This document provides an overview of managing transactions and concurrency in web applications. It discusses how web applications are stateless and how Entity Framework tracks changes to entities. It also covers different approaches for concurrency, including optimistic concurrency using timestamps and custom properties, as well as using transactions to maintain data consistency across multiple requests. Demo code examples are provided for modifying and deleting entities, optimistic concurrency, and custom transactions.

1. 05 | Managing transactions and
concurrency
Adam Tuliper | Technical Evangelist
Christopher Harrison | Content Developer

2. Module Overview
• Working in a web application
• Managing concurrency

3. Working in a web application

4. What's special about web applications?
Edit Request Accept Request
Load Data
Build FormView Form

5. Web applications are stateless
• EF uses entity tracking to detect changes
– Entities can only be tracked if they're attached to a data context
• When the page is returned to the user, the data context goes
away
• When the user returns updated object to the server, the server
sees that as a new object
– Not a modification to an existing object

6. Basic process for updates and deletes
• Attach the object to the context
• Set the state as Modified or Deleted
• SaveChanges
• Notes, updates the entire object, not individual properties

7. DEMO
Modifying and deleting entities

8. Managing concurrency

9. Things can change
• Who knows how long someone will have their page up
• Options
– Optimistic
• TimeStamp/RowVersion
• ConcurrencyCheck to customize property
– Pessimistic
• Set a flag on a row to prevent modification
• Requires more work

10. Optimistic concurrency with RowVersion/TimeStamp
• RowVersion and TimeStamp mean the same thing
• Basic steps
– Add a property of type byte[]
– Decorate the property with TimestampAttribute
[Timestamp()]
public byte[] RowVersion { get; set; }

11. What happens if something's changed
• EF automatically supports optimistic concurrency
• Adds WHERE statement to UPDATE and DELETE statements
• Throws OptimisticConcurrencyException if Timestamp has
changed

12. DEMO
Optimistic concurrency

13. Custom property
• If you want more control over how concurrency is handled, you
can choose which property or properties will be examined by EF
– Useful for legacy apps or databases that don't support timestamps
• Add ConcurrencyCheckAttribute to property
• EF will do the same WHERE check as before

14. DEMO
Custom property optimistic concurrency

15. Transactions

16. Saving multiple objects
• SaveChanges is transactional
• If you need a transaction to maintain across multiple calls, use
TransactionScope

17. DEMO
Custom transactions

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