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• Searching for patterns to create a TCP Connection Pool for high performance messaging

  - by JoeGeeky

  I'm creating a new Client / Server application in C# and expect to have a fairly high rate of connections. That made me think of database connection pools which help mitigate the expense of creating and disposing connections between the client and database. I would like to create a similar capability for my application and haven't been able to find any good examples of how to apply this pattern. Do I really need to spin up an instance of a TcpClient every time I want to send a message to the server and receive a receipt message? Each connection is expected to transport between 1-5KB with each receiving a 1KB response message. I realize this question is somewhat vague, but I am starting from scratch so I am open to suggestions. Even if that means my suppositions are all wrong.

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• Can SQLAlchemy DateTime Objects Only Be Naive?

  - by Sean M

  I am working with SQLAlchemy, and I'm not yet sure which database I'll use under it, so I want to remain as DB-agnostic as possible. How can I store a timezone-aware datetime object in the DB without tying myself to a specific database? Right now, I'm making sure that times are UTC before I store them in the DB, and converting to localized at display-time, but that feels inelegant and brittle. Is there a DB-agnostic way to get a timezone-aware datetime out of SQLAlchemy instead of getting naive datatime objects out of the DB?

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• Should an event-sourced aggregate root have access to the event sourcing repository?

  - by JD Courtoy

  I'm working on an event-sourced CQRS implementation, using DDD in the application / domain layer. I have an object model that looks like this: public class Person : AggregateRootBase { private Guid? _bookingId; public Person(Identification identification) { Apply(new PersonCreatedEvent(identification)); } public Booking CreateBooking() { // Enforce Person invariants var booking = new Booking(); Apply(new PersonBookedEvent(booking.Id)); return booking; } public void Release() { // Enforce Person invariants // Should we load the booking here from the aggregate repository? // We need to ensure that booking is released as well. var booking = BookingRepository.Load(_bookingId); booking.Release(); Apply(new PersonReleasedEvent(_bookingId)); } [EventHandler] public void Handle(PersonBookedEvent @event) { _bookingId = @event.BookingId; } [EventHandler] public void Handle(PersonReleasedEvent @event) { _bookingId = null; } } public class Booking : AggregateRootBase { private DateTime _bookingDate; private DateTime? _releaseDate; public Booking() { //Enforce invariants Apply(new BookingCreatedEvent()); } public void Release() { //Enforce invariants Apply(new BookingReleasedEvent()); } [EventHandler] public void Handle(BookingCreatedEvent @event) { _bookingDate = SystemTime.Now(); } [EventHandler] public void Handle(BookingReleasedEvent @event) { _releaseDate = SystemTime.Now(); } // Some other business activities unrelated to a person } With my understanding of DDD so far, both Person and Booking are seperate aggregate roots for two reasons: There are times when business components will pull Booking objects separately from the database. (ie, a person that has been released has a previous booking modified due to incorrect information). There should not be locking contention between Person and Booking whenever a Booking needs to be updated. One other business requirement is that a Booking can never occur for a Person more than once at a time. Due to this, I'm concerned about querying the query database on the read side as there could potentially be some inconsistency there (due to using CQRS and having an eventually consistent read database). Should the aggregate roots be allowed to query the event-sourced backing store by id for objects (lazy-loading them as needed)? Are there any other avenues of implementation that would make more sense?

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• How sophisticated should be DAL?

  - by Andrew Florko

  Basically, DAL (Data Access Layer) should provide simple CRUD (Create/Read/Update/Delete) methods but I always have a temptation to create more sophisticated methods in order to minimize database access roundtrips from Business Logic Layer. What do you think about following extensions to CRUD (most of them are OK I suppose): Read: GetById, GetByName, GetPaged, GetByFilter... e.t.c. methods Create: GetOrCreate methods (model entity is returned from DB or created if not found and returned), Create(lots-of-relations) instead of Create and multiple AssignTo methods calls Update: Merge methods (entities list are updated, created and deleted in one call) Delete: Delete(bool children) - optional children delete, Cleanup methods Where do you usually implement Entity Cache capabilities? DAL or BLL? (My choice is BLL, but I have seen DAL implementations also) Where is the boundary when you decide: this operation is too specific so I should implement it in Business Logic Layer as DAL multiple calls? I often found insufficient BLL operations that were implemented in dozen database roundtrips because developer was afraid to create a bit more sophisticated DAL. Thank you in advance!

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• Why is django admin not accepting Nullable foreign keys?

  - by p.g.l.hall

  Here is a simplified version of one of my models: class ImportRule(models.Model): feed = models.ForeignKey(Feed) name = models.CharField(max_length=255) feed_provider_category = models.ForeignKey(FeedProviderCategory, null=True) target_subcategories = models.ManyToManyField(Subcategory) This class manages a rule for importing a list of items from a feed into the database. The admin system won't let me add an ImportRule without selecting a feed_provider_category despite it being declared in the model as nullable. The database (SQLite at the moment) even checks out ok: >>> .schema ... CREATE TABLE "someapp_importrule" ( "id" integer NOT NULL PRIMARY KEY, "feed_id" integer NOT NULL REFERENCES "someapp_feed" ("id"), "name" varchar(255) NOT NULL, "feed_provider_category_id" integer REFERENCES "someapp_feedprovidercategory" ("id"), ); ... I can create the object in the python shell easily enough: f = Feed.objects.get(pk=1) i = ImportRule(name='test', feed=f) i.save() ...but the admin system won't let me edit it, of course. How can I get the admin to let me edit/create objects without specifying that foreign key?

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• Does anyone have a backup strategy for SQL Azure databases?

  - by Pete

  I'm using SQL Azure on a project and it works great. The problem is that the usual backup features do not exist. I have exported the database a couple of times using SQLAzureMW ( http://sqlazuremw.codeplex.com/ ) but this tool is now choking trying to download the database data with bcp. In any case, it's not as nice a solution as SQL Server backups. Is anyone aware of a commercial or open source tool, or other technique, for making reliable backups of SQL Azure databases? This is really a showstopper.

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• Catching constraint violations in JPA 2.0.

  - by Dennetik

  Consider the following entity class, used with, for example, EclipseLink 2.0.2 - where the link attribute is not the primary key, but unique nontheless. @Entity public class Profile { @Id private Long id; @Column(unique = true) private String link; // Some more attributes and getter and setter methods } When I insert records with a duplicate value for the link attribute, EclipseLink does not throw a EntityExistsException, but throws a DatabaseException, with the message explaining that the unique constraint was violated. This doesn't seem very usefull, as there would not be a simple, database independent, way to catch this exception. What would be the advised way to deal with this? A few things that I have considered are: Checking the error code on the DatabaseException - I fear that this error code, though, is the native error code for the database; Checking the existence of a Profile with the specific value for link beforehand - this obviously would result in an enormous amount of superfluous queries.

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• Error in MySQL Workbench Forward Engineered Stored Procedures

  - by colithium

  I am using MySQL Workbench (5.1.18 OSS rev 4456) to forward engineer a SQL CREATE script. For every stored procedure, the automatic process outputs something like: DELIMITER // USE DB_Name// DB_Name// DROP procedure IF EXISTS `DB_Name`.`SP_Name` // USE DB_Name// DB_Name// CREATE PROCEDURE `DB_Name`.`SP_Name` (id INT) BEGIN SELECT * FROM Table_Name WHERE Id = id; END// The two lines that are simply the database name followed by the delimiter are errors and are reported as such when running the script. As long as they are ignored, it looks like everything gets created just fine. But why would it add those lines? I am creating the database in the WAMP environment which uses MySQL 5.1.36

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• Is this a good job description? What title would you give this position?

  - by Zack Peterson

  Department: Information Technology Reports To: Chief Information Officer Purpose: Company's ________________ is specifically engaged in the development of World Wide Web applications and distributed network applications. This person is concerned with all facets of the software development process and specializes in software product management. He or she contributes to projects in an application architect role and also performs individual programming tasks. Essential Duties & Responsibilities: This person is involved in all aspects of the software development process such as: Participation in software product definitions, including requirements analysis and specification Development and refinement of simulations or prototypes to confirm requirements Feasibility and cost-benefit analysis, including the choice of architecture and framework Application and database design Implementation (e.g. installation, configuration, customization, integration, data migration) Authoring of documentation needed by users and partners Testing, including defining/supporting acceptance testing and gathering feedback from pre-release testers Participation in software release and post-release activities, including support for product launch evangelism (e.g. developing demonstrations and/or samples) and subsequent product build/release cycles Maintenance Qualifications: Bachelor's degree in computer science or software engineering Several years of professional programming experience Proficiency in the general technology of the World Wide Web: Hypertext Transfer Protocol (HTTP) Hypertext Markup Language (HTML) JavaScript Cascading Style Sheets (CSS) Proficiency in the following principles, practices, and techniques: Accessibility Interoperability Usability Security (especially prevention of SQL injection and cross-site scripting (XSS) attacks) Object-oriented programming (e.g. encapsulation, inheritance, modularity, polymorphism, etc.) Relational database design (e.g. normalization, orthogonality) Search engine optimization (SEO) Asynchronous JavaScript and XML (AJAX) Proficiency in the following specific technologies utilized by Company: C# or Visual Basic .NET ADO.NET (including ADO.NET Entity Framework) ASP.NET (including ASP.NET MVC Framework) Windows Presentation Foundation (WPF) Language Integrated Query (LINQ) Extensible Application Markup Language (XAML) jQuery Transact-SQL (T-SQL) Microsoft Visual Studio Microsoft Internet Information Services (IIS) Microsoft SQL Server Adobe Photoshop

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• How do I display a field's hidden characters in the result of a query in Oracle?

  - by Chris Williams

  I have two rows that have a varchar column that are different according to a Java .equals(). I can't easily change or debug the Java code that's running against this particular database but I do have access to do queries directly against the database using SQLDeveloper. The fields look the same to me (they are street addresses with two lines separated by some new line or carriage feed/new line combo). Is there a way to see all of the hidden characters as the result of a query?I'd like to avoid having to use the ascii() function with substr() on each of the rows to figure out which hidden character is different. I'd also accept some query that shows me which character is the first difference between the two fields.

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• asp.net application install folder

  - by Maximilian Csuk

  Disclaimer: this is not a question about how to install asp.net or an application using it! Hi! I am pretty sure many of you have once installed some kind of forum, blog or CMS (mostly PHP powered applications). All of these contain a folder mostly named "install" where (after you copied the files to the webserver) point your browser to to complete the installation by entering for example database information (servername, username, password, ...). After that, most applications suggest that you delete this folder or at least change the permissions so nobody from the outside can access it anymore. Now to my question: how would you go about that in the asp.net world? I don't really like the "install folder"-approach and I thought there might be a different mechanism for .net/IIS. The person installing my application should be able to enter his database information as painless as possible, which should ultimatively be stored in the web.config file. If it makes a difference, I am using asp.net MVC. Thanks for your help!

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• asp.net webservice user management across pages

  - by nakori

  I'm developing a site that will display confidential readonly information, with data fetched from a WCF service. My question: What is the best approach to user management across different information pages. The service returns a collection with customer info after a secure login. My idea is to have a Customer object class that is stored in session. Is it possible to use things like HttpContext.Current.User.Identity.IsAuthenticated followed by HttpContext.Current.Session["UserId"] without using a database with role-based security? Would I be better off with a combination of local database, Linq to SQL or datasets rather than using just class objects for data fetched from service? thanks, nakori

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• Setting multiple datasource for a report in Asp.net

  - by Nandini

  Hi all, I have a report whose data is derived from two stored procedures.so i need to set these two datasources for generating the report.But the reports which have only one SP, ie.only one datasource works properly. For setting the datasource, i wrote code like this: dim reportdocument as ReportDocument Dim reportPath As String = Server.MapPath("CrystalRpts\Report.rpt") ReportDocument.Load(reportPath) 'Function for Setting the Connection SetDBLogonForReport(MyConnectionInfo, ReportDocument) dim dt1 as datatable=Datasource1 dim dt2 as datatable=Datasource2 dt1.merge(dt2) reportdocument.setDataSource(dt1) CrystalReportViewer.ReportSource=reportdocument But, the report is not generating.it shows the following error The Report requires additional information Servername:- Server Database:- Database UserID:- Password:- But the reports which have only one SP, ie.only one datasource works properly.What colud be reason for this error?

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• What arguments to use to explain why a SQL DB is far better then a flat file

  - by jamone

  The higher ups in my company were told by good friends that flat files are the way to go, and we should switch from MS SQL server to them for everything we do. We have over 300 servers and hundreds of different databases. From just the few I'm involved with we have 10 billion records in quite a few of them with upwards of 100k new records a day and who knows how many updates... Me and a couple others need to come up with a response saying why we shouldn't do this. Most of our stuff is ASP.NET with some legacy ASP. We thought that making a simple console app that tests/times the same interactions between a flat file (stored on the network) and SQL over the network doing large inserts, searches, updates etc along with things like network disconnects randomly. This would show them how bad flat files can be espically when you are dealing with millions of records. What things should I use in my response? What should I do with my demo code to illustrate this? My sort list so far: Security Concurent access Performance with large ammounts of data Ammount of time to do such a massive rewrite/switch Lack of transactions PITA to map relational data to flat files I fear that this will be a great post on the Daily WTF someday if I can't stop it now.

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• Using property file in hibernate mapping

  - by Zoltan Hamori

  Hi, I have a two nodes environment using the same database. In the database there is a resource table like RESOURCE_ID, CODE, NODE The content of the NODE column can be 1 or 2 depending on which node can use it. As I need to deploy the same ear to the two nodes, I would like to map this table like this: <hibernate-mapping> <class name="ResourceVO" table="RESOURCE" dynamic-update="true" optimistic-lock="dirty" where="NODE=${node.value}" > I would like to store the node.value property on the file system, so the instances could identify which resource to use. Is it possible in hibernate?

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• Free MySQL synchronization tool

  - by beny

  Hi, does anybody know some free tool for synchronization MySQL database (data and structure) like in Navicat for Windows ?

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• Rollback in lucene

  - by Petrick Lim

  Is there a rollback in lucene? I'm saving & updating database repository & lucene repository simultaneously so that the lucene index & database are in sync.. ex. CustomerRepository.add(customer); SupplierRepository.add(supplier); CustomerLuceneRepository.add(customer); SupplierLuceneRepository.add(supplier); // If this here fails i cannot rollback the customer above DataContext.SubmitChanges();

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• Django: Geocoding an address on form submission?

  - by User

  Trying to wrap my head around django forms and the django way of doing things. I want to create a basic web form that allows a user to input an address and have that address geocoded and saved to a database. I created a Location model: class Location(models.Model): address = models.CharField(max_length=200) city = models.CharField(max_length=100) state = models.CharField(max_length=100, null=True) postal_code = models.CharField(max_length=100, null=True) country = models.CharField(max_length=100) latitude = models.DecimalField(max_digits=18, decimal_places=10, null=True) longitude = models.DecimalField(max_digits=18, decimal_places=10, null=True) And defined a form: class LocationForm(forms.ModelForm): class Meta: model = models.Location exclude = ('latitude','longitude') In my view I'm using form.save() to save the form. This works and saves an address to the database. I created a module to geocode an address. I'm not sure what the django way of doing things is, but I guess in my view, before I save the form, I need to geocode the address and set the lat and long. How do I set the latitude and longitude before saving?

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• Query DNSBL or other block lists using PHP

  - by 55skidoo

  Is there any way to use PHP code to query a DNSBL (block list) provider and find out if the IP address submitted is a bad actor? I would like to take an existing IP address out of a registration database, then check whether it's a known block-listed IP address by performing a lookup on it, then if it's a blacklisted, do an action on it (such as, delete entry from registration database). Most of the instructions I have seen assume you are trying to query the blocklist via a mail server, which I can't do. I tried querying via web browser by typing in queries such as "58.64.xx.xxx.dnsbl.sorbs.net" but that didn't work.

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• nth smallest number among two databases of size n each using divide and conquer

  - by urfriend

  we have two databases of size n containing numbers without repeats. So, in total we have 2n elements. They can be accessed through a query to one database at a time. The query is such that you give it a k and it returns kth smallest entry in that database. we need to find nth smallest entry among all the 2n elements in O(logn) queries. the idea is to use divide and conquer but i need some help thinking through this. thanks!

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• Removing $_SESSION['layout']['action'] globally from all users!

  - by sologhost

  Ok, I am storing a session variable like so to load up users layouts faster if it's set instead of calling the database. But since the layout can be changed via the Administrator, I'd like to be able to globally remove all sessions where $_SESSION['layout']['action'] is set for all users. $_SESSION['layout']['action'] = array(a ton of indexes and mulit-dimensional arrays); Now, I know it's being stored into my database sessions table, there's a column for session_id, last_update, and data. So, question I have is how to remove that session array key ['action'] from all users. Using $_SESSION = array(); session_destroy(); Does not work. Basically, session_start() is being loaded on every page load, so I just want to remove all ['action'] keys from ['layout']. Is this possible to do? Thanks

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• How to manipulate a gridview in asp.net when the columns in the gridview are generated during runtim

  - by Nandini

  Hi guys, In my application,i have a gridview in which columns are created at runtime.Actually these columns are created when i am entering data in a database table. My gridview is like this:- Description | Column1 | Column2 | Column3 | ...... |....... |......... Input volt | 55 | 56 | 553 |........ Output volt | 656 | 45 | 67 | where Column1,Column2,column3 may vary during runtime.i need to enter values to these columns during runtime.But i cant bind these columns because these are created during runtime. The first column "Description" will not change.It will remain constant.For each description,there will be values for each column.At last these data will be saved to the database.How to add columns in the gridview during runtime?

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• When should I open and close a connection to SQL Server

  - by Martin

  I have a simple static class with a few methods in it. Each of those methods open a SqlConnection, query the database and close the connection. This way, I am sure that I always close the connection to the database, but on the other hand, I don't like to always open and close connection. Below is an example of what my methods look like. public static void AddSomething(string something) { using (SqlConnection connection = new SqlConnection("...")) { connection.Open(); // ... connection.Close(); } } Considering that the methods are inside a static class, should I have a static member containing a single SqlConnection? How and when should I drop it? What are the best practices?

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• How do I hide data/field in a List in J2ME

  - by pi

  Hi, I am working on a J2ME app which has dynamically generated Lists. Items on this list may be consequently selected, and the selection processed within the commandAction block. Is there a way to have the IDs of variables populating the List (from a remote database) included in the List item definition as in: this.append("A", null); this.append("B", null); or: String[] arrayOfValues = {"A", "B"}; new List("Menu", List.IMPLICIT, arrayOfValues, null); such that when an item is selected, perhaps A, I can also have its database ID for perhaps further processing. Is it possible to hide a field/data? Thanks.

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• What arguments to use to explain why SQL Server is far better then a flat file

  - by jamone

  The higher ups in my company were told by good friends that flat files are the way to go, and we should switch from SQL Server to them for everything we do. We have over 300 servers and hundreds of different databases. From just the few I'm involved with we have 10 billion records in quite a few of them with upwards of 100k new records a day and who knows how many updates... Me and a couple others need to come up with a response saying why we shouldn't do this. Most of our stuff is ASP.NET with some legacy ASP. We thought that making a simple console app that tests/times the same interactions between a flat file (stored on the network) and SQL over the network doing large inserts, searches, updates etc along with things like network disconnects randomly. This would show them how bad flat files can be especially when you are dealing with millions of records. What things should I use in my response? What should I do with my demo code to illustrate this? My sort list so far: Security Concurrent access Performance with large amounts of data Amount of time to do such a massive rewrite/switch Lack of transactions PITA to map relational data to flat files NTFS doesn't support tons of files in a directory well I fear that this will be a great post on the Daily WTF someday if I can't stop it now.

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