When Should I Dispose of My Data Context?

When Should Data Contexts Be Disposed of?

In developing a data access layer for an application, managing data contexts can be a crucial aspect. This article examines the best practices for disposing of data contexts in code.

The provided code sample demonstrates a simplified implementation of retrieving data from the database and saving it back. The code includes a private DataContext member and a public save method for persisting changes to the database. This approach keeps the DataContext alive even after the method call returns, which can raise questions about proper resource management.

To address this, the LINQ to SQL team suggests using the IDisposable interface to explicitly release unmanaged resources. One reason is to enforce contract adherence when the application logic requires holding references to entities beyond the expected lifespan of the DataContext. Calling Dispose ensures that deferred loaders referencing the DataContext will fail if they attempt to use it, preventing potential errors.

Another benefit is resource management. Disposing of a DataContext forces it to clear its cache of materialized entities. This helps prevent memory leaks in cases where a cached entity could accidentally hold references to all entities materialized through that DataContext.

However, it's worth noting that disposing of DataContexts is not always necessary. Automatic connection closing mechanisms exist within the DataContext implementation. These mechanisms rely on the application enumerating all results of a query to trigger connection closure. If the application prematurely exits enumeration, connections may remain open. As a precaution, one may consider using the Dispose pattern as a workaround in such situations.

In summary, while not strictly necessary in most cases, disposing of DataContexts using the IDisposable interface is recommended for resource management and contract enforcement. This practice facilitates adherence to the "dispose everything that implements IDisposable" rule and reduces the likelihood of resource leaks.

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