Скачать или смотреть How to Use INSTEAD OF Triggers in PostgreSQL for Managing View Inserts

Discover how to implement a PostgreSQL trigger function to effectively handle inserts into views by dynamically managing data between base tables with this comprehensive guide.
---
This video is based on the question https://stackoverflow.com/q/76228914/ asked by the user 'Marnix.hoh' ( https://stackoverflow.com/u/9762137/ ) and on the answer https://stackoverflow.com/a/76243891/ provided by the user 'JohnH' ( https://stackoverflow.com/u/20151367/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: PostgreSQL insert all the matching columns on NEW in a INSTEAD OF trigger

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Managing Inserts with PostgreSQL's INSTEAD OF Triggers

When working with PostgreSQL views, you may often find yourself needing to manage complex data structures involving multiple tables. A common scenario is wanting to intercept an INSERT operation into a view and split it into separate INSERT operations for the underlying base tables. In this guide, we'll explore how to achieve this using INSTEAD OF triggers while considering performance and organization best practices.

The Problem

Let’s consider a practical example to illustrate the issue:

Example Tables and View

You have two tables: usr_static and usr_version. Here’s their structure:

[[See Video to Reveal this Text or Code Snippet]]

You also have a view that combines data from both tables:

[[See Video to Reveal this Text or Code Snippet]]

Now, when you attempt to insert data into this view, like so:

[[See Video to Reveal this Text or Code Snippet]]

You wish to create a trigger that performs the following automatic INSERT operations:

[[See Video to Reveal this Text or Code Snippet]]

The Challenge

The challenge lies in creating a single trigger function that can dynamically handle multiple views, mapping the corresponding NEW values to the correct columns in usr_static and usr_version. The goal is to avoid hardcoding column names in the trigger function to enhance reusability across multiple views.

The Solution: Dedicated Trigger Functions

While it may seem desirable to create a single trigger for multiple views, this approach can lead to performance issues, as it requires querying system catalogs to dynamically generate INSERT statements. Instead, we recommend crafting dedicated trigger functions for each view.

Creating a Trigger Function

Here’s a simplified example of how to create a trigger function specifically for the usr view. Below is a PostgreSQL function that handles the insertion logic for splitting the data into the appropriate base tables:

[[See Video to Reveal this Text or Code Snippet]]

Enhancing the Trigger Function

For added functionality, consider using dynamic code generation to create tailor-made trigger functions for different views, while still avoiding performance bottlenecks. Here’s an advanced function to generate the trigger automatically based on system catalogs:

[[See Video to Reveal this Text or Code Snippet]]

This function dynamically constructs the necessary INSERT statements based on the underlying table structure correlated to the view, making it a more flexible solution.

Performance Considerations

Optimize the trigger function to handle inserts efficiently.

Always consider the complexity of your view and underlying tables, especially during large-scale data operations.

Test performance implications thoroughly before deploying in a production environment.

Conclusion

Using INSTEAD OF triggers in PostgreSQL allows for a powerful way to manage inserts into views by distributing the data to corresponding base tables. Although there are more advanced methods to create dynamic triggers, the best practice in many cases is still to define dedicated trigger functions for each view. This ensures optimal performance while keeping your database schema clean and maintainable.

Explore the world of PostgreSQL triggers further to see how you can streamline your data operations effectively!