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  • C++ return a "NULL" object if search result not found

    - by aduric
    I'm pretty new to C++ so I tend to design with a lot of Java-isms while I'm learning. Anyway, in Java, if I had class with a 'search' method that would return an object T from a Collection< T that matched a specific parameter, I would return that object and if the object was not found in the collection, I would return a NULL. Then in my calling function I would just check if(T != NULL) { ... } In C++, I'm finding out that I can't return a NULL if the object doesn't exist. I just want to return an 'indicator' of type T that notifies the calling function that no object has been found. I don't want to throw an exception because it's not really an exceptional circumstance. class Node { .... Attr& getAttribute(const string& attribute_name) const { //search collection //if found at i return attributes[i]; //if not found return NULL; } private: vector<Attr> attributes; }

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  • Comparing all properties of an object using expression trees

    - by stringargs
    Hi, I'm trying to write a simple generator that uses an expression tree to dynamically generate a method that compares all properties of an instance of a type to the properties of another instance of that type. This works fine for most properties, like int an string, but fails for DateTime? (and presumably other nullable value types). The method: static Delegate GenerateComparer(Type type) { var left = Expression.Parameter(type, "left"); var right = Expression.Parameter(type, "right"); Expression result = null; foreach (var p in type.GetProperties()) { var leftProperty = Expression.Property(left, p.Name); var rightProperty = Expression.Property(right, p.Name); var equals = p.PropertyType.GetMethod("Equals", new[] { p.PropertyType }); var callEqualsOnLeft = Expression.Call(leftProperty, equals, rightProperty); result = result != null ? (Expression)Expression.And(result, callEqualsOnLeft) : (Expression)callEqualsOnLeft; } var method = Expression.Lambda(result, left, right).Compile(); return method; } On a DateTime? property it fails with: Expression of type 'System.Nullable`1[System.DateTime]' cannot be used for parameter of type 'System.Object' of method 'Boolean Equals(System.Object)' OK, so it finds an overload of Equals that expects object. So why can't I pass a DateTime? into that, as it's convertible to object? If I look at Nullable<T>, it indeed has an override of Equals(object o). PS: I realize that this isn't a proper generator yet as it can't deal with null values, but I'll get to that :)

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  • how to synchronize database table and directory with php

    - by twmulloy
    hello, I have a directory with files and a database table with what should be the same files. I would like to be able to synchronize the database table with the directory. What would be the most efficient way to do this? or would I realistically only be able to do this in a brute manner? Here's my approach: 1. retrieve all of the files in the directory as array 2. retrieve all of the filenames in the database table as array 3. loop through the file values in the directory array and use in_array() on the database table array to verify the filename is in that array, and if not then start building an array to insert the missing filenames. run db query to add each missing file row to database table 4. loop through directory array and use in_array() on the directory array and anything not found in the directory array will just be deleted from the table. Is there a better way to go about this? or something better for this in php than in_array()?

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  • Problem with object serialization in Applet-Servlet communication

    - by Bruce
    Hi guys, I spent a lot of time on thinking what is wrong with the following code. I send the object from my applet to servlet and then I read the object from servlet. Everything goes fine till reading serialized object from the servlet - I got IOException. Thank you in advance! Here is the code: Applet: try { URL servletURL = new URL(this.getCodeBase().getProtocol(), this.getCodeBase().getHost(), this.getCodeBase().getPort(), "/MyApplet"); URLConnection servletConnection = servletURL.openConnection(); servletConnection.setDoInput( true ); servletConnection.setDoOutput( true ); servletConnection.setUseCaches( false ); servletConnection.setRequestProperty( "Content-Type", "application/x-java-serialized-object" ); ObjectOutputStream output; output = new ObjectOutputStream( servletConnection.getOutputStream( ) ); output.writeObject( someObject ); output.flush( ); output.close( ); ObjectInputStream input = new ObjectInputStream( servletConnection.getInputStream( ) ); // Here I got the exception myObject = ( SomeObject ) input.readObject( ); } catch (java.io.IOException ioe) { System.err.println(ioe.getStackTrace()); } catch (Exception e) { System.err.println(e.getStackTrace()); } Servlet: response.setContentType("application/x-java-serialized-object"); try { ObjectInputStream inputFromApplet = new ObjectInputStream(request.getInputStream()); SomeObject myObject = (SomeObject) inputFromApplet.readObject(); ObjectOutputStream outputToApplet = new ObjectOutputStream(response.getOutputStream()); outputToApplet.writeObject(myObject); outputToApplet.flush(); } catch(Exception e) { // ... }

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  • How do I force a restore over an existing database?

    - by Ian Boyd
    I have a database, and i want to force a restore over top of it. I check the option: Overwrite the existing database (WITH REPLACE) But, as expected, SSMS is unable to overwrite the existing database. Of course i don't want different filenames; i want to overwrite the existing database. How do i force a restore over an existing database? And for Google search crawler: File '%s' is claimed by '%s'(4) and '%s"(3). The WITH MOVE clause can be used to relocate one or more files. RESTORE DATABASE is terminating abnormally. (Microsoft SQL Server, Error: 3176) Update The script (before i deleted the database, because i needed to get it done) was: RESTORE DATABASE [HealthCareGovManager] FILE = N'HealthCareGovManager_Data', FILE = N'HealthCareGovManager_Archive', FILE = N'HealthCareGovManager_AuditLog' FROM DISK = N'D:\STAGING\HealthCareGovManager10232013.bak' WITH FILE = 1, MOVE N'HealthCareGovManager_Data' TO N'D:\CGI Data\HealthCareGovManager.MDF', MOVE N'HealthCareGovManager_Archive' TO N'D:\CGI Data\HealthCareGovManager.ndf', MOVE N'HealthCareGovManager_AuditLog' TO N'D:\CGI Data\HealthCareGovManager.ndf', MOVE N'HealthCareGovManager_Log' TO N'D:\CGI Data\HealthCareGovManager.LDF', NOUNLOAD, REPLACE, STATS = 10 I used the UI to delete the existing database, so that i could use the UI to force an overwrite of the (non)existing database. Hopefully there can be an answer so that the next guy can have an answer. No, nobody was in the context of the database (The error message from other connections is quite different from this error, and i only got to see this error after i killed the other connections).

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  • processing json objects in jsp

    - by user98534
    i have a JSON object sent from the browser to the jsp page. how do i receive that object and process it in jsp. do i need any specific parsers? i have used the following piece of code. but it wouldnt work. essentially i should read the contents of the object and print them in the jsp. <%@page language="java" import="jso.JSONObject"%> <% JSONObject inp=request.getParameter("param1"); %> <% for(int i=0;i<inp.size();i++) {%> <%=inp.getString(i)%> <% } %>

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  • XCode copies blank database when doing build...

    - by Incognitii
    I've noticed that even though I placed my sqlite3 database in the "resources" folder, and even though I checked the "Copy file" box, when I do a build, XCode creates an empty database toi the application folder it's building...so it's FINDING the database, and OPENING it, but there's nothing IN it, so when I do a sqlite3_prepare_v2, I get a SQLITE_ERROR... Help! What am I doing wrong?

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  • Hibernate session method to update object

    - by EugeneP
    I need this roadmap of a Hibernate managed object instance. First, I create an instance with initial properties and persist this object in a db. Then session associated with this object is closed. But still, I serialize my object and on the next step deserialize it, invoke some setters, and again, I need to update what changed in a database. What methods of Hibernate session should I use? persist() or save() on the first step and saveOrUpdate() on the second? In fact I see that saveOrUpdate() can be used on each step. What would you recommend?

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  • PHP object class variable

    - by mck89
    I have built a class in PHP and I must declare a class variable as an object. Everytime I want to declare an empty object I use: $var=new stdClass; But if I use it to declare a class variable as class foo { var $bar=new stdClass; } a parse error occurs. Is there a way to do this or must I declare the class variable as an object in the constructor function? PS: I'm using PHP 4.

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  • Accessing database problem

    - by anarche
    Ok, so I've got an SQLiteOpenHelper that prepares and returns a SQLiteDatabase object; this is written singleton-pattern, so the database is opened once and only closed when the Activity closes. From there I have three database wrappers encapsulating the queries (some returning cursors to datasets, some inserting data) used by the Activity. I want to insert data from one View, then have that automatically update in another View on the same Dialogue. I'm writing this on a notepad and testing on the phone (since the emulator crashes the notepad...), so I can't pull up stacktraces atm. So questions: 1) are there limitations to writing to a database, when there are cursors open on the database? 2) Does a Cursor.requery()? call update the ListView with the cursor as a data connector?

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  • Google App Engine - Dealing with concurrency issues of storing an object

    - by Spines
    My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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  • How can I pass methods in javascript?

    - by peterjwest
    I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this: a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }} b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) }) c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) }) I want to know if there is a simpler way to pass methods attached to their original objects.

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  • How to Shrink Transaction log in sql server database in replication

    - by Renju
    Hi I'm having a production database and its replicated report database. How to shrink the transaction log files in the production database as the log file size is increasing. I had tried DBCC SHRINKFILE and SHRINKDATABASE commands but it does not work for me. I can't detach and shrink and attach back as the db in replication. Please help me in this issue.

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  • Dynamically create and cast objects at runtime

    - by vaibhav bindroo
    Let's say we have 2 classes A and B public class A{ private int member1; A() { member1 = 10; } public getMember(){ return member1; } } Class B is also on the same lines except that its member variable is named member2 and gets intitialized to say 20 inside the constructor. My Requirement : At runtime , I get a string which contains a className ( could be A or B). I want to dynamically create an object of this class along with invoking the constructor. How can I achieve this . I don't want to use interfaces for common functionality of above classes Morever, later on I set the properties of this raw object using Propery Builder Bean Util class based on a list of columns . Class clazz = Class.forName("className"); Obj obj = clazz.newInstance(); How I can dynamically convert that obj to className object.

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  • c# - Object reference not set to an instance of an object.

    - by tom
    Line 30: sUsername.Trim(); Line 31: sPassword.Trim(); Line 32: string ConnectionString = WebConfigurationManager.ConnectionStrings["dbnameConnectionString"].ConnectionString; Line 33: SqlConnection myConnection = new SqlConnection(ConnectionString); Line 34: try Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Any ideas? I don't understand the error.

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  • populate object graph from database

    - by Rama
    Hi, I would like to know the best way to populate an object that has a collection of child objects and each child object may inturn have a collection of objects, from database without making multiple calls to the database to get child objects for each object. basically in hierarchical format something like for example a customer has orders and each order has order items. is it best to retrieve the data in xml format (SQL server 2005), or retrieve a dataset by joining the related tables together and then map that the data to the object? thanks in advance for your help.

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  • Database.ExecuteNonQuery does not return

    - by dan-waterbly
    I have a very odd issue. When I execute a specific database stored procedure from C# using SqlCommand.ExecuteNonQuery, my stored procedure is never executed. Furthermore, SQL Profiler does not register the command at all. I do not receive a command timeout, and no exeception is thrown. The weirdest thing is that this code has worked fine over 1,200,000 times, but for this one particular file I am inserting into the database, it just hangs forever. When I kill the application, I receive this error in the event log of the database server: "A fatal error occurued while reading the input stream from the network. The session will be terminated (input error: 64, output error: 0). Which makes me think that the database server is receiving the command, though SQL Profiler says otherwise. I know that the appropiate permissions are set, and that the connection string is right as this piece of code and stored procedure works fine with other files. Below is the code that calls the stored procedure, it may be important to note that the file I am trying to insert is 33.5MB, but I have added more than 10,000 files larger than 500MB, so I do not think the size is the issue: using (SqlConnection sqlconn = new SqlConnection(ConfigurationManager.ConnectionStrings["TheDatabase"].ConnectionString)) using (SqlCommand command = sqlconn.CreateCommand()) { command.CommandText = "Add_File"; command.CommandType = CommandType.StoredProcedure; command.CommandTimeout = 30 //should timeout in 30 seconds, but doesn't... command.Parameters.AddWithValue("@ID", ID).SqlDbType = SqlDbType.BigInt; command.Parameters.AddWithValue("@BinaryData", byteArr).SqlDbType = SqlDbType.VarBinary; command.Parameters.AddWithValue("@FileName", fileName).SqlDbType = SqlDbType.VarChar; sqlconn.Open(); command.ExecuteNonQuery(); } There is no firewall between the server making the call and the database server, and the windows firewalls have been disabled to troubleshoot this issue.

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