Dealing with optimistic concurrency in entity framework

When you update a database record with the entity values, the database values are overwritten by the entity values (default behavior). Database of genomic variants In a real world situation it is quite possible that database values might have got changed after selecting them for modification. Database viewer In such cases, your update operation might be overwriting changes made by someone else.

H data recovery registration code free download That is why it becomes important to detect if concurrency violation has occurred. Database hardware You can then take some corrective action or at least inform the user about such a violation. Database roles To that end this article shows how to detect concurrency violation in EF and also the possible ways to deal with the situation. B tree database management system Detecting Concurrency Violation

Entity Framework can be configured to use optimistic concurrency while updating database records. Database file That means no locks are held on the data being modified. Data recovery near me The data is updated only if the database values at the time of fetching the data and the database values currently stored in the database match. Database job description To understand how the concurrency violation can be detected, let’s develop a simple application that updates Employee details from Employees table. Data recovery 94fbr The Employees table consists of the columns shown by the following data model:

As you can see the Employees table has five columns: EmployeeID, FirstName, LastName, Title and UpdateToken. Database foreign key Most of the columns are self explanatory except UpdateToken. Database as a service The UpdateToken column is of type rowversion. Iphone 6 data recovery The rowversion data type ensures that the column holds a different value every time that record is updated. Database google drive A rowversion column is automatically updated by the SQL Server and it won’t play any direct role in your application data. Data recovery geek squad Why do you need a rowversion column here? That’s because it allows us to detect if a record has been changed after the initial selection. Database recovery pending However, merely adding a rowversion column is not sufficient. Data recovery prices In the entity framework designer you also need to set the ConcurrencyMode property of the UpdateToken property to Fixed. Database sharding The following figure shows how this is done:

As you can see the Concurrency Mode is changed from None to Fixed. Database keys with example Changing this setting will cause EF to use the UpdateToken column in the WHERE clause of the UPDATE queries it generates. Data recovery xfs This way a row is updated only when value of UpdateToken at the time of initial fetch matches with the current value in the database. Database management systems 3rd edition If they don’t match no record is updated and EF concludes that there was a concurrency violation.

You can also detect a concurrency violation without using rowversion column. Database engineer salary In that case you need to set ConcurrencyMode for each property that you wish to include in the WHERE clause. Jstor database Using rowversion column simplifies your job and the resultant query. E m database Creating a Web Form

In order to bind this DetailsView with EF data model you need to write two methods in the code behind – DetailsView1_GetItems() and DetailsView1_UpdateItem(). Data recovery richmond va The former method returns all the Employee objects from the Employees DbSet as IQueryable whereas the later method updates employee details back to the database. Data recovery software Below the DetailsView place a Label (not shown in the figure) to display the concurrency violation error.

The DetailsView1_GetItems() method creates an instance of EmployeeDbEntities context. Data recovery advisor It then selects all Employee objects from Employees DbSet and returns them to the caller.

The above code finds an existing Employee based on the EmployeeID. Database host name Remember that this EmployeeID is passed by the DetailsView only if DataKeyNames property is set. Database performance The TryUpdateModel() method then sets the properties of the existing Employee from the values entered in the DetailsView. Data recovery broken hard drive The code then halts the execution for 15 seconds. Database xe This is done purely for the sake of testing. Database yml mysql Adding this delay will allow you to switch to the physical database table and modify its data manually to test the concurrency violation. 5 database is locked An alternative is to set a breakpoint at SaveChanges() method to halt the execution and then change the database values manually.

The try…catch block is an important piece of code because it traps the concurrency violation error and displays it to the user. Database fundamentals The try block attempts to save the changes back to the database by calling SaveChanges() method. Database concepts If there are pending changes but SaveChanges() causes zero records to be updated it indicates a concurrency violation. Database icon If such a violation is detected EF throws DbUpdateConcurrencyException exception. Database versioning The DbUpdateConcurrencyException class resides in System.Data.Entity.Infrastructure namespace. Database 2013 The catch block simply displays the error in the Label control.

To test what you developed so far, run the Web Form and modify an employee record. Database cursor After clicking the Update button quickly switch to the database in Server Explorer of Visual Studio and modify the same record with some different values (you have 15 seconds to do this change!) and wait to see what is thrown on the screen. Database list The following figure shows a sample run of the Web Form with the error:

During the above test run you will find that after the error message is displayed to the user, the DetailsView shows the latest data from the database. Database queries must be Handling Concurrency Violation

• Update the entity under consideration from the latest data from the database table. Database journal Then show that data to the user so that he can take the necessary action.

The first approach is quite easy and that is what you used in the preceding example. Data recovery boston The second approach requires you to load database values in an entity and present them to the user. Database connection You can do that in the catch block as shown below: …

As you can see the DbUpdateConcurrencyException class provides access to the entity causing the error. S memo data recovery The Reload() method called on an entity loads the values from the database into that entity. Database structure You then change the mode of the DetailsView to ReadOnly so that user can read the new values.

In the third approach, you make the current database values as the original values and then attempt SaveChanges() again. Data recovery iso This approach is shown below: …

Here, you set the OriginalValues of the entity under consideration to the current values from the database (obtained by calling GetDatabaseValues()). Iphone 6 data recovery software You then attempt SaveChanges() again.

In the Part 1 we learnt the basics of Cryptography and related .NET Framework classes. Cpu z database In this article we are going to see how to work with Secret Key Encryption using Triple-DES algorithm.

The System.Security.Cryptography namespace contains a class called TripleDESCryptoServiceProvider that provides Triple-DES encryption to your data. Data recovery kickass DES stands for Data Encryption Standard and the word triple is used because it encrypts the original data thrice.

The encryption algorithms employ use a chaining technique to encrypt the data. A database can best be described as In this technique the entire data to be encrypted is divided in smaller blocks. Os x database The previously encrypted block of data is used to encrypt the current one and the process repeats.

The Initialization Vector (IV) serves as a seed that is used to encrypt and decrypt the first block of bytes. Database field This ensures that no two blocks of data produce the same block of encrypted text.

In this example we will first create a class called SecurityHelper that will help us encrypt and decrypt string data. Data recovery diy Here is the code for the class: Imports System.Security.Cryptography

• We create a class called SecurityHelper with two functions Encrypt() and Decrypt(). Database transaction The former accepts the string to be encrypted and returns encrypted form of the string as a byte array. Data recovery mac hard drive The later accepts the encrypted data in the form of a byte array and returns decrypted data as a string.

• The key and initialization vector can be supplied externally by you or TripleDESCryptoServiceProvider class can generate one automatically for you. H2 database tutorial If user has not supplied key and IV we call GenerateKey() and GenerateIV() methods respectively. Database interview questions These methods create a random key and IV automatically for you. R studio data recovery free download We assign the generated key and IV to public variables Key and IV.

• Then we call CreateEncryptor() method of TripleDESCryptoServiceProvider class and collect its return value in a variable of type ICryptoTransform. Data recovery bad hard drive The ICryptoTransform interface defines the basic operations of cryptographic transformations.

• Next, we write the data to be encrypted to the CryptoStream object. Database field definition The CryptoStream object stores the encrypted version of the data in the supplied memory stream.

Decryption process is similar but follows reverse path. Data recovery windows 7 The only major difference between encryption and decryption code is that in case of decryption we call CreateDecryptor() method of TripleDESCryptoServiceProvider class.

In this article we saw how TripleDESCryptoServiceProvider class can be used to encrypt and decrypt string data. Nexus 4 data recovery With little or no modification you can reuse the class for your own requirements. Database version 706 Some common uses of this algorithm can be – storing passwords in database, string confidential data such as bank account numbers etc. Cindia data recovery in database. Database tutorial In the example above we used memory stream to put our data but you can also use FileStream to save the data to a disk file. R database packages In the next article we will see how to use public-key encryption.

Security is key consideration for many applications. Database disk image is malformed Providing authentication and authorization services to your application is just one part of the overall security. Windows 8 data recovery software What about the data that is being used and transferred in the application? That is where cryptography comes into picture. Database naming standards Cryptography is a huge topic by itself. Data recovery training online In this series of articles I am going to confined our discussion only to .NET Framework and cryptographic classes provided by it.

Many times application provide security features such as login forms and role based security. Database query However, what if someone intercepts the data that is being flown over the network? What if someone plays with the data that is being transmitted over the network? What if someone opens SQL Server database that is storing passwords? Cryptography provides solution to such questions. Database isolation levels Using .NET Cryptographic classes you can encrypt the data that is being flown in your system or network and then decrypt when you want authenticated user to modify or read it. Database version control In short Cryptography provides following features:

In Secret Key Cryptography the data being protected is encrypted using a single secret key. Database record definition This key is known only to sender and receiver. Database glossary The sender encrypts the data using the secret key. Data recovery druid The receiver decrypts the data using the same secret key. Data recovery houston tx It is very important to keep the key secret otherwise anybody having the key can decrypt the data.

Unlike secret key encryption, public key encryption uses two keys. Database 2010 One is called public key and the other is called as private key. Dayz database map The public key is not kept secret at all where as private key is kept confidential by the owner of that key. Database website template The data encrypted by private key can be decrypted only using its corresponding public key and data encrypted using public key can be decrypted using its private key. 7 data recovery registration code Naturally, in order to encrypt the data being transmitted you need to use public key. 7 databases in 7 weeks pdf This data can be decrypted only with the corresponding private key.

Digital signatures are used to verify identity of the sender and ensure data integrity. Database key definition They are often used along with public key encryption. Database hierarchy Digital signature work as follows:

• Sender applies hash algorithm to the data being sent and creates a message digest. Data recovery on mac Message digest is compact representation of the data being sent.

Hash algorithms create a fixed length output for a given variable length data. Data recovery kali linux If somebody changes the original data even slightly then the hash generated will be different than original hash. I card data recovery They are often used with digital signatures.

While working with cryptography classes many times you need to generate cryptographic keys. Database name Random number generators are used for this purpose. Database quiz .NET provides a class called RNGCryptoServiceProvider to generate such random numbers.