How do you determine the level of transactional isolation when working with a database?

The transaction isolation level determines how transactions see each other's changes and prevents issues such as dirty reads, non-repeatable reads, and phantom reads.

In C# when working with a database through ADO.NET or Entity Framework, the isolation level is set via the IsolationLevel property of the transaction object. For example, when using TransactionScope or DbTransaction, you can specify the desired level:

using (var transaction = connection.BeginTransaction(IsolationLevel.Serializable))
{
    // database operations
    transaction.Commit();
}

Main isolation levels:

• Read Uncommitted — the lowest, allows dirty reads.
• Read Committed — prevents dirty reads.
• Repeatable Read — prevents non-repeatable reads.
• Serializable — the strictest, prevents phantom reads.

The choice of level depends on data integrity requirements and performance.