Understanding CRC Effects in Progress 4GL: What You Need to Know

Описание: Discover how changes in Progress 4GL impact `CRC` values, including adding or removing objects, and learn the best practices for maintaining your code integrity.
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This video is based on the question https://stackoverflow.com/q/69927031/ asked by the user 'Bharat' ( https://stackoverflow.com/u/13885125/ ) and on the answer https://stackoverflow.com/a/70537389/ provided by the user 'Tom Bascom' ( https://stackoverflow.com/u/123238/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding CRC Effects in Progress 4GL: What You Need to Know

As someone who's just begun exploring Progress 4GL, you may be wondering about how certain changes in your database can impact the CRC (Cyclic Redundancy Check) values, specifically regarding compiled code and its relationship with database objects. This guide aims to clarify which types of changes have an effect on CRC and which do not, ensuring you have a solid grasp of these concepts as you work with Progress 4GL.

What is CRC and Why is it Important?

CRC is a mechanism used to detect errors in data. In the context of Progress 4GL, the CRC value relates instructions in the compiled code (or r-code) with database structures. Understanding how changes to database objects can affect the CRC is crucial for maintaining code integrity and avoiding runtime errors.

Key Changes and Their Effects on CRC

Here’s a breakdown of different types of modifications you might consider when working within Progress 4GL, specifically regarding their effects or lack thereof on CRC.

1. Object Additions: No Impact on Existing R-Code

Adding Tables, Fields, and Indexes:

These actions do not invalidate existing r-code. While the new objects cannot be used by the existing r-code, they also won't cause any issues or errors in that code.

2. Dynamic Query Considerations

Dynamic Queries:

It’s essential to keep in mind that dynamically coded queries can still access new objects. The compiler does not enforce CRC matching for these dynamic references, which means you need to be vigilant when working with dynamic code.

3. Object Removals: Behavior Changes

Removing Objects:

If you delete a table, field, or index that is referenced in your r-code, that code will fail. You will need to re-compile your code following the deletion. Notably:

Different indexes might be selected by the compiler if an index is deleted.

Deleted tables and fields require code modifications to ensure proper function.

4. Minor Changes: No Disruption

Altering Attributes:

Changing certain properties, such as a field's FORMAT, does not break anything and thus has no impact on CRC.

5. Renaming Objects: Breakage Occurs

Renaming:

If you change the name of an object, this will lead to broken code. References to the old names become invalid, necessitating code updates to reflect the new terminologies.

6. Replacing Deleted Objects: Caveat

Replacing Deleted Objects:

If you delete an object and then create a new object with the same name and structure, this often does not require a recompilation. However, it’s wise to approach this with caution and avoid making a habit out of it, as unintentional errors can arise.

Conclusion

Understanding how modifications to database objects in Progress 4GL can influence the CRC is essential for maintaining your application's stability and performance. Here’s a quick recap of important points:

Adding new objects has no negative impact on existing r-code.

Deleting objects will require you to recompile any code that references them.

Minor attribute changes are safe, while renaming objects can cause issues.

Keeping these principles in mind will help you navigate the complexities of Progress 4GL with greater confidence. If you have any questions or need clarification on any specific topic, feel free to ask!