generally accepted that recurrent neural nets are Turing complete. Now I was searching for some papers which proofs this. What I found so far: Turing computability with neural nets, Hava T. Siegelmann and Eduardo D. Sontag, 1991 I think this is only interesting from a theoretical point of view because it needs to have the neuron activity of infinite exactness (to encode the state somehow as a rational number). S. Franklin and M. Garzon, Neural computability This needs an unbounded number of neurons and also doesn't really seem to be that much practical. (Note that another question of mine tries to point out this kind of problem between such theoretical results and the practice.) I'm searching mostly for some neural net which really can execute some code which I can also simulate and test in practice. Of course, in practice, they would have some kind of limited memory. Does anyone know something like this?

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  • Linq Query - Average Time (DateTime data types)

    - by Jade
    I have a database that has the following records in a DateTime field: 2012-04-13 08:31:00.000 2012-04-12 07:53:00.000 2012-04-11 07:59:00.000 2012-04-10 08:16:00.000 2012-04-09 15:11:00.000 2012-04-08 08:28:00.000 2012-04-06 08:26:00.000 I want to run a linq to sql query to get the average time from the records above. I tried the following: (From o In MYDATA Select o.SleepTo).Average() Since "SleepTo" is a datetime field I get an error on Average(). If I was trying to get the average of say an integer, the above linq query works. What do I need to do to get it to work for datetimes?

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  • Slow query with unexpected scan

    - by zerkms
    Hello I have this query: SELECT * FROM SAMPLE SAMPLE INNER JOIN TEST TEST ON SAMPLE.SAMPLE_NUMBER = TEST.SAMPLE_NUMBER INNER JOIN RESULT RESULT ON TEST.TEST_NUMBER = RESULT . TEST_NUMBER WHERE SAMPLED_DATE BETWEEN '2010-03-17 09:00' AND '2010-03-17 12:00' the biggest table here is RESULT, contains 11.1M records. The left 2 tables about 1M. this query works slowly (more than 10 minutes) and returns about 800 records. executing plan shows clustered index scan over all 11M records. RESULT.TEST_NUMBER is a clustered primary key. if I change 2010-03-17 09:00 to 2010-03-17 10:00 - i get about 40 records. it executes for 300ms. and plan shows clustered index seek if i replace * in SELECT clause to RESULT.TEST_NUMBER (covered with index) - then all become fast in first case too. this points to hdd io issues, but doesn't clarifies changing plan. so, any ideas?

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  • MYSQL Query with 2 columns in Table A related to 1 column in Table B

    - by CYREX
    I have 2 Tables, User and Mail. In User Table i have 2 columns that i will use, the ID column which makes the relation with the Mail Table and it is the Index of User Table and the Name column. In Mail Table i have Receiver Column and Sender Column. Both columns, Receiver and Sender have a number that relates to the ID Column in the User Table. In the User Table is where the name columns resides and i want to make a query that shows me the Receiver and Sender Columns but with the name of the user, not the ID. Up to this point i have this: SELECT name AS Send, name AS Receive FROM mail,user WHERE sender=guid; I know there is still a part of the query missing but i can not figure out what else to put to tell it to show in the SEND output column the name of the sender and in the RECEIVE output column the name of the receiver.

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  • SHA1 Password returns as cleartext after DB query

    - by Code Sherpa
    Hi. I have a SHA1 password and PasswordSalt in my aspnet_Membership table. but, when I run a query from the server (a Sql Query), the reader reveals that the pass has returned as its cleartext equivalent. I am wondering if my web.config configuration is causing this? <membership defaultProvider="CustomMembershipProvider" userIsOnlineTimeWindow="20" hashAlgorithmType="SHA1"> <providers> <clear/> <add name="CustomMembershipProvider" type="Custom.Utility.CustomMembershipProvider" connectionStringName="MembershipDB" enablePasswordRetrieval="false" enablePasswordReset="true" requiresUniqueEmail="false" requiresQuestionAndAnswer="false" passwordStrengthRegularExpression="" minRequiredPasswordLength="1" minRequiredNonalphanumericCharacters="0" passwordFormat="Hashed" thanks in advance...

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  • Combining query rows in a loop

    - by icemanind
    I have the following ColdFusion 9 code: <cfloop from="1" to="#arrayLen(tagArray)#" index="i"> <cfquery name="qryGetSPFAQs" datasource="#application.datasource#"> EXEC searchFAQ '#tagArray[i]#' </cfquery> </cfloop> The EXEC executes a stored procedure on the database server, which returns rows of data, depending on what the parameter is. What I am trying to do is combine the queries into one query object. In other words, if it loops 3 times and each loop returns 4 rows, I want a query object that has all 12 rows in one object. How do I acheive this?

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  • SQL Not Exists in this Query - is it possible

    - by jason barry
    This is my script - it simply looks for the image file associated to a person record. Now the error will display if there is NO .jpg evident when the query runs. Msg 4860, Level 16, State 1, Line 1 Cannot bulk load. The file "C:\Dev\ClientServices\Defence\RAN\Shore\Config\Photos\002054.2009469432270600.001.jpg" does not exist. Is there a way to write this query to 'IF not exists then set id_number = '002054.2009469432270427.001' - so it wil always display this photo for any records without a picture. ALTER procedure [dbo].[as_ngn_sp_REP_PH108_photo] (@PMKEYS nvarchar(50)) AS ---exec [as_ngn_sp_REP_PH108_photo] '8550733' SET NOCOUNT ON DECLARE @PATH AS NVARCHAR(255) DECLARE @ID_NUMBER NVARCHAR(27) DECLARE @SQL AS NVARCHAR(MAX) EXEC DB_GET_DB_SETTING'STAFF PICTURE FILE LOCATION', 0, @PATH OUTPUT IF RIGHT(@PATH,1) <> '\' SET @PATH = @PATH + '\' SELECT @ID_NUMBER = ID_NUMBER FROM aView_person WHERE EXTRA_CODE_1 = @PMKEYS SET @PATH = @PATH + @ID_NUMBER + '.jpg' SET @SQL = 'SELECT ''Picture1'' [Picture], BulkColumn FROM OPENROWSET(Bulk ''' + REPLACE(@PATH,'''','''''') + ''', SINGLE_BLOB) AS RAN' EXEC SP_EXECUTESQL @SQL

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  • django - order query set by postgres function

    - by thebiglife
    My initial question was here and was related to the postgres backend. http://stackoverflow.com/questions/2408965/postgres-subquery-ordering-by-subquery Now my problem has moved onwards to the Django ORM layer. I essentially want to order a query by a postgres function ('idx', taken from the above stackoverflow work) I've gone through trying to use model.objects.extra(order_by ) or simply order_by but I believe both of these need the order_by parameter to be an attribute or a field known to Django. I'm trying to think how to solve this without having to revert to using an entirely raw SQL query through a model manager.

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  • Use SQL query to populate property in nHibernate mapping file

    - by brainimus
    I have an object which contains a property that is the result of an SQL statement. How do I add the SQL statement to my nHibernate mapping file? Example Object: public class Library{ public int BookCount { get; set; } } Example Mapping File: <hibernate-mapping> <class name="Library" table="Libraries"> <property name="BookCount" type="int"> <- This is where I want the SQL query to populate the value. -> </class> </hibernate-mapping> Example SQL Query: SELECT COUNT(*) FROM BOOKS WHERE BOOKS.LIBRARY_ID = LIBRARIES.ID

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  • RPC command to initiate a software install

    - by ericmayo
    I was recently working with a product from Symantech called Norton EndPoint protection. It consists of a server console application and a deployment application and I would like to incorporate their deployment method into a future version of one of my products. The deployment application allows you to select computer workstations running Win2K, WinXP, or Win7. The selection of workstations is provided from either AD (Active Directory) or NT Domain (WINs/DNS NetBIOS lookup). From the list, one can click and choose which workstations to deploy the end point software which is Symantech's virus & spyware protection suite. Then, after selecting which workstations should receive the package, the software copies the setup.exe program to each workstation (presumable over the administrative share \pcname\c$) and then commands the workstation to execute setup.exe resulting in the workstation installing the software. I really like how their product works but not sure what they are doing to accomplish all the steps. I've not done any deep investigations into this such as sniffing the network, etc... and wanted to check here to see if anyone is familiar with what I'm talking about and if you know how it's accomplished or have ideas how it could be accomplished. My thinking is that they are using the admin share to copy the software to the selected workstations and then issuing an RPC call to command the workstation to do the install. What's interesting is that the workstations do this without any of the logged in users knowing what's going on until the very end where a reboot is necessary. At which point, the user gets a pop-up asking to reboot now or later, etc... My hunch is that the setup.exe program is popping this message. To the point: I'm looking to find out the mechanism by which one Windows based machine can tell another to do some action or run some program. My programming language is C/C++ Any thoughts/suggestions appreciated.

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  • Need help optimizing MYSQL query with join

    - by makeee
    I'm doing a join between the "favorites" table (3 million rows) the "items" table (600k rows). The query is taking anywhere from .3 seconds to 2 seconds, and I'm hoping I can optimize it some. Favorites.faver_profile_id and Items.id are indexed. Instead of using the faver_profile_id index I created a new index on (faver_profile_id,id), which eliminated the filesort needed when sorting by id. Unfortunately this index doesn't help at all and I'll probably remove it (yay, 3 more hours of downtime to drop the index..) Any ideas on how I can optimize this query? In case it helps: Favorite.removed and Item.removed are "0" 98% of the time. Favorite.collection_id is NULL about 80% of the time. SELECT `Item`.`id`, `Item`.`source_image`, `Item`.`cached_image`, `Item`.`source_title`, `Item`.`source_url`, `Item`.`width`, `Item`.`height`, `Item`.`fave_count`, `Item`.`created` FROM `favorites` AS `Favorite` LEFT JOIN `items` AS `Item` ON (`Item`.`removed` = 0 AND `Favorite`.`notice_id` = `Item`.`id`) WHERE ((`faver_profile_id` = 1) AND (`collection_id` IS NULL) AND (`Favorite`.`removed` = 0) AND (`Item`.`removed` = '0')) ORDER BY `Favorite`.`id` desc LIMIT 50;

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  • Performing complex query with Dynamics CRM 4.0

    - by dub
    Hi, I have two custom entites, Product and ProductType, linked together in many-to-one relationship. Product has a lookup field to ProductType. I'm trying to write a query to fetch Type1 products with a price over 100, and Type2 products with a price lower than 100. Here's how I would do it in SQL : select * from Product P inner join ProductType T on T.Id = P.TypeId where (T.Code = 'Type1' and P.Price >= 100) or (T.Code = 'Type2' and P.Price < 100) I can't figure out a way to build a QueryExpression to do exactly that. I know I could do it with two queries, but I'd like to minimize roundtrips to the server. Is there a way to perform that query in only one operation ? Thanks!

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  • How much trust can I put behind a computer system? How can I measure trust?

    - by danmine
    How much trust can I put in a standard computer running windows? To what certainty can I be sure it will run my code the way I wrote it? How can I be sure that if I declare something like "int j = 5;", j will alway be 5? Is there a way to measure trust in a standard x86 computer system? What kind of protections are there to make sure that j = 5? I'm thinking about critical systems where nothing can be off even by one bit and everything must run exactly the way it was written to run.

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  • DataTable linq query iteration

    - by Ravi
    Hi, I want to Enumerate Linq Query. Below i specified example. EX: DataTable _slidingDataTable = new DataTable("test"); for(int i=0; i<5;i++) { DataRow row = _slidingDataTable.NewRow(); startPosition = DateTime.Now; for(int i=0; i<5;i++) { _slidingDataTable.Columns.Add("TransferTime"); row[columnName] = startPosition ; _slidingDataTable.Columns.Add("TransferData"); row[columnName] = "Test"+i; } _slidingDataTable.Rows.Add(row); } var query1 = from myRow in _slidingDataTable.AsEnumerable() where myRow.Field<DateTime>("TransferTime") == startPosition select myRow; This query output should be collection of rows. How to get collection row & iterate.

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  • sql query need a help.

    - by benjamin button
    If i have a table with two fields.customer id and order. let's say i have in total order ID 1,2,3,4 all the customer can have all the four orders.like below 1234 1 1234 2 1234 3 1234 4 3245 3 3245 4 5436 2 5436 4 you can see above that 3245 customer doesnt have order id 1 and 2. how could i print in the query output like 3245 1 3245 2 5436 1 5436 3 EDIT: i dont order table but i have list of order's like we can hard code it in the query(1,2,3,4) i dont have an orders table.

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  • Wordpress Custom Query

    - by InnateDev
    I have posts that use a custom field for start date and end date. Query_posts returns an array of posts that exist in the category I'm filtering. How do I query posts using this custom field that has date i.e. 03/11/2010 and not the full array. Pagination works on the full array so it returns all posts. I can use an if else to only show the posts newer that today, then pagination doesn't work. Would I have to build a custom mysql query?

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