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• Am I understanding premature optimization correctly?

  - by Ed Mazur

  I've been struggling with an application I'm writing and I think I'm beginning to see that my problem is premature optimization. The perfectionist side of me wants to make everything optimal and perfect the first time through, but I'm finding this is complicating the design quite a bit. Instead of writing small, testable functions that do one simple thing well, I'm leaning towards cramming in as much functionality as possible in order to be more efficient. For example, I'm avoiding multiple trips to the database for the same piece of information at the cost of my code becoming more complex. One part of me wants to just not worry about redundant database calls. It would make it easier to write correct code and the amount of data being fetched is small anyway. The other part of me feels very dirty and unclean doing this. :-) I'm leaning towards just going to the database multiple times, which I think is the right move here. It's more important that I finish the project and I feel like I'm getting hung up because of optimizations like this. My question is: is this the right strategy to be using when avoiding premature optimization?

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• LINQ to SQL: Reusable expression for property?

  - by coenvdwel

  Pardon me for being unable to phrase the title more exact. Basically, I have three LINQ objects linked to tables. One is Product, the other is Company and the last is a mapping table Mapping to store what Company sells which products and by which ID this Company refers to this Product. I am now retrieving a list of products as follows: var options = new DataLoadOptions(); options.LoadWith<Product>(p => p.Mappings); context.LoadOptions = options; var products = ( from p in context.Products select new { ProductID = p.ProductID, //BackendProductID = p.BackendProductID, BackendProductID = (p.Mappings.Count == 0) ? "None" : (p.Mappings.Count > 1) ? "Multiple" : p.Mappings.First().BackendProductID, Description = p.Description } ).ToList(); This does a single query retrieving the information I want. But I want to be able to move the logic behind the BackendProductID into the LINQ object so I can use the commented line instead of the annoyingly nested ternary operator statements for neatness and re-usability. So I added the following property to the Product object: public string BackendProductID { get { if (Mappings.Count == 0) return "None"; if (Mappings.Count > 1) return "Multiple"; return Mappings.First().BackendProductID; } } The list is still the same, but it now does a query for every single Product to get it's BackendProductID. The code is neater and re-usable, but the performance now is terrible. What I need is some kind of Expression or Delegate but I couldn't get my head around writing one. It always ended up querying for every single product, still. Any help would be appreciated!

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• Sharing a COM port over TCP

  - by guinness

  What would be a simple design pattern for sharing a COM port over TCP to multiple clients? For example, a local GPS device that could transmit co-ordinates to remote hosts in realtime. So I need a program that would open the serial port and accept multiple TCP connections like: class Program { public static void Main(string[] args) { SerialPort sp = new SerialPort("COM4", 19200, Parity.None, 8, StopBits.One); Socket srv = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); srv.Bind(new IPEndPoint(IPAddress.Any, 8000)); srv.Listen(20); while (true) { Socket soc = srv.Accept(); new Connection(soc); } } } I would then need a class to handle the communication between connected clients, allowing them all to see the data and keeping it synchronized so client commands are received in sequence: class Connection { static object lck = new object(); static List<Connection> cons = new List<Connection>(); public Socket socket; public StreamReader reader; public StreamWriter writer; public Connection(Socket soc) { this.socket = soc; this.reader = new StreamReader(new NetworkStream(soc, false)); this.writer = new StreamWriter(new NetworkStream(soc, true)); new Thread(ClientLoop).Start(); } void ClientLoop() { lock (lck) { connections.Add(this); } while (true) { lock (lck) { string line = reader.ReadLine(); if (String.IsNullOrEmpty(line)) break; foreach (Connection con in cons) con.writer.WriteLine(line); } } lock (lck) { cons.Remove(this); socket.Close(); } } } The problem I'm struggling to resolve is how to facilitate communication between the SerialPort instance and the threads. I'm not certain that the above code is the best way forward, so does anybody have another solution (the simpler the better)?

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• Your Django Development process/steps (Step by Step)

  - by AJ

  I want to know step by step process of how folks develop on Django here. I have seen that whenever I try to create a website in Django, I always get confused amongst: DB Schema/models.py UI/Template Structure Login module urls.py views.py How do you approach this? I may have missed something. You do not need to elaborate everything, just stepwise what you do. If you do two things at the same time (or side-by-side), that would also be helpful to mention. Thanks a lot.

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• How to keep form items selected after post request?

  - by Ole Jak

  I have a simple html form. On php page. A simple list is placed on form. I submit this form (selected list items) to this page so it gives me page refresh. I want items which were POSTED to be selected after form was submited. How to do such thing? For my form I use such code: <form action="FormPage.php" method="post"> <select id="Streams" class="multiselect ui-widget-content ui-corner-all" multiple="multiple" name="Streams[]"> <?php $query = " SELECT s.streamId, s.userId, u.username FROM streams AS s JOIN user AS u ON s.userId = u.id LIMIT 0 , 30 "; $streams_set = mysql_query($query, $connection); confirm_query($streams_set); $streams_count = mysql_num_rows($streams_set); while ($row = mysql_fetch_array($streams_set)){ echo '<option value="' , $row['streamId'] , '"> ' , $row['username'] , ' (' , $row['streamId'] ,')' ,'</option> '; } ?> </select> <br/> <input type="submit" class="ui-state-default ui-corner-all" name="submitForm" id="submitForm" value="Play Stream from selected URL's!"/> </fieldset> </form>

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• Removing the Default Wrap Character From all records

  - by aceinthehole

  I am using BizTalk 2009 and I have a flat file that is similar to the following "0162892172","TIM ","LastName ","760 "," ","COMANCHE ","LN " "0143248282","GEORGE ","LastName ","625 "," ","ENID ","AVE " When I parse it and start mapping it I need to get rid of the quotation marks. I have marked the Wrap Character attribute for the schema as a quotation mark but it doesn't remove it when BizTalk is parsing the file. Is there an easy way to specify the removal of a wrap character or am I going to have to run it through a script functiod every time? Also I would like to be able to remove the trailing spaces as well, if at all possible.

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• design pattern tools to use?

  - by ajsie

  i have noticed that every area has some tools you can use to make things easier. eg. css = dreamweaver doctrine/propel = orm designer // you dont have to hardcore code schemas manually and remembering all the syntax/variables mysql = mysql workbench // the same etc. in this way you get aided and dont have to type things the hard way, and can learn the structure, but then use GUI tools to help you develop faster. now i'm learning design patterns (singleton, factory, command, memento etc) and im wondering if there are some kind of tools you can use that will help you develop faster. i dont know exactly what tools i'm trying to find, just helping me when coding with design patterns (schema drawings? references?) are there any?

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• Modifying annotation attribute value at runtime in java

  - by Lici

  Hi folks: some methods in our model pojos have been annotated like this: @Column(name="cli_clipping_id", updatable=false, columnDefinition = "varchar(" + ModelUtils.ID_LENGTH + ") COLLATE utf8_bin") columnDefinition attribute is database vendor dependant, so when trying to drop schema in HSQLDB using Hibernate it fails: [ERROR] 16 jun 12:58:42.480 PM main [org.hibernate.tool.hbm2ddl.SchemaExport] Unexpected token: COLLATE in statement [create table cms.edi_editorial_obj (edi_uuid varchar(23) COLLATE ] To fix this, i'm thinking on this solution (but don't want to spend time if it isn't possible) , at runtime, for each method column annotated: Get @Column annotation Create a copy of the column annotation, setting columnDefinition null using javaassist. set column method annotation to the copy column annotation object overriding the old one (i don't know it this is possible) Is it possible to "hack" these methods this way? Any help would be much appreciated ...

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• Difference in select for update of ... in Oracle Database 10g and 11g

  - by sax

  Hi, I found out that Oracle Database 10g and 11g treat the following PL/SQL block differently (I am using scott schema for convenience): DECLARE v_ename bonus.ename%TYPE; BEGIN SELECT b.ename INTO v_ename FROM bonus b JOIN emp e ON b.ename = e.ename JOIN dept d ON d.deptno = e.deptno WHERE b.ename = 'Scott' FOR UPDATE OF b.ename; END; / While in 10g (10.2) this code ends successfully (well NO_DATA_FOUND exception is raised but that is expected), in 11g (11.2) it raises exception "column ambiguously defined". And that is definitely not expected. It seems like it does not take into account table alias because I found out that when I change the column in FOR UPDATE OF e.empno (also does not work) to e.mgr (which is unique) it starts working. So is this some error in 11g? Any thoughts?

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• xml to xsd to c# class - C# 3.0, .net 3.5

  - by uno

  Following this articlelink text one of the comments from 'zanoni' said he did it this way Using .NET 3.5: [XmlRoot] public class EmailConfiguration { [XmlElement] public string DataBoxID { get; set; } [XmlElement] public DefaultSendToAddressCollectionClass DefaultSendToAddressCollection { get; set; } } public class DefaultSendToAddressCollectionClass { [XmlElement] public string[] EmailAddress { get; set; } } How would I get my class to be as what he described? I ran the xsd tool and it is in the fashion as what shane posted in the above link [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "2.0.50727.3038")] [System.SerializableAttribute()] [System.Diagnostics.DebuggerStepThroughAttribute()] [System.ComponentModel.DesignerCategoryAttribute("code")] [System.Xml.Serialization.XmlTypeAttribute(AnonymousType=true)] [System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=false)] public partial class EmailConfiguration : object, System.ComponentModel.INotifyPropertyChanged { private string dataBoxIDField; private EmailConfigurationDefaultSendToAddressCollection[] defaultSendToAddressCollectionField; /// <remarks/> [System.Xml.Serialization.XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified)] public string DataBoxID { get { return this.dataBoxIDField; } set { this.dataBoxIDField = value; this.RaisePropertyChanged("DataBoxID"); } }

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• Multi join query returns to many results and improperly matched

  - by Woot4Moo

  I have the following minimal schema in Oracle: http://sqlfiddle.com/#!4/c1ed0/14 The queries I have run yield too many results and this query: select cat.*, status.*, source.* from cats cat, status status, source source Left OUTER JOIN source source2 on source2.sourceid = 1 Right OUTER JOIN status status2 on status2.isStray =0 order by cat.name will yield incorrect results. What I am expecting is a table that looks like the following however I cannot seem to come up with the correct SQL. NAME AGE LENGTH STATUSID CATSOURCE ISSTRAY SOURCEID CATID Adam 1 25 null null null 1 2 Bill 5 1 null null null null null Charles 7 5 null null null null null Steve 12 15 1 1 1 1 1 In plain English what I am looking for is to return all known cats + their associated cat source + their cat status while retaining null values. The only information I will have is the source that I am curious about. I also only want the cats that have a status of either STRAY or UNKNOWN (null)

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• How to write automated tests for SQL queries?

  - by James

  The current system we are adopting at work is to write some extremely complex queries which perform multiple calculations and have multiple joins / sub-queries. I don't think I am experienced enough to say if this is correct or not so I am agreeing and attempting to function with this system as it has clear benefits. The problem we are having at the moment is that the person writing the queries makes a lot of mistakes and assumes everything is correct. We have now assigned a tester to analyse all of the queries but this still proves extremely time consuming and stressful. I would like to know how we could create an automated procedure (without specifically writing it with code if possible as I can work out how to do that the long way) to verify a set of 10+ different inputs, verify the output data and say if the calculations are correct. I know I could write a script using specific data in the database and create a script using c# (the db is SQL Server) and verify all the values coming out but I would like to know what the official "standard" is as my experience is lacking in this area and I would like to improve. I am happy to add more information if required, add a comment if necessary. Thank you. Edit: I am using c#

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• SQL Find duplicate sets

  - by Aheho

  given this Schema: table tblSET SetID int PK SetName nvarchar(100) Table tblSetItem SetID int PK ItemID int PK tblSetItem.SetID is a FK into the tblSet Table. Some data: tblSet SetID SetName 1 Red 2 Blue 3 Maroon 4 Yellow 5 Sky tblSetItem SetID ItemID 1 100 1 101 2 100 2 108 2 109 3 100 3 101 4 101 4 108 4 109 4 110 5 100 5 108 5 109 I'd like a way to identify which sets contain the same items. In the example above Red and Maroon contain the same items (100,101) and Blue and Sky contain the same values (100,108,109) Is there a sql query which would provide this answer?

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• Is there a way to query if array field contains a certain value in Doctrine2?

  - by dpimka

  Starting out with Symfony2 + Doctrine. I have a table with User objects (fos_user), for which my schema contains a roles column of an 'array' type. Doctrine saves fields of this type by serializing them from php 'array' to 'longtext' (in mysql's case). So let's say I have the following users saved into DB: **User1**: array(ROLE_ADMIN, ROLE_CUSTOM1) **User2**: array(ROLE_ADMIN, ROLE_CUSTOM2) **User3**: array(ROLE_CUSTOM2) Now in my controller I want to select all users with ROLE_ADMIN set. Is there a way to write a DQL query which would directly return me User1 and User2? Or do I need to fetch all users to have Doctrine to unserialize roles column and then for each of them do in_array('ROLE_ADMIN', $user-getRoles())? I have searched the DQL part of the manual, but so far did not find anything similar to my needs...

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• Database design for a Fantasy league

  - by Samidh T

  Here's the basic schema for my database Table user{ userid numeber primary key, count number } Table player{ pid number primary key, } Table user-player{ userid number primary key foreign key(user), pid number primary key foreign key(player) } Table temp{ pid number primary key, points number } Here's what I intend to do... After every match the temp table is updated which holds the id of players that played the last match and the points they earned. Next run a procedure that will match the pid from temp table with every uid of user-player table having the same pid. add the points from temp table to the count of user table for every matching uid. empty temp table. My questions is considering 200 players and 10000 users,Will this method be efficient? I am going to be using mysql for this.

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• NSNotification vs. Delegate Protocols?

  - by jr

  I have an iPhone application which basically is getting information from an API (in XML, but maybe JSON eventually). The result objects are typically displayed in view controllers (tables mainly). Here is the architecture right now. I have NSOperation classes which fetch the different objects from the remote server. Each of these NSOperation classes, will take a custom delegate method which will fire back the resulting objects as they are parsed, and then finally a method when no more results are available. So, the protocol for the delegates will be something like: (void) ObjectTypeResult:(ObjectType *)result; (void) ObjectTypeNoMoreResults; I think the solution works well, but I do end up with a bunch of delegate protocols around and then my view controllers have to implement all these delegate methods. I don't think its that bad, but I'm always on the lookout for a better design. So, I'm thinking about using NSNotifications to remove the use of the delegates. I could include the object in the userInfo part of the notification and just post objects as received, and then a final event when no more are available. Then I could just have one method in each view controller to receive all the data, even when using multiple objects in one controller.† So, can someone share with me some pros/cons of each approach. Should I consider refactoring my code to use Events rather then the delegates? Is one better then the other in certain situations? In my scenario I'm really not looking to receive notifications in multiple places, so maybe the protocol based delegates are the way to go. Thanks!

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• Zero KB SQLite File created by Core Data on application start up

  - by Tots

  I'm developing an iPhone application using Core Data. I had everything working and had to make an adjustment to the database schema and change the relationships through the xcdatamodel file. I deleted the my project's sqlite file in Library/Application Support/iPhone Simulator/3.1.3//Documents. Build and run the application, it creates the sqlite file, but its empty with a file size of 0 KB. At a minimum the table information should be in there. There are no errors/warning in the console. Anyone have an idea what is wrong?

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• How to view existing data in Core Data?

  - by mshsayem

  Well, may be this question is silly, but I couldn't find a way (except programmatically). I built a project (for iPhone OS 3.0) which uses Core Data. The xcdatamodel file shows the schema description, but I want to see the data in tabular form (like the management studio for mssql server or phpmyadmin for mysql). Is there any way (except coding)? What is that? Also, which file (in disk/device) those data are stored into? [ I built the tutorial (from apple) on Core Data, named Locations. They used this line somewhere in the code: NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"Locations.sqlite"]]; But, I did not see any "xxxxx.sqlite" file in project location (nor in the disk).]

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• Jetty 7 will not allow me to customize a session cookie path

  - by Bob Obringer

  Using Jetty 7.0.2, I am unable to set a custom session cookie path. I am hosting multiple sites on the same server using apache to proxy requests to the proper context. (replaced http as htp as stackoverflow thinks my multiple links might be spam) <VirtualHost *:80> ServerName context.domain.com ProxyRequests On ProxyPreserveHost Off <Proxy *:80> Order deny,allow Allow from 127.0.0.1 </Proxy> ProxyPass / htp://localhost:8080/context/ ProxyPassReverse / htp://localhost:8080/context/ <Location /> Order allow,deny Allow from all </Location> </VirtualHost> Jetty is running on the same server on port 8080 and my context is available @ /context The user accesses the application @ htp://context.domain.com but jetty is setting the path for the session cookie @ /context. This prevents the browser from accessing the cookie since the the actual path to the context is not being used. I need to override Jetty's default setting to set the cookie for the context, and set the path at the root ( / ). In my Jetty's webdefault.xml I have the following, which is partially working: <context-param> <param-name>org.eclipse.jetty.servlet.SessionCookie</param-name> <param-value>CustomCookieName</param-value> </context-param> <context-param> <param-name>org.eclipse.jetty.servlet.SessionPath</param-name> <param-value>/</param-value> </context-param> The cookie is properly set with a custom name, but it is NOT setting the SessionPath. No matter what I set the value to... it refuses to set a cookie at any path but /context. This has been driving me crazy so any help would be greatly appreciated.

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• Use MySQL trigger to update another table when duplicate key found

  - by Jason

  Been scratching my head on this one, hoping one of you kind people and direct me towards solving this problem. I have a mysql table of customers, it contains a lot of data, but for the purpose of this question, we only need to worry about 4 columns 'ID', 'Firstname', 'Lastname', 'Postcode' Problem is, the table contains a lot of duplicated customers. A new table is being created where each customer is unique and for us, we decide a unique customer is based on 'Firstname', 'Lastname' and 'Postcode' However, (this is the important bit) we need to ensure each new "unique" customer record also can be matched to the original multiple entries of that customer in the original table. I believe the best way to do this is to have a third table, that has 'NewUniqueID', 'OldCustomerID'. So we can search this table for 'NewUniqueID' = '123' and it would return multiple 'OldCustomerID' values where appropriate. I am hoping to make this work using a trigger and the on duplicate key syntax. So what would happen is as follows: An query is run taking the old customer table and inserting it in to the new unique table. (A standard Insert Select query) On duplicate key continue adding records, but add one entry in to the third table noting the 'NewUniqueID' that duped along with the 'OldCustomerID' of the record we were trying to insert. Hope this makes sense, my apologies if it isn't clear. I welcome and appreciate any thoughts on this one! Many thanks Jason

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• Problem opening Solr *.jsp pages with urllib2.urlopen.

  - by nestling

  I'm trying to open a page at http://localhost:8983/solr/admin/stats.jsp but urllib2.urlopen returns a blank string. It works fine for solr/ and solr/admin, but for all the pages above /solr/admin/ I get nothing but a blank string. 76]: t = urllib2.urlopen('http://localhost:8983/solr/admin/stats.jsp') 77]: s = t.read() 78]: s 78]: 79]: type(s) 79]: <type 'str'> 80]: urllib2.urlopen('http://localhost:8983/solr/admin/registry.jsp').read() 80]: In [84]: urllib2.urlopen('http://localhost:8983/solr/admin/schema.jsp').read() Out[84]: I know this isn't a problem with urllib2, but beyond that I am at a loss. I wish solr (or jetty) had an easy to get to log file, so that perhaps it could tell me its side of the story.

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• How to use named_scope to incrementally construct a complex query?

  - by wbharding

  I want to use Rails named_scope to incrementally build complex queries that are returned from external methods. I believe I can get the behavior I want with anonymous scopes like so: def filter_turkeys Farm.scoped(:conditions => {:animal => 'turkey'}) end def filter_tasty Farm.scoped(:conditions => {:tasty => true}) end turkeys = filter_turkeys is_tasty = filter_tasty tasty_turkeys = filter_turkeys.filter_tasty But say that I already have a named_scope that does what these anonymous scopes do, can I just use that, rather than having to declare anonymous scopes? Obviously one solution would be to pass my growing query to each of the filter methods, a la def filter_turkey(existing_query) existing_query.turkey # turkey is a named_scoped that filters for turkey end But that feels like an un-DRY way to solve the problem. Oh, and if you're wondering why I would want to return named_scope pieces from methods, rather than just build all the named scopes I need and concatenate them together, it's because my queries are too complex to be nicely handled with named_scopes themselves, and the queries get used in multiple places, so I don't want to manually build the same big hairy concatenation multiple times.

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• Questions about the Backpropogation Algorithm

  - by Colemangrill

  I have a few questions concerning backpropogation. I'm trying to learn the fundamentals behind neural network theory and wanted to start small, building a simple XOR classifier. I've read a lot of articles and skimmed multiple textbooks - but I can't seem to teach this thing the pattern for XOR. Firstly, I am unclear about the learning model for backpropogation. Here is some pseudo-code to represent how I am trying to train the network. [Lets assume my network is setup properly (ie: multiple inputs connect to a hidden layer connect to an output layer and all wired up properly)]. SET guess = getNetworkOutput() // Note this is using a sigmoid activation function. SET error = desiredOutput - guess SET delta = learningConstant * error * sigmoidDerivative(guess) For Each Node in inputNodes For Each Weight in inputNodes[n] inputNodes[n].weight[j] += delta; // At this point, I am assuming the first layer has been trained. // Then I recurse a similar function over the hidden layer and output layer. // The prime difference being that it further divi's up the adjustment delta. I realize this is probably not enough to go off of, and I will gladly expound on any part of my implementation. Using the above algorithm, my neural network does get trained, kind of. But not properly. The output is always XOR 1 1 [smallest number] XOR 0 0 [largest number] XOR 1 0 [medium number] XOR 0 1 [medium number] I can never train the [1,1] [0,0] to be the same value. If you have any suggestions, additional resources, articles, blogs, etc for me to look at I am very interested in learning more about this topic. Thank you for your assistance, I appreciate it greatly!

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• jpa-Primarykey relationship

  - by megala

  Hi created student entity in gogole app engine datastore using JPA. Student---Coding @Entity @Table(name="StudentPersonalDetails", schema="PUBLIC") public class StudentPersonalDetails { @Id @Column(name = "STUDENTNO") private Long stuno; @Basic @Column(name = "STUDENTNAME") private String stuname; public void setStuname(String stuname) { this.stuname = stuname; } public String getStuname() { return stuname; } public void setStuno(Longstuno) { this.stuno = stuno; } public Long getStuno() { return stuno; } public StudentPersonalDetails(Long stuno,String stuname) { this.stuno = stuno; this.stuname = stuname; } } I stored Property value as follows Stuno Stuname 1 a 2 b If i stored Again Stuno No 1 stuname z means it wont allow to insert the record But. It Overwrite the value Stuno Stuname 1 z 2 b How to solve this?

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• pyramid - How to handle complex URL in a elegant way?

  - by Lingfeng Xiong

  I'm writing a admin website which control several websites with same program and database schema but different content. The URL I designed like this: http://example.com/site A list of all sites which under control http://example.com/site/{id} A brief overview of select site with ID id http://example.com/site/{id}/user User list of target site http://example.com/site/{id}/item A list of items sold on target site http://example.com/site/{id}/item/{iid} Item detailed information # ...... something similar As you can see, nearly all URL are need the site_id. And in almost all views, I have to do some common jobs like query Site model against database with the site_id. Also, I have to pass site_id whenever I invoke request.route_path. So... is there anyway for me to make my life easier? Thanks in advance.

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